CR16HCS5,CR16HCS9,CR16MAR5,CR16MAS5,
CR16MAS9,CR16MBR5,CR16MCS5,CR16MCS9
CR16HCS5 CR16HCS9 CR16MAR5 CR16MAS5 CR16MAS9 CR16MBR5 CR16MCS5 CR16MCS9
Family of 16-bit CAN-enabled CompactRISC Microcontrollers
Literature Number: SNOS999B
©2001 National Semiconductor Corporation
www.national.com
CR16HCS5/CR16HCS9/CR16MAR5/CR16MAS5 CR16MAS9/CR16MBR5/CR16MCS5/CR16MCS9 Family of 16-bit CAN-en-
abled CompactRISC Microcontrollers
Interrupt
Control
January 2002
CR16HCS5/CR16HCS9/CR16MAR5/CR16MAS5
CR16MAS9/CR16MBR5/CR16MCS5/CR16MCS9
Family of 16-bit CAN-enabled CompactRISC
Microcontrollers
1.0 General Description
The family of 16-bit CompactRISC™ microcontroller is
based on a Reduced Instruction Set Computer (RISC) ar-
chitecture. The device operates as a complete microcom-
puter with all system timing, interrupt logic, flash program
memory or ROM memory, RAM, EEPROM data memory,
and I/O ports included on-chip. It is ideally suited to a wide
range of embedded controller applications because of its
high performance, on-chip integrated features and low
power consumption resulting in decreased system cost.
The device offers the high performance of a RISC architec-
ture while retaining the advantages of a traditional Com-
plex Instruction Set Computer (CISC): compact code, on-
chip memory and I/O, and reduced cost. The CPU uses a
three-stage instruction pipeline that allows execution of up
to one instruction per clock cycle, or up to 25 million in-
structions per second (MIPS) at a clock rate of 24 MHz.
The device contains a FullCAN class, CAN serial interface
for low/high speed applications with 15 orthogonal mes-
sage buffers, each supporting standard as well as extend-
ed message identifiers.
TRI-STATE® is a registered trademark of National Semiconductor Corporation.
64k-Byte
Flash
Program
Memory
CR16CAN
Core Bus
Peripheral Bus
Clock Generator
Slow Clk*
Processing
Unit
I/O µWire/SPI 12-ch
Fast Clk
3k-Byte
Peripheral
Bus
Controller
Power-on-Reset
2176-Byte
RAM EEPROM
Data
MIWU 2 Analog
Comparators
Timing and
Watchdog
Power
Manage-
ment
2x
MFT
2x
USART
CR16B
RISC Core
8-bit A/D
ACCESS
bus 4x
VTU
Memory Memory
FullCAN 2.0B
1.5k-Byte
ISP
Please note that not all family members contain same peripheral modules and features.
Block Diagram
Obsolete
www.national.com 2
Table of Contents
1.0 General Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2.0 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.0 Device Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
3.1 CR16B CPU Core . . . . . . . . . . . . . . . . . . . . . . . . . .5
3.2 Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
3.3 Input/Output Ports . . . . . . . . . . . . . . . . . . . . . . . . . .5
3.4 Bus Interface Unit . . . . . . . . . . . . . . . . . . . . . . . . . .5
3.5 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
3.6 Multi-Input Wake-up. . . . . . . . . . . . . . . . . . . . . . . . .6
3.7 Dual Clock and Reset . . . . . . . . . . . . . . . . . . . . . . .6
3.8 Power Management. . . . . . . . . . . . . . . . . . . . . . . . .6
3.9 Multi-Function Timer . . . . . . . . . . . . . . . . . . . . . . . .6
3.10 Versatile timer unit. . . . . . . . . . . . . . . . . . . . . . . . . .6
3.11 Real-Time TIMER and Watchdog . . . . . . . . . . . . . .6
3.12 USART. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
3.13 MICROWIRE/SPI. . . . . . . . . . . . . . . . . . . . . . . . . . .6
3.14 CR16CAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
3.15 ACCESS.bus Interface . . . . . . . . . . . . . . . . . . . . . .7
3.16 A/D Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
3.17 Analog Comparators . . . . . . . . . . . . . . . . . . . . . . . .7
3.18 Development Support . . . . . . . . . . . . . . . . . . . . . . .7
4.0 Device Pinouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
4.1 Pin Description. . . . . . . . . . . . . . . . . . . . . . . . . . . .10
5.0 System Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1 ENV0 and ENV1 Pins . . . . . . . . . . . . . . . . . . . . . .12
5.2 Module Configuration (MCFG) Register . . . . . . . .12
5.3 Module Status (MSTAT) Register . . . . . . . . . . . . .12
6.0 Input/Output Ports. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1 Port Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
6.2 Open-Drain Operation . . . . . . . . . . . . . . . . . . . . . .14
7.0 CPU and Core Registers . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1 General-Purpose Registers. . . . . . . . . . . . . . . . . .15
7.2 Dedicated Address Registers . . . . . . . . . . . . . . . .15
7.3 Processor Status Register. . . . . . . . . . . . . . . . . . .15
7.4 Configuration Register. . . . . . . . . . . . . . . . . . . . . .16
7.5 Addressing Modes. . . . . . . . . . . . . . . . . . . . . . . . .16
7.6 Stacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
7.7 Instruction Set . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
8.0 Bus Interface Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1 Bus Cycles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
8.2 BIU Control Registers . . . . . . . . . . . . . . . . . . . . . .18
8.3 Wait and Hold States Used . . . . . . . . . . . . . . . . . .20
9.0 Memory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
9.1 Flash EEPROM Program Memory. . . . . . . . . . . . .22
9.2 RAM Memory. . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
9.3 Flash EEPROM Data Memory. . . . . . . . . . . . . . . .25
9.4 ISP Memory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
10.0 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
10.1 Interrupt Operation. . . . . . . . . . . . . . . . . . . . . . . . .31
10.2 Non-Maskable Interrupt . . . . . . . . . . . . . . . . . . . . .32
10.3 Maskable Interrupts . . . . . . . . . . . . . . . . . . . . . . . .32
10.4 Interrupt Registers . . . . . . . . . . . . . . . . . . . . . . . . .33
10.5 Interrupt Programming Procedures . . . . . . . . . . . .35
11.0 Power Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
11.1 Active Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
11.2 Power Save Mode . . . . . . . . . . . . . . . . . . . . . . . . .36
11.3 Idle Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
11.4 Halt Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
11.5 Clock Inputs and Reset Configuration . . . . . . . . . .36
11.6 Switching Between Power Modes . . . . . . . . . . . . .36
12.0 Dual Clock and Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
12.1 External Crystal Network. . . . . . . . . . . . . . . . . . . .39
12.2 Main System Clock . . . . . . . . . . . . . . . . . . . . . . . .40
12.3 Slow System Clock . . . . . . . . . . . . . . . . . . . . . . . .40
12.4 Power-On Reset . . . . . . . . . . . . . . . . . . . . . . . . . .41
12.5 External Reset. . . . . . . . . . . . . . . . . . . . . . . . . . . .41
12.6 Dual Clock and Reset Registers . . . . . . . . . . . . . .41
12.7 Slow Clock Prescaler Register (PRSSC). . . . . . . .41
12.8 Slow Clock Prescaler 1 Register (PRSSC1) . . . . .41
13.0 Multi-Input Wake-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
13.1 Wake-Up Edge Detection Register (WKEDG). . . .42
13.2 Wake-Up Enable Register (WKENA). . . . . . . . . . .42
13.3 Wake-Up Interrupt Control Register 1 (WKCTRL1)43
13.4 Wake-Up Interrupt Control Register 1 (WKCTRL2)43
13.5 Wake-Up Pending Register (WKPND) . . . . . . . . . .43
13.6 Wake-Up Pending Clear Register (WKPCL) . . . . .43
13.7 Programming Procedures . . . . . . . . . . . . . . . . . . .44
14.0 Real-Time Timer and WATCHDOG. . . . . . . . . . . . . . . . .45
14.1 TWM Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . .45
14.2 Timer T0 Operation . . . . . . . . . . . . . . . . . . . . . . . .45
14.3 WATCHDOG Operation . . . . . . . . . . . . . . . . . . . . .46
14.4 TWM Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . .46
14.5 WATCHDOG Programming Procedure . . . . . . . . .47
15.0 Multi-Function Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
15.1 Timer Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . .49
15.2 Timer Operating Modes . . . . . . . . . . . . . . . . . . . . .51
15.3 Timer Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . .54
15.4 Timer I/O Functions . . . . . . . . . . . . . . . . . . . . . . . .54
15.5 Timer Registers . . . . . . . . . . . . . . . . . . . . . . . . . . .56
16.0 Versatile-Timer-Unit (VTU) . . . . . . . . . . . . . . . . . . . . . . .58
16.1 VTU Functional Description . . . . . . . . . . . . . . . . . .58
16.2 VTU Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
17.0 MICROWIRE/SPI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
17.1 MICROWIRE Operation . . . . . . . . . . . . . . . . . . . . .65
17.2 Master Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66
17.3 Slave Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67
17.4 Interrupt Generation. . . . . . . . . . . . . . . . . . . . . . . .68
17.5 MICROWIRE Interface Registers. . . . . . . . . . . . . .68
18.0 USART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71
18.1 Functional Overview. . . . . . . . . . . . . . . . . . . . . . . .71
18.2 USART Operation . . . . . . . . . . . . . . . . . . . . . . . . .71
18.3 USART Registers. . . . . . . . . . . . . . . . . . . . . . . . . .75
18.4 Baud Rate Calculations . . . . . . . . . . . . . . . . . . . . .77
19.0 ACCESS.bus Interface. . . . . . . . . . . . . . . . . . . . . . . . . . .78
19.1 ACB Protocol Overview . . . . . . . . . . . . . . . . . . . . .78
19.2 ACB Functional Description . . . . . . . . . . . . . . . . . .79
19.3 ACB Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . .82
19.4 Usage Hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84
20.0 CR16CAN Module. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85
20.1 Functional Description . . . . . . . . . . . . . . . . . . . . . .85
20.2 Basic CAN Concepts . . . . . . . . . . . . . . . . . . . . . . .87
20.3 Message Transfer . . . . . . . . . . . . . . . . . . . . . . . . .95
20.4 Acceptance Filtering. . . . . . . . . . . . . . . . . . . . . . . .96
20.5 Receive Structure. . . . . . . . . . . . . . . . . . . . . . . . . .97
20.6 Transmit Structure . . . . . . . . . . . . . . . . . . . . . . . .100
20.7 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103
20.8 Time Stamp Counter . . . . . . . . . . . . . . . . . . . . . .105
20.9 Memory Organization. . . . . . . . . . . . . . . . . . . . . .105
20.10 System Start-Up and Multi-Input Wake-Up . . . . .116
21.0 Analog Comparators . . . . . . . . . . . . . . . . . . . . . . . . . . .118
21.1 Analog Comparator Control/Status Register
(CMPCTRL). . . . . . . . . . . . . . . . . . . . . . . . . . . . . .118
21.2 Analog Comparator Usage. . . . . . . . . . . . . . . . . .118
22.0 A/D Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .119
22.1 Operating Modes . . . . . . . . . . . . . . . . . . . . . . . . .119
22.2 A/D Converter Registers . . . . . . . . . . . . . . . . . . .120
22.3 A/D Converter Programming . . . . . . . . . . . . . . . .122
23.0 Memory Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123
24.0 Register Layouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .129
24.1 Register layout . . . . . . . . . . . . . . . . . . . . . . . . . . .129
25.0 ELECTRICAL AND THERMAL CHARACTERISTICS . .136
26.0 Appendix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .152
26.1 CR16CAN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .152
26.2 8/16-bit microwire/spi (MWSPI16) . . . . . . . . . . . .154
26.3 Timing and watchdog module . . . . . . . . . . . . . . .154
Obsolete
3www.national.com
1.0 General Description (Continued)
The device has up to 64K bytes of reprogrammable flash EE-
PROM program memory or ROM memory, 1.5K bytes of
flash EEPROM In-System-Programming memory, 3K bytes
of static RAM, 2K bytes of non-volatile EEPROM data mem-
ory and 128 bytes with high endurance, two USARTs, two 16-
bit multi-function timers, one SPI/MICROWIRE-PLUS™ seri-
al interface, a 12-channel A/D converter, two analog compar-
ators, WATCHDOG™ protection mechanism, and up to 56
general-purpose I/O pins.
The device operates with a high-frequency crystal as the
main clock source and either the prescaled main clock
source or with a low frequency (32.768 kHz) oscillator in
Power Save mode. The device supports several Power Save
modes which are combined with multi-source interrupt and
wake-up capabilities.
This device also has a Versatile Timer Unit (VTU) with four
timer sub-systems, a CAN interface, and ACCESS.bus syn-
chronous serial bus interface.
Powerful cross-development tools are available from Nation-
al Semiconductor and third party suppliers to support the de-
velopment and debugging of application software for the
device. These tools let you program the application software
in C and are designed to take full advantage of the Compac-
tRISC architecture.
In the following text, device is always referred to the family of
16-bit CAN-enabled CompactRISC Microtroller.
2.0 Features
•CPU Features
—Fully static core, capable of operating at any rate from
0 to 24 MHz (4 MHz minimum in active mode)
—50 ns instruction cycle time with a 20 MHz external
clock frequency
—Multi-source vectored interrupts (internal, external,
and on-chip peripheral)
—Dual clock and reset
•On-chip power-on reset
•On-Chip Memory
—Up to 64K bytes flash EEPROM program memory; can
be programmed, erased, and reprogrammed by soft-
ware (100K cycles)
—3K bytes of static RAM data memory
—For flash program memory devices, 1.5k bytes flash
EEPROM memory is available to store boot loader
code (100K cycles)
—2K bytes of non-volatile EEPROM data memory with
low endurance (25K cycles) and 128 bytes with high
endurance (100K cycles)
•On-Chip Peripherals
—Two Universal Synchronous/Asynchronous Receiver/
Transmitter (USART) devices
—Programmable Idle Timer and real-time clock (T0)
—Two dual 16-bit multi-function timers (MFT1 and MFT2)
—8/16-bit SPI/MICROWIRE-PLUS serial interface
—12-channel, 8-bit Analog-to-Digital (A/D) converter
with external voltage reference, programmable sam-
ple-and-hold delay, and programmable conversion fre-
quency
—ACCESS.bus synchronous serial bus
—FullCAN interface with 15 message buffers complaint
to CAN specification 2.0B active
—Versatile Timer Unit with four subsystems (VTU)
—Two analog comparators
—Integrated WATCHDOG logic
•I/O Features
—Up to 56 general-purpose I/O pins (shared with on-chip
peripheral I/O pins)
—Programmable I/O pin characteristics: TRI-STATE out-
put, push-pull output, weak pull-up input, high-imped-
ance input
—Schmitt triggers on general purpose inputs
•Power Supply
—4.5V to 5.5V single-supply operation
•Temperature Range
—–40°C to +85°C
—–40°C to +125°C
•Development Support
—Real-time emulation and full program debug capabili-
ties available
—CompactRISC tools provide C programming and de-
bugging support
Obsolete
www.national.com 4
CR16 CompactRISC Microcontroller with CAN Interface Family Selection Guide
Programmable devices
Factory Programmed devices
ROM devices
Note: All devices contains Access.bus (ACB), Clock and Re-
set, MICROWIRE/API, Multi-Input Wake-Up (MIWU), Power
Management (PMM), and the Real-Time Timer and Watch-
dog (TWM) modules. Access.bus is compatible with I2C bus
offered by Philips Semiconductor.
CR16 CompactRISC Microcontroller with CAN Interface
Family Devices
National Semiconductor currently offers a variety of the
CR16 CompactRISC Microcontrollers with CAN interface.
The CR16MCS offer complete functionality in an 80-pin
PQFP package.
NSID Speed
(MHz) Flash/
(kByte)
EEPROM
Data
Memory
(Bytes)
SRAM
(kBytes) USART Timer I/Os Temp.
Range Peripherals Package
Type
CR16MCS9VJEx 16 64 2176 3 2 2MFT,
VTU 56 E, I ADC, CAN,
Comparators 80 PQFP
CR16MAS9VJEx 24 64 3 2 2MFT,
VTU 56 E, I ADC, CAN,
Comparators 80 PQFP
NSID Speed
(MHz) Flash/
(KByte)
EEPROM
Data
Memory
(Bytes)
SRAM
(kBytes) USART Timer I/Os Temp.
Range Peripherals Package
Type
CR16MCS9VJExy 16 64 2176 3 2 2MFT,
VTU 56 E, I ADC, CAN,
Comparators 80 PQFP
CR16MCS9VJExy 24 64 2176 3 2 2MFT,
VTU 56 E, I ADC, CAN,
Comparators 80 PQFP
NSID Speed
(MHz)
Flash/
ROM
(KByte)
EEPROM
Data
Memory
(Bytes)
SRAM
(kBytes) USART Timer I/Os Temp.
Range Peripherals Package
Type
CR16HCS9VJEx 24 64 2176 3 2 2MFT,
VTU 56 E, I ADC, CAN,
Comparators 80 PQFP
CR16MCS5VJEx 24 64 2176 3 2 2MFT,
VTU 56 E, I ADC, CAN,
Comparators 80 PQFP
CR16MBR5VJEx 24 32 2176 3 2 2MFT,
VTU 56 E, I ADC, CAN,
Comparators 80 PQFP
CR16MAR5VJEx 24 32 3 2 2MFT,
VTU 56 E, I CAN, 80 PQFP
CR16MAS5VJEx 24 64 3 2 2MFT,
VTU 56 E, I CAN, 80 PQFP
Note:
•Suffix x in the NSID is defined below:
Temperature Ranges:
I = Industrial
E = Extended
•Suffix y in the NSID defines the ROM code.
-40°C to +85°C is represented when x is 8
-40°C to +125°C is represented when x is 7
Obsolete
5www.national.com
3.0 Device Overview
The devices are complete microcomputers with all system
timing, interrupt logic, program memory, data memory, and I/
O ports included on-chip, making it well-suited to a wide
range of embedded controller applications.
3.1 CR16B CPU CORE
The device uses a CR16B CPU core module. This is the
same core used in other CompactRISC family member de-
signs, like DECT or GSM chipsets.
The high performance of the CPU core results from the im-
plementation of a pipelined architecture with a two-bytes-per-
cycle pipelined system bus. As a result, the CPU can support
a peak execution rate of one instruction per clock cycle.
Compared with conventional RISC processors, the device
differs in the following ways:
—The CPU core can use on-chip rather than external
memory. This eliminates the need for large and com-
plex bus interface units.
—Most instructions are 16 bits, so all basic instructions
are just two bytes long. Additional bytes are sometimes
required for immediate values, so instructions can be
two or four bytes long.
—Non-aligned word access is allowed. Each instruction
can operate on 8-bit or 16-bit data.
—The device is designed to operate with a clock rate in
the 10 to 24 MHz range rather than 100 MHz or more.
Most embedded systems face EMI and noise con-
straints that limit clock speed to these lower ranges. A
lower clock speed means a simpler, less costly silicon
implementation.
—The instruction pipeline uses three stages. A smaller
pipeline eliminates the need for costly branch predic-
tion mechanisms and bypass registers, while maintain-
ing adequate performance for typical embedded
controller applications.
For more information, please refer to the CR16B Program-
mer’s Reference Manual, Literature #: 633150.
3.2 MEMORY
The CompactRISC architecture supports a uniform linear ad-
dress space of 2 megabytes. The device implementation of
this architecture uses only the lowest 128K bytes of address
space. Four types of on-chip memory occupy specific inter-
vals within this address space:
•64K bytes of flash EEPROM program memory (100K cy-
cles)
•48K bytes ROM programm memory version available also
(100K cycles)
•3K bytes of static RAM
•2K bytes of EEPROM data memory with low endurance
(25K cycles)
•128 bytes with high endurance (100K cycles)
•1.5K bytes flash EEPROM memory for ISP code
The 3K bytes of static RAM are used for temporary storage
of data and for the program stack and interrupt stack. Read
and write operations can be byte-wide or word-wide, depend-
ing on the instruction executed by the CPU. Each memory
access requires one clock cycle; no wait cycles or hold cycles
are required.
There are two types of flash EEPROM data memory storage.
The 2K bytes of EEPROM data memory with low endurance
(25K cycles) and 128 bytes of flash EEPROM data memory
with high endurance (100K cycles) are used for non-volatile
storage of data, such as configuration settings entered by the
end-user.
The 64K bytes of flash EEPROM program memory are used
to store the application program. It has security features to
prevent unintentional programming and to prevent unautho-
rized access to the program code. This memory can be pro-
grammed with a device external programming unit or with the
device installed in the application system (in-system pro-
gramming).
There is a factory programmed boot memory used to store
In-System-Programming (ISP) code. (This code allows pro-
gramming of the program memory via one of the USART in-
terfaces in the final application.)
For flash EEPROM program and data memory, the device in-
ternally generates the necessary voltages for programming.
No additional power supply is required.
3.3 INPUT/OUTPUT PORTS
The device has 56 software-configurable I/O pins, organized
into seven 8-pin ports called Port B, Port C, Port F, Port G,
Port H, Port I, and Port L. Each pin can be configured to op-
erate as a general-purpose input or general-purpose output.
In addition, many I/O pins can be configured to operate as a
designated input or output for an on-chip peripheral module
such as the USART, timer, A/D converter, or MICROWIRE/
SPI interface.
The I/O pin characteristics are fully programmable. Each pin
can be configured to operate as a TRI-STATE output, push-
pull output, weak pull-up input, or high-impedance input.
3.4 BUS INTERFACE UNIT
The Bus Interface Unit (BIU) controls the interface between
the on-chip modules to the internal core bus. It determines
the configured parameters for bus access (such as the num-
ber of wait states for memory access) and issues the appro-
priate bus signals for each requested access.
The BIU uses a set of control registers to determine how
many wait states and hold states are to be used when ac-
cessing flash EEPROM program memory, ISP memory and
the I/O area (Port B and Port C). Upon start-up the configu-
ration registers are set for slowest possible memory access.
To achieve fastest possible program execution, appropriate
values should be programmed. These settings vary with the
clock frequency and the type of on-chip device being access-
ed.
Obsolete
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3.5 INTERRUPTS
The Interrupt Control Unit (ICU31L) receives interrupt re-
quests from internal and external sources and generates in-
terrupts to the CPU. An interrupt is an event that temporarily
stops the normal flow of program execution and causes a
separate interrupt service routine to be executed. After the in-
terrupt is serviced, CPU execution continues with the next in-
struction in the program following the point of interruption.
Interrupts from the timers, USARTs, MICROWIRE/SPI inter-
face, multi-input wake-up, and A/D converter are all
maskable interrupts; they can be enabled or disabled by the
software. There are 32 of these maskable interrupts, orga-
nized into 32 predetermined levels of priority.
The highest-priority interrupt is the Non-Maskable Interrupt
(NMI), which is generated by a signal received on the NMI in-
put pin.
3.6 MULTI-INPUT WAKE-UP
The Multi-Input Wake-Up (MIWU16) module can be used for
either of two purposes: to provide inputs for waking up (exit-
ing) from the HALT, IDLE, or Power Save mode; or to provide
general-purpose edge-triggered maskable interrupts from
external sources. This 16-channel module generates four
programmable interrupts to the CPU based on the signals re-
ceived on its 16 input channels. Channels can be individually
enabled or disabled, and programmed to respond to positive
or negative edges.
3.7 DUAL CLOCK AND RESET
The Dual Clock and Reset (CLK2RES) module generates a
high-speed main system clock from an external crystal net-
work. It also provides the main system reset signal and a
power-on reset function.
This module also generates a slow system clock (32.768
kHz) from another external crystal network. The slow clock is
used for operating the device in power-save mode. Without a
32.768kHz external crystal network, the low speed system
clock can be derived from the high speed clock by a prescal-
er.
Also, two independent clocks divided down from the high
speed clock are available on output pins.
3.8 POWER MANAGEMENT
The Power Management Module (PMM) improves the effi-
ciency of the device by changing the operating mode and
therefore the power consumption according to the required
level of activity.
The device can operate in any of four power modes:
—Active: The device operates at full speed using the
high-frequency clock. All device functions are fully op-
erational.
—Power Save: The device operates at reduced speed
using the slow clock. The CPU and some modules can
continue to operate at this low speed.
—IDLE: The device is inactive except for the Power Man-
agement Module and Timing and Watchdog Module,
which continue to operate using the slow clock.
—HALT: The device is inactive but still retains its internal
state (RAM and register contents).
3.9 MULTI-FUNCTION TIMER
The Multi-Function Timer (MFT16) module contains two inde-
pendent timer/counter units called MFT1 and MFT2, each
containing a pair of 16-bit timer/counter registers. Each timer/
counter unit can be configured to operate in any of the follow-
ing modes:
—Processor-Independent Pulse Width Modulation
(PWM) mode, which generates pulses of a specified
width and duty cycle, and which also provides a gener-
al-purpose timer/counter.
—Dual Input Capture mode, which measures the
elapsed time between occurrences of external events,
and which also provides a general-purpose timer/
counter.
—Dual Independent Timer mode, which generates sys-
tem timing signals or counts occurrences of external
events.
—Single Input Capture and Single Timer mode, which
provides one external event counter and one system
timer.
3.10 VERSATILE TIMER UNIT
The Versatile Timer Unit (VTU) module contains four inde-
pendent timer subsystems, each operating in either dual 8-bit
PWM configuration, as a single 16-bit PWM timer, or a 16-bit
counter with two input capture channels. Each of the four tim-
er subsystems offer an 8-bit clock prescaler to accommodate
a wide range of frequencies.
3.11 REAL-TIME TIMER AND WATCHDOG
The Timing and Watchdog Module (TWM) generates the
clocks and interrupts used for timing periodic functions in the
system. It also provides Watchdog protection against soft-
ware errors. The module operates on the slow system clock.
The real-time timer can generate a periodic interrupt to the
CPU at a software-programmed interval. This can be used
for real-time functions such as a time-of-day clock. The real-
time timer can trigger a wake-up condition from power-save
mode via the Multi-Input Wake-Up module.
The Watchdog is designed to detect program execution er-
rors such as an infinite loop or a “runaway” program. Once
Watchdog operation is initiated, the application program
must periodically write a specific value to a Watchdog regis-
ter, within specific time intervals. If the software fails to do so,
a Watchdog error is triggered, which resets the device.
3.12 USART
The USART supports a wide range of programmable baud
rates and data formats, and handles parity generation and
several error detection schemes. The baud rate is generated
on-chip, under software control.
There are two independent USARTs in the device and they
offer a wake-up condition from the power-save mode via the
Multi-Input Wake-Up module.
3.13 MICROWIRE/SPI
The MICROWIRE/SPI (MWSPI) interface module supports
synchronous serial communications with other devices that
conform to MICROWIRE or Serial Peripheral Interface (SPI)
specifications. It supports 8-bit and 16-bit data transfers.
Obsolete
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The MICROWIRE interface allows several devices to com-
municate over a single system consisting of four wires: serial
in, serial out, shift clock, and slave enable. At any given time,
the MICROWIRE interface operates as the master or a slave.
The support supports the full set of slave select for multi-
slave implementation.
In master mode, the shift clock is generated on chip under
software control. In slave mode, a wake-up out of power-
save mode is triggered via the Multi-Input Wake-Up module.
3.14 CR16CAN
The CR16CAN device contains a FullCAN class, CAN serial
bus interface for applications that require a high speed (up to
1MBits per second) or a low speed interface with CAN bus
master capability. The data transfer between CAN and the
CPU is established by 15 memory mapped message buffers,
which can be individually configured as receive or transmit
buffers. An incoming message is filtered by two masks, one
for the first 14 message buffers and another one for the 15th
message buffer to provide a basic CAN path. A priority de-
coder allows any buffer to have the highest or lowest transmit
priority. Remote transmission requests can be processed au-
tomatically by automatic reconfiguration to a receiver after
transmission or by automated transmit scheduling upon re-
ception. In addition, a time stamp counter (16-bits wide) is
provided to support real time applications.
The CR16CAN device is a fast core bus peripheral, which al-
lows single cycle byte or word read/write access. A set of di-
agnostic features (such as loopback, listen only, and error
identification) support the development with the CR16CAN
module and provide a sophisticated error management tool.
The CR16CAN receiver can trigger a wake-up condition out
of the power-save modes via the Multi-Input Wake-Up mod-
ule.
3.15 ACCESS.BUS INTERFACE
The ACCESS.bus interface module (ACB) is a two-wire seri-
al interface with the ACCESS.bus physical layer. It is also
compatible with Intel’s System Management Bus (SMBus)
and Philips’ I2C bus. The ACB module can be configured as
a bus master or slave, and can maintain bi-directional com-
munications with both multiple master and slave devices.
The ACCESS.bus receiver can trigger a wake-up condition
out of the power-save modes via the Multi-Input Wake-Up
module.
3.16 A/D CONVERTER
The A/D Converter (ADC) module is a 12-channel multi-
plexed-input analog-to-digital converter. The A/D Converter
receives an analog voltage signal on an input pin and con-
verts the analog signal into an 8-bit digital value using suc-
cessive approximation. The CPU can then read the result
from a memory-mapped register. The module supports four
automated operating modes, providing single-channel or 4-
channel operation in single or continuous mode.
The device has a separate pin, Vref, for the A/D reference
voltage.
3.17 ANALOG COMPARATORS
The Dual Analog Comparator (ACMP2) module contains two
independent analog comparators with all necessary control
logic. Each comparator unit compares the analog input volt-
ages applied to two input pins and determines which voltage
is higher. The CPU uses a memory-mapped register to con-
trol the comparator and to obtain the comparison results. The
comparison result can also be applied to comparator output
pins.
3.18 DEVELOPMENT SUPPORT
A powerful cross-development tool set is available from Na-
tional Semiconductor and third parties to support the devel-
opment and debugging of application software for the
CR16MCS9. The tool set lets you program the application
software in C and is designed to take full advantage of the
CompactRISC architecture.
There are In-System Emulation (ISE) devices available for
the device from iSYSTEM™, as well as lower-cost evaluation
boards. See your National Semiconductor sales representa-
tive for current information on availability and features of em-
ulation equipment and evaluation boards.
Obsolete
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4.0 Device Pinouts Table 1Package Pin Assignments
Pin Name Alternate Function(s) Pin Number Type
PH4 MWCS 1I/O
PH5 MD1D0 2I/O
PH6 MD0D1 3I/O
PH7 MSK 4I/O
PB0 D0 5I/O
PB1 D1 6I/O
PB2 D2 7I/O
PB3 D3 8I/O
PB4 D4 9I/O
PB5 D5 10 I/O
PB6 D6 11 I/O
PB7 D7 12 I/O
ENV0/CLKOUT1 13 I/O
SDA 14 I/O
SCL 15 I/O
GND 16 PWR
Vcc 17 PWR
GND 18 PWR
CANTx 19 O
CANRx 20 I
PC0 D8 21 I/O
PC1 D9 22 I/O
PC2 D10 23 I/O
PC3 D11 24 I/O
PC4 D12 25 I/O
PC5 D13 26 I/O
PC6 D14 27 I/O
PC7 D15 28 I/O
PG7 CKX1 29 I/O
PG6 TDX1 30 I/O
PG5 RDX1 31 I/O
PG4 TIO6 32 I/O
PG3 TIO5 33 I/O
PG2 CKX2 34 I/O
PG1 TDX2 35 I/O
PG0 RDX2 36 I/O
CLKOUT2 37 O
ENV1/CLK137 I/O
PF7 TIO4 38 I/O
PF6 TIO3 39 I/O
PF5 T2B 40 I/O
PF4 T2A 41 I/O
PF3 TIO2 42 I/O
PF2 TIO1 43 I/O
PF1 TIB 44 I/O
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PF0 TIA 45 I/O
NMI 46 I
X1CKO 47 O
X1CKI 48 I
GND 49 PWR
Vcc 50 PWR
GND 51 PWR
X2CKO 52 O
X2CKI 53 I
RESET254 I
PI0 ACH0355 I/O
PI1 ACH1356 I/O
PI2 ACN2357 I/O
PI3 ACH3358 I/O
PI4 ACH4359 I/O
PI5 ACH5360 I/O
PI6 ACH6361 I/O
PI7 ACH7362 I/O
Vref 63 PWR
AGND 64 PWR
AVcc 65 PWR
PH0 ACH83, WUI4 66 I/O
PH1 ACH93, WUI5 67 I/O
PH2 ACH103, WUI6 68 I/O
PH3 ACH113, WUI7 69 I/O
GND 70 PWR
Vcc 71 PWR
GND 72 PWR
PL0 COMP1N3, WUI0 73 I/O
PL1 COMP1P3, WUI1 74 I/O
PL2 COMP1O, WUI2 75 I/O
PL3 COMP2O, WUI3 76 I/O
PL4 COMP2P377 I/O
PL5 COMP2N378 I/O
PL6 TIO7 79 I/O
PL7 TIO8 80 I/O
Note 1: The ENV0 and ENV1 pins each have a weak pull-up to keep the input from floating.
Note 2: The RESET input has a weak pulldown.
Note 3: These functions are always enabled, due to the direct low-impedance path to these pins.
Table 1Package Pin Assignments
Pin Name Alternate Function(s) Pin Number Type
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4.1 PIN DESCRIPTION
Some pins have alternate functions which may be enabled.
These pins can be individually configured as general pur-
pose pins, even when the module they belong to is enabled.
The following is a brief description of all device pins.
Table 2Input Pins
Signal Type Active Pin (* for a shared pin) Function
X1CKI OSC High Main oscillator clock input.
X2CKI OSC High 32kHz oscillator clock input.
RESET CMOS Low Chip general reset pin. Schmitt trigger input, asynchronous.
ISE CMOS Low Interrupt input for development system.
T1B CMOS Prog. *Timer 1 input B. Shares pin with I/O port pin PF1.
T2B CMOS Prog. *Timer 2 input B. Shares pin with I/O port pin PF5.
RDX1 CMOS High *USART 1 receive data input. Shares pin with I/O port pin PG5.
RDX2 CMOS High *USART 2 receive data input. Shares pin with I/O port pin PG0.
ACH0 Analog *A2D converter channel 0. Shares pin with I/O port pin PI0
ACH1 Analog *A2D converter channel 1. Shares pin with I/O port pin PI1
ACH2 Analog *A2D converter channel 2. Shares pin with I/O port pin PI2
ACH3 Analog *A2D converter channel 3. Shares pin with I/O port pin PI3
ACH4 Analog *A2D converter channel 4. Shares pin with I/O port pin PI4
ACH5 Analog *A2D converter channel 5. Shares pin with I/O port pin PI5
ACH6 Analog *A2D converter channel 6. Shares pin with I/O port pin PI6
ACH7 Analog *A2D converter channel 7. Shares pin with I/O port pin PI7
ACH8 Analog *A2D converter channel 8. Shares pin with I/O port pin PH0
ACH9 Analog *A2D converter channel 9. Shares pin with I/O port pin PH1
ACH10 Analog *A2D converter channel 10. Shares pin with I/O port pin PH2
ACH11 Analog *A2D converter channel 11. Shares pin with I/O port pin PH3
MWCS CMOS Low *SPI/MICROWIRE slave select. Shares pin with I/O port pin PH4.
NMI CMOS Low External non-maskable interrupt.
ENV0 CMOS Low *Strap to select operating environment.
ENV1 CMOS Low *Strap pin to select operating environment.
ENV2 CMOS Low Strap pin to select operating environment.
CANRx CMOS High CAN receive data input.
Table 3Output Pins
Signal Type Active Pin (* for
a shared pin) Function
X1CKO OSC High Main oscillator clock output.
X2CKO OSC High 32kHz oscillator clock output.
CLK CMOS High *External reference clock for development environment (shared with ENV1).
CLKOUT
1CMOS High *Clock output generated through prescaler (shared with ENV0).
CLKOUT
2CMOS High *Clock output generated through prescaler (shared with ENV1).
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TDX1 CMOS High *USART 1 transmit data output (shared with PG6).
TDX2 CMOS High *USART 2 transmit data output (shared with PG1).
CANTx CMOS High CAN output.
Table 4Input/Output Pins
Signal Type Active Pin (* for a
shared pin) Function
PF[0:7] CMOS High *Generic I/O port. Shared with T1A, T1B, TIO1, TIO2, T2A, T2B, TIO3, TIO4.
PG[0:7] CMOS High *Generic I/O port. Shared with RDX2, TDX2, CKX2, TIO5, TIO6, RDX1, TDX1,
CKX1.
PB[0:7] CMOS High *Generic I/O port.
PC[0:7] CMOS High *Generic I/O port.
PL[0:7] CMOS High *Generic I/O port. Shared with 6 comparator pins, MIWU16 on PL0:3.
PH[0:7] CMOS High *Generic I/O port. Shared with ADC input channels 8-11, MWCS, MDIDO,
MDODI, MSK; MIWU16 on PH4:7.
PI[0:7] CMOS High *Generic I/O port. Shared with ADC input channels 0-7.
T1A CMOS Prog *Timer 1 input A. Shared with I/O port pin PF0.
T2A CMOS Prog *Timer 2 input A. Shared with I/O port pin PF4.
TIO[0:7] CMOS Prog *Versatile timer unit I/Os. Shared with PF2:3, PF6:7, PG3:4, PL6:7.
MDIDO CMOS High *Master In/Slave Out port: SPI/Microwire. Shared with I/O pin PH5,
MDODI CMOS High *Master Out/Slave In port: SPI/Microwire. Shared with I/O pin PH6.
MSK CMOS Prog *SPI/Microwire clock. Shared with I/O pin PH7.
CKX1 CMOS High *USART 1 clock. Shared with I/O pin PG7.
CKX2 CMOS High *USART 2 clock. Shared with I/O pin PG2
SCL CMOS High ACCESS.bus clock I/O.
SDA CMOS High ACCESS.bus data I/O.
Table 5Power Supply
Signal Function
Vcc Main digital power supply (4 total).
Vref Voltage reference supply for analog to digital converter.
AVcc Analog power supply for analog/digital converter.
AGND Analog reference ground supply.
GND Main digital reference ground (8 total).
Table 3Output Pins
Signal Type Active Pin (* for
a shared pin) Function
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5.0 System Configuration
The device has two input pins, ENV0 and ENV1, which are
used to specify the operating environment of the device upon
reset. There are also two system configuration registers,
called the Module Configuration (MCFG) register and the
Module Status (MSTAT) register.
5.1 ENV0 AND ENV1 PINS
Upon reset, the operating mode of the device is determined
by the state of the ENV0 and ENV1 input pins, as indicated
in Table6.
In the case where the ENV1 and ENV0 pins are both high,
the reset algorithm looks at the FLCTRL2.EMPTY bit to de-
termine whether the program memory is empty, and sets the
operating mode accordingly.
The ENV0 and ENV1 pins have on-chip pull-up devices that
are enabled during reset while the pins are being sampled.
Therefore, if they are left unconnected, the inputs are consid-
ered high and the normal operating mode (IRE-Mode) is se-
lected and the CPU starts to execute code at address 0. To
enter any other operating mode, the external hardware must
drive the appropriate input low.
In the case where the ISP-Mode is selected, the chip starts
executing the ISP code residing in the on-chip ISP-Memory
area.
The test modes are Reserved for factory testing and for ex-
ternal programming of the flash EEPROM program memory.
They should not be invoked otherwise.
5.2 MODULE CONFIGURATION (MCFG)
REGISTER
The MCFG register is a byte-wide, read/write register that
sets the clock output features of the device.
Upon reset, the non-reserved bits of this register are cleared
to zero. The start-up software must write a specific value to
this register in order to configure the CLK output pin function.
When the software writes to this register, it must write a zero
to each reserved bit for the device to operate properly. The
register should be written in active mode only, not in power
save, HALT, or IDLE mode. However, the register contents
are preserved during all power modes.
The MCFG register format is shown below.
CLKOE CPU Clock Output Enable. When this bit is
cleared (0), the CLK pin (ENV1) remains in the
high-impedance state. When this bit is set (1) in
normal operating mode, the CLK pin operates
as a CPU clock output.
CLK1OE Generated Clock Output 1 Enable. When
cleared (0), the CLKOUT1 pin (ENV0) stays in
high impedance state. When set (1), the pin
outputs the clock from the prescaler controlled
by PRSSC1.SCDIV1.
CLK2OE Generated Clock Output 2 Enable. When this
bit is set (1) and CLKOE is cleared, the
CLKOUT2 pin (ENV1) outputs the clock from
the prescaler controlled by PRSSC1.SCDIV2.
Otherwise, the CLKOUT2 pin is in high imped-
ance state.
5.3 MODULE STATUS (MSTAT) REGISTER
The MSTAT register is a byte-wide, read-only register that in-
dicates the general status of the device.
The MCFG register format is shown below.
OENV(1:0) Operating Environment. These two bits contain
the values applied to the ENV1 and ENV0 pins
upon reset. These bit values are controlled by
the external hardware upon reset and are held
constant in the register until the next reset.
PGMBUSY Flash EEPROM Programming Busy. This bit is
automatically set to 1 when either the program
memory or the data memory is busy being pro-
grammed or erased. It is cleared to 0 when nei-
ther of the two flash EEPROM memories is
busy being programmed or erased. When this
bit is set, the software should not attempt any
write access to either of these two memories.
Table 6Operating Environment Selection
ENV1 ENV0 Operating Environment
0 0 Test Mode Flash Memory
0 1 Test Mode
1 0 In-System-Programming mode (ISP)
1 1 Internal ROM enabled Mode (IRE), if
program memory is not empty; or ISP-
Mode, if program memory is empty
7 6 5 4 3 2 1 0
Reserved CLK2OE Reserved CLK1OE CLKOE Reserved
74 3 2 1 0
Reserved PGMBUSY Reserved OENV1 OENV0
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6.0 Input/Output Ports
Each device has up to 56 software-configurable I/O pins, or-
ganized into seven ports of up to eight pins per port. The
ports are named Port B, Port C, Port F, Port G, Port H, Port
I, and Port L.
Each pin can be configured to operate as a general-purpose
input or general-purpose output. In addition, many I/O pins
can be configured to operate as a designated input or output
for an on-chip peripheral module such as the USART or the
Multi-Input Wakeup. This is called the pin's “alternate func-
tion.” The alternate functions of all I/O pins are shown in the
pinout diagrams in Table1.
The I/O pin characteristics are fully programmable. Each pin
can be configured to operate as a TRI-STATE output, push-
pull output, weak pull-up input, or high-impedance input. Dif-
ferent pins within the same port can be individually config-
ured to operate in different modes.
Figure1 is a diagram showing the functional features of an I/
O port pin. The register bits, multiplexers, and buffers allow
the port pin to be configured into the various operating
modes.The output buffer is a TRI-STATE buffer with weak
pull-up capability. The weak pull-up, if used, prevents the port
pin from going to an undefined state when it operates as an
input.
The input buffer is disabled when it is not needed to prevent
leakage current caused by an input signal’s level between
Vcc-0.2 and Vss+0.2 [Volts]. When enabled, it buffers the in-
put signal and sends the pin's logic level to the appropriate
on-chip module where it is latched. A Schmitt-Trigger mini-
mizes the effects of electrical noise.
The electrical characteristics and drive capabilities of the in-
put and output buffers are described in Section25.0.
For some pins, a direct low-impedance path is provided be-
tween the pin and an internal analog function. These are the
input pins to the A/D converter and the analog comparators.
6.1 PORT REGISTERS
Each port has an associated set of memory-mapped regis-
ters used for controlling the port and for holding the port data.
In general, there are five such registers:
—PxALT: Port alternate function register
—PxDIR: Port direction register
—PxDIN: Port data input register
—PxDOUT: Port data output register
—PxWKPU: Port weak pull-up register
In the descriptions of the ports and port registers, the lower-
case letter “x” represents the port designation, either B, C, F,
G, H, I, or L. For example, “PxDIR register” means any one
of the port direction registers: PBDIR, PCDIR, PFDIR, and so
on.
All of the port registers are byte-wide read/write registers, ex-
cept for the port data input registers, which are read-only reg-
isters. Each register bit controls the function of the
corresponding port pin. For example, PFDIR.2 (bit 2 of the
PFDIR register) controls the operation of port pin PF2.
Figure 1.I/O Pin Functional Diagram
PIN
Direction
Data Out
Register {
Direction
Register {
Weak pull-up
Register {
Alternate Data Input
MUX1
MUX2
Weak pull-up
Data Out
Alt Device Data Output
Alt
Alt
Alt Device Direction
Data In Read Strobe
Alt
Data Input
MUX3
Alt 1
Alternate Function
enable
*
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6.1.1 Port Alternate Function Register
Each port that supports an alternate function (any port other
than Port B or Port C) has an alternate function register (Px-
ALT). This register determines whether the port pins are used
for general-purpose I/O or for the predetermined alternate
function. Each port pin can be controlled independently.
A bit cleared to 0 in the alternate function register causes the
corresponding pin to be used for general-purpose I/O. In this
configuration, the output buffer is controlled by the direction
register and the data output register. The input buffer is rout-
ed to the data input register. The input buffer is blocked ex-
cept when the buffer is actually being read.
A bit set to 1 in the alternate function register causes the cor-
responding pin to be used for its predetermined peripheral I/
O function. The output buffer data and TRI-STATE configura-
tion are controlled by signals coming from the on-chip periph-
eral device. The input buffer is enabled continuously in this
case. To minimize power consumption, the input signal
should be held within 0.2 volts of the VCC or GND voltage.
A reset operation clears the port alternate function registers
to 0, which programs the pins to operate as general-purpose
I/O ports. This register must be enabled before the corre-
sponding alternate function is enabled.
6.1.2 Port Direction Register
The port direction register (PxDIR) determines whether each
port pin is used for input or for output. A bit cleared to 0 caus-
es the pin to operate as an input, which puts the output buffer
in the high-impedance state. A bit set to 1 causes the pin to
operate as an output, which enables the output buffer.
A reset operation clears the port direction registers to 0,
which programs the pins to operate as inputs.
6.1.3 Port Data Input Register
The data input register (PxDIN) is a read-only register that re-
turns the current state of each port pin. The CPU can read
this register at any time even when the pin is configured as
an output.
6.1.4 Port Data Output Register
The data output register (PxDOUT) holds the data to be driv-
en onto each port pin configured to operate as a general-pur-
pose output. In this configuration, writing to the register
changes the output value. Reading the register returns the
last value written to the register.
A reset operation leaves the register contents unchanged.
Upon power-up, the registers contain unknown values.
6.1.5 Port Weak Pull-Up Register
The weak pull-up register (PxWKPU) determines whether
each port pin uses a weak pull-up on the output buffer. A bit
set to 1 causes the weak pull-up to be used, while a bit
cleared to 0 causes the causes the weak pull-up not to be
used.
The pull-up device, if enabled by the register bit, operates in
the general-purpose I/O mode whenever the port output buff-
er is in the TRI-STATE mode. In the alternate function mode,
the pull-ups are always disabled.
A reset operation clears the port weak pull-up registers to 0,
which disables all pull-ups.
6.2 OPEN-DRAIN OPERATION
A port pin can be configured to operate as an inverting open-
drain output buffer. To do this, the CPU should clear the bit in
the data output register (PxDOUT) and then use the port di-
rection register (PxDIR) to set the value of the port pin. With
the direction register bit set to 1 (direction=out), the value
zero is forced on the pin. With the direction register bit
cleared to 0 (direction=in), the pin is placed in the TRI-STATE
mode. If desired, the internal weak pull-up can be enabled to
pull the signal high when the output buffer is in the TRI-
STATE mode.
Obsolete
15 www.national.com
7.0 CPU and Core Registers
The device uses the same CR16B CPU core as other Com-
pactRISC family members. The core's Reduced Instruction
Set Computer (RISC) architecture allows a processing rate
of up to one instruction per clock cycle.
The CPU core uses a set of internal registers:
—General-purpose registers (R0-R13, RA, and SP)
—Dedicated address registers (PC, ISP, and INTBASE)
—Processor Status Register (PSR)
—Configuration Register (CFG)
All of these registers are 16 bits wide except for the three ad-
dress registers, which are 21 bits wide.
Some register bits are designated as “reserved.” The CPU
must write a zero to each of these bit locations when it writes
to the register. Read operations from reserved bit locations
return undefined values.
7.1 GENERAL-PURPOSE REGISTERS
There are 16 general-purpose registers, designated R0
through R13, RA, and SP. Registers R0 through R13 can be
used for any purpose such as holding variables, addresses,
or index values. The RA register is usually used to store the
return address upon entry into a subroutine. The SP register
is usually used as the pointer to the program run-time stack.
If a general-purpose register is used for a byte-wide opera-
tion, only the low-order byte is referenced or modified. The
high-order byte is not used or affected by a byte-wide opera-
tion.
7.2 DEDICATED ADDRESS REGISTERS
There are three dedicated address registers: the Program
Counter (PC), the Interrupt Stack Pointer (ISP), and the In-
terrupt Base Register (INTBASE). Each of these registers is
21 bits wide.
7.2.1 Program Counter
The PC register contains the address of the least significant
word currently being fetched. It is automatically incremented
or changed by the appropriate amount each time an instruc-
tion is executed.
The least significant bit of the PC is always zero, thus instruc-
tions must always be aligned to an even address in the range
of 0000 to 1FFFE hex.
Upon reset, the PC register is initialized to zero and program
execution starts at that address (if in IRE-Mode). When a re-
set signal is received, bits 1 through 16 of the PC register
(prior to initialization) are stored in register R0. This allows
the software to determine the point in the program at which
the reset occurred.
7.2.2 Interrupt Stack Pointer
The ISP register points to the lowest address of the last item
stored on the interrupt stack. This stack is used by the hard-
ware when an interrupt or trap service procedure is invoked.
7.2.3 Interrupt Base Register
The INTBASE register holds the address of the Dispatch Ta-
ble for interrupts and traps. The least significant bit of the reg-
ister is always zero. Thus, the Dispatch Table starts at an
even address in the range of 0000 to FFFE.
7.3 PROCESSOR STATUS REGISTER
The Processor Status Register (PSR) holds status informa-
tion and selects the operating modes for the CPU core. The
format of the register is shown below.
C bit The Carry (C) bit indicates whether a carry or
borrow occurred after addition or subtraction. It
is set to 1 if a carry or borrow occurred, or
cleared to 0 otherwise.
T bit The Trace (T) bit, when set, causes a Trace
(TRC) trap to be executed after every instruc-
tion. This bit is automatically cleared to 0 when
a trap or interrupt occurs.
L bit The Low (L) bit is set by comparison opera-
tions. In a comparison of unsigned integers, the
bit is set to 1 if the second operand (Rdest) is
less than the first operand (Rsrc). Otherwise, it
is cleared to 0.
F bit The Flag (F) bit is a general condition flag that
is set by various instructions. It may be used to
signal exception conditions or to distinguish the
results of an instruction. For example, integer
arithmetic instructions use this bit to indicate an
overflow condition after an addition or subtrac-
tion operation.
Z bit The Zero (Z) bit is set by comparison opera-
tions. In a comparison of integers, the bit is set
to 1 if the two operands are equal. Otherwise,
it is cleared to 0.
N bit The Negative (N) bit is set by comparison oper-
ations. In a comparison of signed integers, the
bit is set to 1 if the second operand (Rdest) is
less than the first operand (Rsrc). Otherwise, it
is cleared to 0.
E bit The Local Maskable Interrupt Enable (E) bit is
used to enable or disable maskable interrupts.
If this bit and the Global Maskable Interrupt En-
able (I) bit are both set to 1, all maskable inter-
rupts are accepted. Otherwise, only the non-
maskable interrupt is accepted. The E bit is set
to 1 by the Enable Interrupts (EI) instruction
and cleared to 0 by the Disable Interrupts (DI)
instruction.
P bit The Trace Trap Pending (P) bit is used togeth-
er with the Trace (T) bit to prevent a Trace
(TRC) trap from occurring more than once for
any instruction. The P bit may be cleared to 0
(no TRC trap pending) or set to 1 (TRC trap
pending).
15 14 13 12 11 109876543210
Reserved IP E 0NZF00LTC
Obsolete
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I bit The Global Maskable Interrupt Enable (I) bit is
used to enable or disable maskable interrupts.
If this bit and the Local Maskable Interrupt En-
able (E) bit are both set to 1, all maskable inter-
rupts are accepted. Otherwise, only the non-
maskable interrupt is accepted. This bit is auto-
matically cleared to 0 when an interrupt occurs
and automatically set to 1 upon completion of
an interrupt service routine.
Upon reset, all non-reserved bits of the register are cleared
to 0 except for the E bit (bit 9), which is set to 1. When a de-
vice reset occurs, the PSR contents prior to the reset are
stored into register R1, allowing the initialization software to
determine the state of the device prior to the reset operation.
7.4 CONFIGURATION REGISTER
The Configuration (CFG) register is a 16-bit core register that
determines the size of the INTBASE register. For the device,
the CFG register should always be left in its default state
(cleared to zero), resulting in a 16-bit INTBASE register.
7.5 ADDRESSING MODES
Each instruction operates on one or more operands. An op-
erand can be a register or a memory location.
Most instructions use one, two, or three device registers as
operands. The instruction opcode specifies the registers to
be operated on. Some instructions may use an immediate
value (a value provided in the instruction itself) instead of a
register.
Memory locations are accessed only by the Load and Store
commands. The memory location to use for a particular in-
struction can be specified as an absolute, relative, or far-rel-
ative address.
The instruction set supports the following addressing modes:
For additional information on the instruction set and instruc-
tion encoding, see the CompactRISC CR16B Programmer's
Reference manual.
7.6 STACKS
A stack is a one-dimensional data buffer in which values are
entered and removed one at a time. The last valued entered
is the first one removed. A register called the stack pointer
contains the current address of the last item entered on the
stack. In the device, when an item is entered or “pushed”
onto the stack, the stack expands downward in memory (the
stack pointer is decremented). When an item is removed or
“popped” from the stack, the stack shrinks upward in memory
(the stack pointer is incremented).
The device uses two type of stacks: the program stack and
the interrupt stack.
The program stack is used by the software to save and re-
store register values upon entry into and exit from a subrou-
tine. The software can also use the program stack to store
local and temporary variables. The stack pointer for this stack
is the SP register.
The interrupt stack is used to save and restore the program
state when an exception occurs (an interrupt or software
trap). The on-chip hardware automatically pushes the pro-
gram state information onto the stack before the exception
service procedure is executed. Upon exit from the exception
service procedure, the hardware pops this information from
the stack and restores the program state. The stack pointer
for this stack is the ISP register.
7.7 INSTRUCTION SET
Table7 is a summary list of all instructions in the device in-
struction set. For each instruction, the table shows the mne-
monic and a brief description of the operation performed.
In the Mnemonic column, the lower-case letter “i” is used to
indicate the type of integer that the instruction operates on,
either “B” for byte or “W” for word. For example, the notation
ADDi for the “add” instruction means that there are two forms
of this instruction, ADDB and ADDW, which operate on bytes
and words, respectively.
Similarly, the lower-case string “cond” is used to indicate the
type of condition tested by the instruction. For example, the
notation Jcond represents a class of conditional jump instruc-
tions: JEQ for Jump on Equal, JNE for Jump on Not Equal,
and so on.
Register Mode The operand is a general-purpose regis-
ter: R0 through R13, RA, or SP. For exam-
ple:
ADDB R1, R2
Immediate
Mode A constant operand value is specified with-
in the instruction. In a branch instruction,
the immediate operand is a displacement
from the program counter (PC). In the as-
sembly language syntax, a dollar sign indi-
cates an immediate value. For example:
MULW $4, R4
Relative Mode The operand is located in memory. Its ad-
dress is obtained by adding the contents of
a general purpose register to the constant
value encoded into the displacement field
of the instruction. For example:
LOADW 12(R5), R6
Far-Relative
Mode The operand is located in memory. Its ad-
dress is obtained by concatenating a pair
of adjacent general-purpose registers to
form a 21-bit value, and adding this value
to the constant value encoded into the dis-
placement field of the instruction.
Absolute Mode The operand is located in memory. Its ad-
dress is specified within the instruction.
For example:
LOADB 4000, R6
Obsolete
17 www.national.com
For detailed information on all instructions, see the
CompactRISC CR16B Programmer's Reference manual.
Table 7Device Instruction Set Summary
Mnemonic Description
ADDi Add Integer
ADDUi Add Unsigned Integer
ADDCi Add Integer with Carry
ANDi Bitwise Logical AND
ASHUi Arithmetic Shift Unsigned
Bcond Conditional Branch
Bcond0i Compare Register to 0 and Branch
Bcond1i Compare Register to 1and Branch
BAL Branch and Link
BR Unconditional Branch
CBITi Clear Bit in Integer
CMPi Compare Integer
DI Disable Maskable Interrupts
EI Enable Maskable Interrupts
EIWAIT Enable Interrupts and Wait for Interrupt
EXCP Exception
Jcond Conditional Jump
JAL Jump and Link
JUMP Jump
LOADi Load Integer
LOADM Load Multiple Registers
LPR Load Processor Register
LSHi Logical Shift Integer
MOVi Move Integer
MOVXB Move with Sign-Extension
MOVZB Move with Zero-Extension
MULi Multiply Integer
MULSi Multiply Signed
MULUW Multiply Unsigned
NOP No Operation
ORi Bitwise Logical OR
POP Pop Registers from Stack
POPRET Pop and jump RA
PUSH Push Registers on Stack
RETX Return from Exception
Scond Save Condition as Boolean
MULi Multiply Integer
SBITi Set Bit in Integer
STORi Store Integer
STORM Store Registers to Memory
SUBi Subtract Integer
SUBCi Subtract Integer with Carry
TBIT Test Bit
WAIT Wait for Interrupt
XORi Bitwise Logical Exclusive OR
Table 7Device Instruction Set Summary
Mnemonic Description
Obsolete
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8.0 Bus Interface Unit
The Bus Interface Unit (BIU) controls the interface between
the internal core bus and those on-chip modules which are
mapped into BIU zones. These on-chip modules are the flash
EEPROM program memory, the ISP-memory and the I/O-
zone. It determines the configured parameters for bus ac-
cess (such as the number of wait states for memory access)
and issues the appropriate bus signals for the requested ac-
cess.
Note: The device is manufactured in a 224-pin version which
is used in emulation equipment. In the 224-pin device, the
BIU controls access to both on-chip and off-chip memory and
peripherals. Operation of the 224-pin device and the use of
chip-external memory is beyond the scope of this data sheet.
8.1 BUS CYCLES
There are four types of data transfer bus cycles:
—Normal read
—Fast read
—Early write
—Late write
The type of data cycle used in a particular transaction de-
pends on the type of CPU operation (a write or a read), the
type of memory or I/O being accessed, and the access type
programmed into the BIU control registers (early/late write or
normal/fast read).
For read operations, a basic normal read takes two clock cy-
cles, whereas a fast read bus cycle takes one clock cycle.
Upon reset of the device, normal read bus cycles are enabled
by default.
For write operations, a basic late write bus cycle takes two
clock cycles, whereas a basic early write bus cycle takes
three clock cycles. Upon reset of the device, early write bus
cycles are enabled by default. However, late write bus cycles
are needed for ordinary write operations, so this configura-
tion should be changed by the application software (see
Section8.2.1).
In certain cases, one or more additional clock cycles are add-
ed to a bus access cycle. There are two types of additional
clock cycles for ordinary memory accesses, called internal
wait cycles (TIW) and hold (Thold) cycles.
A wait cycle is inserted in a bus cycle just after the memory
address has been placed on the address bus. This gives the
accessed memory more time to respond to the transaction
request. A hold cycle is inserted at the end of a bus cycle.
This holds the data on the data bus for an extended number
of clock cycles.
8.2 BIU CONTROL REGISTERS
The BIU has a set of control registers that determine how
many wait cycles and hold cycles are to be used for access-
ing memory. Upon start-up of the device, these registers
should be programmed with appropriate values so that the
minimum allowable number of cycles is used. This number
varies with the clock frequency used.
There are four applicable BIU registers: the BIU Configura-
tion (BCFG) register, the I/O Configuration (IOCFG) register,
the Static Zone 0 Configuration (SZCFG0) register and the
Static Zone 1Configuration (SZCFG1) register. These regis-
ters control the bus cycle configuration used for accessing
the various on-chip memory types.
Note: A system configuration register called the Module
Configuration (MCFG) register controls the number of wait
cycles used for accessing the EEPROM data memory. This
register is described in Section5.1.
8.2.1 BIU Configuration (BCFG) Register
The BIU Configuration (BCFG) Register is a byte-wide, read/
write register that selects either early write or late write bus
cycles. The register address is F900 hex. Upon reset, the
register is initialized to 07 hex. The register format is shown
below.
EWR Early Write. This bit is cleared to 0 for late write
operation (two clock cycles to write) or set to 1
for early write operation.
Note 1: These bits (bit 1 or bit 2) control the configuration of
the 224-pin device used in emulation equipment. The CPU
should set this bit to 1 when it writes to the register.
Upon reset, the BCFG register is initialized to 07 hex, which
selects early write operation. However, late write operation is
required for normal device operation, so the software should
change the register value to 06 hex.
8.2.2 I/O Zone Configuration (IOCFG) Register
The I/O Zone Configuration (IOCFG) register is a word-wide,
read/write register that sets the timing and bus characteris-
tics of I/O Zone memory accesses. In the device implemen-
tation, the registers associated to Port B and Port C reside in
the I/O memory array. (These ports are used as a 16-bit data
port, if the device operates in development mode.)
7 6 5 4 3 2 1 0
Reserved Note 1 Note 1 EWR
Obsolete
19 www.national.com
The IOCFG register address is F902 hex. Upon reset, the
register is initialized to 069F hex. The register format is
shown below.
WAIT Memory Wait cycles
This field specifies the number of TIW (internal
wait state) clock cycles added for each memory
access, ranging from 000 binary for no addi-
tional TIW wait cycles to 111 binary for seven
additional TIW wait cycles.
HOLD Memory Hold cycles
This field specifies the number of Thold clock
cycles used for each memory access, ranging
from 00 binary for no Thold cycles to 11 binary
for three Thold clock cycles.
BW Bus Width.
This bit defines the bus width of the zone.
If cleared to 0, a bus width of 8-bit is used.
if set to 1, a bus width of 16-bit is used.
For the device, a bus width of 16-bit needs to
be set.
IPST Post Idle.
An idle cycle follows the current bus cycle,
when the next bus cycle accesses a different
zone.
If cleared to 0, no idle cycle is inserted.
If set to 1, one idle cycle is inserted.
The IPST bit can be cleared to 0, as no idle cy-
cles are required for on-chip accesses.
Note: Reserved bits must be cleared to 0 when the CPU
writes to the register.
8.2.3 Static Zone 0 Configuration (SZCFG0) Register
The Static Zone 0 Configuration (SZCFG0) register is a
word-wide, read/write register that sets the timing and bus
characteristics of Zone 0 memory accesses. In the device im-
plementation of the CompactRISC architecture, Zone 0 is oc-
cupied by the flash EEPROM program memory.
The SCCFG0 register address is F904 hex. Upon reset, the
register is initialized to 069F hex. The register format is
shown below.
WAIT Memory Wait cycles
This field specifies the number of TIW (internal
wait state) clock cycles added for each memory
access, ranging from 000 binary for no addi-
tional TIW wait cycles to 111 binary for seven
additional TIW wait cycles. These bits are ig-
nored if the SZCFG0.FRE bit is set to 1.
HOLD Memory Hold cycles
This field specifies the number of Thold clock
cycles used for each memory access, ranging
from 00 binary for no Thold cycles to 11 binary
for three Thold clock cycles. These bits are ig-
nored if the SZCFG0.FRE bit is set to 1.
BW Bus Width.
This bit defines the bus width of the zone.
If cleared to 0, a bus width of 8-bit is used.
if set to 1, a bus width of 16-bit is used.
For the devicedevice a bus width of 16-bit
needs to be set.
FRE Fast Read Enable
This bit enables (1) or disables (0) fast read
bus cycles. A fast read operation takes one
clock cycle. A normal read operation takes at
least two clock cycles.
IPST Post Idle.
An idle cycle follows the current bus cycle,
when the next bus cycle accesses a different
zone.
If cleared to 0, no idle cycle is inserted.
If set to 1, one idle cycle is inserted.
The IPST bit can be cleared to 0, as no idle cy-
cles are required for on-chip accesses.
IPRE Preliminary Idle.
An idle cycle is inserted prior to the current bus
cycle, when the new bus cycle accesses a dif-
ferent zone.
If cleared to 0, no idle cycle is inserted.
If set to 1, one idle cycle is inserted.
The IPRE bit can be cleared to 0, as no idle cy-
cles are required for on-chip accesses.
Note: Reserved bits must be cleared to 0 when the CPU
writes to the register.
8.2.4 Static Zone 1 Configuration (SZCFG1) Register
The Static Zone 1 Configuration (SZCFG1) register is a
word-wide, read/write register that sets the timing and bus
characteristics of Zone 1 memory accesses. In the device im-
plementation of the CompactRISC architecture, Zone 1 is oc-
cupied by the boot ROM memory (ISP-Memory).
The SCCFG1 register address is F906 hex. Upon reset, the
register is initialized to 069F hex. The register format is
shown below.
WAIT Memory Wait cycles
This field specifies the number of TIW (internal
wait state) clock cycles added for each memory
access, ranging from 000 binary for no addi-
tional TIW wait cycles to 111 binary for seven
additional TIW wait cycles. These bits are ig-
nored if the SZCFG0.FRE bit is set to 1.
HOLD Memory Hold cycles
This field specifies the number of Thold clock
15 14 13 12 11 10 9 8
Reserved IPST Reserved
7 6 5 4 3 2 1 0
BW Reserved HOLD WAIT
15 14 13 12 11 10 9 8
Reserved FRE IPRE IPST Reserved
7 6 5 4 3 2 1 0
BW Reserved HOLD WAIT
15 14 13 12 11 10 9 8
Reserved FRE IPRE IPST Reserved
7 6 5 4 3 2 1 0
BW Reserved HOLD WAIT
Obsolete
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cycles used for each memory access, ranging
from 00 binary for no Thold cycles to 11 binary
for three Thold clock cycles. These bits are ig-
nored if the SZCFG0.FRE bit is set to 1.
BW Bus Width.
This bit defines the bus width of the zone.
If cleared to 0, a bus width of 8-bit is used.
if set to 1, a bus width of 16-bit is used.
For the device a bus width of 16-bit needs to be
set.
FRE Fast Read Enable
This bit enables (1) or disables (0) fast read bus
cycles. A fast read operation takes one clock
cycle. A normal read operation takes at least
two clock cycles.
IPST Post Idle.
An idle cycle follows the current bus cycle,
when the next bus cycle accesses a different
zone.
If cleared to 0, no idle cycle is inserted.
If set to 1, one idle cycle is inserted.
The IPST bit can be cleared to 0, as no idle cy-
cles are required for on-chip accesses.
IPRE Preliminary Idle.
An idle cycle is inserted prior to the current bus
cycle, when the new bus cycle accesses a dif-
ferent zone.
If cleared to 0, no idle cycle is inserted.
If set to 1, one idle cycle is inserted.
The IPRE bit can be cleared to 0, as no idle cy-
cles are required for on-chip accesses.
Note: Reserved bits must be cleared to 0 when the CPU
writes to the register.
8.3 WAIT AND HOLD STATES USED
The number of wait cycles and hold cycles inserted into a bus
cycle depends on whether it is a read or write operation, the
type of memory or I/O being accessed, and the control regis-
ter settings.
8.3.1 Flash EEPROM Program Memory
When the CPU accesses the flash EEPROM program mem-
ory (address ranges 0000-BFFF and 1C000-1FFFF), the
number of added wait and hold cycles depends on the type
of access and the BIU register settings.
In fast read mode (SZCFG0.FRE=1), a read operation is a
single cycle access. This limits the maximum CPU operating
frequency to either 10 MHz or 20 MHz (see Section9.1.5).
For a read operation in normal read mode (SZCFG0.FRE=0),
the number of inserted wait cycles is one plus the value writ-
ten to the SZCFG0.WAIT field. The number in this field can
range from zero to seven, so the total number of wait cycles
can range from one to eight. The number of inserted hold cy-
cles is equal to the value written to the SCCFG0.HOLD field,
which can range from zero to three.
For a write operation in fast read mode (SZCFG0.FRE=1),
the number of inserted wait cycles is one. No hold cycles are
used.
For a write operation normal read mode (SZCFG0.FRE=0),
the number of wait cycles is equal to the value written to the
SZCFG0. WAIT field plus one (in the late write mode) or two
(in the early write mode). The number of inserted hold cycles
is equal to the value written to the SCCFG0.HOLD field,
which can range from zero to three.
Writing to the flash EEPROM program memory is a Flash
programming operation that requires some additional steps,
as explained in Section9.3.
8.3.2 RAM Memory
Read and write accesses to on-chip RAM is performed within
a single cycle, regardless of the BIU settings.
8.3.3 EEPROM Data Memory
There is either no wait state or one wait state used when the
CPU accesses the EEPROM data memory (address F000-
F27F hex). The number of required wait states (zero or one)
depends on the CPU clock frequency and operating mode,
and is controlled by programming of the DMCSR.ZEROWS
bit in the MCFG register, as explained in Section9.3. No hold
cycles are used.
8.3.4 Accesses to Peripheral
When the CPU accesses on-chip peripherals in the range of
F800-FAFF hex and FC00-FFFF hex, one wait cycle and one
preliminary idle cycle is used. No hold cycles are used.
The IOCFG register determines the access timing for the ad-
dress range FB00-FB16 hex (Ports B and Port C).
Obsolete
21 www.national.com
8.3.5 Access Timing Summary Table
Table8 is a summary showing the number of access cycles
used for various address ranges.
8.3.6 Recommended Register Settings
Table9 shows the recommended register settings for various
clock rates. Different clock rates require different register set-
tings because the flash EEPROM program memories have
specific setup and hold requirements that can be met only by
using enough wait cycles and hold cycles.
Between clock rates of 10 MHz and 20MHz, the number of
wait states required for memory access (either none or one)
depends on the desired power mode of the program memory.
Table 8Access Timing Table
Address
Range (hex) Memory or
I/O Type Access Cycles
read write
0000-BFFF Flash EEPROM Program
Memory SZCFG0.FRE=1:
1 cycle SZCFG0.FRE=1:
1 cycle
+ BCFG.EWR
(+ programming time)
SZCFG0.FRE=0:
2 cycles
+ SZCFG0.WAIT
+ SZCFG0.HOLD
SZCFG0.FRE=0:
2 cycles
+ BCFG.EWR
+ SZCFG0.WAIT
+ SZCFG0.HOLD
(+ programming time)
C000-CBFF Static RAM Memory 1 cycle 1 cycle
F000-F27F EEPROM Data Memory MCFG.ZEROWS=1:
1 cycle MCFG.ZEROWS=1:
1 cycle
(+ programming time)
MCFG.ZEROWS=0:
2 cycles MCFG.ZEROWS=0:
2 cycles
(+ programming time)
F900-FFFF
F800-F9FF
FC00-FFFF
On-Chip Peripherals 2 cycles 2 cycles
FB00-FBFF Ports B and C 3 cycle
+ IOCFG.WAIT
+ IOCFG.HOLD
3 cycle
+ BCFG.EW
+ IOCFG.WAIT
+ IOCFG.HOLD
Table 9Recommended Register Settings
Clock Rate SZCFG0 SZCFG1 IOCFG
< 10 MHz,
0 wait state 0880 hex 0880 hex 0080 hex
10 to 20MHz,
0 wait state 0880 hex 0880 hex 0080 hex
10 to 20MHz,
1 wait state 0080 hex 0080 hex 0080 hex
> 20 MHz,
1 wait state 0080 hex 0080 hex 0080 hex
Obsolete
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9.0 Memory
The CompactRISC architecture supports a uniform linear ad-
dress space of 2 megabytes, addressed by 21 bits. The de-
vice implementation of this architecture uses only the lowest
128K bytes of address space. Each memory location con-
tains a byte consisting of eight bits.
Various types of on-chip memory occupy specific intervals
within the address space: 64K bytes of flash EEPROM pro-
gram memory, 3K bytes of static RAM, 2K bytes of low endur-
ance EEPROM data memory, 128 bytes of high endurance
EEPROM data memory, and 1.5K bytes of ISP memory. All
of these memories are 16 bits wide, and their contents can
be accessed either as bytes (eight bits wide) or words (16
bits wide except for the program memory which only supports
word access).
The CPU core uses the Load and Store instructions to ac-
cess memory. These instructions can operate on bytes or
words. For a byte access, the CPU operates on a single byte
occupying a specified memory address. For a word access,
the CPU operates on two consecutive bytes. In that case, the
specified address refers to the least significant byte of the
data value; the most significant byte is located at the next
higher address. Thus, the ordering of bytes in memory is
from least to most significant byte, known as “little-endian” or-
dering. For more efficient data access operations, 16-bit vari-
ables should be stored starting at word boundaries (at even
address).
9.1 FLASH EEPROM PROGRAM MEMORY
The flash EEPROM program memory is used to store the ap-
plication program. The 64K bytes of this memory reside in the
address range of 0000-BFFF hex and 1C000-1FFFF in Zone
0 of the CR16B address space. A normal CPU write opera-
tion to this memory has no effect.
The flash EEPROM Program Memory module has the follow-
ing features:
—64K bytes arranged as 32K by 16 bits
—Page size of 64 words
—30 µs programming pulse per word
—Page mode erase with a 1 ms pulse, mass erase with
4ms pulse
—All erased flash EEPROM program memory bits read 1
—Fast single cycle read access
—Flexible software controlled In-System-Programming
(ISP) capability
—Pipelined programming cycles through double-buff-
ered data register, with write access disabled when the
register is full
—Programming high voltage and timing generated on-
chip
—Memory disabled when address is out of range
—Requires valid key for program and erase to proceed
—Provide busy status during programming and erase
—Read accesses disabled during programming and
erase
—Security features to limit read/write access
9.1.1 Reading
Program memory read accesses can operate without wait cy-
cles with a CPU clock rate of up to 20MHz in the normal
mode. At higher clock rates, memory read accesses can op-
erate with one wait state.
The programmed number of wait cycles used (either zero or
one) is controlled by the BIU Configuration (BCFG) register
and the Static Zone 0 Configuration (SZCFG0) register.
These registers are described in Section8.0.
9.1.2 Conventional Programming Modes
The flash EEPROM program memory can be programmed
either with the device plugged into a flash EEPROM pro-
grammer unit (External Programming) or with the device al-
ready installed in the application system (In-System-
Programming).
If the device is programmed using a flash EEPROM program-
mer, the device is set into an external programming mode. In
this mode the device operates as if it were a pure flash mem-
ory device. The flash memory is programmed without involv-
ing any CPU activity.
If the device is to be programmed within the user application,
it can either be done by an user written boot loader or by uti-
lizing a pre-programmed in-system-programming code (ISP-
Code) residing in the boot ROM array of the device.
The device executes the pre-programmed in-system-pro-
gramming code if it operates in the In-System-Programming
Mode (ISP-Mode). To enter the ISP-Mode the device must be
reset (or powered-up) with the ENV0-pin set to low level and
the ENV1-pin set to high level (or left open). Also if the flash
program memory is not programmed yet (FLCTRL2.EMPTY
bit is still set) the device automatically enters the ISP-Mode
after reset, even though both pins ENV0 and ENV1are at
high level (or left open). If the device enters the ISP-Mode it
starts execution at address E000 hex.
In ISP-Mode the program code can be downloaded into the
device using one of the on-chip USARTs and written into the
flash program memory. For more detailed information on the
In-System-Programming features of the pre-programmed
ISP-Code please refer to the ISP-Monitor manual.
9.1.3 User-Coded Programming Routines
Instead of using a flash EEPROM programmer unit or the
conventional in-system programming mode, you can write
your own processor code to program and erase the flash
EEPROM program memory. User-written code is more flexi-
ble than using the other programming methods. Like the con-
ventional in-system programming mode, the device is
programmed while it is installed in the system. It is not nec-
essary to reset the device or use the ENV0/ENV1 pins to
configure the device.
User-written flash programming code must reside outside of
the flash program memory. This is because the entire pro-
gram memory becomes unavailable while programming or
erasing any part of this memory.
9.1.4 Flash EEPROM Programming and Verify
The flash EEPROM program memory programming and
erase can be performed using different methods. It can be
done through user code that is stored in system RAM, or
through In-System-Programming mode, but should not be
programmed through the flash EEPROM program memory it-
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23 www.national.com
self as no instruction or data can be fetched from it while it is
being programmed. All program and erase operations must
be preceded immediately by writing the proper key to the pro-
gram memory key register PGMKEY.
The flash EEPROM program memory is divided into 256
pages, each page containing 64 words (each 16 bits wide).
Each page is further divided into two adjacent rows. A page
erase will erase one page. Programming is done by writing to
all the words within a row, one word following another se-
quentially within one single high voltage pulse. This is sup-
ported through a double-buffered write-data buffer scheme.
Byte programming is not supported. Programming should be
done on erased rows.
A mass erase requires the following code sequence (assum-
ing that this sequence will not be interrupted to do another
flash erase or programming):
1. Check for MSTAT.PGMBUSY not set.
2. Set up flash timing reload registers for mass erase oper-
ation.
3. Set FLCSR.MERASE = 1.
4. If interrupt was enabled, disable interrupt.
5. Write proper key value to PGMKEY.
6. Write to any valid location within the flash EEPROM pro-
gram memory.
7. If interrupt was disabled in step 4, re-enable interrupt.
8. Wait for MSTAT.PGMBUSY to clear.
9. Set FLCSR.MERASE = 0.
10. Restore flash timing reload registers for normal opera-
tion.
A page erase requires the following code sequence (assum-
ing that this sequence will not be interrupted to do another
flash erase or programming):
1. Check for MSTAT.PGMBUSY not set.
2. Set FLCSR.ERASE = 1.
3. If interrupt was enabled, disable interrupt.
4. Write proper key value to PGMKEY.
5. Write to any valid location within the page to be erased.
6. If interrupt was disabled in step 3, re-enable interrupt.
7. Set FLCSR.ERASE = 0.
When programming, the data to be written into the flash EE-
PROM program memory is first written into a double-buffered
write-data buffer. When a piece of data is written to the page
while the flash EEPROM program memory is idle, the write
cycle will start. Due to the double-buffered nature of the write-
data buffer, a second word can be written to the flash EE-
PROM program memory. This will then set FLCSR.PML-
FULL flag indicating the buffer is now full. When the first write
is done, the memory address would be incremented, and the
second word would be written to that address while keeping
the high voltage pulse active; the FLCSR.PMLFULL flag is
cleared. Another word can then be written to the buffer, and
this programming will repeat until there are no more words to
be programmed. This allows pipelined writes to different
words on the same row within the same high voltage pulse.
If the programming sequence exceeds a row, the flash pro-
gramming interface will automatically initiate a programming
pulse for the next row. The FLCSR.PMLFULL bit is also
cleared when programming of the last word of the current
row is completed, e.g. programming of the entire row is com-
pleted and MSTAT.PGMBUSY is cleared. This means, the
separation of the program memory into rows is transparent to
the user, as the transition is handled by the flash program
memory interface. Figure 3 shows a flowchart for a program-
ming sequence.
9.1.5 Erase and Programming Timing
The internal hardware of the device handles the timing of
erase and programming operations. To drive the timing con-
trol circuits, the device divides the system clock by a pro-
grammable prescaler factor. You should select a prescaler
value to produce a program/erase clock of 200 kHz (or as
close as possible to 200 kHz without exceeding 200 kHz).
For the timing control circuit to operate correctly, you must
start
MSTAT.PGMBUSY
=1?
disable interrupt
if necessary
write PGMKEY
re-enable interrupt
if necessary
write memory
last word? done
Yes
No
Yes
Yes FLCSR.PMLFULL
=0?
No
No
Figure 2.Programming Sequence for
the Program Memory
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program the prescaler value in advance and leave it un-
changed while a program or erase operation is in progress.
A similar (but separate) prescaler factor is applied to the EE-
PROM data memory. See Section9.1.7 and Section9.3.4 for
details.
9.1.6 Flash EEPROM Program Memory Control and
Status Register (FLCSR)
The Flash EEPROM Program Memory Control and Status
(FLCSR) register is a byte-wide, read/write register that con-
tains several status and control bits related to the program
memory. All reserved bits must be written with 0 for the mem-
ory to operate properly when writing to this register. Upon re-
set, this register is cleared to zero when the flash memory on
the chip is in the idle state.
The register format is shown below.
PMER Flash EEPROM Program Memory page erase.
When set (1) with MERASE bit cleared, a valid
write to the flash EEPROM program memory
erases the entire flash EEPROM program
memory page pointed to by the write address
rather than performing a write to the addressed
memory location.
PMBUSY Program Memory Busy. This bit is automatical-
ly set to 1 when the flash EEPROM program
memory is busy being programmed, and
cleared to 0 at all other times. (The MSTAT.PG-
MBUSY is also set to 1 whenever the PMBUSY
bit is set to 1.)
PMLFULL Program Memory Write-Latch Buffer Full.
When set (1), the double-buffered data register
for program memory write operations is full.
When cleared (0), the double-buffered data
register is not full.
MERASE Mass Erase Flash EEPROM Program Memory
Array. When set (1) in ISP or test mode, a valid
write to the flash EEPROM program memory
performs an erase to the whole flash EEPROM
program memory rather than perform a write to
the addressed memory location. However, it is
necessary to enter new values into the
FLERASE and FLEND registers to adjust the
mass erase timing before starting the mass
erase.
9.1.7 Program Memory Timing Prescaler Register
(FLPSLR)
The FLPSLR register is a byte-wide, read/write register that
selects the prescaler divider ratio for the flash EEPROM pro-
gram memory programming clock. Before you program or
erase the program memory for the first time, you should pro-
gram the FLPSLR register with the proper prescaler value,
an 8-bit value called FTDIV. The device divides the system
clock by (FTDIV+1) to produce the program memory pro-
gramming clock.
You should choose a value of FTDIV to produce a clock of the
highest possible frequency that is equal to or just less than
200 kHz. For example, if the system clock frequency is 12.5
MHz, use the value 3E hex (62 decimal) for FTDIV, because
12.5 MHz / (62+1) = 198.4 kHz. Do not modify this register
while a flash EEPROM program or erase operation is in
progress.
Upon reset, this register is programmed by default with the
value 63 hex (99 decimal), which is an appropriate setting for
a 20 MHz system clock.
9.1.8 Program Memory Start Time Reload (FLSTART)
The FLSTART register is a byte-wide read/write register that
controls the program and erase start delay time. This value
is loaded into the lower 8 bits of the flash timing counter, and
at the same time, 002 is loaded into the upper 2 bits. Before
you program or erase the program memory for the first time,
program the FLSTART register with the proper prescaler val-
ue, FTSTART. The flash timing counter generates a delay of
(FTSTART+1) prescaler output clocks. The default value
provides a delay time of 10µs when the prescaler output
clock is 200kHz. Do not modify this register while a program
or erase operation is in progress.
Upon reset, this register resets to 0116 when the flash mem-
ory on the chip is in an idle state.
9.1.9 Program Memory Transition Time Reload
Register (FLTRAN)
The FLTRAN register is a byte-wide read/write register that
controls some program/erase transition times. This value is
loaded into the lower 8 bits of the flash timing counter, and at
the same time, 002 is loaded into the upper 2 bits. Before you
program or erase the program memory for the first time, you
should program the FLTRAM register with the proper pres-
caler value, FTTRAN. The flash timing counter generates a
delay of (FTTRAN + 1) prescaler output clocks. The default
value provides a delay time of 5µs when the prescaler output
clock is 200kHz. Do not modify this register while a program
or erase operation is in progress.
Upon reset, this register resets to 0016 when the flash mem-
ory on the chip is in an idle state.
9.1.10 Program Memory Programming Time Reload
Register (FLPROG)
The FLPROG register is a byte-wide read/write register that
controls the programming pulse width. This value is loaded
into the lower 8 bits of the flash timing counter, and at the
same time, 002 is loaded into the upper 2 bits. Before you
program or erase the program memory for the first time, pro-
gram the FLPROG register with the proper prescaler value,
FTPROG. The flash timing counter generates a programming
pulse width of (FTPROG + 1) prescaler output clocks. The
default value provides a delay time of 30µs when the prescal-
er output clock is 200kHz.
Do not modify this register while program/erase operation is
in progress.
Upon reset, this register resets to 0516 when the flash mem-
ory on the chip is in idle state.
7 6 4 3 2 1 0
MERASE Reserved PMLFULL PMBUSY PMER Reserved
Obsolete
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9.1.11 Program Memory Erase Time Reload Register
(FLERASE)
The FLERASE register is a byte-wide read/write register that
controls the erase pulse width. This value is loaded into the
upper 8 bits of the flash timing counter, and at the same time,
112 is loaded into the lower 2 bits. Before you program or
erase the program memory for the first time, program the
FLERASE register with the proper prescaler value, FTER.
The flash timing counter generates a erase pulse width of
4×(FTER + 1) prescaler output clocks. The default value pro-
vides a delay time of 1ms when the prescaler output clock is
200kHz. Do not modify this register while a program or erase
operation is in progress.
Upon reset, this register resets to 3116
when the flash mem-
ory on the chip is in idle state.
For mass erase, this value should be changed to C716 to
generate a pulse width that is four times as long as the page
erase.
9.1.12 Program Memory End Time Reload Register
(FLEND)
The FLEND register is a byte-wide read/write register that
controls the delay time after a program/erase operation. This
value is loaded into the lower 8 bits of the flash timing
counter, and at the same time, 002 is loaded into the upper 2
bits. Before you program or erase the program memory for
the first time, program the FLEND register with the proper
prescaler value, FTEND. The flash timing counter generates
a delay of (FTEND + 1) prescaler output clocks. The default
value provides a delay time of 5µs when the prescaler output
clock is 200kHz. Do not modify this register while program/
erase operation is in progress.
Upon reset, this register resets to 0016 when the flash mem-
ory on the chip is in idle state.
For mass erase, this value should be changed to 1316 to pro-
vide for a delay time twenty times that of the standard delay.
9.1.13 Program Memory Prescaler Count Register
(FLPCNT)
The FLPCNT register is a byte-wide read-only register that
returns the value of the program memory prescaler counter.
FPCNT contains the flash timing prescaler present count val-
ue.
9.1.14 Program Memory Timer Count Register 1
(FLCNT1)
The FLCNT1 register is a byte-wide read-only register that
returns the lower 8 bits of the program memory timing
counter value. FLCNTL is the lower 8 bits of the flash timer
present count value.
9.1.15 Program Memory Timer Count Register 2
(FLCNT2)
The FLCNT2 register is a byte-wide read-only register that
returns the upper 2 bits of the program memory timing
counter value and also the state of the key flash memory in-
terface timing signals. The interface timing signals are only
used in special test modes. Their function is beyond the
scope of this document.
9.1.16 Program Memory Write Key Register (PGMKEY)
The PGMKEY register is a byte-wide, write-only register that
must be written with a key value (A316) immediately prior to
each write to the flash EEPROM program memory. Other-
wise, the write operation to the program memory will fail. This
feature is intended to prevent unintentional programming of
the program memory.
Reading this register always returns FF hex.
Upon reset, the write enable status that is generated as a re-
sult of writing to this key register is cleared.
9.2 RAM MEMORY
The static RAM memory is used for temporary storage of
data and for the program and interrupt stacks. The 3K bytes
of this memory reside in the address range of C000-CBFF
hex. Each memory access requires one clock cycle, for a
byte or word access. No wait cycles or hold cycles are re-
quired. For non-aligned word access, each memory access
requires multiple clock cycles.
9.3 FLASH EEPROM DATA MEMORY
The flash EEPROM data memory is used for non-volatile
storage of data. The 2K bytes of low endurance memory re-
side in the address range of E800-EFFF hex and the 128
bytes of high endurance memory reside in the address range
of F000-F07F hex. The CPU reads or writes this memory by
using ordinary byte-wide or word-wide memory access com-
mands. This memory shares the same array as the ISP flash
program memory.
This memory also support flash memory test mode and there
is no read protection or permanent write protection for this
memory.
9.3.1 Reading
The flash EEPROM data memory read accesses can oper-
ate without wait cycles with a CPU clock rate of up to 20MHz
in the normal mode. At higher clock rates, read accesses can
operate with one wait state.
The programmed number of wait cycles used (either zero or
one) is controlled by a bit in the Data Memory Control Status
register (DMCSR.ZEROWS). This register is described in
Section9.3.3.
9.3.2 Programming
Before you begin programming the flash EEPROM data
memory, you should set the value in the EEPROM Data
Memory Prescaler register. This register sets the prescaler
used to generate the data memory programming clock from
the system clock, as described in Section9.3.4.
A code fetch from ISP flash EEPROM program memory is
not possible while flash EEPROM data memory is being pro-
grammed because they share the same memory array.
After the CPU performs a write to the flash EEPROM data
memory, the on-chip hardware completes the EEPROM pro-
gramming in the background. When programming begins,
the on-chip hardware sets the DMCSR.DMBUSY bit to 1,
and also sets the MSTAT.PGMBUSY bit to 1. When program-
ming is completed, it resets these status bits back to 0. Once
the software writes to the flash EEPROM data memory, it
should not attempt to access the EEPROM data memory
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again until programming is completed and the status bit is re-
set to 0.
The device hardware internally generates the voltages and
timing signals necessary for programming. No additional
power supply is required, nor any software required except to
check the status bit for completion of programming. The min-
imum time required to erase and reprogram a byte or word is
1.1 ms. The programmed values can be verified by using nor-
mal memory read operations. The prescaler output drives a
10-bit counter to generate timing pulses and there are five re-
load registers to produce various pulse widths.
If a reset occurs during a programming or erase operation,
the operation is terminated. The reset is extended until the
flash memory returns to the idle state. Therefore, the timing
logic and program or erase state machine is not cleared on
reset; they are cleared on power-up with the clear signal ac-
tive until the bus signals are in a known state.
The flash EEPROM data memory does not have permanent
read-protection or write-protection features like those avail-
able for the EEPROM program memory. However, the Data
Memory Write Key Register provides a way to “lock” the data
written to the data memory.
9.3.3 Data Memory Control and Status Register
(DMCSR)
The DMCSR register is a byte-wide, read/write register used
with the flash EEPROM data memory or ISP flash EEPROM
program memory. When writing to this register, all reserved
bits must be written with 0 for the memory to operate proper-
ly. There are two status/control bits, as shown in the register
format below.
ZEROWS Zero Wait-State Access. When cleared (0), the
flash EEPROM data memory will be read in two
cycles. When set (1), the flash EEPROM data
memory will be read in one cycle.
DMBUSY Data Memory Busy. This bit is automatically set
to 1 when the flash EEPROM data memory or
the ISP flash EEPROM program memory is
busy being programmed, and cleared to 0 at all
other times. (The MSTAT.PGMBUSY is also set
to 1 whenever the DMBUSY bit is set to 1.)
ERASE Erase ISP Flash Program Memory Page.
When set (1) a valid write to the ISP flash EE-
PROM program memory will erase the entire
ISP flash EEPROM program memory page
pointed to by the write address rather than per-
forming a write to the addressed memory loca-
tion. This bit should be cleared to 0 and remain
cleared after the write operation.
Upon reset, the DMCSR register is cleared to zero when the
flash memory on the chip is in the idle state.
9.3.4 Data Memory Prescaler Register (DMPSLR)
The DMPSLR register is a byte-wide, read/write register that
selects the prescaler divider ratio for the EEPROM data
memory programming clock. Before you write to the data
memory for the first time, you should program the DMPSLR
register with the proper prescaler value, an 8-bit value called
FTDIV. The device divides the system clock by (FTDIV+1) to
produce the data memory programming clock.
You should choose a value of FTDIV to produce a clock of the
highest possible frequency that is equal to or just less than
200 kHz. Upon reset, this register is programmed by default
with the value 63 hex (99 decimal), which is an appropriate
setting for a 20 MHz system clock.
9.3.5 Data Memory Start Time Reload Register
(DMSTART)
The DMSTART register is a byte-wide read/write register that
controls the program/erase start delay time. This value is
loaded into the lower 8 bits of the flash timing counter, and at
the same time, 002 is loaded into the upper 2 bits. Before you
write to the data memory for the first time, you should pro-
gram the DMSTART register with the proper prescaler value,
an 8-bit value called FTSTART. The flash timing counter gen-
erates a delay of (FTSTART + 1) prescaler output clocks. The
default value provides a delay time of 10µs when the prescal-
er output clock is 200kHz. Do not modify this register while
program/erase operation is in progress.
Upon reset, this register resets to 0116 when the flash mem-
ory on the chip is in idle state.
9.3.6 Data Memory Transition Time Reload Register
(DMTRAN)
The DMTRAN register is a byte-wide read/write register that
controls some program/erase transition times. This value is
loaded into the lower 8 bits of the flash timing counter, and at
the same time, 002 is loaded into the upper 2 bits. Before you
write to the data memory for the first time, you should pro-
gram the DMTRAN register with the proper prescaler value,
an 8-bit value called FTTRAN. The flash timing counter gen-
erates a delay of (FTTRAN + 1) prescaler output clocks. The
default value provides a delay time of 5µs when the prescaler
output clock is 200kHz. Do not modify this register while pro-
gram/erase operation is in progress.
Upon reset, this register resets to 0016 when the flash mem-
ory on the chip is in idle state.
9.3.7 Data Memory Programming Time Reload
Register (DMPROG)
The DMPROG register is a byte-wide read/write register that
controls the programming pulse width. This value is loaded
into the lower 8 bits of the flash timing counter, and at the
same time, 002 is loaded into the upper 2 bits. Before you
write to the data memory for the first time, you should pro-
gram the DMPROG register with the proper prescaler value,
an 8-bit value called FTPROG. The flash timing counter gen-
erates a programming pulse width of (FTPROG + 1) prescal-
er output clocks. The default value provides a delay time of
30µs when the prescaler output clock is 200kHz. Do not mod-
ify this register while program/erase operation is in progress.
Upon reset, this register resets to 0516 when the flash mem-
ory on the chip is in idle state.
7 6 5 4 3 2 1 0
Reserved ERASE DMBUSY ZEROWS Reserved
Obsolete
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9.3.8 Data Memory Erase Time Reload Register
(DMERASE)
The DMERASE register is a byte-wide read/write register
that controls the erase pulse width. This value is loaded into
the upper 8 bits of the flash timing counter, and at the same
time, 112 is loaded into the lower 2 bits. Before you write to
the data memory for the first time, you should program the
DMERASE register with the proper prescaler value, an 8-bit
value called FTER. The flash timing counter generates a
erase pulse width of 4×(FTER + 1) prescaler output clocks.
The default value provides a delay time of 1ms when the
prescaler output clock is 200kHz. Do not modify this register
while program/erase operation is in progress.
Upon reset, this register resets to 3116
when the flash mem-
ory on the chip is in idle state.
For mass erase, this value should be changed to C716
when
the flash EEPROM data memory goes to idle mode.
9.3.9 Data Memory End Time Reload Register
(DMEND)
The DMEND register is a byte-wide read/write register that
controls the delay time after a program/erase operation. This
value is loaded into the lower 8 bits of the flash timing
counter, and at the same time, 002 is loaded into the upper 2
bits. Before you write to the data memory for the first time,
you should program the DMEND register with the proper
prescaler value, an 8-bit value called FTEND. The flash tim-
ing counter generates a delay of (FTEND + 1) prescaler out-
put clocks. The default value provides a delay time of 5µs
when the prescaler output clock is 200kHz. Do not modify
this register while program/erase operation is in progress.
Upon reset, this register resets to 0016 when the flash mem-
ory on the chip is in idle state.
For mass erase, this value should be changed to 1316.
9.3.10 Data Memory Prescaler Count Register
(DMPCNT)
The DMPCNT register is a byte-wide read-only register that
returns the value of the data memory prescaler counter.
FPCNT is the flash timing prescaler present count value.
9.3.11 Data Memory Timer Count Register (DMCNT)
The DMCNT register is a word-wide read-only register that
returns the data memory timing counter value. The reserved
bits return 0000002.
FTCNT[0:9] is the flash timer present count value.
9.3.12 Data Memory Write Key Register (DMKEY)
The DMKEY register is a byte-wide, read/write register that
provides a way to “lock” the data contained in the EEPROM
data memory. Upon reset, the register is automatically set to
C9 hex, which is the key value. Writing to the EEPROM data
memory is allowed as long as the DMKEY register contains
this value. When the register contains any value other than
C9 hex, writing the EEPROM data memory is disallowed.
To “lock” the current data stored in the data memory, write an-
other value (such as 00 hex) to the DMKEY register. To “un-
lock” the data memory, write the value C9 hex to the DMKEY
register.
Note: Operation of this register is different in from the
PGMKEY register used with the program memory. It is not
necessary to write the key value to DMKEY every time you
write to the data memory.
9.4 ISP MEMORY
The In-System Program memory is part of the flash memory
array that contains the flash EEPROM data memory. It is not
possible to access the ISP memory while programming the
flash EEPROM data memory or access the flash EEPROM
data memory while programming the ISP memory. The 1.5K
bytes of ISP memory resides in the address range of E000-
E5FF and is used for storing the boot ROM. The ROM con-
tains the code that performs in-system programming, and is
programmed at the factory. In ISP mode, code execution
starts at address E000.
The ISP program memory and flash EEPROM data memory
share the same memory array, which makes it impossible to
access one type of memory while the other is being pro-
grammed.
The ISP memory has the following features:
—1.5K bytes flash EEPROM program memory
—Page size of 4 words, divided into two rows of 2 words
each
—Odd and even bytes within a page can be erased sep-
arately
—30µs programming pulse width per word
—Page mode erase with 1ms pulse, mass erase with
4ms pulse
—All erased memory bits read 1
—Fast read access time
—Requires valid key for program and erase to proceed
—Provide memory protection and security features for
flash EEPROM program memory
—Security features may limit accesses to ISP memory
—Disable memory when address is out of range to pre-
vent accessing data memory
—Mass erase only allowed in test modes
—Provide busy status during programming and erase
—Read/write accesses disabled during programming/
erase
—Programming high voltage and timing generated on-
chip
9.4.1 Reading
The ISP flash EEPROM program memory read accesses
can operate without wait cycles with a CPU clock rate of up
to 20MHz in the normal mode. At higher clock rates, read ac-
cesses can operate with one wait state.
The programmed number of wait cycles used (either zero or
one) is controlled by BIU Configuration (BCFG) register and
the Static Zone 1 Configuration (SZCFG1) register. These
registers are described in Section8.0.
9.4.2 User-Coded Programming Routines
All program and erase operations must be preceded by writ-
ing the proper key to the program memory key register ISP-
KEY. The programming code can be in-system RAM, but
cannot be from ISP flash EEPROM program memory or flash
EEPROM data memory as accesses within these ranges are
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not permitted while ISP flash EEPROM program memory is
being programmed.
The ISP flash memory is divided into 192 pages, each page
containing 4 words (each 16 bits wide). Each page is further
divided into two rows. Erase is carried out one page at a time,
whereas programming is carried out one row (or one partial
row) at a time.
Once an erase or programming operation is started, the PG-
MBUSY bit in the MSTAT register is automatically set, and
then cleared when the operation is complete. All high-voltage
pulses and timing needed for programming and erasing are
provided internally. The program memory cannot be access-
ed while the PGMBUSY bit is set.
Erase Procedure
Erasing a page requires the following code sequence:
1. Verify that the MSTAT.PGMBUSY bit is cleared.
2. Set the DMCSR.ERASE bit to 1.
3. Locally disable interrupts.
4. Write proper key value to the ISPKEY register.
5. Write to any valid page to be erased.
6. Re-enable interrupts disabled in Step 3.
7. Set the DMCSR.ERASE bit to 0.
9.4.3 Programming Procedure
Programming is done by writing one byte or word at a time
and should be done on already erased memory.
Programming the ISP flash EEPROM program memory re-
quires the following code sequence:
1. Verify that the MSTAT.PGMBUSY bit is cleared.
2. Locally disable interrupts.
3. Write proper key value to the ISPKEY register.
4. Write a byte or word to the addressed location.
5. Re-enable interrupts disabled in Step 2.
Programmed values can be verified through normal read op-
erations.
If a reset occurs in the middle of an erase or programming
operation, the operation is terminated. The reset is extended
until the flash EEPROM memory returns to the idle state.
9.4.4 Erase and Programming Timing
The program and erase timing are controlled by the flash EE-
PROM data memory logic.
9.4.5 Memory Control and Protection Features
The last 8 bytes of the ISP memory are reserved for special
functions and some of these bytes provide memory protec-
tion and security for the flash EEPROM program memory.
Read and various types of write protection are provided.
During the reset stretch period, bytes located at E5FE and
E5FF are read out to the FLCTRL2 and FLSEC registers re-
spectively. Upon reset and before an instruction fetch, bytes
located at E5FC and E5FD are read out to the FLCTRL2 and
FLCTRL1 registers respectively. Parts of FLCTRL2 register
are loaded at different times.
E5FE Byte
Upon reset of the chip, the byte located at E5FE is read into
the FLCTRL2 register. It can be written in the ISP or test en-
vironments. It can also be written in the IRE environment
through a byte write instruction when the write instruction is
anywhere within the user boot ROM area (defined above) ex-
cept for the last two words. When the user boot ROM area
has been disabled, this word cannot be programmed in the
IRE environment. Note that when this word is erased for re-
programming, the other words in the same page must first be
saved, and then re-programmed.
CODEAREA[9:8]
The 2 least significant bits in address E5FE
contains the two most significant bits of the 10-
bit CODEAREA field. The description of
CODEAREA is shown in the E5FC section.
EMPTY The EMPTY status indicates if the flash EE-
PROM program memory array is empty or not.
It is located in the 3 most significant bits in ad-
dress E5FE. When two or more bits in the
EMPTY field are set, the flash EEPROM pro-
gram memory is empty. Upon reset of the de-
vice and the environment select pins are all
high, the device operates in ISP environment
rather than IRE environment. After the program
memory has been filled with user code, this
field should be cleared to 0002.
000, 001, 010, 100: Program memory contains user code
011, 101, 11x: Program memory is empty, do not start up in IRE
E5FF Byte
Upon reset, the byte located in the E5FF address is read into
the FLSEC register. This byte cannot be written to in the IRE
environment. The format of the E5FF byte is shown below:
The FROMRD and FROMWR fields in address location
E5FF respectively provide read and write security to the flash
EEPROM program memory array while executing instruc-
tions in all environments except IRE. The user should always
write 00002 to enable security feature.
0000, 0001, 0010, 0100, 1000: Security feature enabled
0011, 0101, 011x, 1001, 101x, 11xx: Security feature disabled
FROMRD Upon reset of the chip, read security is enabled
and 0000 is returned in all environments except
IRE. The internal program code can only be ex-
ecuted in the IRE environment when read se-
curity is activated.
FROMWR Upon reset of the chip, write security is enabled
and program and erase operations to the flash
EEPROM program memory in either program-
ming modes are prevented.
Once read/write security is enabled, the odd numbered bytes
from address E5F9 to E5FF cannot be erased. Once a secu-
rity feature has been enabled, it cannot be undone. To pre-
vent the security status from being erased, the ISP and data
memory array cannot be mass erased.
Note: In flash memory test mode, this condition also pre-
vents the odd numbered bytes of the high endurance flash
EEPROM data memory (F001 to F07F) from being erased;
7 5 4 2 1 0
EMPTY Reserved CODEAREA[9:8]
7 4 3 0
FROMWR FROMRD
Obsolete
29 www.national.com
however, the even numbered bytes of the high endurance
flash EEPROM data memory (F000 to F07E) and the ISP
flash EEPROM program memory (E000 to E5FE) can be
erased.
Read/write is overridden through PADX.
E5FC Byte
Upon reset of the chip, E5FC is read into the FLCTRL2 reg-
ister. The byte at E5FC is written in the ISP or test environ-
ments, or in the IRE environment through a byte-write
instruction when the write instruction is anywhere within the
user boot ROM area except for the last two words. When the
user boot ROM area has been disabled by having a value of
7F16 in BOOTAREA, this word cannot be programmed in the
IRE environment. Note that when this word is erased for re-
programming, the other words in the same page must first be
saved, and then re-programmed also. The E5FC register for-
mat is shown below:
This byte contains the lowest 8 bits of the CODEAREA field.
When appended to the left with the lowest 2 bits in the ad-
dress E5FE, it forms the complete CODEAREA field, which
provides write protection to all or part of the program memo-
ry, see Figure3. When write security is not enabled and
CODEAREA does not contain the value 3FF16, the program
memory range from (CODEAREA×128) to 1FFFF is consid-
ered as protected user code area and cannot be written. The
minimum protected memory range is therefore 256 bytes
when CODEAREA contains the value 3FE. Note that the
C000-FFFF memory range is not considered as program
memory and is not protected by CODEAREA.
Figure 3.Memory Protection through CODEAREA
When CODEAREA contains the value 3FF16, write protec-
tion is disabled. When the user code area overlaps into the
user boot ROM area, the overlap area is governed by a more
restrictive write protection feature, which is the user boot
ROM area. When write security has been enabled, the entire
program memory area is already write protected in all envi-
ronments.
Note that when a new value is written into CODEAREA, write
protection controlled by CODEAREA is updated after the
next device reset.
E5FD Byte
Upon the reset of the chip, the byte located at the E5FD ad-
dress is read into the FLCTRL1 register. This byte can only
be written in the ISP or test environments but not in the IRE
environment. If this byte is erased for re-programming, the
user must first save the other bytes in the same page, and
then re-program those bytes. The format of the E5FD byte is
shown below:
BOOTAREA provides write protection to part of the program
memory, see Figure4. When the write security feature is not
enabled and BOOTAREA does not contain the value 7F16,
then the program memory range from 0 to (BOOTAR-
EA*128)+127 is considered as user boot ROM area and can-
not be written to. The maximum protected memory range is
therefore 16K-127 bytes when BOOTAREA contains the val-
ue 7E16.
Figure 4.Memory Protection through BOOTAREA
When BOOTAREA contains the value 7F16, write protection
is disabled. When write security has been enabled, the entire
program memory area is already write protected in all envi-
ronments.
Note that when a new value is written into BOOTAREA, write
protection controlled by BOOTAREA is updated after the
next device reset.
9.4.6 Test Mode
The ISP flash EEPROM program memory test mode allows
direct access to the flash memory from the device pins, and
bypasses the CR16B core. This test mode also accesses the
flash memory cells that are not used in data memory (three
out of four bytes in each page).
9.4.7 Flash Program Memory Control Register 1
(FLCTRL1)
The FLCTRL1 register is a read-only byte-wide register. The
value of this register is loaded from memory address E5FD16
when the chip comes out of reset. The BOOTAREA field de-
fines a user boot ROM area to be write protected. The Flash
EEPROM Program Memory Control Register 1 format is
shown below:
7 0
CODEAREA[7:0]
0000h
10000h
1FFFFh
Address Map
CR16MHR6
CODEAREA×128
protected user
code area
C000h
non-code area, not
protected
protected user
code area
7
6 0
Reserved BOOTAREA
7 6 0
Reserved BOOTAREA
0000h
3F80h
1FFFFh
Address Map
CR16MHR6
(BOOTAREA×
128)+127
protected user boot
area
boot area maximum limit
Obsolete
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When BOOTAREA has any value other than 7F16, then the
memory at 0 to (BOOTAREA×128)+15 is considered as user
boot ROM area and is write protected. When it has a value of
7F16, then there is no user boot ROM area to be write pro-
tected
9.4.8 Flash Program Memory Control Register 2
(FLCTRL2)
The FLCTRL2 register is a read-only word-wide register. The
value of this register is loaded from memory addresses
E5FC16
and E5FE16 when the chip comes out of reset. When
the device starts execution, the EMPTY bit indicates whether
the flash EEPROM program memory is empty of not, and se-
lects the chip to be in IRE or ISP environment if the external
environment pins are all high. The CODEAREA field defines
a user code area to be write protected. The Flash EEPROM
Program Memory Control Register 2 format is shown below:
EMPTY When the bits are either 0112, 1012, 1102, or
1112, and if the device’s environment select
pins are all high, the device will come out of re-
set in ISP environment instead of IRE environ-
ment.
CODEAREA When it has any value other than 3FF 16, then
the memory (CODEAREA×128) to 1FFFF16 is
considered as user code area and is write pro-
tected. When it has a value of 3FF16
, then there
is no code protection area to be write protect-
ed.
9.4.9 Flash Program Memory Security Register
(FLSEC)
The FLSEC register is a read-only byte-wide register. When
the chip comes out of reset, the value of this register is load-
ed from memory address E5FF16. The FROMRD and
FROMWR field control the read and write security of the flash
EEPROM program memory respectively. The Flash EE-
PROM Program Memory Security register format is shown
below:
0000, 0001, 0010, 0100, 1000: Security feature enabled
0011, 0101, 011x, 1001, 101x, 11xx: Security feature disabled
FROMRD When read security feature is enabled, the
flash EEPROM program memory can only be
read in IRE environment, but will return 000016
in other environments; also, erase to odd num-
bered bytes from address E5F916 to E5FF16
and mass erase to ISP and flash EEPROM
data memory array are ignored unless PADX is
activated (see security override below).
FROMWR Unless PADX is activated (see override below),
when write security feature is enabled, all fur-
ther writes and erases to flash EEPROM pro-
gram memory, erase to odd numbered bytes
from address E5F916 to E5FF16, and mass
erase to ISP and flash EEPROM data memory
array are ignored.
9.4.10 ISP Memory Write Key Register (ISPKEY)
The In-System-Programming Memory Write Key (ISPKEY)
register is a byte-wide, write-only register. It contains the en-
able key to enable writes to ISP flash EEPROM program
memory. A value of 6A16 must be written to this register im-
mediately preceding every write to the ISP flash EEPROM
program memory for the flash write operation to proceed,
otherwise any other write operation will clear the key (the
only exception is that the subsequent write is another write to
this key register with the proper key, in which case the key is
still set). A read always returns FF 16
. Engineering note: on
reset, the write enable status that is generated as a result of
a write to this key register is cleared. The ISP Memory Write
Key register format is shown below:
ISPKYVAL is the ISP Flash Program Memory Write Enable
Key Value.
15 13 12 10 9 0
EMPTY Reserved CODEAREA
7 4 3 0
FROMWR FROMRD
7 0
ISPKYVAL
Obsolete
31 www.national.com
10.0 Interrupts
The Interrupt Control Unit (ICU31L) receives interrupt re-
quests from internal and external sources and generates in-
terrupts to the CPU. Interrupts from the timers, USARTs,
MICROWIRE/SPI interface, Multi-Input Wake-Up, and A/D
converter are all maskable interrupts. The highest-priority in-
terrupt is the Non-Maskable Interrupt (NMI), which is trig-
gered by a falling edge received on the NMI input pin. The
NMI pin is not available on the 44-pin packages.
10.1 INTERRUPT OPERATION
An exception is an event that temporarily stops the normal
flow of program execution and causes execution of a sepa-
rate service routine. Upon completion of the service routine,
execution of the interrupted program continues from the point
at which it was stopped.
There are two kinds of exceptions, called traps and inter-
rupts. A trap is the result of some action or condition in the
program itself, such as execution of an Exception (EXCP) in-
struction. An interrupt is a CPU-external event, such as a sig-
nal received on a Multi-Input Wake-Up input or a request
from an on-chip peripheral module for service.
The operation of traps is beyond the scope of this data sheet.
For information on traps, and for additional detailed informa-
tion on interrupts not provided in this data sheet, please refer
to the CompactRISC CR16B Programmer's Reference Man-
ual.
10.1.1 Interrupt Operation Summary
When an interrupt occurs, the on-chip hardware performs the
following steps:
1. Decrements the Interrupt Stack Point (ISP) by four.
2. Saves the contents of the Program Counter (PC) and
Processor Status Register (PSR) on the interrupt stack.
3. Clears the I, P, and T bits in the Processor Status Reg-
ister (PSR). These are the Global Maskable Interrupt
Enable bit, Trace Trap Pending bit, and Trace bit, re-
spectively.
4. Reads the interrupt vector from the Interrupt Vector Reg-
ister (IVCT).
5. Combines the interrupt vector with the value in the Inter-
rupt Base (INTBASE) register to obtain an address in
the Interrupt Dispatch Table, and loads the dispatch ta-
ble entry into the Program Counter (PC).
From this point onward, the CPU executes the interrupt ser-
vice routine. The service routine ends with a Return from Ex-
ception (RETX) instruction. This returns the CPU to the
interrupted program. The CPU restores the contents of the
PC and PSR registers from the stack and increments the In-
terrupt Stack Pointer by four.
10.1.2 Service Routine Addresses
When an interrupt or trap occurs, the CPU executes a ser-
vice routine. There are different service routines for different
interrupts and traps. Each service routine may reside any-
where in program memory. The starting addresses of the ser-
vice routines are contained in a table called the Dispatch
Table. Entries in the table are organized in the order shown
in Table10.
Table 10Dispatch Table Entries
0: Reserved
1: NMI
2: Reserved
3: Reserved
4: Reserved
5: SVC (Supervisor Call Trap)
6: DVC (Divided by Zero Trap)
7: FLG (Flag Trap)
8: BPT (Breakpoint Trap)
9: TRC (Trace Trap)
10: UND (Undefined Instruction Trap)
11: Reserved
12: Reserved
13: Reserved
14: Reserved
15: Reserved
16: INT0 (Reserved)
17: INT1 (Flash EEPROM Program Memory)
18: INT2 (Reserved)
19: INT3 (Reserved)
20: INT4 (Reserved)
21: INT5 (ADC)
22: INT6 (MIWU Interrupt 3)
23: INT7 (MIWU Interrupt 2)
24: INT8 (MIWU Interrupt 1)
25: INT9 (MIWU Interrupt 0)
26: INT10 (USART 2 Tx)
27: INT11 (USART 1Tx)
28: INT12 (Reserved)
29: INT13 (MICROWIRE/SPI Rx/TX)
30: INT14 (ACCESS.bus)
31: INT15 (USART 2 Rx)
32: INT16 (USART 1 Rx)
33: INT17 (Reserved)
34: INT18 (CAN)
35: INT19 (Reserved)
36: INT20 (Reserved)
37: INT21 (Reserved)
Obsolete
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Each entry in the Dispatch Table consists of two bytes that
provide bits 1 through 16 of the starting address of the corre-
sponding service routine. The full 21-bit address of a service
routine is reconstructed by adding a leading 0 and a trailing
0 to the 16-bit table entry.
The INTBASE register is a pointer to the Dispatch Table.
Upon reset, the initialization software must write the starting
address of the Dispatch Table to the INTBASE register, a 21-
bit register with the five most significant bits and the least sig-
nificant bit always equal to 0. It is typically kept in the flash
EEPROM program memory. The Dispatch Table is 48 words
long.
Each interrupt or trap source has an associated vector num-
ber ranging from 0 to 31, as indicated in Table10. When an
interrupt occurs, the hardware multiplies the vector by 2,
adds the result to the contents of the INTBASE register, and
uses the resulting address to obtain the service routine start-
ing address from the corresponding entry in the Dispatch Ta-
ble. This address is placed in the Program Counter so that
the CPU begins executing the interrupt service routine.
Figure5 summarizes the method used by the device to gen-
erate the starting address of a service routine.
10.1.3 Stack Usage
When an interrupt occurs, the CPU automatically preserves
the contents of the Program Counter (PC) and Processor
Status Register (PSR) by pushing them on the interrupt stack
and decrementing the Interrupt Stack Pointer by four. The
service routine ends with a Return from Exception (RETX) in-
struction, which returns control to the interrupted program by
restoring the PC and PSR values and incrementing the Inter-
rupt Stack Pointer (ISP) by four.
Prior to using any interrupts, the Interrupt Stack Pointer (ISP)
must be initialized so that it points to a space in RAM where
the interrupt stack will be kept. The stack grows downward in
memory (toward address zero) when an interrupt occurs and
items are pushed onto the stack. The stack shrinks upward
in memory when an interrupt service routine ends and items
are popped from the stack.
Many routines need to use the general-purpose registers R0
through R13. To preserve the existing register contents, a
routine can save register contents on the program stack upon
start of the routine and restore the register contents prior to
completion of the routine. The software can also use the pro-
gram stack to transfer data parameters from one routine to
another when the parameters are too large to easily fit into
the registers. A high-level language typically allocates the lo-
cal (non-static) variables on the stack.
The pointer to the program stack is the SP register, which
must be initialized prior to any register save/restore opera-
tions or data transfer operations. Using the program stack, an
interrupt routine needs to initially save the contests of all reg-
isters that it uses, and restore those register contents before
returning to the interrupted program.
10.2 NON-MASKABLE INTERRUPT
A non-maskable interrupt is triggered by a falling edge on the
NMI input pin, which generates a software trap. The NMI pin
is an asynchronous input with Schmitt trigger characteristics
and an internal synchronization circuit. Therefore, no exter-
nal synchronizing is needed.
Upon reset, the non-maskable interrupt is disabled and
should remain disabled until the software initializes the inter-
rupt table, interrupt base, and interrupt stack pointer. It can
be enabled by setting either of two control bits in the External
NMI Control/Status (EXNMI) register. The two bits are called
the EN (Enable) bit and the ENLCK (Enable and Lock) bit.
The EN bit enables the NMI trap until an NMI trap event or a
reset occurs. An NMI trap automatically resets the EN bit. Us-
ing this bit to enable the NMI trap is intended for applications
where the NMI pin is toggled frequently but nested NMI traps
are not needed. The trap service routine should re-enable the
NMI trap by setting the EN bit before returning to the main
program.
The ENLCK bit enables the NMI trap and locks it in the en-
abled state. In other words, it leaves the NMI trap enabled
even after the trap occurs. It can be cleared only by a reset
operation. After the bit is set, an NMI trap is triggered by each
falling edge on the NMI pin, allowing nested NMI traps.
To use the EN bit, the ENLCK must remain cleared to 0. Oth-
erwise, the EN bit is ignored.
10.3 MASKABLE INTERRUPTS
Maskable interrupts can be enabled or disabled under soft-
ware control. There are 31 level-triggered maskable interrupt
sources (including some reserved for future expansion), or-
ganized into levels of priority. If more than one interrupt event
occurs at any given time, the interrupt source with the highest
priority is serviced first. The others must wait until the high-
est-priority interrupt is serviced and is no longer pending.
Figure11 lists the maskable interrupt sources of the device
in order of priority, from the highest-priority interrupt (IRQ31)
to the lowest (IRQ0).
To enable a maskable interrupt, the enable bit must be set in
the applicable peripheral module and also in the appropriate
Interrupt and Enable Mask register, IENAM0 or IENAM1. In
addition, both the Global Maskable Interrupt Enable bit (I)
and the Local Maskable Interrupt Enable bit (E) must be set
to 1 in the PSR register. If either one of these bits is 0, then
all maskable interrupts are disabled. The CR16B core sup-
ports IRQ0, but ICU31L reserves IRQ0 so that it is not con-
nected to any interrupt source.
38: INT22 (Reserved)
39: INT23 (VTUD Interrupt Request 4)
40: INT24 (VTUD Interrupt Request 3)
41: INT25 (VTUD Interrupt Request 3)
42: INT26 (VTUD Interrupt Request 1)
43: INT27 (T2B Timer 2 Interrupt B)
44: INT28 (T2A Timer 2 Interrupt A)
45: INT29 (T1B Timer 1Interrupt B)
46: INT30 (T1A Timer 1Interrupt A)
47: INT31 (RTI Timer 0)
Table 10Dispatch Table Entries
Obsolete
33 www.national.com
Both the E bit and I bit can be controlled with the Load Pro-
cessor Register (LPR) instruction. In addition, the E bit is
easily changed by executing the Enable Interrupts (EI) or
Disable Interrupts (DI) instruction. Using the EI and DI in-
structions avoids the possibility of an interrupt occurring with-
in a read-modify-write operation on the PSR register.
10.4 INTERRUPT REGISTERS
The Interrupt Control Unit uses the following interrupt control
and status registers:
—Non-Maskable Interrupt Status Register (NMISTAT)
—Non-Maskable Interrupt Status Monitor Reg. (NMIMN-
TR)
—External NMI Control/Status Register (EXNMI)
—Interrupt Enable and Mask Register 0 (IENAM0)
—Interrupt Enable and Mask Register 1 (IENAM1)
—Interrupt Vector Register (IVCT)
Figure 5.
INTBASE
~
~
~
~
Non-maskable Interrupt
Reserved
Supervisor Call Trap
Divide By Zero Trap
Flag Trap
Breakpoint Trap
Trace Trap
Undefined Instruction Trap
Maskable Interrupts
NMI
Reserved
Reserved
SVC
DVZ
FLG
BPT
TRC
UND
Reserved
Reserved
ISE
INTn
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16 to 127
In-System Emulator Interrupt
31 0
Reserved
Reserved
DBG Debug Trap
Table 11Maskable Interrupt Priority List
Interrupt Request Source
IRQ31 RTI (Timer 0), highest priority
IRQ30 T1A (Timer 1 input A)
IRQ29 T1B (Timer 1 input B)
IRQ28 T2A (Timer 2 input A)
IRQ27 T2B (Timer 2 input B)
IRQ26 VTUA (VTU Interrupt Request 1)
IRQ25 VTUB (VTU Interrupt Request 2)
IRQ24 VTUC (VTU Interrupt Request 3)
IRQ23 VTUD (VTU Interrupt Request 4)
IRQ22-IRQ19 Reserved
IRQ18 CAN
IRQ17 Reserved
IRQ16 USART1 Rx
IRQ15 USART2 Rx
IRQ14 ACCESS.bus
IRQ13 MICROWIRE/SPI Rx/Tx
IRQ12 Reserved
IRQ11 USART1 Tx
IRQ10 USART2 Tx
IRQ9 MIWU16 Interrupt 0
IRQ8 MIWU16 Interrupt 1
IRQ7 MIWU16 Interrupt 2
IRQ6 MIWU16 Interrupt 3
IRQ5 ADC
IRQ4-IRQ2 Reserved
IRQ1 Flash Program Memory
IRQ0 Reserved, lowest priority
Table 11Maskable Interrupt Priority List
Interrupt Request Source
Obsolete
www.national.com 34
—Interrupt Status Register 0 (ISTAT0)
—Interrupt Status Register 1 (ISTAT1)
—Interrupt Debug Register (IDBG)
The following CPU core registers are also used in processing
interrupts:
—Interrupt Stack Pointer (ISP)
—Interrupt Base Register (INTBASE)
10.4.1 Non-Maskable Interrupt Status Register
(NMISTAT)
The NMISTAT register is a byte-wide, read-only register that
holds the current pending status of the Non-Maskable Inter-
rupt (NMI). This register is cleared upon reset. It is also
cleared each time it is read. The register format is shown be-
low.
EXT External Non-Maskable Interrupt Request.
When set to 1 by the hardware, it indicates an
external Non-Maskable Interrupt request has
occurred. See the description of the EXNMI
register below for more information.
10.4.2 External NMI Control/Status Register (EXNMI)
The EXNMI register is a byte-wide, read/write register that
shows the current state of the NMI pin and also allows the
NMI trap to be enabled by setting either the EN bit or the EN-
LCK bit. Both of these bits are cleared upon reset. When the
software writes to this register, it must write 0 to all reserved
bit positions for the device to function properly. EN, ENLCK,
and TST are cleared upon reset. The register format is
shown below.
EN Enable NMI Trap. When set to 1, NMI traps are
enabled and falling edge on the NMI pin gener-
ates a NMI trap. Each occurrence of an NMI
trap automatically clears the EN bit. The trap
service routine should set the EN bit to 1 before
returning control to the interrupted program.
When EN is cleared to 0, NMI traps are dis-
abled unless they are enabled with the ENLCK
bit. When the ENLCK bit is set to 1, the EN bit
is ignored.
PIN NMI Pin. This bit shows the current state of the
NMI input pin (without logical inversion). A 1 in-
dicates a high level and a 0 indicates a low lev-
el on the pin. This is a read-only bit. In a write
operation, the value written to this bit position is
ignored.
ENLCK Enable and Lock NMI Trap. When set to 1, NMI
traps are enabled and locked in the enabled
state. Each falling edge on the NMI pin gener-
ates a NMI trap, even if a previous NMI trap has
occurred and is still being processed. When
ENLCK is cleared to 0, NMI traps are disabled
unless they are enabled with the EN bit.
10.4.3 Interrupt Vector Register (IVCT)
The IVCT register is a byte-wide, read-only register that con-
tains the encoded value of the enabled and pending
maskable interrupt with the highest priority. The on-chip hard-
ware automatically updates this field whenever there is a
change in the highest-priority enabled and pending maskable
interrupt. The CPU reads this register during an interrupt ac-
knowledge core bus cycle to determine where to begin exe-
cuting the interrupt service routine. The register contents are
guaranteed to be valid at that time. The register is not guar-
anteed to contain valid data during a hardware update oper-
ation. The register format is shown below.
INTVECT Interrupt Vector. This 6-bit field contains the en-
coded value of the enabled and pending
maskable interrupt with the highest priority. For
example, if interrupts IRQ1 and IRQ6 are both
enabled and pending, the higher-priority inter-
rupt is IRQ6. As a result the 6 bit interrupt vec-
tor is 010110.
10.4.4 Interrupt Enable and Mask Register 0 (IENAM0)
The IENAM0 register is a word-wide, read/write register that
enables or disables the individual interrupts IRQ0 through
IRQ15. The register format is shown below.
A bit set to 1 enables the corresponding interrupt. A bit
cleared to 0 disables the corresponding interrupt. Upon re-
set, this register is initialized to FFFF hex.
10.4.5 Interrupt Enable and Mask Register 1 (IENAM1)
The IENAM0 register is a word-wide, read/write register that
enables or disables the individual interrupts IRQ16 through
IRQ31. The register format is shown below.
A bit set to 1 enables the corresponding interrupt. A bit
cleared to 0 disables the corresponding interrupt. Upon re-
set, this register is initialized to FFFF hex.
10.4.6 Interrupt Status Register 0 (ISTAT0)
The ISTAT0 register is a word-wide, read-only register that
indicates which maskable interrupt inputs to the ICU31L
(IRQ0 through IRQ15) are currently active. The register for-
mat is shown below.
IST(15:0) Interrupt Status bits. Each bit indicates the cur-
rent status of an interrupt input to the ICU31L,
corresponding to interrupts IRQ0 through
IRQ15. A bit set to 1 indicates an active inter-
rupt input, even when the interrupt is masked
out by the IENAM0 register. A bit cleared to 0
indicates an inactive interrupt input.
7 6 5 4 3 2 1 0
Reserved EXT
7 6 5 4 3 2 1 0
Reserved ENLCK PIN EN
76543210
0 0 INTVECT
15 0
IENA(15:0)
15 0
IENA(31:16)
15 0
IST(15:0)
Obsolete
35 www.national.com
10.4.7 Interrupt Status Register 1 (ISTAT1)
The ISTAT1 register is a word-wide, read-only register that
indicates which maskable interrupt inputs to the ICU31L
(IRQ16 through IRQ31) are currently active. The register for-
mat is shown below.
IST(31:16) Interrupt Status bits. Each bit indicates the cur-
rent status of an interrupt input to the ICU31L,
corresponding to interrupts IRQ16 through
IRQ31. A bit set to 1 indicates an active inter-
rupt input, even when the interrupt is masked
out by the IENAM0 register. A bit cleared to 0
indicates an inactive interrupt input.
10.4.8 Interrupt Debug Register
The IDBG register is a word-wide read-only register, which
contains various status information of the ICU31L. The low-
est 6 bits contain the INTVECT value during the last read
from address FE00. The next 6 bits contain the INTVECT
value when a maskable interrupt request is sent to the
CR16B core. Upon reset, this register is set to 0000 hex.
10.5 INTERRUPT PROGRAMMING
PROCEDURES
The following subsections provide information on initializing
the device for interrupts, clearing interrupts, and nesting in-
terrupts.
10.5.1 Initialization
Upon reset, all interrupts are disabled. To program the device
for interrupt operation and to enable interrupts, use the fol-
lowing procedure in the application software:
1. Set the Interrupt Stack Pointer (ISP)
2. Load the INTBASE register so that it points to the base
of the Interrupt Dispatch Table.
3. Perform any required preparation steps for the interrupt
service routines.
4. Initialize the peripheral devices that can generate inter-
rupts and set their respective interrupt enable bits.
5. Set the relevant bits in the interrupt mask registers
(IENAM0 and IENAM1)
Note: The MIWU16 interrupts have no local interrupt en-
able bits, which means you can only disable the
MIWU16 interrupts if you clear the specific bits in the IE-
NAM register.
6. Use the Load Processor Register (LPR) instruction to
set I bit in the PSR register.
7. When the device is ready to execute interrupts, set the
E bit in the PSR register by executing the Enable Inter-
rupts (EI) instruction.
Once maskable interrupts are enabled by setting the E and I
bits, you can disable and re-enable all maskable interrupts
locally by using the Enable Interrupts (EI) and Disable Inter-
rupts (DI) instructions, which set and clear the E bit.
10.5.2 Clearing Interrupts
Clearing an interrupt request before it is serviced may cause
a spurious interrupt because the CPU may detect an inter-
rupt not reflected in the Interrupt Vector (IVCT) register. To
ensure reliable operation, clear interrupt requests only while
interrupts are disabled.
Changing the polarity of an interrupt input (for example, in the
Multi-Input Wake-Up module) can cause a spurious interrupt,
and therefore should be done only while interrupts are dis-
abled.
For the same reason, clearing an enable bit in a peripheral
module should be carried out only while the interrupt is dis-
abled.
10.5.3 Nesting Interrupts
Interrupts may be nested, or in other words, an interrupt ser-
vice routine can itself be interrupted by a different interrupt
source. There is no hardware limitation on the number of in-
terrupt nesting levels. However, the interrupt stack must not
be allowed to overflow its allocated memory space.
Unless specifically enabled by the software, nested inter-
rupts will not occur. When the CPU acknowledges an inter-
rupt, the I bit in the PSR register is automatically cleared to 0
for the duration of the service routine, disabling any further
maskable interrupts.
To allow nested interrupts, an interrupt service routine should
first set or clear the respective interrupt enable bits to specify
which peripherals will be allowed to interrupt the current ser-
vice routine. The present interrupt routine should be disabled
(or interrupt pending bit cleared). The service routine should
then set the PSR.I bit to 1, thus enabling maskable interrupts.
This bit can be controlled with the Store Processor Register
(SPR) and Load Processor Register (LPR) instructions.
Note:
Clearing the pending bit of the current interrupt should not be
immediately followed by enabling further interrupts by setting
the I bit in the PSR register. Wait states must be inserted into
the software after clearing the interrupt pending bit and be-
fore another interrupt. Placing a NOP instruction will perform
this instruction. This is because the instruction which resets
the pending bit may not yet be finished when the interrupts
are already enabled again by setting the I bit in the PSR reg-
ister. To avoid this situation the user has to make sure that
prior to enabling the interrupt an additional instruction is in-
serted. This could look like the example below:
SBITi $0, T1ICRL # clear pending bit
NOP # NOP instruction
MOVW $0x0a00, r0 # enable further interrupts
LPR r0, psr
A CBITi or SBITi instruction may be used to clear the interrupt
pending bit. In such cases, a spurious interrupt may occur.
15 0
IST(31:16)
Obsolete
www.national.com 36
11.0 Power Management
The Power Management Module (PMM) improves the effi-
ciency of the device by changing the operating mode (and
therefore the power consumption) according to the required
level of device activity.
The device can operate in any of four power modes:
—Active
—Power Save
—Idle
—Halt
Table12 summarizes the main properties of the four operat-
ing modes: the state of the high-frequency oscillator (on or
off), the type of clock used by most modules, and the clock
used by the Timing and Watchdog Module (TWM).
The low-frequency oscillator continues to operate in all four
modes and power must be provided continuously to the de-
vice power supply pins. In the Halt mode, however, the inter-
nal SLCLK does not toggle, and as a result, the TWM timer
and Watchdog Module do not operate. For the Power Save
and Idle modes, the high-frequency oscillator can be turned
on or off under software control, as long as the low-frequency
oscillator is used.
11.1 ACTIVE MODE
In the Active mode, all device modules are fully operational.
This is the operating mode upon reset. Most device modules
use the clock generated by the high-frequency clock oscilla-
tor. The clock rate is determined by the external crystal net-
work.
Power consumption in the Active mode can be reduced by
selectively disabling unused modules and/or by executing
the WAIT instruction. When WAIT is executed, the core stops
executing new instructions and waits for an interrupt.
11.2 POWER SAVE MODE
In the Power Save mode, all device modules operate off the
low-frequency clock. If the low-frequency clock is generated
from an external crystal network, the high-frequency clock
oscillator can be turned off to further reduce power consump-
tion.
All on-chip modules continue to operate in the Power Save
mode, with the SLCLK acting as their system clock. If this
mode is entered by using the WAIT command, the CPU is in-
active and waits for an interrupt to wake up. Otherwise, CPU
continues to function normally at the lower frequency of the
slow clock.
The low frequency of the clock in Power Save mode limits the
operation of modules such as the USARTs, MICROWIRE in-
terface, A/D Converter, and timers because they are driven
by the slow clock rather than the normal high-speed clock. In
order to work properly in Power Save mode, modules that
perform real-time operations (such as a USART baud rate
generator) must be reprogrammed to use the slower clock.
To reduce power consumption as much as possible, the pro-
gram should execute a WAIT instruction during periods of
CPU inactivity.
11.3 IDLE MODE
In the Idle mode, the clock is stopped for most of the device.
Only the Power Management Module and Timing and Watch-
dog Module continue to operate. Both of these modules use
the slow clock in this mode.
11.4 HALT MODE
In the Halt mode, all device clocks are disabled and the high-
frequency oscillator is shut off. In this mode, the device con-
sumes the least possible power while maintaining the device
memory and register contents. The low-frequency oscillator
continues to operate in this mode, but with very low power
consumption due to its power-optimized design.
11.5 CLOCK INPUTS AND RESET
CONFIGURATION
The system uses a high frequency clock Active mode. The
source of this clock in the device is a high frequency crystal
oscillator. The Oscillating High Frequency Clock (OHFC) in-
put indicates to the Power Management Module (PMM)
when this clock is stable and therefore usable. The clock can
be used when OHFC is set to 1. The PMM does not use the
high frequency clock when OHFC is set to 0. OHFC can be
the output of a clock monitor or a strapped input signal to this
module.
The low frequency clock is used in Power Save mode as the
system clock source. In Idle mode, it is used as the clock
source for the PMM and the TWM, both of which remain
clocked. The clock source may be a low frequency clock os-
cillator or the prescaler from the high frequency clock.
The Oscillating Low Frequency Clock (OLFC) input indicates
to the PMM when the clock is stable and therefore usable.
When OLFC is set to 1, it indicates that the clock can be
used. When OLFC is set to 0, the PMM does not use the low
frequency clock. OLFC is generated by the “slow clock good”
output of the Dual Clock and Reset module (CLK2RES).
While in reset (i.e., the reset signal is active), the PMM out-
puts the clock as long as the clock selected for use upon re-
set is stable (OHFC or OLFC are 1). If the clock selected is
not stable, the PMM clock output remains low.
11.6 SWITCHING BETWEEN POWER MODES
Switching from a higher to a lower power consumption mode
is accomplished by writing an appropriate value to the Power
Management Control/Status Register (PMCSR). Switching
from a lower power consumption mode to the Active mode is
usually triggered by a hardware interrupt. Figure6 shows the
four power consumption modes and the events that trigger a
transition from one mode to another.
Table 12Power Mode Operating Summary
Mode High-Frequency
Oscillator Clock Used TWM Clock
Active On Main Clock Slow Clock
Power Save On or Off Slow Clock Slow Clock
Idle On or Off None Slow Clock
Halt Off None None
Obsolete
37 www.national.com
Some of the power-up transitions are based on the occur-
rence of a wake-up event. An event of this type can be either
a maskable interrupt or a non-maskable interrupt (NMI). All
of the maskable hardware wake-up events are gathered and
processed by the Multi-Input Wake-Up Module, which is ac-
tive in all modes. Once a wake-up event is detected, it is
latched until an interrupt acknowledge cycle occurs or a reset
is applied.
A wake-up event causes a transition to the Active mode and
restores normal clock operation, but does not start execution
of the program. It is the interrupt service routine associated
with the wake-up source (MIWU16 or NMI) that causes actu-
al program execution to resume.
11.6.1 Power Management Control/Status Register
(PMCSR)
The Power Management Control/Status Register (PMCSR)
is a byte-wide, read/write register that controls the operating
power mode (Active, Power Save, Idle, or Halt) and enables
or disables the high-frequency oscillator in the Power Save
and Idle modes. The two most significant bits, OLFC and
OHFC, are read-only status bits controlled by the hardware.
Upon reset, the non-reserved bits of this register are cleared.
The format of the register is shown below.
PSM Power Save Mode. When this bit is 0, the de-
vice operates in the Active mode. Writing a 1 to
this bit position puts the device into the Power
Save mode, either immediately or upon execu-
tion of the next WAIT instruction, depending on
the WBPSM bit.
The PSM bit can be set and cleared by the soft-
ware. It is also cleared by the hardware when a
hardware wake-up event is detected.
DHF Disable High-Frequency Oscillator. This bit en-
ables (0) or disables (1) the high-frequency os-
cillator in the Power Save or Idle mode. (The
high-frequency oscillator is always enabled in
Active mode and always disabled in Halt mode,
regardless of this bit settings.) The DHF bit is
cleared automatically when a hardware wake-
up event is detected.
IDLE Idle Mode. When this bit is set and the device
is in Power Save mode, the device enters the
Idle mode upon execution of a WAIT instruc-
tion. In order to enter the Idle mode directly
from the Active mode, the WBPSM bit must be
set before the WAIT instruction is executed.
The IDLE bit can be set and cleared by the soft-
ware. When a hardware wake-up event is de-
tected, this bit is cleared automatically and the
device returns to the Active mode.
HALT Halt Mode. When this bit is set and the device
is in Idle mode, the device enters the Halt mode
upon execution of a WAIT instruction. In order
to enter the Halt mode directly from the Active
mode, the WBPSM bit must be set before the
WAIT instruction is executed.
The Halt bit can be set and cleared by the soft-
ware. When a hardware wake-up event is de-
tected, this bit is cleared automatically and the
device returns to the Active mode.
WBPSM Wait Before Entering Power Save Mode. When
the CPU writes a 1 to the PSM bit, the WBPSM
determines when the transition from Active to
Power Save mode is done. If the WBPSM bit is
0, the switch to Power Save mode is initiated
immediately; the PSM bit in the register is set
to 1 upon completion of the switch to Power
Save mode. If the WBPSM bit is 1, the device
continues to operate in Active mode until the
next WAIT instruction, and then enters the
Power Save mode. In this case, the PSM bit is
set to 1 immediately, even if a WAIT instruction
has not yet been executed.
In the Active mode, the WBPSM bit must be set
in order to enter the Idle or Halt mode.
OHFC Oscillating High-Frequency Clock. This read-
only bit indicates the status of the high-frequen-
cy clock. If this bit is 1, the high-frequency clock
is available and stable. If this bit is 0, the high-
frequency clock is either disabled, not available
to the Power Management Module, or operat-
ing but not yet stable. The device can switch to
the Active mode only when this bit is 1.
OLFC Oscillating Low-Frequency Clock. This read-
only bit indicates the status of the low-frequen-
cy (slow) clock. If this bit is 1, it indicates that
the slow clock is running and stable. The slow
clock can be either the prescaled fast clock (the
default) or the external oscillator (if selected).
The Dual Clock module will not allow a transi-
tion to the slow crystal mode unless the slow
crystal is operating, so this bit should be 1 un-
der normal circumstances.
The device can switch from the Active mode to
the Power Save or Idle mode only if the OLFC
bit is 1. There is no such restriction on switch-
ing to the Halt mode.
Figure 6.Power Modes and Transitions
7 6 5 4 3 2 1 0
OLFC OHFC WBPSM Reserved HALT IDLE DHF PSM
Active
Power Save
Idle
Halt
IDLE =1
and WAIT
PSM =1
HW event
or PSM =0
HALT =1
HW event
and WAIT
Reset
HW event
Obsolete
www.national.com 38
11.6.2 Active to Power Save Mode
A transition from the Active mode to the Power Save mode is
accomplished by writing a 1 to the PMCSR.PSM bit. The
transition to Power Save mode is either initiated immediately
or upon execution of the next WAIT instruction, depending on
the PMCSR.WBPSM bit.
For an immediate transition to Power Save mode (PMC-
SR.WBPSM=0), the CPU continues to operate using the low-
frequency clock. The PMCSR.PSM bit is set to 1 when the
transition to the Power Save mode is completed.
For a transition upon the next WAIT instruction (PMC-
SR.WBPSM=1), the CPU continues to operate in the Active
mode until it executes a WAIT instruction. Upon execution of
the WAIT instruction, the device enters the Power Save
mode and the CPU waits for the next interrupt event. In this
case, the PMCSR.PSM bit is set to 1 when it is written, even
before the WAIT instruction is executed.
11.6.3 Entering the Idle Mode
Entry into the Idle mode is accomplished by writing a 1 to the
PMCSR.IDLE bit and then executing a WAIT instruction.
The Idle mode can be entered only from the Active or Power
Save mode. For entry from the Active mode, the PMC-
SR.WBPSM bit must be set before the WAIT instruction is ex-
ecuted.
11.6.4 Disabling the High-Frequency Clock
In systems where the low-frequency crystal is available and
is used to generate the Slow Clock (SLCLK), power con-
sumption can be reduced further in the Power Save or Idle
mode by disabling the high-frequency clock. This is accom-
plished by writing a 1 to the PMCSR.DHF bit before execut-
ing the WAIT instruction that puts the device in the Power
Save or Idle mode. The high-frequency clock is turned off
only after the device enters the Power Save or Idle mode.
The CPU operates on the low-frequency clock in Power Save
mode. It can turn off the high-frequency clock at any time by
writing a 1 to the PMCSR.DHF bit.
The high-frequency oscillator is always enabled in Active
mode and always disabled in Halt mode, regardless of the
PMCSR.DHF bit setting.
Immediately following power-up and entry into the Active
mode, the software must wait for the low-frequency clock to
become stable before it can put the device in the Power Save
mode. It should monitor the PMCSR.OLFC bit for this pur-
pose. Once this bit is set to 1, the slow clock is stable and the
Power Save mode can be entered.
11.6.5 Entering the Halt Mode
Entry into the Halt mode is accomplished by writing a 1 to the
PMCSR.HALT bit and then executing a WAIT instruction.
The Halt mode can be entered only from the Active or Power
Save mode. For entry from the Active mode, the PMC-
SR.WBPSM bit must be set before the WAIT instruction is ex-
ecuted.
11.6.6 Software-Controlled Transition to Active Mode
A transition from the Power Save mode to the Active mode
can be accomplished by either a software command or a
hardware wake-up event. The software method is to write a
0 to the PMCSR.PSM bit. The value of the register bit chang-
es only after the transition to the Active mode is completed.
If the high-frequency oscillator is disabled for Power Save op-
eration, the oscillator must be enabled and allowed to stabi-
lize before the transition to Active mode. To enable the high-
frequency oscillator, the software writes a 0 to the PMC-
SR.DHF bit. Before writing a 0 to the PMCSR.PSM bit, the
software should first monitor the PMCSR.OHFC bit to deter-
mine whether the oscillator has stabilized.
11.6.7 Wake-Up Transition to Active Mode
A hardware wake-up event switches the device directly from
Power Save, Idle, or Halt mode to the Active mode.
Hardware wake-up events are:
•a Non-Maskable Interrupt (NMI)
•a valid wake-up event on a Multi-Input Wake-Up channel
When a wake-up event occurs, the on-chip hardware per-
forms the following steps:
1. Clears the PMCSR.DHF bit, thus enabling the high-fre-
quency clock (if it was disabled).
2. Waits for the PMCSR.OHFC bit to be set, which indi-
cates that the high-frequency clock is operating and is
stable.
3. Switches the device into the Active mode.
11.6.8 Power Mode Switching Protection
The Power Management Module has several mechanisms to
protect the device from malfunctions caused by missing or
unstable clock signals.
The PMCSR.OHFC and PMCSR.OLFC bits indicate the cur-
rent status of the high-frequency and low-frequency clock os-
cillators, respectively. The software can check the
appropriate bit before it changes to an operating mode that
requires the clock. A status bit set to 1 indicates an operating,
stable clock. A status bit cleared to 0 indicates a clock that is
disabled, not available, or not yet stable.
During a power mode transition, if there is a request to switch
to a mode that uses clock with its status bit cleared to 0, the
switch is delayed until that bit is set to 1 by the hardware.
When the system is built without an external crystal network
for the low-frequency clock, the high-frequency clock is divid-
ed by a prescaler factor to produce the low-frequency clock.
In this situation, the high-frequency clock is disabled only in
the Halt mode, and cannot be disabled for the Power Save or
Idle mode, regardless of the software command issued.
Without an external crystal network for the low-frequency
clock, the device comes out of the Halt or Idle mode and en-
ters the Active mode with the high-speed oscillator used as
the clock. The device can still enter the Power Save from the
Active mode by using the high-frequency-clock divider to
generate the slow clock (PMCSR.DHF=0).
Note: For correct operation in the absence of a low-frequen-
cy crystal, the X2CKI pin must be tied low (not left floating) so
that the hardware can detect the absence of the crystal.
Obsolete
39 www.national.com
12.0 Dual Clock and Reset
The Dual Clock and Reset module (CLK2RES) generates a
high-speed main system clock from an external crystal net-
work and a slow clock (32.768 kHz or other rate) for operat-
ing the device in Power Save mode. It also provides the main
system reset signal, a power-on reset function, a main clock
prescaler to generate two additional low speed clocks, and
an 32kHz oscillator start-up delay.
Figure7 is block diagram of the Dual Clock and Reset mod-
ule.
12.1 EXTERNAL CRYSTAL NETWORK
An external crystal network is required at pins X1CKI and
X1CKO for the main clock. A similar external crystal network
may be used at pins X2CKI and X2CKO for the slow clock in
packages that have these pins. If an external crystal network
is not used for the slow clock, the clock is generated by divid-
ing the fast main clock.
The crystal oscillator you choose may require external com-
ponents different from the ones specified above. In that case,
consult with National’s engineer for the component specifica-
tions
The crystals and other oscillator components should be
placed close to the X1CKI/X1CLO and X2CKI/X2CLO device
input pins to keep the printed trace lengths to an absolute
minimum.
Figure8 shows the required crystal network at X1CKI/
X1CKO and optional crystal network at X2CKI/X2CKO.
Table13 shows the component specifications for the main
crystal network and Table14 shows the component specifi-
cations for the 32.768 kHz crystal network.
Figure 7.Dual Clock and Reset Module Block Diagram
8-Bit
14-Bit Timer
6-Bit Timer
Start-Up-Delay
Start-Up-Delay
Preset
Preset
Power-On-Reset
System
Reset
Stop
Main Osc In
Reset
X1CKI
X1CKO
X2CKI
X2CKO
Main Osc.
32kHz Osc.
Stop Main Osc.
Stop 32kHz Osc.
Main Clk
Good Main
Clk
Low Speed
Clk
Good Low
Speed Clk
Stop Low
Speed Clk
Time-out
Time-out
Mux
Prescaler
Div.
by-2
4-Bit
Prescaler
2 Low
Speed Clk
4-Bit
Prescaler
Outputs
Obsolete
www.national.com 40
Choose capacitor component values in the tables obtain the
specified load capacitance for the crystal when combined
with the parasitic capacitance of the trace, socket, and pack-
age (which can vary from 0 to 8 pF). As a guideline, the load
capacitance is:
CL = (C1 * C2)/(C1+C2) + Cparasitic
C2 > C1
C1 can be trimmed to obtain the desired load capacitance.
The start-up time of the 32.768 kHz oscillator can vary from
one to six seconds. The long start-up time is due to the high
“Q” value and high serial resistance of the crystal necessary
to minimize power consumption in Power Save mode.
12.2 MAIN SYSTEM CLOCK
The main system clock is generated by the main oscillator. It
can be stopped by the Power Management Module to reduce
power consumption during periods of reduced activity. When
the main clock is restarted, a 14-bit timer generates a “Good
Main Clk” signal after a start-up delay of 32,768 clock cycles.
This signal is an indicator that the main clock oscillator is sta-
ble.
The “Stop Main Osc” signal from the Power Management
Module stops and starts the main oscillator. When this signal
is asserted, it presets the 14-bit timer to 3FFF hex and stops
the main oscillator. When the signal goes inactive, the main
oscillator starts and the 14-bit timer counts down from its pre-
set value. When the timer reaches zero, it stops counting and
asserts the “Good Main Clk” signal.
12.3 SLOW SYSTEM CLOCK
The slow (32.768 kHz) clock is necessary for operating the
device in Power Save modes and to provide a clock source
for modules such as the Timing and Watchdog Module.
The slow clock operates in a manner similar to the main
clock. The “Stop Slow Osc” signal from the Power Manage-
ment Module stops and starts the slow oscillator. When this
signal is asserted, it presets a 6-bit timer to 3F hex and dis-
ables the slow oscillator. When the signal goes inactive, the
slow oscillator starts and the 6-bit timer counts down from its
preset value. When the timer reaches zero, it stops counting
Figure 8.External Crystal Network
Table 13Component Values of the High Frequency Crystal Circuit
Component Parameters Values Values Values Values Values Tolerance
Oscillator Resonance Frequency
Type
Max. Serial Resistance
Max. Shunt Capacitance
Load Capacitance
4 MHz
AT-Cut
75 Ω
4 pF
12 pF
12 MHz
AT-Cut
35 Ω
4 pF
15 pF
16 MHz
AT-Cut
35 Ω
4 pF
15 pF
20 MHz
AT-Cut
35 Ω
4 pF
20 pF
24 MHz
AT-Cut
35 Ω
4 pF
20 pF
N/A
Crystal Resistor R1 1 MΩ1 MΩ1 MΩ1 MΩ1 MΩ5%
Resistor R2 0 Ω0 Ω0 Ω0 Ω0 Ω5%
Capacitor C1, C2 22 pF 20 pF 20 pF 20 pF 20 pF 20%
X1CKI / X2CKI
X1CKO / X2CKO
R1
R2
XTAL
C2
C1
Table 14Component Values of the Low Frequency Crystal Circuit
Component Parameters Values Tolerance
Oscillator Resonance Frequency
Type
Maximum Serial Resistance
Maximum Shunt Capacitance
Load Capacitance
32.768kHz
Parallel
N-Cut or XY-bar
40 kΩ
2 pF
9-13 pF
N/A
Crystal Resistor R1 10-20 MΩ5%
Resistor R2 4.7 kΩ5%
Capacitor C1, C2 20 pF 20%
Obsolete
41 www.national.com
and asserts the “Good Low Speed Clk” signal, thus indicating
that the slow clock is stable.
For systems that do not require a reduced power consump-
tion mode, the external crystal network may be omitted for
the slow clock. In that case, the slow clock can be created by
dividing the main clock by a prescaler factor. The prescaler
circuit consists of a fixed divide-by-2 counter and a program-
mable 8-bit prescaler register. This allows a choice of clock
divisors ranging from 2 to 512. The resulting slow clock fre-
quency must not exceed 100 kHz.
A software-programmable multiplexer selects either the
prescaled main clock or the 32.768 kHz oscillator as the slow
clock. Upon reset, the prescaled main clock is selected, en-
suring that the slow clock is always present initially. Selection
of the 32.768 kHz oscillator as the slow clock disables the
clock prescaler, which allows the CLK1 oscillator to be turned
off during power-save operation, thus reducing power con-
sumption and radiated emissions. This can be done only if
the module detects a togging low-speed oscillator. If the low-
speed oscillator is not operating, the prescaler remains avail-
able as the slow clock source.
12.4 POWER-ON RESET
The Power-On Reset circuit generates a system reset signal
upon power-up and holds the signal active for a period of
time to allow the crystal oscillator to stabilize. The circuit de-
tects a power turn-on condition, which presets the 14-bit tim-
er to 3FFF hex. Once oscillation starts and the clock
becomes active, the timer starts counting down. When the
count reaches zero, the 14-bit timer stops counting and the
internal reset signal is deactivated (unless the RESET pin is
held low).
The circuit sets a power-on reset flag bit upon detection of a
power-on condition. The CPU can read this flag to determine
whether a reset was caused by a power-up or by the RESET
input.
Note: Power-On Reset circuit cannot be used to detect a
drop in the supply voltage.
12.5 EXTERNAL RESET
An active-low reset input pin called RESET allows the device
to be reset at any time. When the signal goes low, it gener-
ates an internal system reset signal that remains active until
the RESET signal goes high again.
12.6 DUAL CLOCK AND RESET REGISTERS
The Dual Clock and Reset module (CLK2RES) contains two
registers: the Clock and Reset Control register (CRCTRL)
and the Slow Clock Prescaler register (PRSSC).
12.6.1 Clock and Reset Control Register (CRCTRL)
Clock and Reset Control Register (CRCTRL) is a byte-wide
read/write register that contains the power-on reset flag and
selects the type of slow clock. The register format is shown
below.
SCLK Slow Clock Select. When this bit is set to 1, the
32.728 kHz oscillator is used for the slow clock.
When this bit is cleared to 0, the prescaled
main clock is used for the slow clock. Upon re-
set, this bit is cleared to 0.
POR Power-On Reset. This bit is set to 1 by the
hardware when a power-on condition is detect-
ed, allowing the CPU to determine whether a
power-up has occurred. The CPU can clear
this bit to 0 but cannot set it to 1. Any attempt
by the CPU to set this bit is ignored.
12.7 SLOW CLOCK PRESCALER REGISTER
(PRSSC)
The Slow Clock Prescaler (PRSSC) register is a byte-wide
read/write register that holds the clock divisor used to gener-
ate the slow clock from the main clock. The format of the reg-
ister is shown below.
SCDIV Slow Clock Divisor. If the clock divider is en-
abled (CRCTRL.SCLK=0), the main clock is di-
vided by (SCDIV+1)*2 to produce the slow
system clock. Upon reset, PRSSC register is
set to FF hex.
12.8 SLOW CLOCK PRESCALER 1 REGISTER
(PRSSC1)
The Slow Clock Prescaler 1 (PRSSC1) register is a byte-
wide read/write register that holds the clock divisor used to
generate the two additional slow clocks from the high-speed
clock. Upon reset, the register is set to 00. The format of the
register is shown below.
SCDIV1 Slow Clock Divisor 1. The main clock is divided
by (SCDIV1+1) to obtain the first slow system
clock.
SCDIV1 Slow Clock Divisor 2. The main clock is divided
by (SCDIV2+1) to obtain the second slow sys-
tem clock.
7 6 5 4 3 2 1 0
Reserved POR SCLK
7 6 5 4 3 2 1 0
SCDIV
7 4 3 0
SCDIV2 SCDIV1
Obsolete
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13.0 Multi-Input Wake-Up
The Multi-Input Wake-Up (MIWU16) module monitors its 16
input channels for a software-selectable trigger condition.
Upon detection of a trigger condition, the module generates
an interrupt request and if enabled, a wake-up request. A
wake-up request can be used by the power management unit
to exit the Halt, Idle, or Power Save mode and return to the
active mode. An interrupt request generates an interrupt to
the CPU (interrupt IRQ2), allowing interrupt processing in re-
sponse to external events.
The wake-up event only activates the clocks and CPU, but
does not by itself initiate execution of any code. It is the inter-
rupt request associated with the MIWU16 that gets the CPU
to start executing code, by jumping to the proper interrupt
routine. Therefore, setting up the MIWU16 interrupt handler
is essential for any wake-up operation.
There are four interrupt requests that can be routed to the
ICU as shown in Figure9. Each of the 16 MIWU channels
can be programmed to activate one of these four interrupt re-
quests.
The input pins for the Multi-Input Wake-Up channels are
named WUI0 through WUI15.
Each input can be configured to trigger on rising or falling
edges, as determined by the setting in the WKEDG register.
Each trigger event is latched into the WKPND register. If a
trigger event is enabled by its respective bit in the WKENA
register, an active wake-up/interrupt signal is generated. The
software can determine which channel has generated the ac-
tive signal by reading the WKPND register.
The Multi-Input Wake-Up module is active at all times, includ-
ing the Halt mode. All device clocks are stopped in this mode.
Therefore, detecting an external trigger condition and the
subsequent setting of the pending flag are not synchronous
to the system clock.
13.1 WAKE-UP EDGE DETECTION REGISTER
(WKEDG)
The Wake-Up Edge Detection (WKEDG) register is a word-
wide read/write register that controls the edge sensitivity of
the Multi-Input Wake-Up pins. Register bits 0 through 15 con-
trol input pins WUI0 through WUI15, respectively. A bit
cleared to 0 configures the corresponding input to trigger on
a rising edge (a low-to-high transition). A bit set to 1 config-
ures the corresponding input to trigger on a falling edge (a
high-to-low transition).
This register is cleared upon reset, which configures all 16 in-
puts to be triggered on rising edges.
The register format is shown below.
13.2 WAKE-UP ENABLE REGISTER (WKENA)
The Wake-Up Enable (WKENA) register is a word-wide read/
write register that enables or disables each of the Multi-Input
Wake-Up channels. Register bits 0 through 15 control chan-
nels WUI0 through WUI15, respectively. A bit cleared to 0
disables the wake-up function and a bit set to 1 enables the
function.
This register is cleared upon reset, which disables all eight
wake-up/interrupt channels.
WUI0 PL0
WUI1 PL1
WUI2 PL2
WUI3 PL3
WUI4 PH0
WUI5 PH1
WUI6 PH2
WUI7 PH3
WUI8 TWM-T0OUT
WUI9 ACCESS.bus
WUI10 Canards
WUI11 MWCS
WUI12 RDX1
WUI13 RDX2
WUI14 Comparator 1
WUI15 Comparator 2
15 0
WKED15-WKED0
Obsolete
43 www.national.com
The register format is shown below.
13.3 WAKE-UP INTERRUPT CONTROL
REGISTER 1 (WKCTL1)
The Wake-Up Interrupt Control Register 1 (WKICTL1) regis-
ter is a word-wide read/write register that selects the interrupt
request signal for the associated channels WUI0 to WUI7.
Upon reset, WKICTL1 is set to 0, which selects MIWU Inter-
rupt Request 0 for all eight channels. The register format is
shown below.
WKINTR0:7 Wake-Up Interrupt Request Select. Each field
selects which of the following four interrupt re-
quests outputs to the ICU31L are to be activat-
ed for the corresponding channel.
00 enables MIWU Interrupt Request 0
01 enables MIWU Interrupt Request 1
10 enables MIWU Interrupt Request 2
11 enables MIWU Interrupt Request 3
13.4 WAKE-UP INTERRUPT CONTROL
REGISTER 1 (WKCTL2)
The Wake-Up Interrupt Control Register 2 (WKICTL2) regis-
ter is a word-wide read/write register that selects the interrupt
request signal for the associated channels WUI8 to WUI15.
Upon reset, WKICTL2 is set to 0, which selects MIWU Inter-
rupt Request 0 for all eight channels. The register format is
shown below.
WKINTR8:5 Wake-Up Interrupt Request Select. Each field
selects which of the following four interrupt re-
quests outputs to the ICU31L are to be activat-
ed for the corresponding channel.
00 enables MIWU Interrupt Request 0
01 enables MIWU Interrupt Request 1
10 enables MIWU Interrupt Request 2
11 enables MIWU Interrupt Request 3
13.5 WAKE-UP PENDING REGISTER (WKPND)
The Wake-Up Pending (WKPND) register is a word-wide
read/write register in which the Multi-Input Wake-Up module
latches any detected trigger conditions. Register bits 0
through 15 serve as latches for channels WUI0 through
WUI15, respectively. A bit cleared to 0 indicates that no trig-
ger condition has occurred. A bit set to 1 indicates that a trig-
ger condition has occurred and is pending on the
corresponding channel. This register is cleared upon reset.
The CPU can only write a 1 to any bit position in this register.
If the CPU attempts to write a 0, it has no effect on that bit.
To clear a bit in this register, the CPU must use the WKPCL
register (described below). This implementation prevents a
potential hardware-software conflict during a read-modify-
write operation on the WKPND register.
The register format is shown below.
13.6 WAKE-UP PENDING CLEAR REGISTER
(WKPCL)
The Wake-Up Pending Clear (WKPCL) register is a word-
wide write-only register that lets the CPU clear bits in the WK-
PND register. Writing a 1 to a bit position in the WKPCL reg-
ister clears the corresponding bit in the WKPND register.
Writing a 0 leaves the corresponding bit in the WKPND reg-
ister unchanged.
Reading this register location returns unknown data. There-
fore, do not use a read-modify-write sequence to set the in-
dividual bits. In other words, do not attempt to read the
Figure 9.Multi-Input Wake-Up Module Block Diagram
Peripheral Bus
15 0
WKENA
WUI0
WUI15
0
15
. . . . . . . . . .
WKEDG WKPND
To Power Mgt
Wake-Up Signal
EXINT3:0 to ICU
WKICTL1-2
4
15 0
WKEN15-WKEN0
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
WKINTR
7WKINTR
6WKINTR
5WKINTR
4WKINTR
3WKINTR
2WKINTR
1WKINTR
0
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
WKINTR
15 WKINTR
14 WKINTR
13 WKINTR
12 WKINTR
11 WKINTR
10 WKINTR
9WKINTR
8
15 0
WKPD15-WKPD0
Obsolete
www.national.com 44
register and do a logical OR with the register value. Instead,
just write the mask directly to the register address.
The register format is shown below.
13.7 PROGRAMMING PROCEDURES
To set up and use the Multi-Input Wake-Up function, use the
following procedure. Performing the steps in the order shown
will prevent false triggering of a wake-up condition. This
same procedure should be used following a reset because
the wake-up inputs are left floating, resulting in unknown data
on the input pins.
1. Clear the WKENA register to disable the wake-up chan-
nels.
2. If the input originates from an I/O port (the usual case),
set the corresponding bit in the port direction register to
configure the I/O pin to operate as an input.
3. Write the WKEDG register to select the desired type of
edge sensitivity (clear to 0 for rising edge, set to 1 for fall-
ing edge).
4. Set all bits in the WKPCL register to clear any pending
bits in the WKPND register.
5. Set up the WKICTL1 and WKICTL2 registers to define
the interrupt request signal used for each channel.
6. Set the bits in the WKENA register corresponding to the
wake-up channels to be activated.
To change the edge sensitivity of a wake-up channel, use the
following procedure. Performing the steps in the order shown
will prevent false triggering of a wake-up/interrupt condition.
1. Clear the WKENA bit associated with the input to be re-
programmed.
2. Write the new value to the corresponding bit position in
the WKEDG register to reprogram the edge sensitivity of
the input.
3. Set the corresponding bit in the WKPCL register to clear
the pending bit in the WKPND register.
4. Set the same WKENA bit to re-enable the wake-up func-
tion.
15 0
WKCL15-WKCL0
Obsolete
45 www.national.com
14.0 Real-Time Timer and WATCHDOG
The Timing and WATCHDOG Module (TWM) generates the
clocks and interrupts used for timing periodic functions in the
system, and also provides Watchdog protection against soft-
ware errors. The module operates off the slow clock either
generated by the external 32kHz oscillator or from the pres-
caled high speed system clock. The maximum operating
clock frequency is 100kHz.
The WATCHDOG is designed to detect program execution
errors. Once WATCHDOG operation is initiated, the software
must periodically write a specific value to a WATCHDOG reg-
ister. If the software fails to do so, a WATCHDOG error is trig-
gered, which resets the device.
The TWM is flexible in allowing selection of a variety of clock
ratios and clock sources for the WATCHDOG circuit. Once
the software configures the TWM, it can lock the configura-
tion for a higher level of protection against erroneous soft-
ware action. Once locked, the TWM can be released only by
a device reset.
14.1 TWM STRUCTURE
Figure10 is a block diagram showing the internal structure of
the Timing and WATCHDOG module. There are two main
sections: the Real-Time Timer (T0) section at the top and the
WATCHDOG section on the bottom.
All counting activities of the module are based on the slow
clock (SLCLK). A prescaler counter divides this clock to
make a slower clock. The prescaler factor is defined by a 3-
bit field in the Timer and WATCHDOG Prescaler register,
which selects either 1, 2, 4, 8, 16, or 32 and the divide-by fac-
tor. Thus, the prescaled clock period can be set to 1, 2, 4, 8,
16, or 32 times the slow clock period. The prescaled clock
signal is called T0IN.
14.2 TIMER T0 OPERATION
Timer T0 is a programmable 16-bit down counter that can be
used as the time base for real-time operations such as a pe-
riodic audible tick. It can also be used to drive the WATCH-
DOG circuit.
The timer starts counting from the value loaded into the
TWMT0 register and counts down on each rising edge of
T0IN. When the timer reaches zero, it is automatically reload-
ed from the TWMT0 register and continues counting down
from that value. Thus, the frequency of the timer is:
fSLCLK / [(TWMT0+1) * prescaler]
When an external crystal oscillator is used as the SLCLK
source or when the fast clock is divided accordingly, fSLCLK
is 32.768 kHz.
The value stored in TWMT0 can range from 0001 hex to
FFFF hex.
Figure 10.Timing and WATCHDOG Module Block Diagram
(TWCP)
16-bit Timer (Timer0)
5-bit pre-scaler counter
WATCHDOG Timer
Peripheral Bus
CLKIN1
T0OUT
WATCHDOG ERROR
TWMT0 register
WDCNT
WDSDM
WATCHDOG
Service
Logic
Restart
Underflow
T0CSR Contrl. Reg.
Restart
Underflow
T0LINT
WDERR
(to ICU)
(to Multi-Input-
Wake-Up)
slow clock from
dual clock and
reset module
REAL TIME TIMER (T0)
WATCHDOG
T0IN
Obsolete
www.national.com 46
When the counter reaches zero, an internal timer signal
called T0OUT is set to 1 for one T0IN clock cycle. This signal
sets the TC bit in the TWMT0 Control and Status Register
(T0CSR). It also generates an interrupt called RTI (IRQ14) if
the interrupt is enabled by the T0CSR.T0INTE bit.
If the software loads TWMT0 with a new value, the timer uses
that value the next time that it reloads the 16-bit timer register
(in other words, after reaching zero). The software can restart
the timer at any time (on the very next edge of the T0IN clock)
by setting the Restart (RST) bit in the T0CSR register. The
T0CSR.RST bit is cleared automatically upon restart of the
16-bit timer.
Note: If the user wishes to switch to power save or idle mode
after setting T0CSR.RST, the user must wait for reset opera-
tion to complete before doing the switch.
14.3 WATCHDOG OPERATION
The WATCHDOG is an 8-bit down counter that operates on
the rising edge of a specified clock source. Upon reset, the
WATCHDOG is disabled; it does not count and no WATCH-
DOG signal is generated. A write to either the WATCHDOG
Count (WDCNT) register or the WATCHDOG Service Data
Match (WDSDM) register starts the counter. The WATCH-
DOG counter counts down from the value programmed in to
the WDCNT register. Once started, only a reset can stop the
WATCHDOG from operating.
The WATCHDOG can be programmed to use either T0OUT
or T0IN as its clock source (the output and input of Timer T0,
respectively). The TWCFG.WDCT0I bit controls this clock
selection.
The software must periodically “service” the WATCHDOG.
There are two ways to service the WATCHDOG, the choice
depending on the programmed value of the WDSDME bit in
the Timer and WATCHDOG Configuration (TWCFG) register.
If TWCFG.WDSDME bit is cleared to 0, the WATCHDOG is
serviced by writing a value to the WDCNT register. The value
written to the register is reloaded into the WATCHDOG
counter. The counter then continues counting down from that
value.
If TWCFG.WDSDME bit is set to 1, the WATCHDOG is ser-
viced by writing the value 5C hex to the WATCHDOG Service
Data Match (WDSDM) register. This reloads the WATCH-
DOG counter with the value previously programmed into the
WDCNT register. The counter then continues counting down
from that value.
A WATCHDOG error signal is generated by any of the follow-
ing events:
—The WATCHDOG serviced too late.
—The WATCHDOG serviced too often.
—The WDSDM register is written with a value other than
5C hex when WDSDM type servicing is enabled
(TWCFG.WDSDME=1).
A WATCHDOG error condition resets the device.
14.3.1 Register Locking
The Timer and WATCHDOG Configuration (TWCFG) regis-
ter is used to set the WATCHDOG configuration. It controls
the WATCHDOG clock source (T0IN or T0OUT), the type of
WATCHDOG servicing (using WDCNT or WDSDM), and the
locking state of the TWCFG, TWCPR, TIMER0, T0CSR, and
WDCNT registers. A register that is locked cannot be read or
written. A write operation is ignored and a read operation re-
turns unpredictable results.
If the TWCFG register is itself locked, it remains locked until
the device is reset. Any other locked registers also remain
locked until the device is reset. This feature prevents a run-
away program from tampering with the programmed
WATCHDOG function.
14.3.2 Power Save Mode Operation
The Timer and WATCHDOG Module is active in both the
Power Save and Idle modes. The clocks and counters con-
tinue to operate normally in these modes. The WDSDM reg-
ister is accessible in the Power Save and Idle modes, but the
other TWM registers are accessible only in the Active mode.
Therefore, WATCHDOG servicing must be carried out using
the WDSDM register in the Power Save or Idle mode.
In the Halt mode, the entire device is frozen, including the
Timer and WATCHDOG Module. Upon return to the Active
mode, operation of the module resumes at the point at which
it was stopped.
Note: After a restart or WATCHDOG service through WD-
CNT, do not enter Power Save mode for a period equivalent
to 5 slow clock cycles.
14.4 TWM REGISTERS
The TWM registers controls the operation of the Timing and
WATCHDOG Module. There are six such registers:
—Timer and WATCHDOG Configuration Register
(TWCFG)
—Timer and WATCHDOG Clock Prescaler Register
(TWCP)
—TWM Timer 0 Register (TWMT0)
—TWMT0 Control and Status Register (T0CSR)
—WATCHDOG Count Register (WDCNT)
—WATCHDOG Service Data Match Register (WDSDM)
The WDSDM register is accessible in both Active and Power
Save mode. The other TWM registers are accessible only in
Active mode.
14.4.1 Timer and WATCHDOG Configuration Register
(TWCFG)
The TWCFG register is a byte-wide, read/write register that
selects the WATCHDOG clock input and service method,
and also allows the WATCHDOG registers to be selectively
locked. Once a bit is set, that bit cannot be cleared until the
device resets. Upon reset, the non-reserved bits of the regis-
ter are all cleared to 0. The register format is shown below.
LTWCFG Lock TWCFG Register. When cleared to 0, ac-
cess to the TWCFG register is allowed. When
set to 1, the TWCFG register is locked. A
locked register cannot be read or written; a
read operation returns unpredictable values
and a write operation is ignored. Locking the
TWCFG register remains in effect until the de-
vice is reset.
7 6 5 4 3 2 1 0
Reserved WDSDME WDCT0I LWDCNT LTWMT0 LTWCP LTWCFG
Obsolete
47 www.national.com
LTWCP Lock TWCP Register. When cleared to 0, ac-
cess to the TWCP register is allowed. When
set to 1, the TWCP register is locked.
LTWMT0 Lock TWMT0 Register. When cleared to 0, ac-
cess to the TWMT0 and T0CSR registers are
allowed. When set to 1, the TWMT0 and
T0CSR registers are locked.
LWDCNT Lock LDWCNT Register. When cleared to 0,
access to the LDWCNT register is allowed.
When set to 1, the LDWCNT register is locked.
WDCT0I WATCHDOG Clock from T0IN. When cleared
to 0, the T0OUT signal (the output of Timer T0)
is used as the WATCHDOG clock. When set to
1, the T0IN signal (the prescaled slow clock) is
used as the WATCHDOG clock.
WDSDME WATCHDOG Service Data Match Enable.
When cleared to 0, WATCHDOG servicing is
accomplished by writing a count value to the
WDCNT register; write operations to the
WATCHDOG Service Data Match (WDSDM)
register are ignored. When set to 1, WATCH-
DOG servicing is accomplished by writing the
value 5C hex to the WDSDM register.
14.4.2 Timer and WATCHDOG Clock Prescaler
Register (TWCP)
The TWCP register is a byte-wide, read/write register that
defines the prescaler value used for dividing the low frequen-
cy clock to generate the T0IN clock. Upon reset, the non-re-
served bits of the register are cleared to 0. The register
format is shown below.
MDIV Main Clock Divide. This 3-bit field defines the
prescaler factor used for dividing the low speed
device clock to create the T0IN clock. The al-
lowed 3-bit values and the corresponding clock
divisors and clock rates are listed below.
14.4.3 TWM Timer 0 Register (TWMT0)
The TWMT0 register is a word-wide, read/write register that
defines the T0OUT interrupt rate. Upon reset, TWMT0 regis-
ter is initialized to FFFF hex. The register format is shown be-
low.
PRESET Timer T0 Preset. Timer T0 is reloaded with this
value on each underflow. Thus, the frequency
of the Timer T0 interrupt is the frequency of
T0IN divided by (PRESET+1). The allowed val-
ues of PRESET are 0001 hex through FFFF
hex.
14.4.4 TWMT0 Control and Status Register (T0CSR)
The T0CSR register is a byte-wide, read/write register that
controls Timer T0 and shows its current status. Upon reset,
the non-reserved bits of the register are cleared to 0. The
register format is shown below.
RST Restart. When this bit is set to 1, it forces the
timer to reload the value in the TWMT0 register
on the next rising edge of the selected input
clock. The RST bit is reset automatically by the
hardware on the same rising edge of the se-
lected input clock. Writing a 0 to this bit position
has no effect. Upon reset, the non-reserved
bits of the register are cleared to 0.
TC Terminal Count. This bit is set to 1 by the hard-
ware when the Timer T0 count reaches zero
and is cleared to 0 when the software reads the
T0CSR register. It is a read-only bit. Any data
written to this bit position is ignored.
T0INTE Timer T0 Interrupt Enable. When this bit is set
to 1, it enables an interrupt to the CPU each
time the Timer T0 count reaches zero. When
this bit is cleared to 0, Timer T0 interrupts are
disabled.
14.4.5 WATCHDOG Count Register (WDCNT)
The WDCNT register is a byte-wide, write-only register that
holds the value that is loaded into the WATCHDOG counter
each time the WATCHDOG is serviced. The WATCHDOG is
started by the first write to this register. Each successive write
to this register restarts the WATCHDOG count with the writ-
ten value. Upon reset, this register is initialized to 0F hex.
14.4.6 WATCHDOG Service Data Match Register
(WDSDM)
The WSDSM register is a byte-wide, write-only register used
for servicing the WATCHDOG. When this type of servicing is
enabled (TWCFG.WDSDME=1), the WATCHDOG is ser-
viced by writing the value 5C hex to the WSDSM register.
Each such servicing reloads the WATCHDOG counter with
the value previously written to the WDCNT register. Writing
any data other than 5C hex triggers a WATCHDOG error.
Writing to the register more than once in one WATCHDOG
clock cycle also triggers a WATCHDOG error signal. If this
type of servicing is disabled (TWCFG.WDSDME=0), any
write to the WSDSM register is ignored.
14.5 WATCHDOG PROGRAMMING
PROCEDURE
The highest level of protection against software errors is
achieved by programming and then locking the WATCHDOG
registers and using the WDSDM register for servicing. This is
the procedure:
76543210
Reserved MDIV
MDIV Clock Divisor TOIN Frequency
(fSCLK=32.768 kHz)
000 1 32.768 kHz
001 2 16.384 kHz
010 4 8.192 kHz
011 84.096 kHz
100 16 2.056 kHz
101 32 1.024 kHz
other Reserved N/A
15 14 13 12 11 109876543210
PRESET
76543 2 10
Reserved T0INTE TC RST
Obsolete
www.national.com 48
1. Write the desired values into the TWM Clock Prescaler
register (TWCP) and the TWM Timer 0 register
(TWMT0) to control the T0IN and T0OUT clock rates.
The frequency of T0IN can be programmed to any of six
frequencies ranging from 1/32*f SLCLK to fSLCLK . The fre-
quency of T0OUT is equal to the frequency of T0IN di-
vided by (1+PRESET), where PRESET is the value
written to the TWMT0 register.
2. Configure the WATCHDOG clock to use either T0IN or
T0OUT by setting or clearing the TWCFG.WDCT0I bit.
3. Write the initial value into the WDCNT register. This
starts operation of the WATCHDOG and specifies the
maximum allowed number of WATCHDOG clock cycles
between service operations.
4. Lock the WATCHDOG registers and enable the
WATCHDOG Service Data Match Enable function by
setting bits 0, 1, 2, 3, and 5 in the TWCFG register.
5. Service the WATCHDOG by periodically writing the val-
ue 5C hex to the WDSDM register at an appropriate rate.
Servicing must occur at least once per period pro-
grammed into the WDCNT register, but no more than
once in a single WATCHDOG input clock cycle.
Obsolete
49 www.national.com
15.0 Multi-Function Timer
The Multi-Function Timer (MFT16) module contains two inde-
pendent timer/counter units called MFT1 and MFT2, each
containing a pair of 16-bit timer/counters. Each timer/counter
unit offers a choice of clock sources for operation and can be
configured to operate in any of the following modes:
•Processor-Independent Pulse Width Modulation (PWM)
mode, which generates pulses of a specified width and
duty cycle, and which also provides a general-purpose
timer/counter
•Dual Input Capture mode, which measures the elapsed
time between occurrences of external events, and which
also provides a general-purpose timer/counter
•Dual Independent Timer mode, which generates system
timing signals or counts occurrences of external events
•Single Input Capture and Single Timer mode, which pro-
vides one external event counter and one system timer
The two timer units, MFT1 and MFT2, are identical in opera-
tion and separately programmable. Each timer unit uses two
I/O pins, called T1A and T1B (for Timer MFT1) or T2A and
T2B (for Timer MFT2). The timer I/O pins are alternate func-
tions of the Port F I/O pins.
In the description of the timers, the lower-case letter “n” rep-
resents the timer number, either 1 or 2. For example, “TnA”
means I/O pin T1A or T2A.
15.1 TIMER STRUCTURE
Figure11 is a block diagram showing the internal structure of
each timer. There are two main functional blocks: a Timer/
Counter and Action block and a Clock Source block. The
Timer/Counter and Action block contains two separate timer/
counter units, called Timer/Counter I and Timer/Counter II (a
total of four timer/counter unit in both MFT1 and MFT2).
15.1.1 Timer/Counter Block
The Timer/Counter block contains the following functional
blocks:
—two 16-bit counters, Timer/Counter I (TnCNT1) and
Timer/Counter II (TnCNT2)
—two 16-bit reload/capture registers, TnCRA and
TnCRB
—control logic necessary to configure the timer to oper-
ate in any of the four operating modes
—interrupt control and I/O control logic
In a power-saving mode that uses the low-frequency (32.768
kHz) clock as the system clock, the synchronization circuit
requires that the slow clock operate at no more than one-
fourth the speed of the 32.768 kHz system clock.
15.1.2 Clock Source Block
The Clock Source block generates the signals used to clock
the two timer/counter registers. The internal structure of the
Clock Source block is shown in Figure12.
Counter Clock Source Select
There are two clock source selectors that allow the software
to independently select the clock source for each of the two
16-bit counters from any one of the following sources:
—no clock (which stops the counter)
—prescaled system clock
—external event count based on TnB
—pulse accumulate mode based on TnB
—slow clock (derived from the low-frequency oscillator or
divided from the high-speed oscillator)
Prescaler
The 5-bit clock prescaler allows the software to run the timer
with a prescaled clock signal. The prescaler consists of a 5-
bit read/write prescaler register (TnPRSC) and a 5-bit down
counter. The system clock is divided by the value contained
in the prescaler register plus 1. Thus, the timer clock period
can be set to any value from 1 to 32 divisions of the system
clock period. The prescaler register and down counter are
both cleared upon reset.
Figure 11.Multi-Function Timer Block Diagram
Reload/Capture
A
Timer/Counter
1
Reload/Capture
Timer/Counter
2
B
Timer/Counter
Clock Source Action
System
Clock
TnB
Toggle/Capture/Interrupt
Mode Select + Control
PWM/Capture/Counter
TnA
External Event
Interrupt A
Interrupt B
Clock Prescaler/Selector
Obsolete
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External Event Clock
The TnB I/O pin can be configured to operate as an external
event input clock for either of the two 16-bit counters. This in-
put can be programmed to detect either rising or falling edg-
es. The minimum pulse width of the external signal is one
system clock cycle. This means that the maximum frequency
at which the counter can run in this mode is one-half of the
system clock frequency. This clock source is not available in
the capture modes (modes 2 and 4) because the TnB pin is
used as one of the two capture inputs.
Pulse Accumulate Mode
The counter can also be configured to count prescaler output
clock pulses when the TnB is high and not count when TnB
is low, as illustrated in Figure13. The resulting count is an in-
dicator of the cumulative time that TnB is high. This is called
the “pulse accumulate” mode. In this mode, an AND gate
generates a clock signal for the counter whenever a prescal-
er clock pulse is generated and TnB input is high. (The polar-
ity of the TnB signal is programmable, so the counter can
count when TnB is low rather than high.) The pulse accumu-
late mode is not available in the capture modes (modes 2 and
4) because the TnB pin is used as one of the two capture in-
puts.
Slow Clock
The slow clock is generated by the Dual Clock and Reset
(CLK2RES) module. The clock source is either the divided
fast clock or the external 32.768 kHz clock crystal (if available
and selected). The slow clock can be used as the clock
source for the two 16-bit counters. Because the slow clock
can be asynchronous to the system clock, a circuit is provid-
ed to synchronize the clock signal to the high-frequency sys-
tem clock before it is used for clocking the counters. The
synchronization circuit requires that the slow clock operate at
no more than one-fourth the speed of the system clock.
Limitations in Low-Power Modes
The Power Save mode uses the low-frequency clock as the
system clock. In this mode, the slow clock cannot be used as
a clock source for the timers because both CLK and SLCLK
are driven then at the same frequency, and the 2:1 system-
clock to input clock ratio needed for the synchronization can-
not be maintained. However, the External Event Clock and
Pulse Accumulate Mode will still work, as long as the external
event pulses are at least the size of the whole slow-clock pe-
riod. Using the prescaled system clock will also work, but at
a much slower rate than the original system clock.
Some Power Save modes stops the system clock (the high-
frequency and/or low-frequency clock) completely. If the sys-
tem clock is stopped, the timer stops counting until the sys-
tem clock resumes operation.
In the Idle or Halt mode, the system clock stops completely,
which stops the operation of the timers. In that case, the tim-
ers stop counting until the system clock resumes operation.
Figure 12.Clock Source Block Diagram
Prescaler Register
TnPRSC
Prescaler Counter
5-bit
System
Clock
Reset
TnB
Pulse
Accumulate
External
Event
No Clock
Prescaled
Clock
Counter I
Clock
Select
Counter II
Clock
Select
Counter I
Clock
Counter II
Clock
Synchr.
Figure 13.Pulse Accumulate Mode Operation
TnB
Prescaler Output
Counter Clock
Obsolete
51 www.national.com
15.2 TIMER OPERATING MODES
Each timer/counter unit can be configured to operate in any
of the following modes:
—Processor-Independent Pulse Width Modulation
(PWM) mode
—Dual Input Capture mode
—Dual Independent Timer mode
—Single Input Capture and Single Timer mode
Upon reset, the timers are disabled. To configure and start
the timers, the software must write a set of values to the reg-
isters that control the timers. The registers are described in
Section15.5.
15.2.1 Mode 1: Processor-Independent PWM
Mode 1 is the Processor-Independent Pulse Width Modula-
tion (PWM) mode, which generates pulses of a specified
width and duty cycle, and which also provides a separate
general-purpose timer/counter.
Figure14 is a block diagram of the Multi-Function Timer con-
figured to operate in Mode 1. Timer/Counter I (TnCNT1)
functions as the time base for the PWM timer. It counts down
at the clock rate selected for the counter. When an underflow
occurs, the timer register is reloaded alternately from the
TnCRA and TnCRB register, and counting proceeds down-
ward from the loaded value.
On the first underflow, the timer is loaded from TnCRA, then
from TnCRB on the next underflow, then from TnCRA again
on the next underflow, and so on. Every time the counter is
stopped and restarted, it always obtains its first reload value
from TnCRA. This is true whether the timer is restarted upon
reset, after entering Mode 1 from another mode, or after
stopping and restarting the clock with the Timer/Counter I
clock selector.
The timer can be configured to toggle the TnA output bit upon
each underflow. This generates a clock signal on TnA with
the width and duty cycle determined by the values stored in
the TnCRA and TnCRB registers. This is a “processor-inde-
pendent” PWM clock because once the timer is set up, no
more action is required from the CPU to generate a continu-
ous PWM signal.
The timer can be configured to generate separate interrupts
upon reload from TnCRA and TnCRB. The interrupts can be
enabled or disabled under software control. The CPU can
determine the cause of each interrupt by looking at the
TnAPND and TnBPND flags, which are set by the hardware
upon each occurrence of a timer reload.
In Mode 1, Timer/Counter II (TnCNT2) can be used either as
a simple system timer, an external event counter, or a pulse
accumulate counter. The clock counts down using the clock
selected with the Timer/Counter II clock selector. It generates
an interrupt upon each underflow if the interrupt is enabled
with the TnDIEN bit.
15.2.2 Mode 2: Dual Input Capture
Mode 2 is the Dual Input Capture mode, which measures the
elapsed time between occurrences of external events, and
which also provides a separate general-purpose timer/
counter.
Figure15 is a block diagram of the Multi-Function Timer con-
figured to operate in Mode 2. The time base of the capture
timer depends on Timer/Counter I, which counts down using
the clock selected with the Timer/Counter I clock selector.
Figure 14.Mode 1: Processor-Independent PWM Block Diagram
Reload A = Time 1
Timer/Counter I
Reload B = Time 2
Timer I
Clock
Underflow
TnA
TnAIEN
TnAPND
TnCNT1
TnCRA
TnCRB
TnBIEN
TnBPND
Timer
Interrupt A
Timer
Interrupt B
TnAEN
Timer/Counter II
TnCNT2
Timer II
Clock TnDIEN
TnDPND
Timer
Interrupt D
TnB
Clock
Selector
Underflow
Obsolete
www.national.com 52
The TnA and TnB pins function as capture inputs. A transition
received on the TnA pin transfers the timer contents to the
TnCRA register. Similarly, a transition received on the TnB
pin transfers the timer contents to the TnCRB register. Each
input pin can be configured to sense either rising or falling
edges.
The TnA and TnB inputs can be configured to preset the
counter to FFFF hex upon reception of a valid capture event.
In this case, the current value of the counter is transferred to
the corresponding capture register and then the counter is
preset to FFFF hex. Using this approach allows the software
to determine the on-time and off-time and period of an exter-
nal signal with a minimum of CPU overhead.
The values captured in the TnCRA register at different times
reflect the elapsed time between transitions on the TnA pin.
The same is true for the TnCRB register and the TnB pin. The
input signal on TnA or TnB must have a pulse width equal to
or greater than one system clock cycle.
There are three separate interrupts associated with the cap-
ture timer, each with its own enable bit and pending flag. The
three interrupt events are reception of a transition on TnA, re-
ception of a transition on TnB, and underflow of the TnCNT1
counter. The enable bits for these events are TnAIEN, TnBI-
EN, and TnCIEN, respectively.
In Mode 2, Timer/Counter II (TnCNT2) can be used as a sim-
ple system timer. The clock counts down using the clock se-
lected with the Timer/Counter II clock selector. It generates
an interrupt upon each underflow if the interrupt is enabled
with the TnDIEN bit.
Neither Timer/Counter I (TnCNT1) nor Timer/Counter II
(TnCNT2) can be configured to operate as an external event
counter or to operate in the pulse accumulate mode because
the TnB input is used as a capture input. Attempting to select
one of these configurations will cause one or both counters
to stop.
15.2.3 Mode 3: Dual Independent Timer/Counter
Mode 3 is the Dual Independent Timer mode, which gener-
ates system timing signals or counts occurrences of external
events.
Figure16 is a block diagram of the Multi-Function Timer con-
figured to operate in Mode 3. The timer is configured to oper-
ate as a dual independent system timer or dual external
event counter. In addition, Timer/Counter I can generate a
50% duty cycle PWM signal on the TnA pin. The TnB pin can
be used as an external event input or pulse accumulate input
and can be used as the clock source for either Timer/Counter
I or Timer/Counter II. Both counters can also be clocked by
the prescaled system clock.
Figure 15.Mode 2: Dual Input Capture Block Diagram
Capture A
Timer/Counter I
Capture B
TnCNT1
TnCRA
TnCRB
Timer/Counter II
TnCNT2
Timer I
Clock
Timer II
Clock
TnB
TnA
TnAIEN
TnAPND
Timer
Interrupt I
TnBIEN
TnBPND
Timer
Interrupt I
TnCIEN
TnCPND Timer
Interrupt I
Underflow
TnDIEN
TnDPND
Timer
Interrupt II
Underflow
TnAEN
Preset
Preset
TnBEN
Obsolete
53 www.national.com
Timer/Counter I (TnCNT1) counts down at the rate of the se-
lected clock. Upon underflow, it is reloaded from the TnCRA
register and counting proceeds down from the reloaded val-
ue. In addition, the TnA pin is toggled on each underflow if
this function is enabled by the TnAEN bit. The initial state of
the TnA pin is software-programmable. When the TnA pin is
toggled from low to high, it sets the TnCPND interrupt pend-
ing flag and also generates an interrupt if the interrupt is en-
abled by the TnAIEN bit.
Because TnA toggles on every underflow, a 50% duty cycle
PWM signal can be generated on TnA without any further ac-
tion from the CPU once the pulse train is initiated.
Timer/Counter II (TnCNT2) counts down at the rate of the se-
lected clock. Upon underflow, it is reloaded from the TnCRB
register and counting proceeds down from the reloaded val-
ue. In addition, each underflow sets the TnDPND interrupt
pending flag and generates an interrupt if the interrupt is en-
abled by the TnDIEN bit.
15.2.4 Mode 4: Input Capture Plus Timer
Mode 4 is the Single Input Capture and Single Timer mode,
which provides one external event counter and one system
timer.
Figure17 is a block diagram of the Multi-Function Timer con-
figured to operate in Mode 4. This mode offers a combination
of Mode 3 and Mode 2 functions. Timer/Counter I is used as
a system timer as in Mode 3 and Timer/Counter II is used as
a capture timer as in Mode 2, but with a single input rather
than two inputs.
Timer/Counter I (TnCNT1) operates the same as in Mode 3.
It counts down at the rate of the selected clock. Upon under-
flow, it is reloaded from the TnCRA register and counting pro-
ceeds down from the reloaded value. The TnA pin is toggled
on each underflow if this function is enabled by the TnAEN
bit. When the TnA pin is toggled from low to high, it sets the
TnCPND interrupt pending flag and also generates an inter-
rupt if the interrupt is enabled by the TnAIEN bit. A 50% duty
cycle PWM signal can be generated on TnA without any fur-
ther action from the CPU once the pulse train is initiated.
Timer/Counter II (TnCNT1) counts down at the rate of the se-
lected clock. The TnB pin functions as the capture input. A
transition received on TnB transfers the timer contents to the
TnCRB register. The input pin can be configured to sense ei-
ther rising or falling edges.
The TnB input can be configured to preset the counter to
FFFF hex upon reception of a valid capture event. In this
case, the current value of the counter is transferred to the
capture register and then the counter is preset to FFFF hex.
The values captured in the TnCRB register at different times
reflect the elapsed time between transitions on the TnA pin.
The input signal on TnB must have a pulse width equal to or
greater than one system clock cycle.
There are two separate interrupts associated with the cap-
ture timer, each with its own enable bit and pending flag. The
two interrupt events are reception of a transition on TnB and
underflow of the TnCNT2 counter. The enable bits for these
events are TnBIEN and TnDIEN, respectively.
Neither Timer/Counter I (TnCNT1) nor Timer/Counter II
(TnCNT2) can be configured to operate as an external event
Figure 16.Mode 3: Dual Independent Timer/Counter Block Diagram
Reload A
Timer/Counter I
Reload B
Timer I
Clock TnA
TnAIEN
TnAPND
TnCNT1
TnCRA
TnCRB
TnDIEN
TnDPND
Timer
Interrupt I
Timer
Interrupt II
TnAEN
Timer/Counter II
TnCNT2
Timer II
Clock
TnB
Clock
Selector
Underflow
Underflow
Obsolete
www.national.com 54
counter or to operate in the pulse accumulate mode because
the TnB input is used as a capture input. Attempting to select
one of these configurations will cause one or both counters
to stop. In this mode, Timer/Counter II must be enabled at all
times.
15.3 TIMER INTERRUPTS
Each Multi-Function Timer unit has four interrupt sources,
designated A, B, C, and D. Interrupt sources A, B, and C are
mapped into a single system interrupt called Timer Interrupt
I, while interrupt source D is mapped into a system interrupt
called Timer Interrupt II. Each of the four interrupt sources
has its own enable bit and pending flag. The enable flags are
named TnAIEN, TnBIEN, TnCIEN, and TnDIEN. The pend-
ing flags are named TnAPND, TnBPND, TnCPND, and TnD-
PND.
For Multi-Function Timer unit MFT1, Timer Interrupts I and II
are system interrupts T1A and T1B (IRQ13 and IRQ12), re-
spectively. For Multi-Function Timer unit MFT2, Timer Inter-
rupts I and II are system interrupts T2A and T2B (IRQ11 and
IRQ10), respectively.
Table15 shows the events that trigger interrupts A, B, C, and
D in each of the four operating modes. Note that some inter-
rupt sources are not used in some operating modes, as indi-
cated by the notation “N/A” (Not Applicable) in the table.
15.4 TIMER I/O FUNCTIONS
Each Multi-Function Timer unit uses two I/O pins, called T1A
and T1B (for Timer MFT1) or T2A and T2B (for Timer MFT2).
The function of each pin depends on the timer operating
mode and the TnAEN and TnBEN enable bits. Table16
shows the functions of the pins in each operating mode, and
for each combination of enable bit settings.
When pin TnA is configured to operate as a PWM output
(TnAEN = 1), the state of the pin is toggled on each underflow
of the TnCNT1 counter. In this case, the initial value on the
pin is determined by the TnAOUT bit. For example, to start
with TnA high, the software should set the TnAOUT bit to 1
prior to enabling the timer clock. This option is available only
when the timer is configured to operate in Mode 1, 3, or 4 (in
other words, when TnCRA is not used in Capture mode).
Figure 17.Mode 4: Input Capture Plus Timer Block Diagram
Reload A
Timer/Counter I
Capture B
Timer I
Clock TnA
TnAIEN
TnAPND
TnCNT1
TnCRA
TnCRB
Timer
Interrupt I
TnATEN
Timer/Counter II
TnCNT2
Timer II
Clock
Underflow
TnDIEN
TnDPND
Timer
Interrupt II
TnBIEN
TnBPND
Timer
Interrupt I
TnB
TnBEN
Preset
Obsolete
55 www.national.com
Table 15Timer Interrupts Overview
Sys. Int. Interrupt
pending
flag
Mode 1 Mode 2 Mode 3 Mode 4
PWM + Counter Dual Input Capture +
counter Dual Counter Single Capture +
counter
Timer
Int. I
(TnA Int.)
TnAPND TnCNT1 reload from
TnCRA Input capture on TnA
transition TnCNT1 reload from
TnCRA TnCNT1 reload from
TnCRA
TnBPND TnCNT1 reload from
TnCRB Input Capture on TnB
transition N/A Input Capture on TnB
transition
TnCPND N/A TnCNT1 underflow N/A N/A
Timer
Int. II
(TnB Int.)
TnDPND TnCNT2 underflow TnCNT2 underflow TnCNT2 reload from
TnCRB TnCNT2 underflow
Table 16Timer I/O Functions
I/O TnAEN
TnBEN
Mode 1 Mode 2 Mode 3 Mode 4
PWM + Counter Dual Input Capture +
counter Dual Counter Single Capture +
counter
TnA TnAEN=0
TnBEN=X No Output Capture TnCNT1 into
TnCRA No Output toggle No Output toggle
TnAEN=1
TnBEN=X Toggle Output on
underflow of TnCNT1 Capture TnCNT1 into
TnCRA and preset
TnCNT1
Toggle Output on
underflow of TnCNT1 Toggle Output on
underflow of TnCNT1
TnB TnAEN=X
TnBEN=0 Ext. Event or Pulse
Accumulate Input Capture TnCNT1 into
TnCRB Ext. Event or Pulse
Accumulate Input Capture TnCNT2 into
TnCRB
TnAEN=X
TnBEN=1 Ext. Event or Pulse
Accumulate Input Capture TnCNT1 into
TnCRB and preset
TnCNT1
Ext. Event or Pulse
Accumulate Input Capture TnCNT2 into
TnCRB and preset
TnCNT2
Obsolete
56 www.national.com
15.5 TIMER REGISTERS
The following CPU-accessible registers are used to control
the Multi-Function Timers:
—Clock Prescaler Register (TnPRSC)
—Clock Unit Control Register (TnCKC)
—Timer/Counter I Register (TnCNT1)
—Timer/Counter II Register (TnCNT2)
—Reload/Capture A Register (TnCRA)
—Reload/Capture B Register (TnCRB)
—Timer Mode Control Register (TnCTRL)
—Timer Interrupt Control Register (TnICTL)
—Timer Interrupt Clear Register (TnICLR)
15.5.1 Clock Prescaler Register (TnPRSC)
The Clock Prescaler (TnPRSC) register is a byte-wide, read/
write register that holds the current value of the 5-bit clock
prescaler (CLKPS). This register is cleared upon reset. The
register format is shown below.
CLKPS Clock Prescaler. When the timer is configured
to use the prescaled clock, the system clock is
divided by CLKPS+1 to produce the timer
clock. Thus, the system clock divide-by factor
can range from 1 to 32.
15.5.2 Clock Unit Control Register (TnCKC)
The Clock Unit Control (TnCKC) register is a byte-wide, read/
write register that selects the clock source for each timer/
counter. Selecting the clock source also starts the counter.
This register is cleared upon reset, which disables the timer/
counters. The register format is shown below.
C1CSEL Counter I Clock Select. This 3-bit field defines
the clock mode for Timer/Counter I as follows:
000 = no clock (timer/counter I stopped)
001 = prescaled system clock
010 = external event on TnB (modes 1 and 3
only)
011 = pulse accumulate mode based on TnB
(modes 1 and 3 only)
100 = slow clock *
other values = undefined
C2CSEL Counter II Clock Select. This 3-bit field defines
the clock mode for Timer/Counter II as follows:
000 = no clock (Timer/Counter II stopped
modes 1, 2, and 3 only)
001 = prescaled system clock
010 = external event on TnB (modes 1 and 3
only)
011 = pulse accumulate mode based on TnB
(modes 1 and 3 only)
100 = slow clock *
other values = undefined
* Operation of the slow clock is determined by the CRC-
TRL.SCLK control bit, as described in Section12.6.1.
15.5.3 Timer/Counter I Register (TnCNT1)
The Timer/Counter I (TnCNT1) register is a word-wide, read/
write register that holds the current count value for Timer/
Counter I. The register contents are not affected by a reset
and are unknown upon power-up.
15.5.4 Timer/Counter II Register (TnCNT2)
The Timer/Counter II (TnCNT2) register is a word-wide, read/
write register that holds the current count value for Timer/
Counter II. The register contents are not affected by a reset
and are unknown upon power-up.
15.5.5 Reload/Capture A Register (TnCRA)
The Reload/Capture A (TnCRA) register is a word-wide,
read/write register that holds the reload or capture value for
Timer/Counter I. The register contents are not affected by a
reset and are unknown upon power-up.
15.5.6 Reload/Capture B Register (TnCRB)
The Reload/Capture B (TnCRB) register is a word-wide,
read/write register that holds the reload or capture value for
Timer/Counter II. The register contents are not affected by a
reset and are unknown upon power-up.
15.5.7 Timer Mode Control Register (TnCTRL)
The Timer Mode Control (TnCTRL) register is a byte-wide,
read/write register that sets the operating mode of the timer/
counter and the TnA and TnB pins. This register is cleared
upon reset. The register format is shown below.
MDSEL Mode Select. This 2-bit field sets the operating
mode of the timer/counter as follows:
00 = Mode 1: PWM plus system timer
01 = Mode 2: Dual Input Capture plus system
timer
10 = Mode 3: Dual Timer/Counter
11 = Mode 4: Single Input Capture and Single
Timer
TnAEDG TnA Edge Polarity. When cleared (0), input pin
TnA is sensitive to falling edges (high to low
transitions). When set (1), input pin TnA is sen-
sitive to rising edges (low to high transitions).
TnBEDG TnB Edge Polarity. When cleared (0), input pin
TnB is sensitive to falling edges (high to low
transitions). When set (1), input pin TnB is sen-
sitive to rising edges (low to high transitions). In
pulse accumulate mode, when this bit is set (1),
the counter is enabled only when TnB is high;
when this bit is cleared (0), the counter is en-
abled only when TnB is low.
TnAEN TnA Enable. When set (1), the TnA pin is en-
abled to operate as a preset input or as a PWM
output, depending on the timer operating
mode. In Mode 2 (Dual Input Capture), a tran-
sition on the TnA pin presets the TnCNT1
counter to FFFF hex. In the other modes, TnA
functions as a PWM output. When this bit is
7 6 5 4 3 2 1 0
Reserved CLKPS
7 6 5 4 3 2 1 0
Reserved C2CSEL C1CSEL
7 6 5 4 3 2 1 0
Reserved TnAOUT TnBEN TnAEN TnBEDG TnAEDG MDSEL
Obsolete
57 www.national.com
cleared (0), operation of the pin for the timer/
counter is disabled.
TnBEN TnB Enable. When set (1), the TnB pin in en-
abled to operate in Mode 2 (Dual Input Cap-
ture) or Mode 4 (Single Input Capture and
Single Timer). A transition on the TnB pin pre-
sets the corresponding timer/counter to FFFF
hex (TnCNT1 in Mode 2 or TnCNT2 in Mode
4). When this bit is cleared (0), operation of the
pin for the timer/counter is disabled. This bit
setting has no effect in Mode 1 or Mode 3.
TnAOUT TnA Output Data. This is a status bit that indi-
cates the current state of the TnA pin when the
pin is used as a PWM output. When set (1), the
TnA pin is high; when cleared (0), the TnA pin
is low. The hardware sets and clears this bit,
but the software can also read or write this bit
at any time and thus control the state of the out-
put pin. In case of conflict, a software write has
precedence over a hardware update. This bit
setting has no effect when TnA is used as an
input.
15.5.8 Timer Interrupt Control Register (TnICTL)
The Timer Interrupt Control (TnICTL) register is a byte-wide,
read/write register that contains the interrupt enable bits and
interrupt pending bits for the four timer interrupt sources,
designated A, B, C, and D. The condition that causes each
type of interrupt depends on the operating mode, as shown
in Table15.
This register is cleared upon reset. The register format is
shown below.
TnAPND Timer Interrupt Source A Pending. When this
bit is set (1), it indicates that timer interrupt con-
dition “A” has occurred. When this bit is cleared
(0), it indicates that the interrupt condition has
not occurred. For an explanation of interrupt
conditions A, B, C, and D, see Table15
This bit can be set by the hardware or by the
software. To clear this bit, the software must
use the Timer Interrupt Clear Register (TnI-
CLR). Any attempt by the software to directly
write a 0 to this bit is ignored.
TnBPND Timer Interrupt Source B Pending. See the de-
scription of TnAPND.
TnCPND Timer Interrupt Source C Pending. See the de-
scription of TnAPND.
TnDPND Timer Interrupt Source D Pending. See the de-
scription of TnAPND.
TnAIEN Timer Interrupt A Enable. When set (1), this bit
enables an interrupt on each occurrence of in-
terrupt condition “A.” When cleared (0), an oc-
currence of interrupt condition “A” does not
generate an interrupt to the CPU, but still sets
the associated pending flag (TnAPND). For an
explanation of interrupt conditions A, B, C, and
D, see Table15.
TnBIEN Timer Interrupt B Enable. See the description
of TnAIEN.
TnCIEN Timer Interrupt C Enable. See the description
of TnAIEN.
TnDIEN Timer Interrupt D Enable. See the description
of TnAIEN.
15.5.9 Timer Interrupt Clear Register (TnICLR)
The Timer Interrupt Clear (TnICLR) register is a byte-wide,
write-only register that allows the software to clear the TnAP-
ND, TnBPND, TnCPND, and TnDPND bits in the Timer Inter-
rupt Control (TnICTRL) register. The register format is shown
below.
TnACLR Timer Pending A Clear. When written with a 1,
the Timer Interrupt Source A Pending bit
(TnAPND) is cleared in the Timer Interrupt
Control register (TnICTL). Writing a 0 to the
TnACLR bit has no effect.
TnBCLR Timer Pending B Clear. See the description of
TnACLR.
TnCCLR Timer Pending C Clear. See the description of
TnACLR.
TnDCLR Timer Pending D Clear. See the description of
TnACLR.
76543210
TnDIEN TnCIEN TnBIEN TnAIEN TnDPND TnCPND TnBPND TnAPND
7 6 5 4 3 2 1 0
Reserved TnDCLR TnCCLR TnBCLR TnACLR
Obsolete
www.national.com 58
16.0 Versatile-Timer-Unit (VTU)
The Versatile Timer Unit (VTU) contains four fully indepen-
dent 16-bit timer subsystems. Each timer subsystem can op-
erate either as dual 8-bit PWM timers, as a single 16-bit
PWM timer, or as a 16-bit counter with 2 input capture chan-
nels. These timer subsystems offers an 8-bit clock prescaler
to accommodate a wide range of system frequencies.
The Versatile Timer Unit offers the following features:
•The Versatile Timer Unit (VTU) can be configured to pro-
vide:
—Eight fully independent 8-bit PWM channels
—Four fully independent 16-bit PWM channels
—Eight 16-bit input capture channels
•The VTU consists of four timer subsystems, each of which
contains:
—a 16-bit counter
—two 16-bit capture / compare registers
—an 8-bit fully programmable clock prescaler
•Each of the four timer subsystems can operate in the fol-
lowing modes:
—low power mode, i.e. all clocks are stopped
—dual 8-bit PWM mode
—16-bit PWM mode
—dual 16-bit input capture mode
•The Versatile-Timer-Unit controls a total of eight I/O pins,
each of which can function as either:
—PWM output with programmable output polarity
—Capture input with programmable event detection and
timer reset
•A flexible interrupt scheme with
—four separate system level interrupt requests
—a total of 16 interrupt sources each with a separate in-
terrupt pending flag and interrupt enable bit
16.1 VTU FUNCTIONAL DESCRIPTION
The Versatile-Timer-Unit (VTU) is comprised of four timer
subsystems. Each timer subsystem contains an 8-bit clock
prescaler, a 16-bit up-counter and two 16-bit registers. Each
timer subsystem controls two I/O pins which either function
as PWM outputs or capture inputs depending on the mode of
operation. There are four system level interrupt requests,
one for each timer subsystem. Each system level interrupt re-
quest is controlled by four interrupt pending flags with asso-
ciated enable/disable bits. All four timer subsystems are fully
independent and each may operate as a dual 8-bit PWM tim-
er, a 16-bit PWM timer or as a dual 16-bit capture timer. Fig-
ure 18 illustrates the main elements of the Versatile-Timer-
Unit (VTU).
Prescaler
Counter
C2PRSC
==
COUNT2
PERCAP2
DTYCAP2
I/O control I/O control
TIO3 TIO4
compare - capture
compare - capture
07
015
Prescaler
Counter
C3PRSC
==
COUNT3
PERCAP3
DTYCAP3
I/O control I/O control
TIO5 TIO6
compare - capture
compare - capture
07
015
Prescaler
Counter
C4PRSC
==
COUNT4
PERCAP4
DTYCAP4
I/O control I/O control
TIO7 TIO8
compare - capture
compare - capture
07
015
Prescaler
Counter
C1PRSC
==
COUNT1
PERCAP1
DTYCAP1
I/O control I/O control
TIO1 TIO2
compare - capture
compare - capture
07
015
Timer Subsystem 1 Timer Subsystem 2 Timer Subsystem 3 Timer Subsystem 4
MODE
IO1CTL IO2CTL
INTPND
INTCTL
015
015
015
015
015
Figure 18.VTU Block Diagram
Obsolete
59 www.national.com
16.1.1 Dual 8-bit PWM Mode
Each timer subsystem may be configured to generate two
fully independent PWM waveforms on the respective TIOx
pins. In this mode, the counter COUNTx is split and operates
as two independent 8-bit counters. Each counter increments
at the rate determined by the clock prescaler.
Each of the two 8-bit counters may be started and stopped
separately via the associated TxRUN bits. Once either of the
two 8-bit timers is running the clock prescaler starts counting.
Once the clock prescaler counter value matches the value of
the associated CxPRSC register field, COUNTx is incre-
mented.
The period of the PWM output waveform is determined by
the value of the PERCAPx register. The TIOx output starts at
the default value as pro-grammed via the IOxCTL.PxPOL bit.
Once the counter value reaches the value of the period reg-
ister PERCAPx, the counter is reset to 0016 upon the next
counter increment. Upon the following increment from 00 16
to 0116, the TIOx output will change to the opposite of the de-
fault value.
The duty cycle of the PWM output waveform is controlled by
the DTYCAPx register value. Once the counter value reach-
es the value of the duty cycle register DTYCAPx, the PWM
output TIOx changes back to its default value upon the next
counter increment. Figure19 illustrates this concept.
The period time is determined by the following formula:
PWMperiod = (PERCAPx + 1) * (CxPRSC + 1) * TCLK
The duty cycle in percent is calculated as follows:
DutyCycle[%] = (DTYCAPx / (PERCAPx+1)) *100
If the duty cycle register (DTYCAPx) holds a value which is
greater then the value held in the period register (PERCAPx)
the TIOx output will remain at the opposite of its default value
which corresponds to a duty cycle of 100%. If the duty cycle
register (DTYCAPx) register holds a value of 0016, the TIOx
output will remain at the default value which corresponds to
a duty cycle of 0%. In that case the value contained in the
PERCAPx register is irrelevant. This scheme allows the duty
cycle to be programmed in a range from 0% to 100%.
In order to allow fully synchronized updates of the period and
duty cycle compare values, the PERCAPx and DTYCAPx
registers are double buffered when operating in PWM mode.
Therefore if the user writes to either the period or duty cycle
register while either of the two PWM channels is enabled, the
new value will not take effect until the counter value matches
the previous period value or the timer is stopped.
Reading the PERCAPx or DTYCAPx register will always re-
turn the most recent value written to it.
The counter registers can be written if both 8-bit counters are
stopped. This allows the user to preset the counters before
starting and therefore generate PWM output waveforms with
a phase shift relative to one another. If the counter is written
with a value other then 0016 it will start incrementing from that
value while TIOx remains at its default value until the first
0016 to 0116
transition of the counter value occurs. If the
counter is preset to values which are smaller or equal then
the value held in the period register (PERCAPx) the counter
will count up until a match between the counter value and the
PERCAPx register value occurs. The counter will then be re-
set to 0016 and continue counting up. Alternatively the
counter may be written with a value which is greater then the
00
COUNTx
PERCAPx
DTYCAPx
TIOx (PxPOL=0)
TIOx (PxPOL=1)
TxRUN=1
01
00
01
02 03 04
05 06 07 08 09 0A
02 03 04
05 06 07 08 09 0A
Figure 19.VTU PWM generation
Obsolete
www.national.com 60
value held in the period register. In that case the counter will
count up to FF16
and then roll over to 0016. In any case the
TIOx pin always changes its state at the 0016 to 0116
transi-
tion of the counter.
The user software may only write to the COUNTx register if
both TxRUN bits of a timer subsystem are cleared. Any
writes to the counter register while either timer is running will
be ignored.
The two I/O pins associated with a timer subsystem function
as independent PWM outputs in the dual 8-bit PWM mode. If
a PWM timer is stopped via its associated MODE.TxRUN bit
the following actions result:
—The associated TIOx pin will return to its default value
as defined by the IOxCTL.PxPOL bit.
—The counter will stop and will retain its last value.
—Any pending updates of the PERCAPx and DTYCAPx
register will be completed.
—The prescaler counter will be stopped and reset if both
MODE.TxRUN bits are cleared.
Figure20 illustrates the configuration of a timer subsystem
while operating in dual 8-bit PWM mode. The numbering in
Figure20 refers to timer subsystem 1 but equally applies to
the other three timer subsystems.
16.1.2 16-Bit PWM Mode
Each of the four timer subsystems may be independently
configured to provide a single 16-bit PWM channel. In this
case the lower and upper bytes of the counter are concate-
nated to form a single 16-bit counter.
Operation in 16-bit PWM mode is conceptually identical to
the dual 8-bit PWM operation as outlined under Dual 8-bit
PWM Mode on page 59. The 16-bit timer may be started or
stopped with the lower MODE.TxRUN bit, i.e. T1RUN for tim-
er subsystem 1.
The two TIOx outputs associated with a timer subsystem can
be used to produce either two identical PWM waveforms or
two PWM waveforms of opposite polarities. This can be ac-
complished by setting the two PxPOL bits of the respective
timer subsystem to either identical or opposite values.
Figure21 illustrates the configuration of a timer subsystem
while operating in 16-bit PWM mode. The numbering in
Figure21 refers to timer subsystem 1 but equally applies to
the other three timer subsystems.
Figure 21.VTU 16-bit PWM Mode
16.1.3 Dual 16-Bit Capture Mode
In addition to the two PWM modes, each timer subsystem
may be configured to operate in an input capture mode which
provides two 16-bit capture channels. The input capture
mode can be used to precisely measure the period and duty
cycle of external signals.
In capture mode the counter COUNTx operates as a 16-bit
up-counter while the two TIOx pins associated with a timer
subsystem operate as capture inputs. A capture event on the
TIOx pins causes the contents of the counter register
(COUNTx) to be copied to the PERCAPx or DTYCAPx regis-
ters respectively.
Starting the counter is identical to the 16-bit PWM mode, i.e.
setting the lower of the two MODE.TxRUN bits will start the
counter and the clock prescaler. In addition, the capture
event inputs are enabled once the MODE.TxRUN bit is set.
The TIOx capture inputs can be independently configured to
detect a capture event on either a positive transition, a neg-
ative transition or both a positive and a negative transition. In
addition, any capture event may be used to reset the counter
COUNTx and the clock prescaler counter. This avoids the
need for the user software to keep track of timer overflow
conditions and greatly simplifies the direct frequency and
duty cycle measurement of an external signal.
Figure22 illustrates the configuration of a timer subsystem
while operating in capture mode. The numbering in Figure22
Prescaler
Counter
C1PRSC
==
COUNT1[15:8]
PERCAP1[15:8]
DTYCAP1[15:8]
TIO2
compare
compare
07
815
COUNT1[7:0]
PERCAP1[7:0]
DTYCAP1[7:0]
compare
compare
07
[7:0]
[15:8]
S
R
Q
P2POL
TIO1
S
R
Q
P1POL
T1RUN
T2RUN
Res Res
TMOD1=01
Figure 20.VTU Dual 8-bit PWM Mode
Prescaler
Counter
C1PRSC
==
COUNT1[15:0]
PERCAP1[15:0]
DTYCAP1[15:0]
TIO2
compare
compare
07
0
15 [15:0]
S
R
Q
P2POL
TIO1
S
R
Q
P1POL
T1RUN
Restart
TMOD1=10
Obsolete
61 www.national.com
refers to timer subsystem 1 but equally applies to the other
three timer subsystems.
Figure 22.VTU Dual 16-bit Capture Mode
16.1.4 Low Power Mode
In case a timer subsystem is not used, the user can place it
in a low-power-mode. All clocks to a timer subsystem are
stopped and the counter and prescaler contents are frozen
once low-power-mode is entered. The user may continue to
write to the MODE, INTCTL, IOxCTL and CLKxPS registers.
Write operations to the INTPND register are allowed; but if a
timer subsystem is in low power mode, its associated inter-
rupt pending bits cannot be cleared. The user cannot write to
the COUNTx, PERCAPx and DTYCAPx registers of a timer
subsystem while it is in low-power-mode. All registers can be
read at any time.
16.1.5 Interrupts
The Versatile-Timer-Unit (VTU) has a total of 16 interrupt
sources, four for each of the four timer subsystems. All inter-
rupt sources have a pending flag and an enable bit associat-
ed with them. All interrupt pending flags are denoted IxAPD
through IxDPD where “x” relates to the specific timer sub-
system. There is one system level interrupt request for each
of the four timer subsystems.
Figure23 illustrates the interrupt structure of the versatile
timer module.
Figure 23.VTU Interrupt Request Structure
Each of the timer pending flags - IxAPD through IxDPD - is
set by a specific hardware event depending on the mode of
operation, i.e., PWM or Capture mode. Table17 outlines the
specific hardware events relative to the operation mode
which cause an interrupt pending flag to be set.
16.1.6 ISE Mode operation
The VTU supports breakpoint operation of the In-System-
Emulator (ISE). If FREEZE is asserted, all timer counter
clocks will be inhibited and the current value of the timer reg-
isters will be frozen; in capture mode, all further capture
events are disabled. Once FREEZE becomes inactive,
counting will resume from the previous value and the capture
input events are re-enabled.
16.2 VTU REGISTERS
The Versatile-Timer-Unit contains a total of 19 user accessi-
ble registers. All registers are word-wide and are initialized to
a known value upon reset. All software accesses to the VTU
registers must be word accesses.
Prescaler
Counter
C1PRSC
==
COUNT1[15:0]
PERCAP1[15:0]
DTYCAP1[15:0]
capture
capture
07
0
15
[15:0]
TIO1
C1EDG
T1RUN
Restart
2 0
TIO2
C2EDG
2 0
cap
cap
rst rst
TMOD1=11
I1APD
I1BPD
I1CPD
I1DPD
I1AEN
I1BEN
I1CEN
I1DEN System
Interrupt
Request 1
I4APD
I4BPD
I4CPD
I4DPD
I4AEN
I4BEN
I4CEN
I4DEN System
Interrupt
Request 4
Table 17 VTU Interrupt Sources
Pending Flag Dual 8-bit PWM Mode 16-bit PWM Mode Capture Mode
IxAPD Low Byte Duty Cycle match Duty Cycle match Capture to DTYCAPx
IxBPD Low Byte Period match Period match Capture to PERCAPx
IxCPD High Byte Duty Cycle match N/A Counter Overflow
IxDPD High Byte Period match N/A N/A
Obsolete
www.national.com 62
16.2.1 Mode Control Register (MODE)
The Mode Control (MODE) registries a word-wide read/write
register which controls the mode selection of all four timer
subsystems. The register is cleared (000016) upon reset.
TxRUN Timer start/stop. If set (1), the associated
counter and clock prescaler is started depend-
ing on the mode of operation. Once set, the
clock to the clock prescaler and the counter are
enabled and the counter will increment each
time the clock prescaler counter value matches
the value defined in the associated clock pres-
caler field (CxPRSC).
TMODx Timer System Operating Mode. This 2-bit wide
field enables or disables the Timer Subsystem
and defines it’s operating mode.
00: Low-Power-Mode enabled. All clocks to
the counter subsystem are stopped. The
counter is stopped regardless of the val-
ue of the TxRUN bits. Read operations
to the Timer Subsystem will return the
last value; the user shall not perform any
write operations to the Timer Subsystem
while it is disabled since those will be ig-
nored.
01: Dual 8-bit PWM mode enabled. Each 8-
bit counter may individually be started or
stopped via its associated TxRUN bit.
The TIOx pins will function as PWM out-
puts.
10: 16-bit PWM mode enabled. The two 8-
bit counters are concatenated to form a
single 16-bit counter. The counter may
be started or stopped with the lower of
the two TxRUN bits, i.e. T1RUN,
T3RUN, T5RUN and T7RUN. The TIOx
pins will function as PWM outputs.
11: Capture Mode enabled. Both 8-bit
counters are concatenated and operate
as a single 16-bit counter. The counter
may be started or stopped with the lower
of the two TxRUN bits, i.e., T1RUN,
T3RUN, T5RUN and T7RUN. The TIOx
pins will function as capture inputs.
16.2.2 I/O Control Register 1 (IO1CTL)
The I/O Control Register 1 (IO1CTL) is a word-wide read/
write register. The register controls the functionality of the
I/O pins TIO1 through TIO4 depending on the selected mode
of operation. The register is cleared (000016) upon reset.
CxEDG Capture Edge Control. Defines the polarity of a
capture event and the reset of the counter. The
value of this three bit field has no effect while
operating in PWM mode.
PxPOL PWM Polarity. While operating in PWM mode
the bit defines the output polarity of the corre-
sponding PWM output (TIOx).
0 = The PWM output is set (1) upon the 0016
to 0116
transition of the counter and will
be reset (0) once the counter value
matches the duty cycle value.
1 = The PWM output is reset (0) upon the
0016
to 01 16 transition of the counter and
will be set (1) once the counter value
matches the duty cycle value.
Once a counter is stopped, the output will assume the value
of PxPOL, i.e., its initial value. The PxPOL bit has no effect
while operating in capture mode.
16.2.3 I/O Control Register 2 (IO2CTL)
The I/O Control Register 2 (IO2CTL) is a word-wide read/
write register. The register controls the functionality of the
I/O pins TIO5 through TIO8 depending on the selected mode
of operation. The register is cleared (0000) upon reset.
The functionality of the bit fields of the IO2CTL register is
identical to the ones described in the IO1CTL register sec-
tion.
16.2.4 Interrupt Control Register (INTCTL)
The Interrupt Control (INTCTL) register is a word-wide read/
write register. It contains the interrupt enable bits for all 16 in-
terrupt sources of the Versatile-Timer-Unit. Each interrupt en-
able bit corresponds to an interrupt pending flag located in
the Interrupt Pending Register (INTPND). All INTCTL regis-
ter bits are solely under software control. The register is
cleared (000016
) upon reset..
IxAEN Timer x interrupt A enable . Enable/Disable an
interrupt request based on the corresponding
IxAPD flag being set. The associated IxAPD
15 14 13 12 11 10 9 8
TMOD4 T8RUN T7RUN TMOD3 T6RUN T5RUN
7 6 5 4 3 2 1 0
TMOD2 T4RUN T3RUN TMOD1 T2RUN T1RUN
15 14 12 11 10 8 76 4 32 0
P4POL C4EDG P3POL C3EDG P2POL C2EDG P1POL C1EDG
CxEDG Capture Counter Reset
000 rising edge No
001 falling edge No
010 rising edge Yes
011 falling edge Yes
100 both edges No
101 both edges rising edge
110 both edges falling edge
111 both edges both edges
15 14 12 11 10 8 76 4 32 0
P8POL C8EDG P7POL C7EDG P6POL C6EDG P5POL C5EDG
15 14 13 12 11 10 9 8
I4DEN I4CEN I4BEN I4AEN I3DEN I3CEN I3BEN I3AEN
7 6 5 4 3 2 1 0
I2DEN I2CEN I2BEN I2AEN I1DEN I1CEN I1BEN I1AEN
Obsolete
63 www.national.com
flag will be updated regardless of the value of
the IxAEN bit.
0Enable system interrupt request for the
IxAPD pending flag
1Disable system interrupt request for the
IxAPD pending flag
IxBEN Timer x interrupt B enable. Enable/Disable an
interrupt request based on the corresponding
IxBPD flag being set. The associated IxBPD
flag will be updated regardless of the value of
the IxBEN bit.
0Enable system interrupt request for the
IxBPD pending flag
1Disable system interrupt request for the
IxBPD pending flag
IxCEN Timer x interrupt C enable. Enable/Disable an
interrupt request based on the corresponding
IxCPD flag being set. The associated IxCPD
flag will be updated regardless of the value of
the IxCEN bit.
0Enable system interrupt request for the
IxCPD pending flag
1Disable system interrupt request for the
IxCPD pending flag
IxDEN Timer x interrupt D enable. Enable/Disable an
interrupt request based on the corresponding
IxDPD flag being set. The associated IxDPD
flag will be updated regardless of the value of
the IxDEN bit.
0Enable system interrupt request for the
IxDPD pending flag
1Disable system interrupt request for the
IxDPD pending flag
16.2.5 Interrupt Pending Register (INTPND)
The Interrupt Pending (INTPND) register is a word-wide
read/write register which contains all 16 interrupt pending
flags. There are four interrupt pending flags called IxAPD
through IxDPD per timer subsystem. Each interrupt pending
flag is set by a hardware event and can be cleared if the user
software writes a 1 to the bit position. The value will remain
unchanged if a 0 is written to the bit position. All interrupt
pending flags are cleared (0) upon reset.
IxAPD Timer x interrupt A pending. If set (1), indicates
that an interrupt condition for the related timer
subsystem has occurred. Table 17 on page 61
lists the hardware condition which causes this
bit to be set.
IxBPD Timer x interrupt B pending. If set (1), indicates
that an interrupt condition for the related timer
subsystem has occurred. Table 17 on page 61
lists the hardware condition which causes this
bit to be set.
IxCPD Timer x interrupt C pending. If set (1), indicates
that an interrupt condition for the related timer
subsystem has occurred. Table 17 on page 61
lists the hardware condition which causes this
bit to be set.
IxDPD Timer x interrupt D pending. If set (1), indicates
that an interrupt condition for the related timer
subsystem has occurred. Table 17 on page 61
lists the hardware condition which causes this
bit to be set.
16.2.6 Clock Prescaler Register 1 (CLK1PS)
CLK1PS is a word-wide read/write register. The register is
split into two 8-bit wide field called C1PRSC and C2PRSC.
Each field holds the 8-bit clock prescaler compare value for
timer subsystems 1 and 2 respectively. The register is
cleared upon reset.
C1PRSC Clock Prescaler 1 compare value. Holds the 8-
bit prescaler value for timer subsystem 1. The
counter of timer subsystem is incremented
each time when the clock prescaler compare
value matches the value of the clock prescaler
counter. The divide-by-ratio is equal to
C1PRSC+1 i.e. a value of 0016
results in a di-
vide by 1 whereas the maximum divide-by ratio
is 256 for a C1PRSC value of FF16.
C2PRSC Clock Prescaler 2 compare value. Holds the 8-
bit prescaler value for timer subsystem 2. The
functionality of this field is identical to the one
described for C1PRSC in the previous para-
graph.
16.2.7 Clock Prescaler Register 2 (CLK2PS)
The Clock Prescaler Register 2 (CLK2PS) is a word-wide
read/write register. The register is split into two 8-bit wide
fields called C3PRSC and C4PRSC. Each field holds the 8-
bit clock prescaler compare value for timer subsystems 3 and
4 respectively. The register is cleared upon reset.
C3PRSC Clock Prescaler 3 compare value. Holds the 8-
bit prescaler value for timer subsystem 3. The
functionality of this field is identical to the one
described for C1PRSC on page 63.
C4PRSC Clock Prescaler 4 compare value. Holds the 8-
bit prescaler value for timer subsystem 4. The
functionality of this field is identical to the one
described for C1PRSC on page 63.
16.2.8 Counter Registers (COUNTx)
The Counter (COUNTx) registers are word wide read/write
registers. There are a total of four registers called COUNT1
through COUNT4, one for each of the four timer subsystems.
The user software may read the registers at any time. Read-
15 14 13 12 11 10 9 8
I4DPD I4CPD I4BPD I4APD I3DPD I3CPD I3BPD I3APD
76543210
I2DPD I2CPD I2BPD I2APD I1DPD I1CPD I1BPD I1APD
15 8
7 0
C2PRSC C1PRSC
15 8
7 0
C4PRSC C3PRSC
Obsolete
www.national.com 64
ing the register will return the current value of the counter.
The register may only be written if the counter is stopped i.e.
if both TxRUN bits associated with a timer subsystem are
cleared. The registers are cleared upon reset (0000).
16.2.9 Period/Capture Registers (PERCAPx)
The Period/Capture (PERCAPx) registers are word-wide
read/write registers. There are a total of four registers called
PERCAP1 through PERCAP4, one for each timer sub-
system. The register hold the period compare value in PWM
mode of the counter value at the time the last associated cap-
ture event occurred. In PWM mode the register is double
buffered. If a new period compare value is written while the
counter is running, the write will not take effect until counter
value matches the previous period compare value or until the
counter is stopped. Reading may take place at any time and
will return the most recent value which was written. The PER-
CAPx registers are reset to 0000 upon reset.
16.2.10 Duty Cycle / Capture Registers (DTYCAPx)
The Duty Cycle/Capture (DTYCAPx) registers are word-wide
read/write registers. There are a total of four registers called
DTYCAP1 through DTYCAP4, one for each timer sub-
system. The registers hold the period compare value in PWM
mode or the counter value at the time the last associated
capture event occurred. In PWM mode the register is double
buffered. If a new duty cycle compare value is written while
the counter is running, the write will not take effect until the
counter value matches the previous period compare value or
until the counter is stopped. In other words, the update takes
effect on period boundaries only. Reading may take place at
any time and will return the most recent value which was writ-
ten. The DTYCAPx registers are reset to 000016 upon reset.
15 0
CNTx
15 0
PCAPx
15 0
DCAPx
Obsolete
65 www.national.com
17.0 MICROWIRE/SPI
MICROWIRE/PLUS is a synchronous serial communications
protocol, originally implemented in National Semiconductor's
COPS™ and HPC™ families of microcontrollers to minimize
the number of connections, and therefore the cost, of com-
municating with peripherals.
The device has an enhanced MICROWIRE/SPI interface
module (MWSPI) that can communicate with all peripherals
that conform to MICROWIRE or Serial Peripheral Interface
(SPI) specifications. This enhanced MICROWIRE interface
is capable of operating as either a master or slave and in 8-
or 16-bit mode. Figure24 shows a typical enhanced MI-
CROWIRE interface application.
The enhanced MICROWIRE interface module includes the
following features:
—Programmable operation as a Master or Slave
—Programmable shift-clock frequency (master only)
—Programmable 8- or 16-bit mode of operation
—8- or 16-bit serial I/O data shift register
—Two modes of clocking data
—Serial clock can be low or high when idle
—16-bit read buffer
—Busy flag, Read Buffer Full flag, and Overrun flag for
polling and as interrupt sources
—Supports multiple masters
—Maximum bit rate of 10M bits/second (master mode)
5M bits/second (slave mode) at 20MHz system clock
—Supports very low-end slaves with the Slave Ready
output
—Echo back enable/disable (Slave only)
17.1 MICROWIRE OPERATION
The MICROWIRE interface allows several devices to be con-
nected on one three-wire system. At any given time, one of
these devices operates as the master while all other devices
operate as slaves.
The master device supplies the synchronous clock (MSK) for
the serial interface and initiates the data transfer. The slave
devices respond by sending (or receiving) the requested da-
ta. Each slave device uses the master’s clock for serially
shifting data out (or in), while the master shifts the data in (or
out).
The three-wire system includes: the serial data in signal
(MDIDO for master mode, MDODI for slave mode), the serial
data out signal (MDODI for master mode, MDIDO for slave
mode) and the serial clock (MSK).
In slave mode, an optional fourth signal (MCS) may be used
to enable the slave transmit. At any given time, only one
slave can respond to the master. Each slave device has its
own chip select signal (MCS) for this purpose.
The MICROWIRE interface allows the device to operate ei-
ther as a master or slave transferring 8- or 16-bits of data.
This is configured via the MMNS bit.
Figure25 shows a block diagram of the enhanced MICROW-
IRE serial interface in the device.
17.1.1 Shifting
The MICROWIRE interface is a full duplex transmitter/receiv-
er. A 16-bit shifter, which can be split into a low and high byte,
is used for both transmitting and receiving. In 8-bit mode,
only the lower 8-bits are used to transfer data. The transmit-
ted data is shifted out through MDODI pin (master mode) or
MDIDO pin (slave mode), starting with the most significant
bit. At the same time, the received data is shifted in through
MDIDO pin (master mode) or MDODI pin (slave mode), also
starting with the most significant bit first.
The shift in and shift out are controlled by the MSK clock. In
each clock cycle of MSK, one bit of data is transmitted/re-
ceived. The 16-bit shifter is accessible via the MWDAT regis-
ter. Reading the MWDAT register returns the value in the
read buffer. Writing to the MWDAT register updates the 16-
bit shifter.
17.1.2 Reading
The enhanced MICROWIRE interface implements a double
buffer on read. As illustrated in Figure25, the double read
Figure 24.MICROWIRE Interface
DO
5Chip Select Lines
CS CS CS CS
MDIDO
DO
MDIDO
MDODI MDODI
DI DI DI DI
Master Slave
MSK MSK
SK SK SK SK
8-Bit
A/D 1K Bit
EEPROM LCD
Display
driver
VF
Display
Driver
I/O
Lines I/O
Lines
MCS
MCS
DO
Obsolete
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buffer consists of the 16-bit shifter and a buffer, called the
read buffer.
The 16-bit shifter loads the read buffer with new data when
the data transfer sequence is completed and previous data in
the read buffer has been read. In master mode, an Overrun
error occurs when the read buffer is full, the 16-bit shifter is
full and a new data transfer sequence starts.
When 8-bit mode is selected, the lower byte of the shift reg-
ister is loaded into the lower byte of the read buffer and the
read buffer’s higher byte remains unchanged.
The “Receive Buffer Full” (MRBF) bit indicates if the MWDAT
register holds valid data. The MOVR bit indicates that an
overrun condition has occurred.
17.1.3 Writing
The “MICROWIRE Busy” (MBSY) bit indicates whether the
MWDAT register can be written. All write operations to the
MWDAT register update the shifter while the data contained in
the read buffer is not affected. Undefined results will occur if
the MWDAT register is written to while the MBSY bit is set to 1.
17.1.4 Clocking Modes
Two clocking modes are supported: the normal mode and the
alternate mode.
In the normal mode, the output data, which is transmitted on
the MDODI pin (master mode) or the MDIDO pin (slave
mode), is clocked out on the falling edge of the shift clock
MSK. The input data, which is received via the MDIDO pin
(master mode) or the MDODI pin (slave mode), is sampled
on the rising edge of MSK.
In the alternate mode, the output data is shifted out on the ris-
ing edge of MSK on the MDODI pin (master mode) or MDIDO
pin (slave mode). The input data, which is received via MDI-
DO pin (master mode) or MDODI pin (slave mode), is sam-
pled on the falling edge of MSK.
The clocking modes are selected with the MSKM bit. The
MIDL bit allows selection of the value of MSK when it is idle
(when there is no data being transferred). Various MSK clock
frequencies can be programmed via the MCDV bits. Figures
27, 28, 29, and 30 show the data transfer timing for the nor-
mal and the alternate modes with the MIDL bit equal to 0 and
equal to 1.
Note that when data is shifted out on MDODI (master mode)
or MDIDO (slave mode) on the leading edge of the MSK
clock, bit 14 (16-bit mode) is shifted out on the second lead-
ing edge of the MSK clock. When data are shifted out on
MDODI (master mode) or MDIDO (slave mode) on the trail-
ing edge of MSK, bit 14 (16-bit mode) is shifted out on the first
trailing edge of MSK.
17.2 MASTER MODE
In Master mode, the MSK pin is an output for the shift clock,
MSK. When data is written to the (MWnDAT register), eight
or sixteen MSK clocks, depending on the mode selected, are
generated to shift the eight or sixteen bits of data and then
Figure 25.MICROWIRE Block Diagram
Master
Master
Slave
Slave
16-bit Shift Register
Master
Clock Prescaler + Select
8
16-bit Read Buffer
MWDAT
System Clock
Write Data
Read Data
Control + Status
Interrupt Request
Data In
Data Out
MSK
MCS
MDODI
MDIDO
MSK
8
Obsolete
67 www.national.com
MSK goes idle again. The MSK idle state can be either high
or low, depending on the MIDL bit.
17.3 SLAVE MODE
In Slave mode, the MSK pin is an input for the shift clock
MSK. MDIDO is placed in TRI-STATE mode when MCS is in-
active. Data transfer is enabled when MCS is active.
The slave starts driving MDIDO when MCS is activated. The
most significant bit (lower byte in 8-bit mode or upper byte in
16-bit mode) is output onto the MDIDO pin first. After eight or
sixteen clocks (depending on the selected mode), the data
transfer is completed.
Figure 26.Normal Mode, MIDL Bit = 0
Figure 27.Normal Mode, MIDL Bit = 1
Figure 28.Alternate Mode, MIDL Bit = 0
Data In
MSB msb-1 msb-2 5 Bit 1 Bit 0
End of Transfer
MSB msb-1 msb-2 Bit 1 Bit 0
Sample PointShift Out
Data Out
MSK
(lsb)
(lsb)
Data Out
Data In
msb msb-1 msb-2 Bit 1 Bit 0 (lsb)
End of Transfer
Sample Point
Shift Out
msb msb-1 msb-2 Bit 1 Bit 0 (lsb)
MSK
End of Transfer
Data Out
Data In
msb msb-1 msb-2 Bit 1 Bit 0 (lsb)
msb msb-1 msb-2 Bit 1 Bit 0 (lsb)
MSKn
Sample Point
Shift Out
Obsolete
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If a new shift process starts before MWDAT was written, i.e.,
while MWDAT does not contain any valid data, and the “Echo
Enable” (MECH) bit is set to 1, the data received from MDO-
DI is transmitted on MDIDO in addition to being shifted to
MWDAT. If the MECH bit is cleared to 0, the data transmitted
on MDIDO is the data held in the MWDAT register, regard-
less of its validity. The master may negate the MCS signal to
synchronize the bit count between the master and the slave.
In the case that the slave is the only slave in the system, MCS
can be tied to VSS.
17.4 INTERRUPT GENERATION
An interrupt is generated in any of the following cases:
—When the read buffer is full (MRBF=1) and the “Enable
Interrupt for Read” bit is set (MEIR=1).
—Whenever the shifter is not busy, i.e. the MBSY bit is
cleared (MBSY=0) and the “Enable Interrupt for Write”
bit is set (MEIW=1).
—When an overrun condition occurs (MOVR is set to 1)
and the “Enable Interrupt on Overrun” bit is set
(MEIO=1). This usage is restricted to master mode.
Figure30 illustrates the various interrupt capabilities of this
module.
17.5 MICROWIRE INTERFACE REGISTERS
The software interacts with the MICROWIRE interface by ac-
cessing the MICROWIRE registers. There are five such reg-
isters:
—MICROWIRE Data Register (MWDAT)
—MICROWIRE Control Register (MWCTL)
—MICROWIRE Status Register (MWSTAT)
17.5.1 MICROWIRE Data Register (MWDAT)
The MWDAT register is a word-wide, read/write register used
to transmit and receive data through the MDODI and MDIDO
pins. Figure31 shows the hardware structure of the register.
Figure 29.Alternate Mode, MIDL Bit = 1
End of Transfer
Sample PointShift Out
Data Out
Data In
msb msb-1 msb-2 Bit 1 Bit 0 (lsb)
msb msb-1 msb-2 Bit 1 Bit 0 (lsb)
MSKn
Figure 30.MWSPI Interrupts
Interrupt
MWSPI
MOVR = 1
MRBF = 1
MBSY = 0
MEIW
MEIR
MEIO
Obsolete
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17.5.2 MICROWIRE Control Register (MWCTL)
Upon reset, all non-reserved bits are cleared to 0. The regis-
ter format is shown below.
MEN MICROWIRE Enable. This bit enables (1) or
disables (0) the MICROWIRE interface mod-
ule. Clearing this bit disables the module,
clears the status bits in the MICROWIRE status
register (the MBSY, MRBF, and MOVR flags in
MWSTAT), and places the MICROWIRE inter-
face pins in the states described in Table18.
MMNS MICROWIRE Master/Slave Select. When
cleared to 0, the device operates as a slave.
When set to 1, the device operates as the mas-
ter.
MMOD MICROWIRE Mode Select (8- or 16-bit). When
set to 0, the device operates in 8-bit mode.
When set to 1, the device operates in 16-bit
mode. This bit should only be changed when
the module is disabled or the MICROWIRE in-
terface is idle (MWSTAT.MBSY=0).
MECH MICROWIRE Echo Back. This bit enables (1)
or disables (0) the echo back function in slave
mode. This bit should be written only when the
MICROWIRE interface is idle (MWSTAT.MB-
SY=0). The MECH bit is ignored in master
mode. The MWDAT register is valid from the
time the register has been written until the end
of the transfer.
In the echo back mode, MDODI is transmitted
(echoed back) on MDIDO if MWDAT does not
contain any valid data. With the echo back
function disabled, the data held in the MWDAT
register is transmitted on MDIDO, whether or
not the data is valid.
MEIO MICROWIRE Enable Interrupt on Overrun.
This bit enables or disables the overrun error
interrupt. When set to 1, an interrupt is gener-
ated when the Receive Overrun Error flag
(MWSTAT.MOVR) is set. Otherwise, no inter-
rupt is generated when an overrun error oc-
curs. This bit should only be enabled in master
mode.
MEIR MICROWIRE Enable Interrupt for Read. When
set to 1, an interrupt is generated when the
Read Buffer Full flag (MWSTAT.MRBF) is set.
Otherwise, no interrupt is generated when the
read buffer is full.
MEIW MICROWIRE Enable Interrupt for Write. When
set to 1, an interrupt is generated when the
Busy bit (MWSTAT.MBSY) is cleared, which in-
dicates that a data transfer sequence has been
completed and the read buffer is ready to re-
ceive the new data. Otherwise, no interrupt is
generated when the Busy bit is cleared.
MSKM MICROWIRE Clocking Mode. When cleared to
0, the device uses the normal clocking mode.
When set to 1, the device uses the alternate
Figure 31.MWDAT Register Structure
Shift Register
Read Buffer
Low-Byte High-Byte
write
(store)
1
0
MWMOD
DOUT
DIN
read
(store & MWMOD)
Low-Byte High-Byte
MWDAT
15 9 8 7 6 5 4 3 2 1 0
MCDV
[6:0] MIDL MSKM MEIW MEIR MEIO MECH MMOD MMNS MEN
Table 18Pin Values with MICROWIRE
Disabled
MSK Master: MnIDL Bit
Slave: input
MCS Input
MDIDO Master: input
Slave: TRI-STATE
MDODI Master: known Value
Slave: input
Obsolete
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clocking mode. In the normal mode, the output
data is clocked out on the falling edge of MSK
and the input data is sampled on the rising
edge of MSK. In the alternate mode, the output
data is clocked out on the rising edge of MSK
and the input data is sampled on the falling
edge of MSK.
MIDL MICROWIRE Idle. This bit sets the value of the
MSK output when the MICROWIRE interface is
idle: 0 for low or 1 for high. This bit should be
changed only when the MICROWIRE interface
module is disabled (MEN=0) or when no bus
transaction is in progress (MWSTAT.MBSY=0).
MCDV MICROWIRE Clock Divider Value. This 7-bit
field specifies the divide-by factor used for gen-
erating the MSK shift clock from the system
clock. The divide-by factor is 2*(MCDV[6:0]+1).
This allows selection of a divide-by ratio from 2
to 256. This field is ignored in slave mode
(MWCTL1.MMNS=0).
17.5.3 MICROWIRE Status Register (MWSTAT)
The MICROWIRE Status Register is a word-wide, read-only
register that shows the current status of the MICROWIRE in-
terface module. Upon reset, all non-reserved bits are cleared
to 0. The register format is shown below.
MBSY MICROWIRE Busy. This bit, when set to 1, in-
dicates that the MICROWIRE shifter is busy.
In master mode, MBSY is set to 1 when the
MWDAT register is written. In slave mode, this
bit is set to 1 on the first leading edge of MSK
when MCS is asserted or when the MWDAT
register is written, whatever occurs first.
In both master and slave modes, this bit is
cleared to 0 when the MICROWIRE data trans-
fer sequence is completed and the read buffer
is ready to receive the new data; in other
words, when the previous data held in the read
buffer has already been read.
If the previous data in the read buffer has not
been read and a new data has been received
into the shift register, the MBSY will not be
cleared, as the transfer could not be complet-
ed. This is because the contents of the shift
register could not be copied into the read buff-
er.
MRBF MICROWIRE Read Buffer Full. This bit, when
set to 1, indicates that the MICROWIRE read
buffer is full and ready to be read by the soft-
ware. It is set to 1 when the shifter loads the
read buffer, which occurs upon completion of a
transfer sequence if the read buffer is empty.
The MRBF bit is updated when the MWDAT
register is read. At that time, the MRBF bit is
cleared to 0 if the shifter does not contain any
new data (in other words, the shifter is not re-
ceiving data or has not yet received a full byte
of data). The MRBF bit remains set to 1 if the
shifter already holds new data at the time that
MWDAT is read. In that case, MWDAT is imme-
diately reloaded with the new data and is ready
to be read by the software.
MOVR MICROWIRE Receive Overrun Error. This bit,
when set to 1 in master mode, indicates that a
receive overrun error has occurred. This error
occurs when the read buffer is full, the 8-bit
shifter is full, and a new data transfer sequence
starts. This bit is undefined in slave mode.
The MOVR bit, once set, remains set until
cleared by the software. The software clears
this bit by writing a 1 to its bit position. Writing
a 0 to this bit position has no effect. No other
bits in the MWSTAT register are affected by a
write operation to the register.
15 3 2 1 0
Reserved MOVR MRBF MBSY
Obsolete
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18.0 USART
The USART module is a full-duplex Universal Synchronous/
Asynchronous Receiver/Transmitter that supports a wide
range of software-programmable baud rates and data for-
mats. It handles automatic parity generation and several er-
ror detection schemes. There are one or two independent
USART modules in each device, depending on the package
type.
Each USART module offers the following features:
—Full-duplex double-buffered receiver/transmitter
—Synchronous or asynchronous operation
—programmable baud rate from SYS_CLK/
[2*(1+2^11)*16] up to SYSCLK/2 for USART config-
ured to run in synchronous mode
—programmable baud rate from SYS_CLK/
[16*(1+2^11)*16] up to SYSCLK/16 for USART config-
ured to run in asynchronous mode
—Programmable framing formats: seven, eight, or nine
data bits; one or two stop bits; and odd, even, mark,
space, or no parity
—Hardware parity generation for data transmission and
parity check for data reception
—Interrupts on “transmit ready” and “receive ready” con-
ditions, separately enabled
—Software-controlled break transmission and detection
—Internal diagnostic capability
—Automatic detection of parity, framing, and overrun er-
rors
18.1 FUNCTIONAL OVERVIEW
Figure32 is a block diagram of the USART module showing
the basic functional units in the USART:
—Transmitter
—Receiver
—Baud Rate Generator
—Control and Error Detection
Note: In the description of the USART, the lower-case letter
“n” represents the USART number. For example, TDXn
means TDX1 or TDX2.
The Transmitter block consists of an 8-bit transmit shift reg-
ister and an 8-bit transmit buffer. Data bytes are loaded in
parallel from the buffer into the shift register and then shifted
out serially on the TDXn pin.
The Receiver block consists of an 8-bit receive shift register
and an 8-bit receive buffer. Data is received serially on the
RDXn pin and shifted into the shift register. Once eight bits
have been received, the contents of the shift register are
transferred in parallel to the receive buffer.
The Transmitter and Receiver blocks both contain exten-
sions for 9-bit data transfers, as required by the 9-bit and
loopback operating modes.
The Baud Rate Generator generates the clock for the syn-
chronous and asynchronous operating modes. It consists of
two registers and a two-stage counter. The registers are
used to specify a prescaler value and a baud rate divisor. The
first stage of the counter divides the USART clock based on
the value of the programmed prescaler to create a slower
clock. The second stage of the counter divides the output of
the first stage based on the programmed baud rate divisor to
create the baud rate clock.
The Control and Error Detection block contains the USART
control registers, control logic, error detection circuit, parity
generator/checker, and interrupt generation logic. The con-
trol registers and control logic determine the data format,
mode of operation, clock source, and type of parity used. The
error detection circuit generates parity bits and checks for
parity, framing, and overrun errors.
18.2 USART OPERATION
The USART has two basic modes of operation: synchronous
and asynchronous. In addition, there are two special-
purpose synchronous and asynchronous modes, called at-
tention and diagnostic. This section describes the operating
modes of the USART.
18.2.1 Asynchronous Mode
The asynchronous mode of the USART enables the device
to communicate with other devices using just two communi-
cation signals: transmit and receive.
In the asynchronous mode, the transmit shift register (TSFT)
and the transmit buffer (UnTBUF) double-buffer the data for
transmission. To transmit a character, a data byte is loaded
in the UnTBUF register. The data is then transferred to the
TSFT register. While the TSFT is shifting out the current char-
acter (LSB first) on the TDXn pin, the UnTBUF register is
loaded by software with the next byte to be transmitted.
When TSFT finishes transmission of the last stop bit of the
current frame, the contents of UnTBUF are transferred to the
TSFT register and the Transmit Buffer Empty flag (UnTBE) is
set. The UnTBE flag is automatically reset by the USART
when the software loads a new character into the UnTBUF
register. During transmission, the UnXMIP bit is set high by
the USART. This bit is reset only after the USART has sent
the last stop bit of the current character and the UnTBUF reg-
ister is empty. The UnTBUF register is a read/write register.
The TSFT register is not user accessible.
In asynchronous mode, the input frequency to the USART is
16 times the baud rate. In other words, there are 16 clock cy-
cles per bit time. In asynchronous mode the baud rate gen-
erator is always the USART clock source.
The receive shift register (RSFT) and the receive buffer (Un-
RBUF) double buffer the data being received. The USART
receiver continuously monitors the signal on the RDXn pin for
a low level to detect the beginning of a start bit. Upon sensing
this low level, the USART waits for seven input clock cycles
and samples again three times. If all three samples still indi-
cate a valid low, then the receiver considers this to be a valid
start bit, and the remaining bits in the character frame are
each sampled three times, around the mid-bit position. For
any bit following the start bit, the logic value is found by ma-
jority voting, i.e. the two samples with the same value define
the value of the data bit. Figure33 illustrates the process of
start bit detection and bit sampling.
Serial data input on the RDXn pin is shifted into the RSFT
register. Upon receiving the complete character, the contents
of the RSFT register are copied into the UnRBUF register
and the Receive Buffer Full flag (UnRBF) is set. The UnRBF
Obsolete
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flag is automatically reset when software reads the character
from the UnRBUF register. The RSFT register is not user ac-
cessible.
18.2.2 Synchronous Mode
The synchronous mode of the USART enables the device to
communicate with other devices using three communication
signals: transmit, receive, and clock. In this mode, data bits
are transferred synchronously with the USART clock signal.
Data bits are transmitted on the rising edges and received on
the falling edges of the clock signal, as shown in Figure34.
Data bytes are transmitted and received least significant bit
(LSB) first.
In the synchronous mode, the transmit shift register (TSFT)
and the transmit buffer (UnTBUF) double-buffer the data for
transmission. To transmit a character, a data byte is loaded
in the UnTBUF register. The data is then transferred to the
TSFT register. The TSFT register shifts out one bit of the cur-
rent character, LSB first, on each rising edge of the clock.
Figure 32.USART Block Diagram
Internal Bus
Sys_clk Baud clock
Baud Clock
TDXn
RDXn
Transmitter
Receiver
Baud Rate Generator
Control and
Error Detection
Parity
Generator/Checker
CKXn
Figure 33.USART Asynchronous Communication
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 116
SampleSample
STARTBIT DATA (LSB)
12345678910 11 12 13 14 15 16 116
Sample
DATABIT
Obsolete
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While the TSFT is shifting out the current character on the
TDXn pin, the UnTBUF register may be loaded by the soft-
ware with the next byte to be transmitted. When the TSFT fin-
ishes transmission of the last stop bit within the current
frame, the contents of UnTBUF are transferred to the TSFT
register and the Transmit Buffer Empty flag (UnTBE) is set.
The UnTBE flag is automatically reset by the USART when
the software loads a new character into the UnTBUF register.
During transmission, the UnXMIP bit is set high by the
USART. This bit is reset only after the USART has sent the
last frame bit of the current character and the UnTBUF reg-
ister is empty.
The receive shift register (RSFT) and the receive buffer
(UnRBUF) double-buffer the data being received. Serial data
received on the RDXn pin is shifted into the RSFT register at
the first falling edge of the clock. Each subsequent falling
edge of the clock causes an additional bit to be shifted into
the RSFT register. The USART assumes a complete charac-
ter has been received after the correct number of rising edg-
es on CKXn (based on the selected frame format) have been
detected. Upon receiving a complete character, the contents
of the RSFT register are copied into the UnRBUF register
and the Receive Buffer Full flag (UnRBF) is set. The UnRBF
flag is automatically reset when the software reads the char-
acter from the UnRBUF register.
The transmitter and receiver may be clocked from either an
external source provided to the CKXn pin or by the internal
baud rate generator. In the latter case, the clock signal is
placed on the CKXn pin as an output.
18.2.3 Attention Mode
The Attention mode is available for networking this device
with other processors. This mode requires the 9-bit data for-
mat with no parity. The number of start bits and number of
stop bits are programmable. In this mode, two types of 9-bit
characters are sent on the network: address characters con-
sisting of 8 address bits and a 1 in the ninth bit position and
data characters consisting of 8 data bits and a 0 in the ninth
bit position.
While in Attention mode, the USART receiver monitors the
communication flow but ignores all characters until an ad-
dress character is received. Upon the receipt of an address
character, the contents of the receive shift register are copied
to the receive buffer. The UnRBF flag is set and an interrupt
(if enabled) is generated. The UnATN bit is automatically re-
set to zero, and the USART begins receiving all subsequent
characters. The software must examine the contents of the
UnRBUF register and respond by accepting the subsequent
characters (by leaving the UnATN bit reset) or waiting for the
next address character (by setting the UnATN bit again).
The operation of the USART transmitter is not affected by the
selection of this mode. The value of the ninth bit to be trans-
mitted is programmed by setting or clearing a bit called
UnXB9 in the USART Frame Select register. The value of the
ninth bit received is read from UnRB9 in the USART Status
Register.
18.2.4 Diagnostic Mode
The Diagnostic mode is available for testing of the USART. In
this mode, the TDXn and RDXn pins are internally connected
together, and data that is shifted out of the transmit shift reg-
ister is immediately transferred to the receive shift register.
This mode supports only the 9-bit data format with no parity.
The number of start and stop bits is programmable.
18.2.5 Frame Format Selection
The format shown in Figure35 consists of a start bit, seven
data bits (excluding parity), and one or two stop bits. If parity
bit generation is enabled by setting the UnPEN bit, a parity
bit is generated and transmitted following the seven data bits.
The format shown in Figure36 consists of one start bit, eight
data bits (excluding parity), and one or two stop bits. If parity
bit generation is enabled by setting the UnPEN bit, a parity
bit is generated and transmitted following the eight data bits.
The format shown in Figure37 consists of one start bit, nine
data bits, and one or two stop bits. This format also supports
the USART attention feature. When operating in this format,
all eight bits of UnTBUF and UnRBUF are used for data. The
Figure 34.USART Synchronous Communication
CKX
TDX
RDX
Sample Input
Figure 35.Seven Data Bit Frame Options
Figure 36.Eight Data Bit Frame Options
1START
BIT 7 BIT DATA S
1a START
BIT 7 BIT DATA 2S
1c START
BIT 7 BIT DATA 2SPA
1b START
BIT 7 BIT DATA SPA
2
START
BIT 8 BIT DATA S
2a START
BIT 8 BIT DATA 2S
2b START
BIT 8 BIT DATA SPA
2c START
BIT 8 BIT DATA 2SPA
Obsolete
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ninth data bit is transmitted and received using two bits in the
control registers, called UnXB9 and UnRB9. Parity is not
generated or verified in this mode.
18.2.6 Baud Rate Generator
The Baud Rate Generator creates the basic baud clock from
the system clock. The system clock is passed through a two-
stage divider chain consisting of a 5-bit baud rate prescaler
(UnPSC) and an 11-bit baud rate divisor (UnDIV).
The relationship between the 5-bit prescaler select (UnPSC)
setting and the prescaler factors is shown in Table19.
A prescaler factor of zero corresponds to “no clock.” The “no
clock” condition is the USART power down mode, in which
the USART clock is turned off to reduce power consumption.
The application program should select the “no clock” condi-
tion before entering a new baud rate. Otherwise, it could
cause incorrect data to be received or transmitted. The
UnPSR register must contain a value other than zero when
an external clock is used at CKXn.
In asynchronous mode, the baud rate is calculated by:
where BR is the baud rate, SYS_CLK is the system clock, N
is the value of the baud rate divisor + 1, and P is the prescaler
divide factor selected by the value in the UnPSR register.
The divide by 16 is performed because in the asynchronous
mode, the input frequency to the USART is 16 times the baud
rate. In synchronous mode, the input clock to the USART
equals the baud rate.
18.2.7 Interrupts
The USART is capable of generating interrupts on:
•Receive Buffer Full
•Receive Error
•Transmit Buffer Empty
Figure38 shows a diagram of the interrupt sources and as-
sociated enable bits.
Figure 37.Nine Data Bit Frame Options
Table 19Prescaler Factors
Prescaler
Select Prescaler
Factor Prescaler
Select Prescaler
Factor
00000 110000 8.5
00001 110001 9
00010 1.5 10010 9.5
00011 210011 10
00100 2.5 10100 10.5
00101 310101 11
00110 3.5 10110 11.5
00111 410111 12
01000 4.5 11000 12.5
01001 511001 13
01010 5.5 11010 13.5
01011 611011 14
3
START
BIT 9 BIT DATA S
3a START
BIT 9 BIT DATA 2S
01100 6.5 11100 14.5
01101 711101 15
01110 7.5 11110 15.5
01111 811111 16
Table 19Prescaler Factors
Prescaler
Select Prescaler
Factor Prescaler
Select Prescaler
Factor
BR
SYS
_
CLK
16
NP
××
()
-------------------------------=
Figure 38.USART Interrupts
UnEEI
UnERI
UnERR
UnRBF
UnFE
UnDOE
UnPE
RX
Interrupt
UnETI
UnTBE TX
Interrupt
Obsolete
75 www.national.com
The interrupts can be individually enabled or disabled using
the Enable Transmit Interrupt (UnETI), Enable Receive Inter-
rupt (UnERI) and Enable Receive Error Interrupt (UnEER)
bits in the UnICTRL register.
A transmit interrupt is generated when both the UnTBE and
UnETI bits are set. To remove this interrupt, software must ei-
ther disable the interrupt by clearing the UnETI bit or write to
the UnTBUF register (thus clearing the UnTBE bit).
A receive interrupt is generated on two conditions:
1. Both the UnRBF and UnERI bits are set. To remove this
interrupt, software must either disable the interrupt by
clearing the UnERI bit or read from the UnRBUF register
(thus clearing the UnRBF bit).
2. Both the UnERR and the UnEEI bits are set. To remove
this interrupt the software must either disable it by clear-
ing the UnEEI bit or read the UnSTAT register (thus
clearing the UnERR bit).
18.2.8 Break Generation and Detection
A line break is generated when the BRK bit is set in the Un-
MDSL register. The TDXn line remains low until the program
resets the BRK bit.
A line break is detected if RDXn remains low for 10 bit times
or longer after a missing stop bit is detected.
18.2.9 Parity Generation and Detection
Parity is only generated or checked with the 7-bit and 8-bit
data formats. It is not generated or checked in the diagnostic
loopback mode, the attention mode, or in the normal mode
with the 9-bit data format. Parity generation and checking are
enabled and disabled via the PEN bit in the UnFRS register.
The UnPSEL bits in the UnFRS register are used to select
odd, even, mark, or space parity.
18.3 USART REGISTERS
The software interacts with the USART by accessing the US-
ART registers. There are eight such registers:
—USART Receive Data Buffer (UnRBUF)
—USART Transmit Data Buffer (UnTBUF)
—USART Baud Rate Prescaler Register (UnPSR)
—USART Baud Rate Divisor Register (UnBAUD)
—USART Frame Select Register (UnFRS)
—USART Mode Select Register (UnMDSL)
—USART Status Register (UnSTAT)
—USART Interrupt Control Register (UnICTRL)
18.3.1 USART Receive Data Buffer (UnRBUF)
The USART Receive Data Buffer is a byte-wide, read/write
register used to receive each data byte.
18.3.2 USART Transmit Data Buffer (UnTBUF)
The USART Transmit Data Buffer is a byte-wide, read/write
register used to transmit each data byte.
18.3.3 USART Baud Rate Prescaler (UnPSR)
The USART Baud Rate Prescaler Register is a byte-wide,
read/write register that contains the 5-bit clock prescaler and
the upper three bits of the baud rate divisor. This register is
cleared upon reset. The register format is shown below.
UnPSC Prescaler. This 5-bit field specifies the prescal-
er value used for dividing the system clock in
the first stage of the two-stage divider chain.
For the prescaler factors corresponding to
each 5-bit value, see Table19.
UnDIV[10:8] Baud Rate Divisor (bits 10-8). This field con-
tains the three highest-order bits (bits 10, 9,
and 8) of the USART baud rate divisor used in
the second stage of the two-stage divider
chain. The remaining bits of the baud rate divi-
sor are contained in the UnBAUD register.
18.3.4 USART Baud Rate Divisor (UnBAUD)
The USART Baud Rate Divisor Register is a byte-wide, read/
write register that contains the lower eight bits of the baud
rate divisor. This register contents are unknown upon power-
up and are left unchanged by a reset operation. The register
format is shown below.
UnDIV[7:0] Baud Rate Divisor (bits 7-0). This field contains
the eight lowest-order bits of the USART baud
rate divisor used in the second stage of the
two-stage divider chain. The three highest-or-
der bits are contained in the UnPSR register.
The divisor value used is the 11-bit UnDIV val-
ue plus 1.
18.3.5 USART Frame Select Register (UnFRS)
The USART Frame Select Register is a byte-wide, read/write
register that controls the frame format, including the number
of data bits, number of stop bits, and parity type. This register
is cleared upon reset. The register format is shown below.
UnCHAR Character Frame Format. This 2-bit field se-
lects the number of data bits per frame, not in-
cluding the parity bit, as follows:
00 = eight data bits per frame
01 = seven data bits per frame
10 = nine data bits per frame
11 = loopback mode; nine data bits per frame
UnSTP Number of Stop Bits. This bit sets the number
of stop bits transmitted in each frame. If this bit
is 0, one stop bit is transmitted. If this bit is 1,
two stop bits are transmitted.
UnXB9 Transmit 9th Data Bit. This bit is the value of
the ninth data bit, either 0 or 1, transmitted
when the USART is configured to transmit nine
data bits per frame. It has no effect when the
USART is configured to transmit seven or eight
data bits per frame.
7 6 5 4 3 2 1 0
UnPSC UnDIV10 UnDIV9 UnDIV8
76543210
UnDIV7 UnDIV6 UnDIV5 UnDIV4 UnDIV3 UnDIV2 UnDIV1 UnDIV0
7 6 5 4 3 2 1 0
Reserved UnPEN UnPSEL UnXB9 UnSTP UnCHAR
Obsolete
www.national.com 76
UnPSEL Parity Select. This 2-bit field selects parity type
as follows:
00 = odd parity
01 = even parity
10 = mark (0)
11 = space (1)
When the USART is configured to transmit nine
data bits per frame, the parity bit is omitted and
the UnPSEL field is ignored.
UnPEN Parity Enable. This bit enables (1) or disables
(0) parity bit generation and parity checking.
When the USART is configured to transmit nine
data bits per frame, there is no parity bit and the
UnPEN bit is ignored.
18.3.6 USART Mode Select Register (UnMDSL)
The USART Mode Select Register is a byte-wide, read/write
register that selects the clock source, synchronization mode,
attention mode, and line break generation. This register is
cleared upon reset. When the software writes to this register,
the reserved bits must be cleared to 0 for proper operation.
The register format is shown below.
UnMOD Mode of Operation. Set to 0 for asynchronous
operation or 1 for synchronous operation.
UnATN Attention Mode. When set to 1, this bit selects
the attention mode of operation for the USART.
When cleared to 0, the attention mode is dis-
abled. The hardware clears this bit after an ad-
dress frame is received. An address frame is a
9-bit character with a 1 in the ninth bit position.
UnBRK Force Transmission Break. Setting this bit to 1
causes the TDXn pin to go low. TDXn remains
low until the UnBRK bit is cleared to 0 by the
software.
UnCKS Synchronous Clock Source. This bit controls
the clock source when the USART operates in
the synchronous mode (UnMOD=1). If the
UnCKS bit is set to 1, the USART operates
from an external clock provided on the CKXn
pin. If the UnCKS bit is cleared to 0, the USART
operates from the baud rate clock produced by
the USART on the CKXn pin. This bit is ignored
when the USART operates in the asynchro-
nous mode.
18.3.7 USART Status Register (UnSTAT)
The USART Status Register is a byte-wide, read-only regis-
ter that contains the receive and transmit status bits. This
register is cleared upon reset. Any attempt by the software to
write to this register is ignored. The register format is shown
below.
UnPE Parity Error. This bit is set to 1 when a parity er-
ror is detected within a received character. This
bit is automatically cleared to 0 by the hard-
ware when the UnSTAT register is read.
UnFE Framing Error. This bit is set to 1 when the US-
ART fails to receive a valid stop bit at the end
of a frame. This bit is automatically cleared to 0
by the hardware when the UnSTAT register is
read.
UnDOE Data Overrun Error. This bit is set to 1 when a
new character is received and transferred to
the UnBUF register before the software has
read the previous character from UnBUF. This
bit is automatically cleared to 0 by the hard-
ware when the UnSTAT register is read.
UnERR Error Status Flag. This bit is set when a parity,
framing, or overrun error occurs (any time that
the UnPE, UnFE, or UnDOE bit is set). It is au-
tomatically cleared to 0 by the hardware when
the UnPE, UnFE, and UnDOE bits are all 0.
UnBKD Break Detect. This bit is set to 1 when a line
break condition occurs. This condition is de-
tected if RDXn remains low for at least ten bit
times after a missing stop bit has been detect-
ed at the end of a frame.
The hardware automatically clears the UnBKD
bit upon read of the UnSTAT register, but only
if the break condition on RXDn no longer ex-
ists. If reading the UnSTAT register does not
clear the UnBKD bit because the break is still
actively driven on the line, the hardware clears
the bit as soon as the break condition no longer
exists (when RXDn returns to a high level).
UnRB9 Received 9th Data Bit. With the USART config-
ured to operate in the 9-bit data format, this is
equal to the ninth data bit of the last frame re-
ceived.
UnXMIP Transmit In Progress. The hardware sets this
bit to 1 when the USART is transmitting data
and clears it to 0 at the end of the last frame bit.
18.3.8 USART Interrupt Control Register (UnICTRL)
The USART Interrupt Control Register is a byte-wide register
that contains the receive and transmit interrupt status flags
(read-only bits) and the interrupt enable bits (read/write bits).
The register is set to 01 hex upon reset. The register format
is shown below.
UnTBE Transmit Buffer Empty. This read-only bit is set
to 1 by the hardware when the USART trans-
fers data from the UnTBUF register to the
transmit shift register for transmission. It is au-
tomatically cleared to 0 by the hardware on the
next write to the UnTBUF register.
UnRBF Receive Buffer Full. This read-only bit is set by
the hardware when the USART has received a
complete data frame and has transferred the
data from the receive shift register to the UnR-
BUF register. It is automatically cleared to 0 by
the hardware when the UnRBUF register is
read.
7 6 5 4 3 2 1 0
Reserved UnCKS UnBRK UnATN UnMOD
7 6 5 4 3 2 1 0
Reserved UnXMIP UnRB9 UnBKD UnERR UnDOE UnFE UnPE
7 6 5 4 3 2 1 0
UnEEI UnERI UnETI Reserved UnRBF UnTBE
Obsolete
77 www.national.com
UnETI Enable Transmitter Interrupt. This read/write
bit, when set to 1, enables generation of an in-
terrupt when the hardware sets the UnTBE bit.
UnERI Enable Receiver Interrupt. This read/write bit,
when set to 1, enables generation of an inter-
rupt when the hardware sets the UnRBF bit.
UnEEI Enable Receive Error Interrupt. This read/write
bit, when set to 1, enables generation of an in-
terrupt when the hardware sets the UnERR bit
in the UnSTAT register.
18.4 BAUD RATE CALCULATIONS
The USART baud rate is determined by the system clock fre-
quency and the values programmed into the UnPSR and Un-
BAUD registers. Unless the system clock frequency is an
exact multiple of the desired baud rate, there will be a small
amount of error in the resulting baud rate clock.
The method of baud rate calculation depends on whether the
USART is configured to operate in the asynchronous or syn-
chronous mode.
18.4.1 Baud Rate in Asynchronous Mode
The equation for calculating the baud rate in asynchronous
mode is:
where BR is the baud rate, SYS_CLK is the system clock, N
is the value of the baud rate divisor + 1, and P is the prescaler
divide factor selected by the value in the UnPSR register.
Assuming a system clock of 5 MHz and a desired baud rate
of 9600, the NxP term according to the equation above is:
The NxP term is then divided by each Prescaler Factor from
Table 19 to obtain a value closest to an integer. The factor for
this example is 6.5.
The baud rate register is programmed with a baud rate divi-
sor of 4 (N = baud rate divisor +1). This produces a baud
clock of:
Note that the percent error is much lower than would be pos-
sible without the non-integer prescaler factor. Refer to the ta-
ble below for more examples.
18.4.2 Baud Rate in Synchronous Mode
The equation for calculating the baud rate in synchronous
mode is:
where BR is the baud rate, SYS_CLK is the system clock, N
is the value of the baud rate divisor + 1, and P is the prescaler
divide factor selected by the value in the UnPSR register.
Use the same procedure to determine the values of N and P
as in the asynchronous mode. In this case, however, only in-
teger prescaler values are allowed.
System
Clock Desired
Baud Rate NPActual
Baud Rate Percent
Error
4 MHz 9600 2 13 9615.385 0.16
5 MHz 9600 56.5 9615.385 0.16
10 MHz 19200 56.5 19230.769 0.16
BR
SYS
_
CLK
16
NP
××
()
-------------------------------=
NP×5
6
×10()
169600×()
----------------------------- 32.552
==
N
32.552
6.5
---------------- 5.008 (N = 5)==
BR 5
6
×10()
1656.5××()
--------------------------------- 9615.385
==
%error
9615.3859600
–
()
9600
--------------------------------------------- 0.16
==
20 MHz 19200 5 13 19230.769 0.16
System
Clock Desired
Baud Rate NPActual
Baud Rate Percent
Error
BR
SYS
_
CLK
2NP××
()
----------------------------=
Obsolete
www.national.com 78
19.0 ACCESS.bus Interface
The ACCESS.bus interface module (ACB) is a two wire serial
interface compatible with the ACCESS.bus physical layer. It
permits easy interfacing to a wide range of low-cost memo-
ries and I/O devices, including: EEPROMs, SRAMs, timers,
A/D converters, D/A converters, clock chips and peripheral
drivers. It is also compatible with Intel’s SMBus and Philips’
I2C bus. The module can be configured as a bus master or
slave, and can maintain bi-directional communications with
both multiple master and slave devices.
This section presents an overview of the bus protocol, and its
implementation by the module.
—ACCESS.bus, SMBus and I2C compliant
—ACCESS.bus master and slave
—Supports polling and interrupt controlled operation
—Generate a wake-up signal on detection of a Start Con-
dition, while in power-down mode
—Optional internal pull-up on SDA and SCL pins
19.1 ACB PROTOCOL OVERVIEW
The ACCESS.bus protocol uses a two-wire interface for bi-
directional communications between the ICs connected to
the bus. The two interface lines are the Serial Data Line
(SDA), and the Serial Clock Line (SCL). These lines should
be connected to a positive supply, via a pull-up resistor, and
remain HIGH even when the bus is idle.
The ACCESS.bus protocol supports multiple master and
slave transmitters and receivers. Each IC has a unique ad-
dress and can operate as a transmitter or a receiver (though
some peripherals are only receivers).
During data transactions, the master device initiates the
transaction, generates the clock signal and terminates the
transaction. For example, when the ACB initiates a data
transaction with an attached ACCESS.bus compliant periph-
eral, the ACB becomes the master. When the peripheral re-
sponds and transmits data to the ACB, their master/slave
(data transaction initiator and clock generator) relationship is
unchanged, even though their transmitter/receiver functions
are reversed.
19.1.1 Data Transactions
One data bit is transferred during each clock pulse. Data is
sampled during the high state of the serial clock (SCL). Con-
sequently, throughout the clock’s high period, the data should
remain stable (see Figure 39). Any changes on the SDA line
during the high state of the SCL and in the middle of a trans-
action aborts the current transaction. New data should be
sent during the low SCL state. This protocol permits a single
data line to transfer both command/control information and
data using the synchronous serial clock.
Figure 39.Bit Transfer
Each data transaction is composed of a Start Condition, a
number of byte transfers (set by the software), and a Stop
Condition to terminate the transaction. Each byte is trans-
ferred with the most significant bit first, and after each byte (8
bits), an Acknowledge signal must follow.
At each clock cycle, the slave can stall the master while it
handles the previous data, or prepares new data. This can be
done for each bit transferred or on a byte boundary by the
slave holding SCL low to extend the clock-low period. Typi-
cally, slaves extend the first clock cycle of a transfer if a byte
read has not yet been stored, or if the next byte to be trans-
mitted is not yet ready. Some microcontrollers with limited
hardware support for ACESS.bus extend the access after
each bit, thus allowing the software time to handle this bit.
Start and Stop
The ACCESS.bus master generates Start and Stop Condi-
tions (control codes). After a Start Condition is generated the
bus is considered busy and it retains this status until a certain
time after a Stop Condition is generated. A high-to-low tran-
sition of the data line (SDA) while the clock (SCL) is high in-
dicates a Start Condition. A low-to-high transition of the SDA
line while the SCL is high indicates a Stop Condition
(Figure40).
Figure 40.Start and Stop Conditions
In addition to the first Start Condition, a repeated Start Con-
dition can be generated in the middle of a transaction. This
allows another device to be accessed, or a change in the di-
rection of the data transfer.
Acknowledge Cycle
The Acknowledge Cycle consists of two signals: the ac-
knowledge clock pulse the master sends with each byte
SDA
SCL
Data Line
Stable:
Data Valid
Change
of Data
Allowed
SDA
SCL S P
Start
Condition Stop
Condition
Obsolete
79 www.national.com
transferred, and the acknowledge signal sent by the receiv-
ing device (Figure 41).
Figure 41.ACCESS.bus Data Transaction
The master generates the acknowledge clock pulse on the
ninth clock pulse of the byte transfer. The transmitter releas-
es the SDA line (permits it to go high) to allow the receiver to
send the acknowledge signal. The receiver must pull down
the SDA line during the acknowledge clock pulse, thus sig-
nalling the correct reception of the last data byte, and its
readiness to receive the next byte. Figure 42 illustrates the
acknowledge cycle.
Figure 42.ACCESS.bus Acknowledge Cycle
The master generates an acknowledge clock pulse after
each byte transfer. The receiver sends an acknowledge sig-
nal after every byte received.
There are two exceptions to the “acknowledge after every
byte” rule.
1. When the master is the receiver, it must indicate to the
transmitter an end of data by not-acknowledging (“neg-
ative acknowledge”) the last byte clocked out of the
slave. This “negative acknowledge” still includes the ac-
knowledge clock pulse (generated by the master), but
the SDA line is not pulled down.
2. When the receiver is full, otherwise occupied, or a prob-
lem has occurred, it sends a negative acknowledge to
indicate that it can not accept additional data bytes.
Addressing Transfer Formats
Each device on the bus has a unique address. Before any
data is transmitted, the master transmits the address of the
slave being addressed. The slave device should send an ac-
knowledge signal on the SDA line, once it recognizes its ad-
dress.
The address is the first seven bits after a Start Condition. The
direction of the data transfer (R/W) depends on the bit sent
after the address — the eighth bit. A low-to-high transition
during a SCL high period indicates the Stop Condition, and
ends the transaction (Figure 43).
Figure 43.A Complete ACCESS.bus Data Transaction
When the address is sent, each device in the system com-
pares this address with its own. If there is a match, the device
considers itself addressed and sends an acknowledge sig-
nal. Depending upon the state of the R/W bit (1:read,
0:write), the device acts as a transmitter or a receiver.
The I2C bus protocol allows sending a general call address
to all slaves connected to the bus. The first byte sent speci-
fies the general call address (0016) and the second byte
specifies the meaning of the general call (for example, “Write
slave address by software only”). Those slaves that require
the data acknowledge the call and become slave receivers;
the other slaves ignore the call.
Arbitration on the Bus
Multiple master devices on the bus, require arbitration be-
tween their conflicting bus-access demands. Control of the
bus is initially determined according to address bits and clock
cycle. If the masters are trying to address the same IC, data
comparisons determine the outcome of this arbitration. In
master mode, the device immediately aborts a transaction if
the value sampled on the SDA lines differs from the value
driven by the device. (Exceptions to this rule are SDA while
receiving data; in these cases the lines may be driven low by
the slave without causing an abort).
The SCL signal is monitored for clock synchronization pur-
pose and allow the slave to stall the bus. The actual clock pe-
riod will be the one set by the master with the longest clock
period or by the slave stall period. The clock high period is
determined by the master with the shortest clock high period.
When an abort occurs during the address transmission, the
master that identify the conflict, give-up the bus and should
switch to slave mode and continue to sample SDA to see if it
is being addressed by the winning master on the AC-
CESS.bus.
19.2 ACB FUNCTIONAL DESCRIPTION
The ACB module provides the physical layer for an AC-
CESS.bus compliant serial interface. The module is config-
urable as either a master or slave device. As a slave device,
the ACB module may issue a request to become the bus
master.
S P
Start
Condition Stop
Condition
SDA
SCL
MSB
ACK ACK
1 2 3 - 6 789 1 2 3 - 8 9
Acknowledgment
Signal From Receiver
Byte Complete
Interrupt Within
Receiver
Clock Line Held
Low by Receiver
While Interrupt
is Serviced
S
Start
Condition
SCL 1 2 3 - 6 7 8 9
Transmitter Stays Off
the Bus During the
Acknowledgment Clock
Acknowledgment
Signal From Receiver
Data Output
by
Transmitter
Data Output
by
Receiver
SP
Start
Condition Stop
Condition
SDA
SCL 1 - 7 8 9 1 - 7 8 9 1 - 7 8 9
Address R/WACK Data ACK Data ACK
Obsolete
www.national.com 80
19.2.1 Master Mode
An ACCESS.bus transaction starts with a master device re-
questing bus mastership. It sends a Start Condition, followed
by the address of the device it wants to access. If this trans-
action is successfully completed, the software can assume
that the device has become the bus master.
For a device to become the bus master, the software should
perform the following steps:
1. Set ACBCTL1.START, and configure ACBCTL1.INTEN
to the desired operation mode (Polling or Interrupt). This
causes the ACB to issue a Start Condition on the AC-
CESS.bus, as soon as the ACCESS.bus is free
(ACBCST.BB=0). It then stalls the bus by holding SCL
low.
2. If a bus conflict is detected, (i.e., some other device pulls
down the SCL signal before this device does), ACB-
ST.BER is set.
3. If there is no bus conflict, ACBST.MASTER and ACB-
ST.SDAST are set.
4. If ACBCTL1.INTEN is set, and either ACBST.BER or
ACBST.SDAST is set, an interrupt is sent to the ICU.
Sending the Address Byte
Once this device is the active master of the ACCESS.bus
(ACBST.MASTER is set), it can send the address on the bus.
The address sent should not be this device’s own address as
defined in ACBADDR.ADDR if ACBADDR.SAEN is set, nor
should it be the global call address if ACBST.GCMTCH is set.
To send the address byte use the following sequence:
1. Configure the ACBCTL1.INTEN bit according to the de-
sired operation mode. For a receive transaction where
the software wants only one byte of data, it should set
the ACBCTL1.ACK bit.
If only an address needs to be sent, set (1) the
ACBCTL1.STASTRE bit.
2. Write the address byte (7-bit target device address), and
the direction bit, to the ACBSDA register. This causes
the module to generate a transaction. At the end of this
transaction, the acknowledge bit received is copied to
ACBST.NEGACK. During the transaction the SDA and
SCL lines are continuously checked for conflict with oth-
er devices. If a conflict is detected, the transaction is
aborted, ACBST.BER is set, and ACBST.MASTER is
cleared.
3. If ACBCTL1.STASTRE is set, and the transaction was
successfully completed (i.e., both ACBST.BER and
ACBST.NEGACK are cleared), ACBST.STASTR is set.
In this case, the ACB stalls any further ACCESS.bus op-
erations (i.e., holds SCL low). If ACBCTL1.INTE is set, it
also sends an interrupt to the core.
4. If the requested direction is transmit, and the start trans-
action was completed successfully (i.e., neither ACB-
ST.NEGACK nor ACBST.BER is set, and no other
master has accessed the device), ACBST.SDAST is set
to indicate that the module awaits attention.
5. If the requested direction is receive, the start transaction
was completed successfully and ACBCTL1.STASTRE is
cleared, the module starts receiving the first byte auto-
matically.
6. Check that both ACBST.BER and ACBST.NEGACK are
cleared. If the ACBCTL1.INTEN bit is set, an interrupt is
generated when either ACBST.BER or ACB-
ST.NEGACK is set.
Master Transmit
After becoming the bus master, the device can start transmit-
ting data on the ACCESS.bus.
To transmit a byte, the software should:
1. Check that the BER and NEGACK bits in ACBST are
cleared and ACBST.SDAST is set. Also, if
ACBCTL1.STASTRE is set, check that ACBST.STASTR
is cleared.
2. Write the data byte to be transmitted to the ACBSDA
register.
When the slave responds with a negative acknowledge, the
ACBST.NEGACK bit is set and the ACBST.SDAST bit re-
mains cleared. In this case, if ACBCTL1.INTEN is set, an in-
terrupt is sent to the core.
Master Receive
After becoming the bus master, the device can start receiving
data on the ACCESS.bus.
To receive a byte, the software should:
1. Check that ACBST.SDAST is set and ACBST.BER is
cleared. Also, if ACBCTL1.STASTRE is set, check that
ACBST.STASTR is cleared.
2. Set the ACBCTL1.ACK bit to 1, if the next byte is the last
byte that should be read. This causes a negative ac-
knowledge to be sent.
3. Read the data byte from the ACBSDA register.
Master Stop
A Stop Condition may be issued only when this device is the
active bus master (ACBST.MASTRER=1). To end a transac-
tion, set (1) ACBCTL1.STOP before clearing the current stall
flag (i.e., ACBST.SDAST, ACBST.NEGACK or ACB-
ST.STASTR). This causes the module to send a Stop Condi-
tion immediately, and clear ACBCTL1.STOP.
Master Bus Stall
The ACB module can stall the ACCESS.bus between trans-
fers while waiting for the core’s response. The ACCESS.bus
is stalled by holding the SCL signal low after the acknowl-
edge cycle. Note that this is interpreted as the beginning of
the following bus operation. The user must make sure that
the next operation is prepared before the flag that causes the
bus stall is cleared.
The flags that can cause a stall in master mode are:
—Negative acknowledge after sending a byte (ACBST-
NEGACK=1).
—ACBST.SDAST bit is set.
—If ACBCTL1.STASTRE=1, after a successful start
(ACBST.STASTR=1).
Repeated Start
A repeated start is performed when this device is already the
bus master (ACBST.MASTER is set). In this case the AC-
CESS.bus is stalled and the ACB is awaiting the core han-
dling due to: negative acknowledge (ACBST.NEGACK=1),
Obsolete
81 www.national.com
empty buffer (ACBST.SDAST=1) and/or a stop after start
(ACBST.STASTR=1).
For a repeated start:
—Set the ACBCTL1.START bit.
—In master receive mode, read the last data item from
ACBSDA.
—Follow the address send sequence, as described in
“Sending the Address Byte” on page 80.
—If the ACB was awaiting handling due to ACBST.STAS-
TR=1, clear it only after writing the requested address
and direction to ACBSDA.
Master Error Detections
The ACB detects illegal Start or Stop Conditions (i.e., a Start
or Stop Condition within the data transfer, or the acknowl-
edge cycle) and a conflict on the data lines of the AC-
CESS.bus. If an illegal action is detected, BER is set, and the
MASTER mode is exited (MASTER is cleared).
Bus Idle Error Recovery
When a request to become the active bus master or a restart
operation fails, the ACBST.BER bit is set to indicate the error.
In some cases, both this device and the other device may
identify the failure and leave the bus idle. In this case, the
start sequence may not be completed and the ACCESS.bus
may remain deadlocked forever.
To recover from deadlock, use the following sequence:
1. Clear the ACBST.BER bit and ACBCST.BB bit.
2. Wait for a time-out period to check that there is no other
active master on the bus (i.e., ACBCST.BB remains
cleared).
3. Disable, and re-enable the ACB to put it in the non-ad-
dressed slave mode.
4. At this point some of the slaves may not identify the bus
error. To recover, the ACB becomes the bus master by
issuing a Start Condition and sends an address field;
then issue a Stop Condition to synchronize all the
slaves.
19.2.2 Slave Mode
A slave device waits in Idle mode for a master to initiate a bus
transaction. Whenever the ACB is enabled, and it is not act-
ing as a master (i.e., ACBST.MASTER is cleared), it acts as
a slave device.
Once a Start Condition on the bus is detected, this device
checks whether the address sent by the current master
matches either:
—The ACBADDR.ADDR value if ACBADDR.SAEN is
set.
—The general call address if ACBCTL1.GCM is set.
This match is checked even when ACBST.MASTER is set. If
a bus conflict (on SDA or SCL) is detected, ACBST.BER is
set, ACBST.MASTER is cleared and this device continues to
search the received message for a match.
If an address match, or a global match, is detected:
—This device asserts its data pin during the acknowl-
edge cycle.
—The ACBCST.MATCH and ACBST.NMATCH bits are
set. If ACBST.XMIT is set (i.e., slave transmit mode),
ACBST.SDAST is set to indicate that the buffer is emp-
ty.
—If ACBCTL1.INTEN is set, an interrupt is generated if
both the INTEN and NMINTE bits in ACBCTL1 regis-
ters are set.
—The software then reads the ACBST.XMIT bit to identi-
fy the direction requested by the master device. It
clears the ACBST.NMATCH bit so future byte transfers
are identified as data bytes.
Slave Receive and Transmit
Slave Receive and Transmit are performed after a match is
detected and the data transfer direction is identified. After a
byte transfer the ACB extend the acknowledge clock until the
software reads or writes the ACBSDA register. The receive
and transmit sequence are identical to those used in the
master routine.
Slave Bus Stall
When operating as a slave, this device stalls the AC-
CESS.bus by extending the first clock cycle of a transaction
in the following cases:
—ACBST.SDAST is set.
—ACBST.NMATCH, and ACBCTL1.NMINTE are set.
Slave Error Detections
The ACB detects illegal Start and Stop Conditions on the AC-
CESS.bus (i.e., a Start or Stop Condition within the data
transfer or the acknowledge cycle). When an illegal Start or
Stop Condition is detected, the BER bit is set and MATCH
and GMATCH are cleared, setting the module to be an unad-
dressed slave.
Power Down
When this device is in Power Save, Idle, or Halt mode, the
ACB module is not active but retains its status. If the ACB is
enabled (ACBCTL2.ENABLE=1) on detection of a Start Con-
dition, a wake-up signal is issued to the MIWU module. Use
this signal to switch this device to Active mode.
The ACB module cannot check the address byte following
the start condition that has awaken this device for a match.
The ACB responds with a negative acknowledge, and the de-
vice should re-send both the Start Condition and the address
after this device has had time to wake up.
Check that the ACBCST.BUSY bit is inactive before entering
Power Save, Idle or Halt mode. This guarantees that this de-
vice does not acknowledge an address sent, and stop re-
sponding later.
19.2.3 SDA and SCL Pins Configuration
The SDA and SCL are open-drain signals. For more informa-
tion, see the I/O configuration section.
19.2.4 ACB Clock Frequency Configuration
The ACB module permits the user to set the clock frequency
used for the ACCESS.bus clock. The clock is set by the
ACBCTL2.SCLFRQ field. This field determines the SCL
clock period used by this device. This clock low period may
be extended by stall periods initiated by the ACB module or
by another ACCESS.bus device. In case of a conflict with an-
other bus master, a shorter clock high period may be forced
by the other bus master until the conflict is resolved.
Obsolete
www.national.com 82
19.3 ACB REGISTERS
The ACCESS.bus Interface uses the following registers:
—ACB Serial Data Register (ACBSDA)
—ACB Status Register (ACBST)
—ACB Status Control Register (ACBCST)
—ACB Control 1 Register (ACBCTL1)
—ACB Control 2 Register (ACBCTL2)
—ACB Own Address Register (ACBADDR)
19.3.1 ACB Serial Data Register (ACBSDA)
The ACB Serial Data Register (ACBSDA) is a byte-wide,
read/write shift register used to transmit and receive data.
The most significant bit is transmitted (received) first and the
least significant bit is transmitted (received) last. Reading or
writing to the ACBSDA register is allowed when ACB-
ST.SDAST is set; or for repeated starts after setting the
START bit. An attempt to access the register in other cases
produces unpredictable results.
19.3.2 ACB Status Register (ACBST)
The ACB Status Register (ACBST) is a byte-wide, read-only
register that maintains current ACB status. Upon reset, and
when the module is disabled, ACBST is cleared (0016).
XMIT Direction Bit. The XMIT bit is set when the ACB
module is currently in master/slave transmit
mode. Otherwise it is cleared.
MASTER MASTER. When set, the MASTER bit indicates
that the module is currently in master mode. It
is set when a request for bus mastership suc-
ceeds. It is cleared upon arbitration loss (BER
is set) or the recognition of a Stop Condition.
NMATCH New match. The NMATCH bit is set when the
address byte following a Start Condition, or re-
peated starts, causes a match or a global-call
match. NMATCH is cleared when 1 is written to
it. Writing 0 to NMATCH is ignored. If
ACBCTL1.INTEN is set, an interrupt is sent
when this bit is set.
STASTR Stall After Start. The STASTR bit is set by the
successful completion of an address sending
(i.e., a Start Condition sent without a bus error,
or negative acknowledge) if ACBCTL1.STAS-
TRE is set. This bit is ignored in slave mode.
When STASTR is set, it stalls the ACCESS.bus
by pulling down the SCL line, and suspends
any other action on the bus (e.g., receives first
byte in master receive mode). In addition, if
ACBCTL1.INTEN is set, it also sends an inter-
rupt to the core. Writing 1 to STASTR clears it.
It is also cleared when the module is disabled.
Writing 0 to STASTR has no effect.
NEGACK Negative acknowledge. This bit is set by hard-
ware when a transmission is not acknowledged
on the ninth clock. (In this case SDAST is not
set.) Writing 1 to NEGACK clears it. It is also
cleared when the module is disabled. Writing 0
to NEGACK is ignored.
BER Bus Error. BER is set by the hardware when a
Start or Stop Condition is detected during data
transfer (i.e., Start or Stop Condition during the
transfer of bits 2 through 8 and acknowledge
cycle), or when an arbitration problem is de-
tected. Writing 1 to BER clears it. It is also
cleared when the module is disabled. Writing 0
to BER is ignored.
SDAST SDA Status. When set, this bit indicates that
the SDA data register is waiting for data (trans-
mit - master or slave) or holds data that should
be read (receive - master or slave). This bit is
cleared when reading from the ACBSDA regis-
ter during a receive, or when written to during a
transmit. When ACBCTL1.START is set, read-
ing ACBSDA register does not clear SDAST.
This enables the ACB to send a repeated start
in master receive mode.
SLVSTP Slave Stop. If set, SLVSTP indicates that a
Stop Condition was detected after a slave
transfer (i.e., after a slave transfer in which
MATCH or GCMATCH is set). Writing 1 to
SLVSTP clears it. It is also cleared when the
module is disabled. Writing 0 to SLVSTP is ig-
nored.
19.3.3 ACB Control Status Register (ACBCST)
ACB Control Status Register (ACBCST) is a byte-wide, read/
write register that maintains current ACB status. Upon reset
and when the module is disabled, the non-reserved bits of
ACBCST are cleared (0).
BUSY BUSY. When BUSY is set, it indicates that the
ACB module is:
•Generating a Start Condition
•In Master mode (ACBST.MASTER is set)
•In Slave mode (ACBCST.MATCH or
ACBCST.GCMTCH is set)
•In the period between detecting a Start and
completing the reception of the address
byte. After this, the ACB either becomes
not busy or enters slave mode.
The BUSY bit is cleared by the completion of
any of the above states, and by disabling the
module. BUSY is a read only bit. It should al-
ways be written with 0.
BB Bus Busy When set, BB indicates the bus is
busy. It is set when the bus is active (i.e., a low
level on either SDA or SCL), or by a Start Con-
dition. It is cleared when the module is dis-
abled, upon detection of a Stop Condition, or
when writing 1 to this bit. See “Usage Hints” on
page 84 for a description of the use of this bit.
This bit should be set when either SDA or SCL
are low. This should be done by sampling the
SDA and SCL lines continuously and, setting
the bit if one of them is low. The bit remains set
7 0
DATA
7 65 43 2 1 0
SLVST
PSDAST BER NEGACK STASTR NMATC
HMASTER XMIT
7 6 5 4 3 2 1 0
Reserved TGSCL TSDA GCMTCH MATCH BB BUSY
Obsolete
83 www.national.com
until cleared by a STOP condition or a one is
written to it.
MATCH Address Match. In slave mode, MATCH is set
when ACBADDR.SAEN is set and the first sev-
en bits of the address byte (the first byte trans-
ferred after a Start Condition) matches the 7-bit
address in the ACBADDR register. It is cleared
by Start Condition, repeated start and Stop
Condition (including illegal Start or Stop Condi-
tion).
GCMTCH Global Call Match bit. In slave mode, GCMTCH
is set when ACBCTL1.GCMEN is set and the
address byte (the first byte transferred after a
Start Condition) is 0016. It is cleared by Start
Condition, repeated Start and Stop Condition
(including illegal Start or Stop Condition).
TSDA Test SDA Line. Reads the current value of the
SDA line. This bit can be used while recovering
from an error condition in which the SDA line is
constantly pulled low by a slave that went out
of synch. This bit is a read-only bit. Data written
to it is ignored.
TGSCL Toggle SCL Line. This bit enables toggling the
SCL line during the process of error recovery.
When the SDA line is low, writing 1 to this bit
toggles the SCL line for one cycle. Writing 1 to
TGSCL when SDA is high is ignored. The bit is
cleared when the clock toggle is completed.
19.3.4 ACB Control 1 Register (ACBCTL1)
ACB Control 1 Register (ACBCTL1) is a byte-wide, read/
write register that configures and controls the ACB module.
Upon reset and while the module is disabled (ACBCTL2.EN-
ABLE=0), the ACBCTL1 is cleared (0016).
START START. This bit is set when a Start Condition
needs to be generated on the ACCESS.bus.
The START bit is cleared when the Start Con-
dition is sent, or upon detection of a Bus Error
(ACBST.BER=1). This bit should be set only
when in Master mode, or when requesting
Master mode.
If this device is not the active master of the bus
(ACBST.MASTER=0), setting START gener-
ates a Start Condition as soon as the
ACCESS.bus is free (ACBCST.BB=0). An ad-
dress send sequence should then be per-
formed.
If this device is the active master of the bus
(ACBST.MASTER=1), when START is set, a
write to the ACBSDA register generates a Start
Condition, then the ACBSDA data is transmit-
ted as the slave’s address and the requested
transfer direction.
This case is a repeated Start Condition. It may
be used to switch the direction of the data flow
between the master and the slave, or to choose
another slave device without using a Stop Con-
dition in between.
STOP STOP. In master mode, setting this bit gener-
ates a Stop Condition that completes or aborts
the current message transfer. This bit clears it-
self after the STOP is issued.
INTEN Interrupt Enable. When INTEN is cleared ACB
interrupt is disabled. When INTEN is set, inter-
rupts are enabled. An interrupt is generated
(the interrupt signals to the ICU is high) upon
one of the following events:
•An address MATCH is detected (ACB-
ST.NMATCH=1) and NMINTE is set.
•A Bus Error occurs (ACBST.BERR=1).
•Negative acknowledge after sending a byte
(ACBST.NEGACK=1).
•An interrupt is generated upon acknowl-
edge of each transaction (same as the
hardware set of the ACBST.SDAST bit).
•In master mode if ACBCTL1.STASTRE=1,
after a successful start (ACBST.STAS-
TR=1).
•Detection of a Stop Condition while in slave
receive mode (ACBST.SLVSTP=1).
ACK Acknowledge bit. When acting as a receiver
(slave or master), this bit holds the value this
device sends during the next acknowledge cy-
cle. Setting this bit to 1 instructs the transmit-
ting device to stop sending data, since the
receiver either does not need, or cannot re-
ceive, any more data. This bit is cleared after
the first acknowledge cycle.
This bit is ignored when in transmit mode.
GCMEN Global Call Match enable. When this bit is set,
it enables the match of an incoming address
byte to the general call address (Start Condi-
tion followed by address byte of 0016
) while the
ACB is in slave mode. When cleared, the ACB
does not respond to a global call.
NMINTE New Match Interrupt Enable. Set NMINTE to
enable the interrupt on a new match (i.e., when
ACBST.NMATCH is set). The interrupt is is-
sued only if ACBCTL1.INTEN is set.
STASTRE Stall After Start Enable. When set enables the
stall after start mechanism. In such a case, the
ACB is stalled after the address byte. When
STASTRE is cleared, ACBST.STASTR is al-
ways cleared.
19.3.5 ACB Control 2 Register (ACBCTL2)
The ACB Control 2 register (ACBCTL2) is a byte-wide, read/
write register that enables/disables the module and deter-
mines ACB clock rate. Upon reset ACBCTL2 is set to 0016.
ENABLE Enable. When this bit is set, the ACB module is
enabled. When the Enable bit is cleared, the
ACB module is disabled, ACBCTL1, ACBST
and ACBCST are cleared, and the clocks are
halted.
SCLFRQ SCL Frequency. This field defines the SCL’s
period (low time and high time) when this de-
7 6 5 43 2 1 0
STAS-
TRE NMINTE GCMEN ACK Reserved INTEN STOP START
7 1 0
SCLFRQ ENABLE
Obsolete
www.national.com 84
vice serves as a bus master. The clock low time
and high time are defined as follows:
tSCLl = tSCLh = 2*SCLFRQ*tCLK
Where tCLK is this device’s clock cycle when in
Active mode.
SCLFRQ may be programmed to values in the
range of 00010002 (810) through 11111112
(12710). Using any other value has unpredict-
able results.
19.3.6 ACB Own Address Register (ACBADDR)
ACB Own Address Register (ACBADDR) is a byte-wide,
read/write register that holds the module’s ACCESS.bus ad-
dress. Reset value is undefined.
ADDR Own Address. Holds the 7-bit ACCESS.bus
address of this device. When in slave mode,
the first seven bits received after a Start Condi-
tion are compared to this field (first bit received
to bit-6, and the last to bit-0). If the address field
matches the received data and SAEN is set, a
match is declared.
SAEN Slave Address Enable. When set SAEN indi-
cates that the ADDR field holds a valid address
and enables the match of ADDR to an incom-
ing address byte. When cleared, the ACB does
not check for an address match.
19.4 USAGE HINTS
1. When the ACB is disabled the ACBCST.BB bit is
cleared. After enabling the ACB (ACBCTL2.ENABLE is
set to 1) in systems with more then one master, the bus
may be in the middle of a transaction with another de-
vice, which is not reflected by BB.
There is a need to allow the ACB to synchronize to the
bus activity status before issuing a request to become
the bus master, to prevent bus errors. Thus, before issu-
ing a request to become the bus master for the first time,
the software should check that there is no activity on the
bus by checking the BB bit after the bus allowed time-out
period.
2. When waking up from power down, before checking
ACBCST.MATCH, use ACBCST.BUSY to make sure
that the address transaction is over.
3. The BB bit is intended to solve a deadlock in which two,
or more, devices detect a usage conflict on the bus and
both devices cease being bus masters at the same time.
In this situation, the BB bits of both devices are active
(because each deduces that there is another master
currently performing a transaction, while in fact no de-
vice is executing a transaction), and the bus would stay
locked until some device sends a ACBCTL1.STOP con-
dition.
The ACBCST.BB bit allows the software to monitor bus
usage, so it can avoid sending a STOP signal in the mid-
dle of the transaction of some other device on the bus.
This bit detects whether the bus remains unused over a
certain period, while the BB bit is set.
4. In some cases the bus may get stuck with the SCL and/
or SDA lines active. A possible cause to this is an erro-
neous Start or Stop Conditions that occur in the middle
of a slave receive session.
When the SCL line is stuck active, there is nothing that
can be done, and it is the responsibility of the module
that holds the bus to release it.
In case of SDA line is stuck active, the ACB module en-
able the release of the bus by using the following se-
quence. Note that in normal cases SCL may be toggled
only by the bus master. This protocol is a recovery
scheme which is an exception that should be used only
in the case where there is no other master on the bus.
The recovery scheme is as follows:
a. Disable and re-enable the module to set it into the
not addressed slave mode.
b Set the ACBCTL1.START bit to make an attempt to
issue a Start Condition.
c. Check if the SDA line is active (low) by reading
ACBCST.TSDA bit. If it is active, issue a single SCL
cycle by writing 1 to ACBCST.TGSCL bit. If the SDA
line is not active, continue from step ‘e’.
d. Check if ACBST.MASTER is set, which indicates
that the Start Condition was sent. If not, repeat step
c and d until the SDA is released.
e. Clear the BB bit. This enables the START bit to be
executed. Continue according to “Bus Idle Error Re-
covery” on page 81.
7 6 0
SAEN ADDR
Obsolete
85 www.national.com
20.0 CR16CAN Module
The CR16CAN device contains a FULL-CAN class, CAN
(Controller Area Network) serial bus interface for low/high
speed applications. It supports the reception and transmis-
sion of extended frames with 29-bit identifier, standard
frames with 11-bit identifier, applications that require a high
speed (up to 1MBit/s), and a low speed CAN interface with
CAN master capability. The data transfer between CAN and
the CPU is established by 15 message buffers, which can be
individually configured as receive or transmit buffers. Every
message buffer includes a status/control register which pro-
vides information about its current status and capabilities to
configure the buffer. All message buffers are able to generate
an interrupt upon the reception of a valid frame or the suc-
cessful transmission of a frame. In addition, an interrupt on
bus errors can be generated.
An incoming message is only accepted if the message iden-
tifier passes one of two acceptance filtering masks. The filter-
ing mask can be configured to receive a single message ID
per buffer or a group of IDs per receive buffer. One of the
buffers uses a separate message filtering procedure. This
provides the capability to establish a BASIC-CAN path. Re-
mote transmission requests can be processed automatically
by automatic reconfiguration to a receiver after transmission
or by automated transmit scheduling upon reception. A prior-
ity decoder allows any buffer to have one of 16 transmit pri-
orities including the highest or lowest absolute priority,
totaling 240 different transmit priorities.
A decided bit time counter (16-bit wide) is provided to support
real time applications. The contents of this counter is cap-
tured into the message buffer RAM upon reception or trans-
mission. The counter can be synchronized via the CAN
network. This synchronization feature allows a reset of the
counter after the reception or transmission of a message in
buffer 0.
The CR16CAN is a fast core bus peripheral which allows sin-
gle cycle byte or word read/write access. The CPU controls
the CR16CAN by modifying the various registers in the
CR16CAN register block. This includes the initialization of
the CAN baud rate, the CAN pin logic level, and the enable/
disable of the CR16CAN. A set of diagnostic features, such
as loopback, listen only and error identification, support the
development with the CR16CAN module and provide a so-
phisticated error management tool.
The CR16CAN implements the following features:
•CAN specification 2.0B
—standard data and remote frames
—extended data and remote frames
—0 - 8 bytes data length
—programmable bit rate up to 1 Mbit/s
•15 message buffers, each configurable as receive or
transmit buffers
—message buffers are 16-bit wide dual-port RAM
—one buffer may be used as BASIC-CAN path
•Remote Frame support
—automatic transmission after reception of a Remote
Transmission Request (RTR)
—auto receive after transmission of a RTR
•Acceptance filtering
—two filtering capabilities: global acceptance mask & in-
dividual buffer identifiers
—one of the buffers uses an independent acceptance fil-
tering procedure
•Programmable transmit priority
•Interrupt capability
—one interrupt vector for all message buffers (receive/
transmit/error)
—each interrupt source can be enabled/disabled
•16-bit counter with time stamp capability on successful re-
ception or transmission of a message
•Power Save capabilities with programmable Wake-Up
over the CAN bus (alternate source for the Multi-Input
Wake-Up module)
•Push-Pull capability of the input/output pins
•Diagnostic functions
—error identification
—loopback and listen-only features for test and initializa-
tion purposes
20.1 FUNCTIONAL DESCRIPTION
As shown in Figure44, the CR16CAN module is separated
into three blocks: the CAN core, the interface management
and a dual ported RAM containing the message buffers.
There are two dedicated device pins for the CR16CAN inter-
face, CANTX as the transmit output and CANRX as the re-
ceive input.
The CAN Core implements the basic CAN protocol features
such as bit-stuffing, CRC calculation/checking and error
management. It controls the transceiver logic and creates er-
ror signals according to the bus rules. In addition, it converts
the data stream from the CPU (parallel data) to the serial
CAN bus data.
The Interface Management is divided into the register block
and the interface management processor. The register block
provides the CAN Interface with control information from the
CPU and in turn provides the CPU with status information
from the CAN module. Additionally it generates the interrupt
to the CPU.
The interface management processor is a state machine ex-
ecuting the CPU’s transmission and reception commands
and controlling the data transfer between several message
buffers and RX/TX shift registers.
Fifteen Message Buffers are memory mapped into RAM to
transmit/receive data via the CAN bus. Eight 16-bit registers
belong to each buffer. One of the registers contains control
and status information about the message buffer configura-
tion and the current state of the buffer. The other registers are
used for the message identifier, a maximum of up to eight
data bytes and the time stamp information. During the re-
ceive process the incoming message will be stored at first in
a hidden receive buffer until the message is valid. Then the
buffer contents will be copied into the first message buffer
which accepts the ID of the received message.
Obsolete
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INTERFACE MANAGEMENT
CANTX
Transceiver Logic
Bit Stream Processor Error Management Logic
TX/RX
CONTROL
CAN CORE
STATUS REGISTER
ACCEPTANCE
MASKS
Message Buffer 0
BTL, RX shift, TX shift, CRC
Figure 44.Block Diagram CR16CAN Interface
TX/RX
Message Buffer 1
Message Buffer 14
TX/RX
Acceptance Filtering
Interface Management
Processor
RAM
data
control status
control
CAN PRESCALER
BTL CONFIG
core bus
CANRX
0 1
2:1
0 1
2:1
CTX
CRX
wakeup
data
Obsolete
87 www.national.com
20.2 BASIC CAN CONCEPTS
This section provides a generic overview of the basic con-
cepts of the Controller Area Network (CAN).
The CAN protocol is a message based protocol that allows a
total of 2032 ( = 211-16) different messages in the standard
format and 512 million ( = 229-16) different messages in the
extended frame format.
Every CAN Frame is broadcasted on the common bus. Each
module receives every frame and filters out the frames which
are not required for the module's task. For example, if a
dashboard sends a request to switch on headlights, the CAN
module responsible for brake lights must not process this
message.
A CAN master module has the ability to set a specific bit
called the “remote data request bit” (RTR) in a frame. Such a
message is also called “Remote Frame”. It causes another
module, either another master or a slave which accepts this
remote frame, to transmit a data frame after the remote
frame has been completed.
Additional modules can be added to an existing network with-
out a configuration change. These modules can either per-
form completely new functions requiring new data, or
process existing data to perform a new functionality.
As the CAN network is message oriented, a message can be
used as a variable which is automatically updated by the con-
trolling processor. If any module cannot process information,
it can send an overload frame.
The CAN protocol allows several transmitting modules to
start a transmission at the same time as soon as they monitor
the bus to be idle. During the start of transmission, every
node monitors the bus line to detect whether its message is
overwritten by a message with a higher priority. As soon as a
transmitting module detects another module with a higher
priority accessing the bus, it stops transmitting its own frame
and switches to receive mode. For illustration, see Figure45.
If a data or remote frame loses arbitration on the bus due to
a higher-prioritized data or remote frame, or if it is destroyed
by an error frame, the transmitting module will automatically
retransmit it until the transmission was successful or the user
has canceled the transmit request.
If a transmitted message loses arbitration, the CR16CAN will
restart transmission at the next possible time with the mes-
sage which has the highest internal transmit priority.
20.2.1 CAN Frame Formats
Communication via the CAN bus is basically established by
means of four different frame types:
—data frame
—remote frame
—error frame
—overload frame
Data and remote frames can be used in both standard and
extended frame format. If no message is being transmitted,
i.e., the bus is idle, the bus is kept at the ‘recessive’ level.
Remote and data frames are non-return to zero (NRZ) coded
with bit-stuffing in every bit field, which holds computable in-
formation for the interface, i.e., start of frame, arbitration field,
control field, data field (if present) and CRC field.
Error and overload frames are also NRZ coded but without
bit-stuffing.
After five consecutive bits of the same value (including insert-
ed stuff bits so that the stuffed bit stream will not have more
than five consecutive bits of the same value), a stuff bit of the
inverted value is inserted into the bit stream by the transmit-
ter and deleted by the receiver. The following shows the
stuffed and destuffed bit stream for consecutive ones and ze-
ros.
MODULE A
TxPIN
RxPIN
MODULE B
BUS LINE RECESSIVE
DOMINANT
MODULE A SUSPENDS TRANSMISSION
RxPIN
TxPIN
Figure 45.CAN message arbitration
Obsolete
www.national.com 88
Frame Fields
Data and remote frames consist of the following different bit
fields:
—Start of Frame
—Arbitration Field
—Control Field
—Data Field
—CRC Field
—ACK Field
—EOF Field
The Start of Frame indicates the beginning of data and re-
mote frames. It consists of a single 'dominant' bit. A node is
only allowed to start transmission when the bus is idle. All
nodes have to synchronize to the leading edge (first edge af-
ter the bus was idle) caused by SOF of the node which starts
transmission first.
The Arbitration field consists of the identifier field and the
RTR (Remote Transmission Request) bit. For extended
frames there is also a SRR (Substitute Remote Request) and
a IDE (ID Extension) bit inserted between ID18 and ID17 of
the identifier field. The value of the RTR bit is 'dominant' in a
data frame and 'recessive' in a remote frame.
The Control field consists of six bits. For standard frames it
starts with the ID Extension bit (IDE) and a reserved bit
(RB0). For extended frames the control field starts with two
reserved bits (RB1, RB0). These bits are followed by the 4-
bit Data Length Code (DLC).
The CR16CAN receiver accepts all possible combinations of
the reserved bits (RB1, RB0). The transmitter must be con-
figured to send only '0' bits.
The DLC indicates the number of bytes in the data field. It
consists of four bits. The data field can be of length zero. The
admissible number of data bytes for a data frame ranges
from 0 to 8.
The Data field consists of the data to be transferred within a
data frame. It can contain 0 to 8 bytes. A remote frame has
no data field.
The CRC field consists of the CRC sequence followed by the
CRC delimiter. The CRC sequence is derived by the trans-
mitter from the modulo 2 division of the preceding bit fields,
starting with the SOF up to the end of the data field, excluding
stuff-bits, by the generator polynomial:
The remainder of this division is the CRC sequence transmit-
ted over the bus. On the receiver side, the module divides all
bit fields up to the CRC delimiter excluding stuff-bits, and
checks if the result is zero. This will then be interpreted as a
valid CRC. After the CRC sequence a single ‘recessive’ bit is
transmitted as the CRC delimiter.
The ACK field is two bits long and contains the ACK slot and
the ACK delimiter. The ACK slot is filled with a ‘recessive’ bit
by the transmitter. This bit is overwritten with a ‘dominant’ bit
by every receiver that has received a correct CRC sequence.
The second bit of the ACK field is a ‘recessive’ bit called the
acknowledge delimiter.
The End of Frame field closes a data and a remote frame.
It consists of seven ‘recessive’ bits.
Data Frame
The structure of a standard and extended data frame is
shown in Figure46.
A CAN data frame consists of the following fields as previ-
ously described:
—Start of Frame (SOF)
—Arbitration field + Extended Arbitration
—Control field
—Data field
—Cyclic Redundancy Check field (CRC)
—Acknowledgment field (ACK)
—End of Frame (EOF)
Remote Frame
Figure47 shows the structure of a standard and extended re-
mote frame.
A remote frame is comprised of the following fields sections,
which is the same as a data frame (see Frame Fields on
page 88) except for the data field, which is not present.
—Start of Frame (SOF)
—Arbitration field + Extended Arbitration
—Control field
—Cyclic Redundancy Check field (CRC)
—Acknowledgment field (ACK)
—End of Frame (EOF)
Note that the DLC must have the same value as the corre-
sponding data frame to prevent contention on the bus. The
RTR bit is ‘recessive’.
original or destuffed bit
stream 10000011111x a
a. x = {0,1}
01111100000x
stuffed bit stream 1000001111101x 0111110000010x
x15
+ x14 + x10 + x8 + x7 + x4 + x3 + 1
Obsolete
89 www.national.com
dr r r r r r r r
STANDARD DATA FRAME (number of bits = 44 + 8N)
START OF FRAME
ID 10
ID0
RTR
IDE
RB0
DLC3
DLC0
DATA FIELD CRC FIELD
CRC
ACKNOWLEDGEMENT
ACK DEL
END OF
IDENTIFIER DATA
11 4 8
16
158 FRAME
8N ( 0 ≤ N ≤ 8)
LENGTH
CODE
d
START OF FRAME
ID28
ID18
SRR
IDENTIFIER
11
IDE
18
RTR
RB1
rrr r r r r
RB0
DLC3
DLC0
DATA FIELD CRC FIELD
CRC
CRC DEL
ACK
ACK DEL
END OF
DATA
4 8 15
8FRAME
8N ( 0 ≤ N ≤ 8)
LENGTH
CODE
28 ... 18 IDENTIFIER
17 ... 0
ID17
ID0
EXTENDED DATA FRAME (number of bits = 64 + 8N)
CRC DEL
10 ... 0
Arbitration Field Control Field
Control Field
Arbitration Field
Bit Stuffing
Bit Stuffing
ddd
d
d
d
rr
Note:
d = dominant
r = recessive
r
r
16
r
r
Figure 46.CAN Data Frame (standard and extended)
Obsolete
www.national.com 90
drdr r r r r r rd
STANDARD REMOTE FRAME (number of bits = 44)
START OF FRAME
ID 10
ID0
RTR
IDE
RB0
DLC3
DLC0
CRC FIELD
CRC
ACKNOWLEDGEMENT
ACK DEL
END OF
IDENTIFIER DATA
11 4
16
15 FRAME
LENGTH
CODE
ID3
d
START OF FRAME
ID28
ID18
SRR
IDENTIFIER
11
IDE
18
RTR
RB1
rdr r r r r r r
RB0
DLC3
DLC0
CRC FIELD
CRC
CRC DEL
ACK
ACK DEL
END OF
DATA
4
16
15 FRAME
LENGTH
CODE
28 ... 18 IDENTIFIER
17 ... 0
ID17
ID0
EXTENDED REMOTE FRAME (number of bits = 64)
CRC DEL
10 ... 0
Control FieldArbitration Field
Control Field
Arbitration Field
Note:
d = dominant
r = recessive
d
r
rr
rr
r
Figure 47.CAN Remote Frame (standard and extended)
Obsolete
91 www.national.com
Error Frame
As shown in Figure48, the Error Frame consists of the error
flag and the error delimiter bit fields. The error flag field is
built up from the various error flags of the different nodes.
Therefore, its length may vary from a minimum of six bits up
to a maximum of twelve bits depending on when a module
has detected the error. Whenever a bit error, stuff error, form
error, or acknowledgment error is detected by a node, this
node starts transmission of an error flag at the next bit. If a
CRC error is detected, transmission of the error flag starts at
the bit following the acknowledge delimiter, unless an error
flag for a previous error condition has already been started.
If a device is in the error active state, it can send a ‘dominant’
error flag, whereas a error passive device is only allowed to
transmit ‘recessive’ error flags. This is done to prevent the
CAN bus from getting stuck due to a local defect. For the var-
ious CAN device states, please refer to Error Detection and
Management on page 92.
Overload Frame
As shown in Figure49, an overload frame consists of the
overload flag and the overload delimiter bit fields. The bit
fields have the same length as the error frame field: six bits
for the overload flag and eight bits for the delimiter. The over-
load frame can only be sent after the end of frame (EOF) field
and in this way destroys the fixed form of the intermission
field. As a result, all other nodes also detect an overload con-
dition and start the transmission of an overload flag. After an
overload flag has been transmitted, the overload frame is
closed by the overload delimiter.
Note: The CR16CAN never initiates an overload frame due
to its inability to process an incoming message. However, it
is able to recognize and respond to overload frames initiated
by other devices.
d d d dd d dd
6 8
≤ 6
rrrrdr r r dr
ERROR
FLAG ECHO
ERROR FLAG ERROR
DELIMITER
DATA FRAME OR
REMOTE FRAME INTER-FRAME SPACE OR
OVERLOAD FRAME
An error frame can start anywhere within a frame.
ERROR FRAME
Note:
d = dominant
r = recessive
Figure 48.CAN Error Frame
rrdrrrrdr rd d d dd
86
OVERLOAD
FLAG OVERLOAD
DELIMITER
OVERLOAD FRAME
INTER-FRAME SPACE OR
ERROR FRAME
END OF FRAME OR
ERROR DELIMITER OR
OVERLOAD DELIMITER
An overload frame can only start at the end of a frame. Note:
d = dominant
r = recessive
Figure 49.CAN Overload Frame
Obsolete
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Interframe Space
Data and remote frames are separated from every preceding
frame (data, remote, error and overload frames) by the inter-
frame space (see Figure50). Error and overload frames are
not preceded by an interframe space; they can be transmit-
ted as soon as the condition occurs. The interframe space
consists of a minimum of three bit fields depending on the er-
ror state of the node.
20.2.2 Error Detection and Management
There are multiple mechanisms in the CAN protocol to detect
errors and inhibit erroneous modules from disabling all bus
activities. Each CAN module includes two error counters, a
receive and a transmit error counter, for error management.
Error Types
The following errors can be detected:
—Bit Error
A CAN device which is currently transmitting also mon-
itors the bus. If the monitored bit value is different from
the transmitted bit value, a bit error is detected. How-
ever, the reception of a ‘dominant’ bit instead of a ‘re-
cessive’ bit during the transmission of a passive error
flag, during the stuffed bit stream of the arbitration field
or during the acknowledge slot is not interpreted as a
bit error.
—Stuff Error
A stuff error is detected if the bit level after 6 consecu-
tive bit times has not changed in a message field that
has to be coded according to the bit stuffing method.
—Form Error
A form error is detected, if a fixed frame bit (e.g., CRC
delimiter, ACK delimiter) does not have the specified
value. For a receiver, a ‘dominant’ bit during the last bit
of End of Frame does not constitute a frame error.
—Bit CRC Error
A CRC error is detected if the remainder of the CRC
calculation of a received CRC polynomial is non-zero.
—Acknowledgment Error
An acknowledgment error is detected whenever a
transmitting node does not get an acknowledgment
from any other node (i.e., when the transmitter does
not receive a ‘dominant’ bit during the ACK frame)
r r r rr rr r
3 8
r r r rr r r r dr
INT SUSPEND
TRANSMIT BUS IDLE DATA FRAME OR
REMOTE FRAME
INT = Intermission
INTERFRAME SPACE
rr r r rr
START OF FRAME
ANY FRAME
Suspend Transmission is only for error passive nodes. Note:
d = dominant
r = recessive
Figure 50.CAN Interframe Space
ERROR
(TEC AND REC) < 128
BUS
TEC > 255
128 occurrences of
Figure 51.CR16CAN Bus States
11 consecutive ‘recessive’ bits
ACTIVE PASSIVE
OFF
(TEC OR REC) > 127
ERROR ERROR
WARNING
(TEC OR REC) > 95
(TEC AND REC) < 96
SYNC
11 consecutive ‘recessive’ bits
received
external RESET or
enable CR16CAN
Obsolete
93 www.national.com
—Synchronize
Once the CR16CAN is enabled, it goes into a synchro-
nization state to synchronize with the bus by waiting for
11 consecutive recessive bits. After that the CR16CAN
becomes error active and can participate in the bus
communication. This state must also be entered after
waking-up the device via the Multi-Input Wake-Up fea-
ture. See System Start-Up and Multi-Input Wake-Up
on page 116.
—Error active
An error active unit can participate in bus communica-
tion and may send an active (‘dominant’) error flag.
—Error Warning
The Error Warning state is a sub-state of Error Active
to indicate a heavily disturbed bus. The CR16CAN be-
haves as in Error Active mode. The device is reset into
the Error Active mode if the value of both counters is
less than 96.
—Error passive
An error passive unit can participate in bus communi-
cation. However, if the unit detects an error it is not al-
lowed to send an active error flag. The unit sends only
a passive (‘recessive’) error flag. A device is error pas-
sive when the transmit error counter or the receive er-
ror counter is greater than 127. A device becoming
error passive will send an active error flag. An error
passive device becomes error active again when both
transmit and receive error counter are less than 128.
—Bus off
A unit that is bus off has the output drivers disabled,
i.e., it does not participate in any bus activity. A device
is bus off when the transmit error counter is greater
than 255. A bus off device will become error active
again after monitoring 128*11 ‘recessive’ bits (includ-
ing bus idle) on the bus. When the device goes from
‘bus off’ to ‘error active’, both error counters will have
the value ‘0’.
Error Counters
The CR16CAN module contains two error counters to per-
form the error management. The receive error counter (REC)
and the transmit error counter (TEC) are 8-bits wide, located
in the 16-bit wide CANEC register. The counters are modified
by the CR16CAN according to the rules listed in Table20 “Er-
ror Counter Handling”.
The Error counters can be read by the users software as de-
scribed under CAN Error Counter Register (CANEC) on
page 115.
Special error handling for the TEC counter is performed in
the following situations:
—A stuff error occurs during arbitration, when a transmit-
ted ‘recessive’ stuff bit is received as a ‘dominant’ bit.
This does not lead to an increment of the TEC.
—An ACK-error occurs in an error passive device and no
‘dominant’ bits are detected while sending the passive
error flag. This does not lead to an increment of the
TEC.
Table 20Error Counter Handling
ConditionaAction
Receive Error Counter Conditions b
A receiver detects a Bit Error during sending an active error flag. increment by 8
A receiver detects a ‘dominant’ bit as the first bit after sending an error flag increment by 8
After detecting the 14th consecutive ‘dominant’ bit following an active error flag or overload
flag, or after detecting the 8th consecutive ‘dominant’ bit following a passive error flag.
After each sequence of additional 8 consecutive ‘dominant’ bits.
increment by 8
Any other error condition (stuff, frame, CRC, ACK) increment by 1
A valid reception or transmission decrement by 1 unless
counter is already 0
Transmit Error Counter Conditions
A transmitter detects a Bit Error during sending an active error flag increment by 8
After detecting the 14th consecutive ‘dominant’ bit following an active error flag or overload flag
or after detecting the 8th consecutive ‘dominant’ bit following a passive error flag.
After each sequence of additional 8 consecutive ‘dominant’ bits.
increment by 8
Any other error condition (stuff, frame, CRC, ACK) increment by 8
A valid reception or transmission decrement by 1 unless
counter is already 0
a. This table provides an overview of the CAN error conditions and the behavior of the CR16CAN; for a detailed
description of the error management and fault confinement rules, please refer to the CAN Specification 2.0B
b. If the MSB (bit 7) of the REC is set, the node is error passive and the REC will not increment any further.
Obsolete
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—If only one device is on the bus and this device trans-
mits a message, it will get no acknowledgment. This
will be detected as an error and the message will be re-
peated. When the device goes ‘error passive’ and de-
tects an acknowledge error, the TEC counter is not
incremented. Therefore the device will not go from ‘er-
ror passive’ to the ‘bus off’ state due to such a condi-
tion.
20.2.3 Bit Time Logic
In the Bit Time Logic (BTL), the CAN bus speed and the Syn-
chronization Jump Width can be configured by the user.
CR16CAN divides a nominal bit time into three time seg-
ments: synchronization segment, time segment 1 (TSEG1)
and time segment 2 (TSEG2). Figure52 shows the various
elements of a CAN bit time.
CAN Bit Time
The number of time quanta in a CAN bit (CAN Bit Time) lies
between 4 and 25. The sample point is positioned between
TSEG1 and TSEG2 and the transmission point is positioned
at the end of TSEG2.
The time segment 1 includes the propagation segment and
the phase segment 1 as specified in the CAN specification
2.0.B. The length of the time segment 1 in time quantas (tq)
is defined by the TSEG1[3:0] bits.
The time segment 2 represents the phase segment 2 as
specified in the CAN specification 2.0.B. The length of the
time segment 2 in time quantas (tq) is defined by the
TSEG2[2:0] bits.
The Synchronization Jump Width (SJW) defines the max-
imum number of time quanta (tq) by which a received CAN
bit can be shortened or lengthened in order to achieve re-
synchronization on ‘recessive’ to ‘dominant’ data transitions
on the bus. In the CR16CAN implementation the SJW has to
be configured less or equal to TSEG1 or TSEG2, whatever is
smaller.
Synchronization
A CAN device expects the transition of the data signal to be
within the synchronization segment of each CAN bit time.
This segment has the fixed length of one time quantum.
However, two CAN nodes never operate at exactly the same
clock rate and furthermore the bus signal may deviate from
the ideal waveform due to the physical conditions of the net-
work (bus length and load). In order to compensate for the
various delays within a network, the sample point can be po-
sitioned by programming the length of time segments 1 and
2 (see Figure52).
In addition to that, two types of synchronization are support-
ed. The BTL logic compares the incoming edge of a CAN bit
with the internal bit timing. The internal bit timing can be
adapted by either hard or soft synchronization (re-synchroni-
zation).
Hard synchronization is done at the beginning of a new
frame with the falling edge on the bus while the bus is idle.
This is interpreted as the SOF. It restarts the internal logic.
Soft synchronization is used during the reception of a bit
stream to lengthen or shorten the internal bit time. Depending
on the phase error (e), the time segment 1 may be increased
or the time segment 2 may be decreased by a specific value,
the re-synchronization jump width (SJW).
The phase error is given by the deviation of the edge to the
SYNC segment, measured in CAN clocks. The value of the
phase error is defined as:
e = 0, if the edge occurs within the SYNC segment.
e > 0, if the edge occurs within TSEG1
e < 0, if the edge occurs within TSEG2 of the previous bit.
Re-synchronization is performed according to the following
rules:
•If the magnitude of e is less or equal to the programmed
value of SJW, re-synchronization will have the same effect
as hard synchronization.
•If e > SJW, the time segment 1 will be lengthened by the
value of the SJW (see Figure53).
•If e < -SJW, the time segment 2 will be shortened by the
value SJW (see Figure 54).
ONE TIME QUANTUM
INTERNAL
TIME QUANTA
ATIME SEGMENT 1 (TSEG1) TIME SEGMENT 2 (TSEG2)
1 tq 2 to 16 tq 1 to 8 tq
SAMPLE
A = synchronization segment (Sync)
Figure 52.Bit Timing
4 to 25 tq
CLOCK
TRANSMISSION
POINT
POINT
Obsolete
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20.2.4 Clock Generator
The CAN prescaler (PSC) is shown is Figure55. It divides
the CKI input clock by the value defined in the CTIM register.
The resulting clock is called time quanta clock and defines
the length of one time quanta (tq).
Please refer to CAN Timing Register (CTIM) on page 112 for
a detailed description of the CTIM register.
Note: PSC is the value of the clock prescaler. TSEG1 and
TSEG2 are the length of time segment 1 and 2 in tq.
The resulting bus clock can be calculated by the equation:
The values of PSC and TSEG 1 and 2 are specified by the
contents of the registers PSC, TSEG1 and TSEG2 as fol-
lows:
PSC = PSC[5:0] + 2
TSEG1 = TSEG1[3:0] + 1
TSEG2 = TSEG2 [2 : 0] + 1
20.3 MESSAGE TRANSFER
The CR16CAN has access to 15 independent message buff-
ers, memory mapped in RAM. Each message buffer consists
of 8 different 16-bit RAM locations and can be individually
configured as a receive message buffer or as a transmit mes-
sage buffer.
BUS SIGNAL
CAN
PREVIOUS ATSEG1 TSEG2 NEXT BIT
CLOCK
BIT
PREVIOUS ATSEG1 TSEG2 NEXT BIT
BIT SJW
“NORMAL” BIT TIME
BIT TIME LENGTHENED BY SJW
e
Figure 53.Re-synchronization (e > SJW)
BUS SIGNAL
CAN
PREVIOUS ATSEG1 TSEG2
CLOCK
BIT “NOMINAL” BIT TIME
PREVIOUS ATSEG1 TSEG2 NEXT BIT
BIT BIT TIME SHORTENED BY SJW
Figure 54.Re-synchronization (e < -SJW)
e
busclock CKI
PSC()x1TSEG1TSEG2++
()
-------------------------------------------------------------------------------------=
Figure 55.Bit Rate Generation
PSC
:-
internal time
bit rate
CKI (1+TSEG1+TSEG2)
:-
quanta clock (1/tq)
Obsolete
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A dedicated acceptance filtering procedure enables the user
to configure each buffer to receive only a single message ID
or a group of messages. One buffer uses an independent fil-
tering procedure, which provides the possibility to establish a
BASIC-CAN path.
For reception of data frame or remote frames, the CR16CAN
follows a “receive on first match” rule which means that a giv-
en message is only received by one buffer — the first one
which matches to the received message ID.
The transmission of a frame can be initiated by the user soft-
ware writing to the transmit status and priority register. An al-
ternate way to schedule a transmission is the automatic
answer to remote frames. In the latter case, the CR16CAN
will schedule every buffer for transmission to respond to re-
mote frames with a given identifier if the acceptance mask
matches. This implies that a single remote frame is able to
poll multiple matching buffers configured to respond to the
triggering remote transmission request.
20.4 ACCEPTANCE FILTERING
Two 32-bit masks are used to filter unwanted messages from
the CAN bus GMASK and BMASK. Figure56 shows the
mask and the buffers controlled by the masks.
The acceptance filtering of the incoming messages for the
buffers 0...13 is done by means of a global filtering mask
(GMASK) and by the buffer ID of each buffer.
The acceptance filtering of incoming messages for buffer 14
is done via a separate filtering mask (BMASK) and by the
buffer ID of each that buffer.
Once a received message is waiting in the hidden buffer (see
Receive Buffer Structure on page 98) to be copied into a buff-
er, CR16CAN scans all buffer configured as receive buffers
for a matching filtering mask. The buffers 0 to 13 are checked
in ascending order beginning with buffer 0. The contents of
the hidden buffer are copied into the first buffer with matching
filtering mask.
Bits holding a “1” in the global filtering mask (GMASK) can be
represented as a “don’t care” of the associated bit of each
buffer identifier, regardless of whether the buffer identifier bit
is “1” or “0”.
This provides the capability to accept only a single ID per
buffer or to accept a group of IDs. The following two exam-
ples illustrate the difference.
Example 1: Acceptance of a Single Identifier
If the global mask is set to 0016 the acceptance filtering of an
incoming message is only determined by the individual buffer
ID. This means that only one message ID is accepted per
buffer.
Example 2: Reception of an Identifier Group
Bits in the global mask register set to ‘1’ change the corre-
sponding bit status within the buffer ID to “don’t care” (“X”).
Therefore all messages which match the non-“don’t care”
bits are accepted.
A separate filtering path is used for buffer 14. For this buffer
the acceptance filtering is established by the buffer ID in con-
junction with the basic filtering mask. This basic mask uses
the same method as the global mask. Setting a bit to “1”
changes the associated bit in the buffer ID to a “don’t care”
bit.
Therefore the basic mask allows a large number of infrequent
messages to be received by this buffer.
Buffer 0
Buffer13
Buffer14
GMASK1
GMASK2
BMASK1
BMASK2
BUFFER_ID
BUFFER_ID
BUFFER_ID
Figure 56.Acceptance Filtering Structure
GMASK1 GMASK2
BUFFER_ID1 BUFFER_ID2
00000000 00000000 00000000 00000
10101010 10101010 10101010 10101
10101010 10101010 10101010 10101
Accepted ID
Figure 57.Acceptance of a Single Identifier
GMASK1 GMASK2
BUFFER_ID1 BUFFER_ID2
00000000 00000000 00000
10101010 10101010 10101010
10101010 XXXXXXXX 10101010
Accepted ID group
10101
10101
Figure 58.Acceptance of a Group of Identifiers
11111111
Obsolete
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Note: If the BMASK register is equal to the GMASK register,
the buffer 14 can be used the same way as the buffers 0 to
13.
The buffers 0 to 13 are scanned prior to buffer 14. Subse-
quently, the buffer 14 will not be checked for a matching ID
when one of the buffers 0 to 13 has already received a mes-
sage.
By setting the BUFFLOCK bit in the configuration register,
the receiving buffer is automatically locked after a reception
of one valid frame. The buffer will be unlocked again after the
CPU has read the data and has written RX_READY in the
buffer status field. With this lock function, the user has the ca-
pability to save several messages with the same identifier or
same identifier group into more than one buffer. For example,
a buffer with the second highest priority will receive a mes-
sage if the buffer with the highest priority has already re-
ceived a message and is now locked (provided that both
buffers use the same acceptance filtering mask).
As shown in Figure59, several messages with the same ID
are received while BUFFLOCK is enabled. The filtering mask
of the buffers 0, 1, 13 and 14 is set to accept this message.
The first incoming frame will be received by buffer 0. As buff-
er 0 is now locked the next frame will be received by buffer 1,
and so on. If all matching receive buffers are full and locked,
a further incoming message will not be received by any buff-
er.
20.5 RECEIVE STRUCTURE
All received frames will initially be buffered in a hidden re-
ceive buffer until the frame is valid. (The validation point for a
received message is the penultimate bit of EOF.) The re-
ceived identifier is then compared to every buffer ID together
with the respective mask and the status. As soon as the val-
idation point is reached, the whole contents of the hidden
buffer is copied into the matching message buffer as shown
in Figure60.
Note: The hidden receive buffer must not be accessed by
the CPU.
The following section gives an overview of the reception of
the different types of frames.
GMASK 00000 11111111 00000000 00000000
01010 XXXXXXXX 10101010 10101010
01010 10101010 10101010 10101010
BUFFER0_ID
BUFFER1_ID
BUFFER14_ID
BUFFER13_ID
BMASK 00000 11111111 00000000 00000000
saved when buffer
is empty
saved when buffer
is empty
saved when buffer
is empty
01010
01010
01010
10101010
10101010 10101010
10101010
1010101010101010
XXXXXXXX
XXXXXXXX
XXXXXXXX
saved when buffer
is empty
received ID
Figure 59.Message Storage with BUFFLOCK Enabled
Obsolete
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The received data frame will be stored in the first matching
receive buffer beginning with buffer 0. For example, if the
message is accepted by buffer 5, then at the time the mes-
sage will be copied, the RX request is cleared and CR16CAN
will not try to match the frame to any subsequent buffer.
All contents of the hidden receive buffer are always copied
into the respective receive buffer. This includes the received
message ID as well as the received Data Length Code
(DLC); therefore when some mask bits are set to don’t care,
the ID field will get the received message ID which could be
different from the previous ID. The DLC of the receiving buff-
er will be updated by the DLC of the received frame. Note
that the DLC of the received message is not compared with
the DLC already present in the CNSTAT register of the mes-
sage buffer. This implies that the DLC code of the CNSTAT
register indicates how may data bytes actually belong to the
latest received message.
The remote frames are handled by the CR16CAN interface
in two different ways. Firstly, remote frames can be received
like data frames by configuring the buffer to be RX_READY
and setting the ID bits including the RTR bit. In that case the
same procedure applies as described for Data Frames. Sec-
ondly, a remote frame can trigger one or more message buff-
er to transmit a data frame upon reception. This procedure is
described under To answer Remote Frames on page 100.
20.5.1 Receive Timing
As soon as CR16CAN receives a dominant bit on the CAN
bus, the receive process is started. The received ID and data
will be stored in the hidden receive buffer if the global or basic
acceptance filtering matches. After the reception of the data,
CR16CAN tries to match the buffer ID of buffer 0...14. The
data will be copied into the buffer after the reception of the 6th
EOF bit as a message is valid at this time. The copy process
of every frame, regardless of the length, takes at least 17 CKI
cycles (see also CPU Access to CR16CAN Registers/Mem-
ory on page 105). Figure61 illustrates the receive timing.
In order to indicate that a frame is waiting in the hidden buffer,
the BUSY bit ST[0] of the selected buffer is set during the
copy procedure. The BUSY bit will be cleared by CR16CAN
right after the data bytes are copied into the buffer. After the
copy process is finished, CR16CAN changes the status field
to RX_FULL. In turn the CPU should change the status field
to RX_READY when the data is processed. When a new
message has been received by the same buffer, before the
CPU changed the status to RX_READY, the CR16CAN will
change the status to RX_OVERRUN to indicate that at least
one frame has been overwritten by a new one. Table21 sum-
marizes the current status and the resulting update from the
CR16CAN.
During the assertion of the BUSY bit, all writes to the receiv-
ing buffer are disabled with the exception of the status field.
Buffer 0
Buffer 13
Buffer 14
BUFFER_ID
BUFFER_ID
BUFFER_ID
HIDDEN
BUFFER
CR16CAN
Figure 60.Receive Buffer Structure
RECEIVE
SOF
ARBITRATION FIELD DATA FIELD
(IF PRESENT) CRC ACK
FIELD EOF
1 BIT 12/29 BIT+ 6 BIT n * 8 BIT 16 BIT 2 BIT 7 BIT
FIELD IFS
3 BIT
+ CONTROL
BUS IDLE
copy to buffer
rx_start
Figure 61.Receive Timing
BUSY
Table 21 Writing to Buffer Status Code During
RX_BUSY
Current Status Resulting Status
RX_READY RX_FULL
RX_NOT_ACTIVE RX_NOT_ACTIVE
RX_FULL RX_OVERRUN
Obsolete
99 www.national.com
If the status is changed during BUSY being active, the status
is updated by the CR16CAN as shown in Table21.
The buffer states are indicated and controlled by the ST[3:0]
bits in the CNSTAT register (see Buffer Status/Control Reg-
ister (CNSTAT) on page 106. The various receive buffer
states are explained in RX Buffer States on page 100.
20.5.2 Receive Procedure
The user has to execute the following procedure to initialize
a message buffer for the reception of a CAN message.
1. Configure the receive masks (GMASK or BMASK, re-
spectively).
2. Configure the buffer ID.
3. Configure the message buffer status as RX_READY.
In order to read the out of a received message, the CPU has
to execute the following steps (see Figure62):
The first step is only applicable if polling is used to get the
status of the receive buffer. It can be deleted for an interrupt
driven receive routine.
1. Read the status (CNSTAT) of the receive buffer. If the
status is RX_READY, no was the message received, ex-
it. If the status is RX_BUSY, copy process from hidden
receive buffer is not completed yet, read CNSTAT again.
If a buffer is configured to RX_READY and its interrupt
is enabled, it will generate an interrupt as soon as the
read buffer
read CNSTAT
RX_READY?
RX_OVERRUN?
RX_FULL? or
Y
N
read buffer (id/data/cntrl)
write RX_READY
exit
Y
N
Y
N
Figure 62.Buffer Read Routine (BUFFLOCK Disabled)
read CNSTAT
Interrupt Entry Point
clear RX_PND
A new message has
receive buffer
(optional, for information)
RX_BUSYx?
been received while
reading data from the
RX_OVERRUN?
RX_BUSYx?
N
Y
Obsolete
www.national.com 100
buffer has received a message and entered the
RX_FULL state (see also Interrupts on page 104). In that
case the procedure described below should be followed.
2. Read the status to determine if a new message has
overwritten the one originally received which triggered
the interrupt.
3. Write RX_READY into CNSTAT.
4. Read the ID/data and message control (DLC/RTR) from
the message buffer.
5. Read the buffer status again and check it is not
RX_BUSYx. If it is, repeat this step until RX_BUSYx has
gone away.
6. If the buffer status is RX_FULL or RX_OVERRUN, one
or more messages were copied. In that case, start over
with step 2.
7. If status is still RX_READY (as set by the CPU at step
2), clear interrupt pending bit and exit.
When the BUFFLOCK function is enabled (see BUFFLOCK
on page 97), it is not necessary to check for new messages
received during the read process from the buffer, as this buff-
er is locked after the reception of the first valid frame. A read
from a locked receive buffer can be performed as shown in
Figure63.
For simplicity only the applicable interrupt routine is shown:
1. Read the ID/data and message control (DLC/RTR) from
the message buffer.
2. Write RX_READY into CNSTAT.
3. Clear interrupt pending bit and exit.
20.5.3 RX Buffer States
As shown in Figure64, a receive procedure starts as soon as
the user has set the buffer from the RX_NOT_ACTIVE state
into the RX_READY state. The status section of CNSTAT
register is set from 00002 to 00102. When a message is re-
ceived, the buffer will be RX_BUSYx during the copy
process from the hidden receive buffer into the message
buffer. Afterwards this buffer is RX_FULL. Now the CPU can
read the buffer data and either reset the buffer status to
RX_READY or receive a new frame before the CPU reads
the buffer. In the second case, the buffer state will automati-
cally change to RX_OVERRUN to indicate that at least one
message was lost. During the copy process the buffer will
again be RX_BUSYx for a short time, but in this case the CN-
STAT status section will be 01012, as the buffer was
RX_FULL (01002) before. After finally reading the last re-
ceived message, the CPU can reset the buffer to
RX_READY.
20.6 TRANSMIT STRUCTURE
In order to transmit a CAN message, the user has to config-
ure the message buffer by changing the buffer status to
TX_NOT_ACTIVE. The buffer is configured for transmission
if the ST[3] bit of the buffer status code (CNSTAT) is set to ‘1’.
In TX_NOT_ACTIVE status, the buffer is ready to receive
data from the CPU. After receiving all transmission data (ID,
data bytes, DLC and PRI), the CPU can start the transmis-
sion by writing TX_ONCE into the buffer status register. Dur-
ing the transmission the status of the buffer is TX_BUSYx.
After successful transmission CR16CAN will reset the buffer
status to TX_NOT_ACTIVE. When the transmission process
fails, the buffer condition will remain TX_BUSYx for re-trans-
mission until the frame was successfully transmitted or the
CPU has canceled the transmission request.
In order to Send a Remote Frame (Remote Transmission
Request) to other CAN nodes, the user needs to set the RTR
bit of the message identifier to “1” (see Storage of Remote
Messages on page 109) and change the status of the mes-
sage buffer to TX_ONCE. After this remote frame has been
transmitted successfully, this message buffer will automati-
cally enter the RX_READY state and is ready to receive the
appropriate answer. Note that the mask bits RTR/XRTR need
to be set to receive a data frame (RTR = 0) in a buffer which
was configured to transmit a remote frame (RTR = 1).
To answer Remote Frames if the CPU writes TX_RTR in the
buffer status register, the buffer will wait for a remote frame.
When a remote frame passes the acceptance filtering mask
of one or more buffers, the buffer status will change to
TX_ONCE_RTR, the contents of the buffer will be transmit-
ted and afterwards CR16CAN will write TX_RTR in the status
code register again.
If the CPU writes TX_ONCE_RTR in the buffer status, the
contents of the buffer will be transmitted, and the successful
transmission the buffer goes into the “wait for Remote
Frame” condition TX_RTR.
20.6.1 Transmit Scheduling
After writing TX_ONCE in the buffer status, the transmission
process begins and the BUSY-bit is set. As soon as a buffer
gets the TX_BUSY status, the buffer is not accessible any-
more by the CPU except for the ST[3:1] bits of the CNSTAT
register. Starting with the beginning of the CRC field of the
current frame, CR16CAN looks for another buffer transmit re-
quest and selects the buffer with the highest priority for the
next transmission by changing the buffer state from
TX_ONCE to TX_BUSY. This transmit request can be can-
celed by the CPU or can be overwritten by another transmit
request of a buffer with a higher priority as long as the trans-
mission of the next frame has not yet started. This means
that between the beginning of the CRC field of the current
frame and the transmission start of the next frame, two buff-
ers, the current buffer and the buffer scheduled for the next
read buffer (id/data/cntrl)
write RX_READY
exit
Figure 63.Buffer Read Routine (BUFFLOCK Enabled)
Interrupt Entry Point
clear RX_PND
Obsolete
101 www.national.com
transmission, are in the BUSY status. In order to cancel the
transmit request of the next frame, the CPU has to change
the buffer state to TX_NOT_ACTIVE. When the transmit re-
quest has been overwritten by another request of a higher
priority buffer, CR16CAN changes the buffer state from
TX_BUSY to TX_ONCE. Thus, the transmit request remains
pending. Figure64 further illustrates the transmit timing.
If the transmit process fails or the arbitration is lost, the trans-
mission process will be stopped and will continue after the in-
terrupting reception or the error signaling has finished (see
Figure65). In that case a new buffer select follows and the
TX process is executed again.
Note: The canceled message can be delayed by a TX re-
quest of a buffer with a higher priority. During TX_BUSY high,
the user cannot change the contents of the message buffer.
In all cases writing to the BUSY bit will be ignored.
20.6.2 Transmit Priority
CR16CAN is able to generate a stream of scheduled mes-
sages without releasing the bus between two messages so
that an optimized performance can be achieved. It will arbi-
trate for the bus right after sending the previous message
and will only release the bus due to a lost arbitration.
If more than one buffer is scheduled for transmission, the pri-
ority is built by the message buffer number and the priority
code in the CNSTAT register. The 8-bit value of the priority is
formed by combining the 4-bit TXPRI value and the 4-bit buff-
er number (0...14) as shown below. The lowest resulting
number results in the highest transmit priority.
Table22 shows the transmit priority configuration if the prior-
ity is set to TXPRI = 0 for all transmit buffers:
Table23 shows the transmit priority configuration if TXPRI is
different from the buffer number:
Note: If two buffers have the same priority (PRI), the buffer
with the lower buffer number will have the higher priority.
TX_BUSY
begin selection of next buffer
if new tx_request
current buffer
TX_BUSY
next buffer
SOF
ARBITRATION FIELD DATA FIELD
(IF PRESENT) CRC ACK
FIELD EOF
1 BIT 12/29 BIT
+ 6 BIT n * 8 BIT 16 BIT 2 BIT 7 BIT
FIELD IFS
3 BIT
Figure 64.Data Transmission
+ CONTROL
BUS IDLE
CPU write TX_ONCE
in buffer status
Table 22Transmit Priority (TXPRI=0)
TXPRI Buffer
Number PRI TX Priority
0 0 0 highest
0 1 1
:
::
::
::
:
0 14 14 lowest
TXPRI BUFFER #
Table 23Transmit Priority (TXPRI not 0)
TXPRI Buffer
Number PRI TX Priority
14 0 224 lowest
13 1 209
12 2 194
11 3179
10 4 164
9 5 149
8 6 134
7 7 119
6 8 104
5 9 89
410 74
311 59
212 44
113 29
014 14 highest
Obsolete
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20.6.3 Transmit Procedure
The transmission of a CAN message has to be executed as
follows (see also Figure65)
1. Configure CNSTAT status field as TX_NOT_ACTIVE. If
the status is TX_BUSY, a previous transmit request is
still pending and the user has no access to the data con-
tents of the buffer. In that case the user may choose to
wait until the buffer becomes available again as shown.
Other options are to exit from the update routine until the
buffer has been transmitted with an interrupt generated,
or the transmission is aborted by an error.
2. Load buffer identifier & data registers. (For remote
frames the RTR bit of the identifier needs to be set and
loading data bytes can be omitted.)
3. Configure CNSTAT status field to the desired value:
—TX_ONCE to trigger the transmission process of a sin-
gle frame.
—TX_ONCE_RTR to trigger the transmission of a single
data frame and then wait for a received remote frame
to trigger consecutive data frames.
—TX_RTR waits for a remote frame to trigger the trans-
mission of a data frame.
Writing TX_ONCE or TX_ONCE_RTR in the CNSTAT status
field will set the internal transmit request for the CR16CAN.
If a buffer is configured as TX_RTR and a remote frame is re-
ceived, the data contents of the addressed buffer will be
transmitted automatically without further CPU activity.
write_buffer
TX_BUSYx?
Y
N
write
write ID/data
write
exit
Figure 65.Buffer Write Routine
TX_ONCE
or
TX_ONCE_RTR
or
TX_RTR
TX_NOT_ACTIVE
(see text)
Obsolete
103 www.national.com
20.6.4 TX Buffer States
The transmission process can be started after the user has
loaded the buffer registers (data, ID, DLC, PRI) and set the
buffer status from TX_NOT_ACTIVE to TX_ONCE, TX_RTR
or TX_ONCE_RTR.
When the CPU writes TX_ONCE, the buffer will be
TX_BUSY as soon as CR16CAN has scheduled this buffer
for the next transmission. After the frame could be success-
fully transmitted, the buffer status will be automatically reset
to TX_NOT_ACTIVE when a data frame was transmitted or
to RX_READY when a remote frame was transmitted.
If the CPU configures the message buffer to
TX_ONCE_RTR, it will transmit its data contents. During the
transmission the buffer state is 11112 as the CPU wrote 11102
into the status section of the CNSTAT register. After the suc-
cessful transmission the buffer enters the TX_RTR state and
waits for a remote frame. When it receives a remote frame, it
will go back into the TX_ONCE_RTR state, transmit its data
bytes and return to TX_RTR. If the CPU writes 10102 into the
buffer status section, it will only enter the TX_RTR state. But
it will not send its data bytes before it waits for a remote
frame. Figure 66 illustrates the possible transmit buffer
states.
Figure 66.Transmit Buffer States
TX_ONCE
TX_NOT_ACTIVE
RX_READY
TX done
request cancelled
Remote transmission
TX_RTR
RTR
CPU writes 1010
transmit failed
CAN
TX_BUSY0
TX_ONCE_RTR
TX_BUSY2
TX done
CAN
schedules TX
transmit
transmit
request cancelled
transmit failed
received
CPU writes 1100
TX request
TX request
CPU writes 1110
CPU writes 1000
CPU writes 1000
schedules TX
1110
1111
1010 1000
1100
0010
1101
*1
*1: TX request delayed
by a TX request of higher
priority message
request sent - now wait
to receive a data frame
Obsolete
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20.7 INTERRUPTS
CR16CAN has access to one interrupt vector in the CR16
CPU. The interrupt process can be initiated from the follow-
ing sources.
•CAN data transfer
—Reception of a valid data frame in the buffer. (Buffer
state changes from RX_READY to RX_FULL or
RX_OVERRUN).
—Successful transmission of a data frame. (Buffer state
changes from TX_ONCE to TX_NOT_ACTIVE or
RX_READY)
—Successful response to a remote frame. (Buffer state
changes from TX_ONCE_RTR to TX_RTR).
—Transmit scheduling. (Buffer state changes from
TX_RTR to TX_ONCE_RTR).
•CAN error conditions is the detection of an CAN error.
(The CEIPND bit in the CIPND register will be set as well
as the corresponding bits in the error diagnostic register
CEDIAG).
The receive/transmit interrupt access to every message buff-
er can be individually enabled/disabled in the CIEN register.
The pending flags of the message buffer are located in the
CIPND register (read only) and can be cleared by resetting
the flags in the CICLR registers.
20.7.1 Highest Priority Interrupt Code
In order to reduce decoding time of the CIPND register, the
buffer interrupt request with the highest priority is placed as
interrupt status code into the IST[3:0] section of the CSTPND
register.
Each of the buffer interrupts as well as the error interrupt can
be individually enabled or disabled in the CAN Interrupt En-
able register (CIEN). As soon as an interrupt condition oc-
curs, every interrupt request is indicated by a flag in the CAN
Interrupt Pending register (CIPND). When the interrupt code
logic for the present highest priority interrupt request is en-
abled, this interrupt will be translated into the IST[3:0] bits of
the CAN Status Pending register (CSTPND). An interrupt re-
quest can be cleared by setting the corresponding bit in the
CAN Interrupt Clear register (CICLR) to ‘1’.
Figure67 illustrates the CR16CAN interrupt management.
The highest priority interrupt source is translated into the bits
IRQ and IST[3:0] as shown in Table24.
Table 24Highest Priority Interrupt Code (ICEN=FFFF)
CAN interrupt
request IRQ IST3 IST2 IST1 IST0
no request 0 0 0 0 0
Error interrupt 1 0 0 0 0
Buffer 0 1 0 0 0 1
Buffer 1 1 0 0 1 0
Buffer 2 1 0 0 1 1
Buffer 3 1 0 1 0 0
Buffer 4 1 0 1 0 1
Buffer 5 1 0 1 1 0
Buffer 6 1 0 1 1 1
Buffer 7 1 1 0 0 0
Buffer 8 1 1 0 0 1
Buffer 9 1 1 0 1 0
Buffer 10 1 1 0 1 1
Buffer 11 1 1 1 0 0
Buffer 12 1 1 1 0 1
Buffer 13 1 1 1 1 0
Buffer 14 1 1 1 1 1
Figure 67.CR16CAN Interrupt Management
CIPND
IST0IST1IST2IST3
ICODE
clear interrupt flags of every
IRQ
CICLR
CIEN
CICEN
message buffer individually
Obsolete
105 www.national.com
20.7.2 Usage Hints
The interrupt code IST[3:0] can be used within the interrupt
handler as a displacement in order to jump to the relevant
subroutine.
The CAN Interrupt Code Enable (CICEN) register is used in
the CAN interrupt handler if the user wants to service all re-
ceive buffer interrupts first followed by all transmit buffer in-
terrupts. In this case, the user can first enable only all receive
buffer interrupts to be coded, scan and service all pending in-
terrupt requests in the order of their priority. Then, the user
changes the CICEN register to disable all receive buffers, but
enable all transmit buffers and service all pending transmit
buffer interrupt requests according to their priorities.
20.8 TIME STAMP COUNTER
CR16CAN features a free running 16-bit timer (CTMR) incre-
menting every bit time recognized on the CAN bus. The val-
ue of this timer during the ACK slot is captured into the TSTP
register of a message buffer after a successful transmission
or reception of a message. Figure68 shows a simplified
block diagram of the Time Stamp counter.
The timer can be synchronized over the CAN network by re-
ceiving or transmitting a message to/from buffer 0. In that
case the TSTP register of buffer 0 captures the current
CTMR value during the ACK slot of a message (as above)
and afterwards the CTMR is reset to 00002. Synchronization
can be enabled or disabled via the CGCR.TSTPEN bit.
20.9 MEMORY ORGANIZATION
CR16CAN occupies 144 words in the memory address
space. This space is separated into 15*8 + 8(reserved)
words for the message buffers and 14 + 2(reserved) words
for control and status.
20.9.1 CPU Access to CR16CAN Registers/Memory
All memory locations occupied by the message buffers are
shared by the CPU and CR16CAN (dual ported RAM). The
CR16CAN and the CPU normally have single cycle access
to this memory. However, if an access contention occurs, the
access to the memory is altered every cycle until the conten-
tion is resolved. This internal access arbitration is transpar-
ent to the user.
Both word and byte access to the buffer RAM are allowed. If
a buffer is busy during the reception of a message (copy pro-
cess from the hidden receive buffer) or is scheduled for trans-
mission, the CPU has no write access to the data contents of
the buffer. Write to the status/control byte and read access to
the whole buffer is always enabled.
All configuration and status registers can either be accessed
by CR16CAN or the CPU only. These registers provide single
cycle word and byte access without any potential wait state.
All register descriptions within the next sections utilize the fol-
lowing layout:
20.9.2 Message Buffer Organization
The message buffers are the communication interfaces be-
tween CAN and the CPU for the transmission and the recep-
tion of CAN frames. There are 15 message buffers located at
fixed addresses in the RAM location. As shown in Table25,
each buffer consists of two words reserved for the identifiers,
4 words reserved for up to eight CAN data bytes, one word is
reserved for time stamp and one word for data length code,
transmit priority code and the buffer status code.
16-bit counter
TSTP register
CAN bits on the bus
ACK slot & buffer 0 active
ACK slot
+1
Reset
Figure 68.Time Stamp Counter
bit 15 ... bit number ... bit 0
... bit name ...
... reset value ...
... CPU access ...
r = register bit is read only
w = register bit is write only
r/w = register bit is read/write
Table 25Message Buffer Organization
ADDR BUFFER
register 15 14 13 12 11 109876543210
xxxE16 ID1 XI28
ID10 XI27
ID9 XI26
ID8 XI25
ID7 XI24
ID6 XI23
ID5 XI22
ID4 XI21
ID3 XI20
ID2 XI19
ID1 XI18
ID0 SRR
RTR IDE XI17 XI16 XI15
xxxC16 ID0 XI14 XI13 XI12 XI11 XI10 XI9 XI8 XI7 XI6 XI5 XI4 XI3 XI2 XI1 XI0 RTR
xxxA16 DATA0 Data
1.7
Data
1.6
Data
1.5
Data
1.4
Data
1.3
Data
1.2
Data
1.1
Data
1.0
Data
2.7
Data
2.6
Data
2.5
Data
2.4
Data
2.3
Data
2.2
Data
2.1
Data
2.0
xxx816 DATA1 Data
3.7
Data
3.6
Data
3.5
Data
3.4
Data
3.3
Data
3.2
Data
3.1
Data
3.0
Data
4.7
Data
4.6
Data
4.5
Data
4.4
Data
4.3
Data
4.2
Data
4.1
Data
4.0
xxx616 DATA2 Data
5.7
Data
5.6
Data
5.5
Data
5.4
Data
5.3
Data
5.2
Data
5.1
Data
5.0
Data
6.7
Data
6.6
Data
6.5
Data
6.4
Data
6.3
Data
6.2
Data
6.1
Data
6.0
xxx416 DATA3 Data
7.7
Data
7.6
Data
7.5
Data
7.4
Data
7.3
Data
7.2
Data
7.1
Data
7.0
Data
8.7
Data
8.6
Data
8.5
Data
8.4
Data
8.3
Data
8.2
Data
8.1
Data
8.0
xxx216 TSTP TSTP15 TSTP14 TSTP13 TSTP12 TSTP11 TSTP10 TSTP
9TSTP
8TSTP
7TSTP
6TSTP
5TSTP
4TSTP
3TSTP
2TSTP
1TSTP
0
xxx016 CNTSTAT DLC3 DLC2 DLC1 DLC0 Reserved PRI3 PRI2 PRI1 PRI0 ST3 ST2 ST1 ST0
Obsolete
www.national.com 106
20.9.3 Buffer Status/Control Register (CNSTAT)
The buffer status, the buffer priority and the data length code
are controlled by manipulating the contents of the Buffer Sta-
tus/Control Register (CNSTAT). CPU and CR16CAN have
access to this register.
ST[3:0] Buffer Status — The CNSTAT register has a
status section, which contains the status infor-
mation of the buffer as shown in Table26. This
section can be modified by CR16CAN.
The ST0 bits acts as a buffer busy indication.
When the BUSY bit is set, any write access to
the buffer is disabled with the exception of the
lower byte of the CNTSTAT register. The
CR16CAN sets this bit if the buffer data is cur-
rently copied from the hidden buffer or if a mes-
sage is scheduled for transmission or is
currently transmitting. The CR16CAN will al-
ways reset this bit on a status update.
15 12 11 8 7 4 3 0
DLC[3:0] Reserved PRI[3:0] ST[3:0]
0
r/w
Table 26Buffer Status Section of the CNSTAT Register
ST3 (DIR) ST2 ST1 ST0 (BUSY) Buffer Status
0 0 0 0 RX_NOT_ACTIVE
0 0 0 1 Reserved for RX_BUSY a
0 0 1 0 RX_READY
0 0 1 1 RX_BUSY0 b
0 1 0 0 RX_FULL
0 1 0 1 RX_BUSY1 b
0 1 1 0 RX_OVERRUN
0 1 1 1 RX_BUSY2 b
1 0 0 0 TX_NOT_ACTIVE
1 0 0 1 Reserved for TX_BUSY c
1 1 0 0 TX_ONCE
1 1 0 1 TX_BUSY0 d
1 0 1 0 TX_RTR
(automatic response to a remote frame)
1 0 1 1 Reserved for TX_BUSY1 e
1 1 1 0 TX_ONCE_RTR
(changes to TX_RTR after transmission)
1 1 1 1 TX_BUSY2 d
a. This condition indicates that the user wrote RX_NOT_ACTIVE to a buffer when the data copy process is still
active.
b. RX_BUSYx indicates that coping is in progress at three possible times
- data is copied for the first time RX_READY → RX_BUSY0
- data is copied for the second time RX_FULL → RX_BUSY1
- data is copied for the third or more time RX_OVERRUN → RX_BUSY2
c. This state indicates that the user wrote TX_NOT_ACTIVE to a transmit buffer which is scheduled for
transmission or is currently transmitting.
d. TX_BUSYx indicates that a buffers is scheduled for transmission or is actively transmitting; it can be due to
one of two cases:
- a message is pending for transmission or is currently transmitting
- an automated answer is pending for transmission or is currently transmitting
e. This condition does not occur
Obsolete
107 www.national.com
PRI[3:0] Transmit Priority Code. The PRI[3:0] bits con-
tain the user defined transmit priority code for
the message buffer.
DLC[3:0] Data Length Code. The DLC[3:0] bits deter-
mine the number of data bytes within a re-
ceived/transmitted frame. For transmission,
these bits need to be set according to the num-
ber of data bytes to be transmitted. For recep-
tion, these bits indicate the number of valid
received data bytes available in the message
buffer. Table27 shows the possible bit combi-
nations for DLC[3:0] for data lengths from 0 to
8 bytes.
Note: The maximum number of data bytes received/trans-
mitted is 8, even if the data length code is set to a value
greater than 8. Thus, if the data length code is greater or
equal to eight bytes, the bits DLC2 to DLC0 are ignored.
20.9.4 Storage of Standard Messages
During the processing of standard frames, the Extended-
Identifier-bit (IDE) is set to “0”. The bits ID1[3:0], ID0[15:0]
are “don’t care” bits. A standard frame with eight data bytes
is shown in Table28.
IDE Identifier Extension. IDE is set to “0” to indicate
that the message is a standard frame using 11
identifier bits. If IDE is set to “1”, the message
stored in the buffer is handled as an extended
frame.
RTR Remote Transmission Request. RTR is set to
“1” to indicate that the message is a remote
frame. For a data frame, the RTR bit is set to
“0”.
ID[10:0]The ID buffer bits ID10 to ID0 are used for the 11
standard frame identifier bits.
Table 27Data Length Coding
Number of data
bytes DLC3 DLC2 DLC1 DLC0
0 0000
1 0001
2 0010
3 0011
4 0100
5 0101
6 0110
7 0111
8 1000
Table 27Data Length Coding
Number of data
bytes DLC3 DLC2 DLC1 DLC0
Table 28Standard Frame with 8 Data Bytes
ADDR BUFFER
register 15 14 13 12 11 109876543210
xxxE16 ID1 ID10 ID9 ID8 ID7 ID6 ID5 ID4 ID3 ID2 ID1 ID0 RTR IDE don’t care
xxxC16 ID0 don’t care
xxxA16 DATA0 Data
1.7
Data
1.6
Data
1.5
Data
1.4
Data
1.3
Data
1.2
Data
1.1
Data
1.0
Data
2.7
Data
2.6
Data
2.5
Data
2.4
Data
2.3
Data
2.2
Data
2.1
Data
2.0
xxx816 DATA1 Data
3.7
Data
3.6
Data
3.5
Data
3.4
Data
3.3
Data
3.2
Data
3.1
Data
3.0
Data
4.7
Data
4.6
Data
4.5
Data
4.4
Data
4.3
Data
4.2
Data
4.1
Data
4.0
xxx616 DATA2 Data
5.7
Data
5.6
Data
5.5
Data
5.4
Data
5.3
Data
5.2
Data
5.1
Data
5.0
Data
6.7
Data
6.6
Data
6.5
Data
6.4
Data
6.3
Data
6.2
Data
6.1
Data
6.0
xxx416 DATA3 Data
7.7
Data
7.6
Data
7.5
Data
7.4
Data
7.3
Data
7.2
Data
7.1
Data
7.0
Data
8.7
Data
8.6
Data
8.5
Data
8.4
Data
8.3
Data
8.2
Data
8.1
Data
8.0
xxx216 TSTP TSTP
15 TSTP
14 TSTP
13 TSTP
12 TSTP
11 TSTP
10 TSTP
9TSTP
8TSTP
7TSTP
6TSTP
5TSTP
4TSTP
3TSTP
2TSTP
1TSTP
0
xxx016 CNTSTAT DLC3 DLC2 DLC1 DLC0 Reserved PRI3 PRI2 PRI1 PRI0 ST3 ST2 ST1 ST0
Obsolete
www.national.com 108
20.9.5 Storage of Messages with Less Than 8 Data
Bytes
The data bytes that are not used for data transfer are “don’t
cares”. If the message is transmitted, the data within these
bytes will be ignored. If the message is received, the data
within these bytes will be overwritten with invalid data.
20.9.6 Storage of Extended Messages
If the IDE bit is set to “1”, the buffer handles extended frames.
The storage of the extended ID follows the descriptions in
Table29. The SRR bit is at the bit position of the RTR bit for
standard frame and needs to be transmitted as “1”.
SRR Substitute Remote Request. SRR replaces the
RTR bit used in standard frames at this bit po-
sition. The SRR bit needs to be set to “1” by the
user if the buffer is configured to transmit a
message with an extended identifier. It will be
received as monitored on the CAN bus.
IDE Identifier Extension. IDE is set to “0” to indicate
that the message is a standard frame using 11
identifier bits. If IDE is set to “1”, the message
stored in the buffer is handled as an extended
frame.
RTR Remote Transmission Request. RTR is set to
“1” to indicate that the message is a remote
frame. For a data frame, the RTR bit is set to
“0”.
ID[28:0] The ID bits 28 to 0 are used to build the 29-bit
identifier of an extended frame.
Table 29Extended Messages with 8 Data Bytes
ADDR BUFFER
register 15 14 13 12 11 109876543210
xxxE16 ID1 ID28 ID27 ID26 ID25 ID24 ID23 ID22 ID21 ID20 ID19 ID18 SRR IDE ID17 ID16 ID15
xxxC16 ID0 ID14 ID13 ID12 ID11 ID10 ID9 ID8 ID7 ID6 ID5 ID4 ID3 ID2 ID1 ID0 RTR
xxxA16 DATA0 Data
1.7
Data
1.6
Data
1.5
Data
1.4
Data
1.3
Data
1.2
Data
1.1
Data
1.0
Data
2.7
Data
2.6
Data
2.5
Data
2.4
Data
2.3
Data
2.2
Data
2.1
Data
2.0
xxx816 DATA1 Data
3.7
Data
3.6
Data
3.5
Data
3.4
Data
3.3
Data
3.2
Data
3.1
Data
3.0
Data
4.7
Data
4.6
Data
4.5
Data
4.4
Data
4.3
Data
4.2
Data
4.1
Data
4.0
xxx616 DATA2 Data
5.7
Data
5.6
Data
5.5
Data
5.4
Data
5.3
Data
5.2
Data
5.1
Data
5.0
Data
6.7
Data
6.6
Data
6.5
Data
6.4
Data
6.3
Data
6.2
Data
6.1
Data
6.0
xxx416 DATA3 Data
7.7
Data
7.6
Data
7.5
Data
7.4
Data
7.3
Data
7.2
Data
7.1
Data
7.0
Data
8.7
Data
8.6
Data
8.5
Data
8.4
Data
8.3
Data
8.2
Data
8.1
Data
8.0
xxx216 TSTP TSTP
15 TSTP
14 TSTP
13 TSTP
12 TSTP
11 TSTP
10 TSTP
9TSTP
8TSTP
7TSTP
6TSTP
5TSTP
4TSTP
3TSTP
2TSTP
1TSTP
0
xxx016 CNTSTAT DLC3 DLC2 DLC1 DLC0 Reserved PRI3 PRI2 PRI1 PRI0 ST3 ST2 ST1 ST0
Obsolete
109 www.national.com
20.9.7 Storage of Remote Messages
During remote frame transfer, the buffer registers DATA[3:0]
are “don’t cares”. If a remote frame is transmitted, the con-
tents of these registers are ignored. If a remote frame is re-
ceived, the contents of these registers will be overwritten with
invalid data. The structure of a message buffer set up for a
remote frame with extended identifier is shown in Table30.
SRR Substitute Remote Request. SRR replaces the
RTR bit used in standard frames at this bit po-
sition. The SRR bit needs to be set to “1” by the
user.
IDE Identifier Extension. IDE is set to “0” to indicate
that the message is a standard frame using 11
identifier bits. If IDE is set to “1”, the message
stored in the buffer is handled as an extended
frame.
RTR Remote Transmission Request. RTR is set to
“1” to indicate that the message is a remote
frame. For a data frame, the RTR bit is set to
“0”.
ID[28:0] The ID bits 28 to 0 are used to build the 29-bit
identifier of an extended frame. The ID1 buffer
bits ID28 to ID18 are used for the 11 standard
frame identifier bits.
20.9.8 CAN Global Configuration Register (CGCR)
The CAN Global Configuration Register (CGCR) is a 16-bit
wide register used to:
•enable/disable the CR16CAN
•configure the BUFFLOCK function for the message buffer
0...14
•enable/disable the time stamp synchronization
•set the logic levels of the CAN Input/Output pins
CANRX/CANTX
•choose the data storage direction (DDIR)
•select the error interrupt type (EIT)
•enable/disable diagnostic functions
CANEN CAN Enable. This bit enables/disables the
CR16CAN. When the CR16CAN is disabled,
all internal states and the TEC and REC
counter registers are cleared. In addition the
CR16CAN clock is disabled. All CR16CAN
control registers and the contents of the mes-
sage memory are left unchanged.
The user needs to make sure that no message
is pending for transmission before the
CR16CAN is disabled.
“0” CR16CAN is disabled
“1” CR16CAN is enabled
CTX Control Transmit. This bit configures the logic
level of the CAN transmit pin CANTX.
“0” dominate state is “0”; recessive state is “1”
Table 30Extended Remote Frame
ADDR BUFFER
register 15 14 13 12 11 10 9876543210
xxxE16 ID1 ID28 ID27 ID26 ID25 ID24 ID23 ID22 ID21 ID20 ID19 ID18 SRR IDE ID17 ID16 ID15
xxxC16 ID0 ID14 ID13 ID12 ID11 ID10 ID9 ID8 ID7 ID6 ID5 ID4 ID3 ID2 ID1 ID0 RTR
xxxA16 DATA0 don’t care
xxx816 DATA1 don’t care
xxx616 DATA2 don’t care
xxx416 DATA3 don’t care
xxx216 TSTP TSTP15 TSTP14 TSTP13 TSTP12 TSTP11 TSTP10 TSTP
9TSTP
8TSTP
7TSTP
6TSTP
5TSTP
4TSTP
3TSTP
2TSTP
1TSTP
0
xxx016 CNTSTAT DLC3 DLC2 DLC1 DLC0 Reserved PRI3 PRI2 PRI1 PRI0 ST3 ST2 ST1 ST0
15 12 11 10 9 8
Reserved EIT DIAGEN INTERNAL LOOPBACK
0
r/w
7 6 5 4 3 2 1 0
IGNACK LO DDIR TSTPEN BUFFLOCK CRX CTX CANEN
0
r/w
Obsolete
www.national.com 110
“1” dominate state is “1”; recessive state is “0”
CRX Control Receive. This bit configures the logic
level of the CAN receive pin CANRX.
“0” dominate state is “0”; recessive state is “1”
“1” dominate state is “1”; recessive state is “0”
BUFFLOC Buffer Lock. With this bit the user can configure
the buffer lock function. If this feature is en-
abled, a buffer will be locked upon a successful
frame reception. The buffer will be unlocked
again by writing RX_READY in the buffer sta-
tus register, i.e., after reading data.
“0” lock function is disabled for all buffers
“1” lock function is enabled for all buffers
TSTPEN Time Sync Enable. The Time Sync bit enables
or disables the time stamp synchronization
function of the CR16CAN.
“0” Time synchronization disabled. The Time
Stamp counter value is not reset upon re-
ception or transmission of a message to/
from buffer 0.
“1” Time synchronization enabled. The Time
Stamp counter value is reset upon recep-
tion or transmission of a message to/from
buffer 0.
DDIR Data Direction. By setting or resetting the DDIR
bit, the user can select the direction the data
bytes are transmitted and received. The
CR16CAN transmits and receives the CAN
data byte Data1 first and the data byte Data8
last (Data1, Data2,...,Data7, Data8).
If DDIR is set to “0” the data contents of a re-
ceived message is stored with the first byte at
the highest data address and the last data at
the lowest data address (see Figure69). The
same applies for transmitted data.
0A16
0816
0616
0416
Data Bytes
Data8Data7
Data6Data5
Data4Data3
Data2Data1
ADDR offset
Data1 Data3Data2 Data4 Data5 Data6 Data7 Data8
t
Sequence of Data Bytes on the Bus
Storage of Data Bytes
in the Buffer Memory
ID CRC
Figure 69.Data Direction Bit set to ‘0’
Obsolete
111 www.national.com
Setting the DDIR bit to “1” will cause the direction of the data
storage to be reversed — the last byte received is stored at the highest address and the first byte is stored at the lowest
address. See Figure70 for illustration.
LO Listen Only — By setting the LO-bit to “1” the
CR16CAN interface is configured to behave
only as a receiver. This means:
•it cannot transmit any message.
•it cannot send a dominant ACK bit.
•when errors are detected on the bus, the
CR16CAN will behave as in the error pas-
sive mode.
Using this listen only function, the CR16CAN
interface can be adjusted when it gets connect-
ed to an operating network with unknown bus
speed.
IGNACK Ignore Acknowledge. If the ignore ACK func-
tion is enabled, then by setting the IGNACK bit
to “1”, CR16CAN does not expect to receive a
dominant ACK bit to indicate the validity of a
transmitted message. It will not send an error
frame when the transmitted frame in not ac-
knowledged by any other CAN node.
This feature can be used in conjunction with
the LOOPBACK option for stand-alone tests
outside of a CAN network.
LOOPBACK Loopback. By setting the LOOPBACK bit, all
messages sent by CR16CAN can also be re-
ceived by a CR16CAN buffer with a matching
buffer ID. However, CR16CAN does not ac-
knowledge a message sent by itself. Therefore
CR16CAN will send an error frame when no
other device connected to the bus has ac-
knowledged the message.
INTERNAL Internal. If the INTERNAL function is enabled,
the TX- and RX-pin of the CR16CAN are inter-
nally connected to each other. This feature can
be used in conjunction with the LOOPBACK
mode. This means that CR16CAN can receive
its own sent messages without connecting an
external transceiver chip to the RX- and TX-
pin; it allows the user to run real stand-alone
tests without any peripheral devices.
DIAGEN Diagnostic Enable. The DIAGEN bit globally
enables or disables the special diagnostic fea-
tures of CR16CAN. This includes the following
functions:
•LO (Listen Only)
•IGNACK (Ignore Acknowledge)
•LOOPBACK (Loopback)
•INTERNAL (Internal Loopback)
•write access to hidden receive buffer
EIT Error Interrupt Type. This bit configures when
the Error Interrupt Pending Bit (CIPND.EIPND)
is set and an error interrupt is generated if en-
abled by the Error Interrupt Enable
(CIEN.EIEN).
“0” The EIPND bit is set on every error on the
CAN bus.
“1” The EIPND bit is set only if the error state
(CSTPND.NS) changes as a result of in-
crementing either the receive or transmit
error counter.
t
ADDRoffset Data Bytes
Data1Data2
Data3Data4
Data5Data6
Data7Data8
Sequence of Data Bytes on the Bus
Storage of Data Bytes
in the Buffer Memory
Data1 Data3Data2 Data4 Data5 Data6 Data7 Data8
ID CRC
Figure 70.Data Direction Bit set to ‘1’
0A16
0816
0616
0416
Obsolete
www.national.com 112
20.9.9 CAN Timing Register (CTIM)
The Can Timing Register (CTIM) defines the configuration of
the Bit Time Logic (BTL).
PSC[6:0] Prescaler Configuration. These bits set the
CAN prescaler. The settings are shown in
Table31
SJW[1:0] Synchronization Jump Width. These bits set
the Synchronization Jump Width which can be
programmed between 1 and 4 time quanta
(see Table32).
Note: The settings of SJW has to be configured to be small-
er or equal to TSEG1 and TSEG2
TSEG1[3:0] Time Segment 1. These bits configure the
length of the Time Segment 1 (TSEG1). It is not
recommended to configure the time segment 1
to be smaller than 2tq. (see Table33).
TSEG2[2:0] Time Segment 2. The TSEG2[2:0] bits set the
number of time quanta (tq) for phase segment
2 (see Table34).
20.9.10 Global Mask Registers (GMSK — GMSKB and
GMSKX)
The GMSKB and GMSKX registers allow you to globally
mask, or “don’t care” the incoming extended/standard identi-
fier bits, RTR/XRTR and IDE. Throughout this document, the
GMSKB and GMSKX 16-bit registers are referenced as a 32-
bit register GMSK.
15 9 8 7 6 3 2 0
PSC[6:0] SJW[1:0] TSEG1[3:0] TSEG2[2:0]
0
r/w
Table 31CAN Prescaler Settings
PS
C6 PS
C5 PS
C4 PS
C3 PS
C2 PS
C1 PS
C0
CAN
prescaler
(PSC)
0 0 0 0 0 0 0 2
0 0 0 0 0 0 1 3
0 0 0 0 0 1 0 4
0 0 0 0 0 1 1 5
0 0 0 0 1 0 0 6
: : : : : : :
1111101 127
1 1 1 1 1 1 0/1 128
Table 32SJW Settings
SJW1 SJW0 Synchronization Jump Width
(SJW)
0 0 1 tq
0 1 2 tq
1 0 3 tq
1 1 4 tq
Table 33Time Segment 1 Settings
TSEG
13 TSEG
12 TSEG
11 TSEG
10 Length of Time
(TSEG1)
0 0 0 0 not recommended
0 0 0 1 2 tq
0 0 1 0 3 tq
0 0 1 1 4 tq
0 1 0 0 5 tq
0 1 0 1 6 tq
0 1 1 0 7 tq
0 1 1 1 8 tq
1 0 0 0 9 tq
1 0 0 1 10 tq
1 0 1 0 11 tq
1 0 1 1 12 tq
1 1 0 0 13 tq
1 1 0 1 14 tq
1 1 1 0 15 tq
1 1 1 1 16 tq
Table 34Time Segment 2 Settings
TSEG22 TSEG21 TSEG20 Length of
TSEG2
000 1 tq
001 2 tq
010 3 tq
011 4 tq
100 5 tq
101 6 tq
110 7 tq
111 8 tq
Obsolete
113 www.national.com
GM[28:15] The following are the bits for the GMSKB reg-
ister.
GM[14:0] The following are the bits for the GMSKX reg-
ister.
For all GMSKB and GMSKX register bits, the following ap-
plies:
—“0” is the incoming identifier bit must match the corre-
sponding bit in the message buffer identifier register.
—“1” accept “1” or “0” (“don’t care”) of the incoming ID bit
independent from the corresponding bit in the mes-
sage buffer ID registers. The corresponding ID bit in
the message buffer will be overwritten by the incoming
identifier bits.
When an extended frame is received from the CAN bus, all
Global Mask bits GM28 through GM0, IDE, RTR and XRTR
are used to mask the incoming message.
During the reception of standard frames only the Global
Mask bits GM28 to GM18, RTR and IDE are utilized.
20.9.11 Basic Mask Registers (BMSK — BMSKB and
BMSKX)
The two registers BMSKB and BMSKX allow to mask the
buffer 14, or “don’t care” the incoming extended/standard
identifier bits, RTR/XRTR and IDE. Throughout this docu-
ment, the two 16-bit registers BMSKB and BMSKX are refer-
enced to as a 32-bit register BMSK.
BM[28:15] The following are the bits for the BMSKB regis-
ter.
BM[14:0] The following are the bits for the BMSKX regis-
ter.
For all BMSKB and BMSKX register bits the following ap-
plies:
—“0” incoming identifier bit must match the correspond-
ing bit in the message buffer identifier register.
—“1” accept “1” or “0” (“don’t care”) of the incoming ID bit
independent from the corresponding bit in the mes-
sage buffer ID registers. The corresponding ID bit in
the message buffer will be overwritten by the incoming
identifier bits.
When an extended frame is received from the CAN bus all
Basic Mask bits BM28 through BM0, IDE, RTR and XRTR
are used to mask the incoming message.
During the reception of standard frames only the Basic Mask
bits BM28 to BM18, RTR and IDE are utilized.
20.9.12 CAN Interrupt Enable Register (CIEN)
The CAN Interrupt Enable (CIEN) register enables the trans-
mit/receive interrupts of the message buffers 0 through 14 as
well as the CAN Error Interrupt.
EIEN Error Interrupt Enable. This bit allows the
CR16CAN to interrupt the CPU if any kind of
CAN receive/transmit errors are detected. This
means any error status change in the error
counter registers REC/TEC is able to generate
an error interrupt if EIEN is enabled.
“0” The error interrupt is disabled and no error
interrupt will be generated.
“1” The error interrupt is enabled and a
change in REC/TEC will cause an inter-
rupt to be generated.
IEN[14:0] Buffer Interrupt Enable. The IEN[14:0] allow
the user to enable/disable interrupt source for
each of the message buffers i.e., IEN14 config-
ures buffer14 and IEN0 configures buffer0.
“0” buffer as interrupt source disabled
“1” buffer as interrupt source enabled
15 5 4 3 2 0
GM[28:18] RTR IDE GM[17:15]
0
r/w
15 1 0
GM[14:0] XRTR
0
r/w
Global Mask GM[28:18] RTR a
a. the RTR bit has a different position in standard and
extended frames
— for standard frames the GMSK_RTR bit is used to
mask this bit
— for extended frames the GMSK_XRTR bit is used to
mask this bit
IDE GM[17:0] XRTR
standard frame ID[10:0] RTR IDE unused
extended frame ID[28:18] SRR IDE ID[17:0] RTR
15 5 4 3 2 0
BM[28:18] RTR IDE BM[17:15]
0
r/w
15 1 0
BM[14:0] XRTR
0
r/w
Basic Mask BM[28:18] RTR a
a. the RTR bit has a different position in standard and
extended frames
— for standard frames the BMSK_RTR bit is used to
mask this bit
— for extended frames the BMSK_XRTR bit is used to
mask this bit
IDE BM[17:0] XRTR
standard frame ID[10:0] RTR IDE unused
extended frame ID[28:18] SRR IDE ID[17:0] RTR
15 14 0
EIEN IEN[14:0]
0
r/w
Obsolete
www.national.com 114
20.9.13 CAN Interrupt Pending Register (CIPND)
The CIPND register indicates any CAN Receive/Transmit In-
terrupt Requests caused by the message buffers 0..14 and
CAN error occurrences.
EIPND Error Interrupt Pending — EIPND indicates the
status change of TEC/REC and will execute an
error interrupt if EIEN is set. The user has the
responsibility to reset EIPND by means of the
CICLR register.
“0” CAN status is not changed
“1” CAN status is changed
IPND[14:0] Buffer Interrupt Pending — IPND[14:0] bits are
set by CR16CAN following a successful trans-
mission or reception of a message to or from
message buffer 0...14, IPND14 for buffer 14
and IPND0 for buffer 0.
“0” no interrupt pending for this message buff-
er
“1” message buffer has generated an inter-
rupt
20.9.14 CAN Interrupt Clear Register (CICLR)
The bits in the CICLR register separately clear all CAN inter-
rupt pending flags caused by the message buffers 0...14 and
from the Error Management Logic.
EICLR Error Interrupt Clear. The EICLR bit can clear
the EIPND bit:
“0” the contents of the EIPND bit is un-
changed
“1” the contents of the EIPND bit is reset
ICLR[14:0] Buffer Interrupt Clear. The user is able to clear
the buffer interrupt pending bits by ICLR[14:0]:
“0” the contents of the respective IPND bit is
unchanged
“1” the contents of the respective IPND bit is
reset
20.9.15 CAN Interrupt Code Enable Register (CICEN)
The CAN Interrupt Code Enable Register (CICEN) deter-
mines whether the interrupt pending flag in IPND should be
translated into the Interrupt Code field of the CSTPND regis-
ter. All interrupt requests, CAN error and buffer 0...14 inter-
rupts can be enabled/disabled separately for the interrupt
code indication field.
EICEN Error Interrupt Code Enable:
“0” error interrupt pending is not indicated in
the interrupt code
“1” error interrupt pending is indicated in the
interrupt code
ICEN[14:0] Buffer Interrupt Code Enable:
“0” buffer interrupt pending is not indicated in
the interrupt code
“1” buffer interrupt pending is indicated in the
interrupt code
20.9.16 CAN Status Pending Register (CSTPND)
The CAN Status Pending Register (CSTPND) contains the
status of the CAN Node and the Interrupt Code.
NS[2:0] CAN Node Status. This bits indicate the status
of the CAN node as it is described in Table35.
IRQ,IST[3:0] Interrupt Code. This section of the Status
Pending Register represents the interrupt
source of the highest priority interrupt currently
pending and enabled in the CICEN register.
Table36 shows the several interrupt codes for
CICEN=FFFF.
15 14 0
EIPND IPND[14:0]
0
r
15 14 0
EICLR ICLR[14:0]
0
w
15 14 0
EICEN ICEN[14:0]
0
r/w
15 8 7 5 4 3 0
Reserved NS[2:0] IRQ IST[3:0]
0
r
Table 35CAN Node Status
NS2 NS1 NS0 Node Status
000 Not Active
010 Error active
011Error Warning Level
1 0 XError passive
1 1 XBus off
Table 36 Highest Priority Interrupt Code
(CICEN = FFFF)
CAN interrupt
request IRQ IST3 IST2 IST1 IST0
no request 0 0 0 0 0
Error interrupt 1 0 0 0 0
Buffer 0 1 0 0 0 1
Buffer 1 1 0 0 1 0
Buffer 2 1 0 0 1 1
Buffer 3 1 0 1 0 0
Buffer 4 1 0 1 0 1
Buffer 5 1 0 1 1 0
Buffer 6 1 0 1 1 1
Buffer 7 1 1 0 0 0
Buffer 8 1 1 0 0 1
Buffer 9 1 1 0 1 0
Obsolete
115 www.national.com
20.9.17 CAN Error Counter Register (CANEC)
The Can Error Counter Register contains the value of the
CAN Receive Error Counter and the CAN Transmit Error
Counter.
REC[7:0] CAN Receive Error Counter. The bits REC[7:0]
holds the value of the receive error counter.
TEC[7:0] CAN Transmit Error Counter. The bits TEC[7:0]
holds the value of the transmit error counter.
20.9.18 CAN Error Diagnostic Register (CEDIAG)
The CAN Error Diagnostic (CEDIAG) register provides infor-
mation about the last detected error. CR16CAN is able to
identify the field within the CAN frame format, in which the er-
ror occurred, and it identifies the bit number of the erroneous
bit within the according frame field. The CPU has read only
access and all bits will be cleared upon reset.
EFID[3:0] Error Field Identifier. The EDIAG bits 3...0 iden-
tify the frame field in which the last error oc-
curred. How the various frame fields are coded
into the EFID bits is shown in Table37.
EBID[5:0] Error Bit Identifier. The EDIAG[9:4] bits contain
the number (position) of the incorrect bit within
the erroneous frame field. The bit number
starts with the value equal to the respective
frame field length minus one at the beginning of
each field and is decremented with each CAN
bit. Figure71 shows an example on how the
EBID is calculated.
Assume the EFID resulted in 11102 and the EBID showed a
value of 111001 2. This means that faulty field was the data
field. To calculate the bit position of the error, the DLC of the
message needs to be known. For example, for a DLC of 8
data bytes, the bit counter starts with the value: 8 x 8 - 1 = 63;
so when EBID[5:0]=1110012 = 57, then the bit number was
63 - 57 = 6.
The following bits provide an information of the error type.
TXE Transmit Error. If set, this bit indicates that the
CR16CAN was an active transmitter at the time
the error occurred. If reset, the CR16CAN was
a receiver.
STUFF Stuff Error. if set, this bit indicates that a the bit
stuffing rule was violated at the time the error
occurred. Note that certain bit fields do no use
bit stuffing and therefore this bit may be ig-
nored in those.
CRC CRC Error. if set, this bit indicates that the CRC
is invalid. This bit should only be used if the
EFID shows the code of the ACK field.
MON Monitor. This bit shows the bus value on the
CANRX pin as seen by the CR16CAN at the
time of the error.
DRIVE Drive. This bit shows the output value on the
CANTX pin at the time of the error. Note that a
Buffer 10 1 1 0 1 1
Buffer 11 1 1 1 0 0
Buffer 12 1 1 1 0 1
Buffer 13 1 1 1 1 0
Buffer 14 1 1 1 1 1
15 8 7 0
REC[7:0] TEC[7:0]
0
r
15 14 13 12 11 10 9 4 3 0
Reserved DRIVE MON CRC STUFF TXE EBID[5:0] EFID[3:0]
0
r
Table 37Error Field Identifier
Field EFID3 EFID2 EFID1 EFID0
ERROR 0000
ERROR DEL 0001
ERROR ECHO 0010
BUS IDLE 0011
ACK 0100
EOF 0101
INTERMISSION 0110
SUSPEND
TRANSMISSION 0111
SOF 1000
ARBITRATION 1001
Table 36 Highest Priority Interrupt Code
(CICEN = FFFF)
CAN interrupt
request IRQ IST3 IST2 IST1 IST0 IDE 1010
EXTENDED
ARBITRATION 1011
R1/R0 1100
DLC 1101
DATA 1110
CRC 1111
Table 37Error Field Identifier
Field EFID3 EFID2 EFID1 EFID0
rrrrrr
incorrect
bit
data field
Figure 71.EBID Example
Obsolete
www.national.com 116
receiver will not drive the bus except during
ACK and during an active error flag.
20.9.19 CAN Timer Register (CTMR)
The current value of the Time Stamp counter as described in
section 20.8 can be monitored via the CAN Timer Register.
The CAN Time register is a free running 16-bit counter. It con-
tains the number of CAN bits recognized by CR16CAN since
the register has been reset. The counter starts to increment
from the value 0000 16 after a hardware reset. If the Timer
Stamp enable flag (TSTPEN) in the CAN global configuration
register (CGCR) is set, the counter will also be reset upon a
message transfer of the message buffer 0.
As described in Time Stamp Counter on page 105, the con-
tents of CTMR are captured into the Time Stamp register of
the message buffer after successfully sending or receiving a
frame.
20.10 SYSTEM START-UP AND MULTI-INPUT
WAKE-UP
After system start-up, all CR16CAN related registers are in
their reset state. The CR16CAN module can be enabled after
all configuration registers are set to their desired value. The
following initial setting need to be made:
—configure the CAN Timing register (CTIM) See “Bit
Time Logic” on page94.
—configure every buffer to its function as receive/trans-
mit Buffer Status/Control Register (CNSTAT) on page
106.
—set the acceptance filtering masks. See “Acceptance
Filtering” on page96.
—enable the CR16CAN interface. See “CAN Global
Configuration Register (CGCR)” on page109.
Before disabling the CR16CAN module, the user has to
make sure that no transmission is still pending.
Note: The device can be awaken from a power saving mode
by an activity on the CAN bus by selecting the CAN RX pin
as an input to the Multi-Input Wake-Up module. In this case
the CR16CAN module must not be disabled before entering
the power saving mode. Disabling the CR16CAN module
also disables the CAN RX pin.
As an alternative, the CAN RX pin can be connected to any
other input pin of the Multi-Input Wake-Up module. This input
channel must then be configured to trigger a wake-up event
on a falling edge (if a dominant bit is represented by a low lev-
el). In this case the CR16CAN module can be disabled be-
fore entering a power saving mode. After the device has
been waken up, the user has to manually enable the
CR16CAN again. All configuration and buffer registers still
contain the same data as prior to the power down phase.
20.10.1 External Connection
The CR16CAN uses two external pins, CANTX and CANRX
to connect to the physical layer of the CAN interface. They
provide the functionality as described in Table38.
The logic levels are configurable by means of two control
flags CTX and CRX of the Global Configuration Register
CGCR (see “CAN Global Configuration Register (CGCR)” on
page 109.
20.10.2 Transceiver Connection
An external Transceiver Chip needs to be connected be-
tween the CAN block and the bus. It is used to establish a bus
connection in differential mode and furthermore provides the
driver and protection requirements.
Figure72 shows a possible ISO-High-Speed configuration.
20.10.3 Timing Requirements
Processing messages and updating message buffers require
a certain number of clock cycles by CR16CAN as shown in
Table39. These requirements may lead to some restrictions
regarding the Bit Time Logic settings and the overall
CR16CAN performance which are described below in more
detail.
15 0
CTMR[15:0]
0
r
Table 38External CR16CAN Pins
Signal Name Type Description
CANTX Output Transmit data to the CAN bus
CANRX Input Receive data from the CAN bus
Table 39CR16CAN Internal Timing
task # cycles a
a. Wait cycles need to be added for CPU access to
the message memory as described in CPU
Access to CR16CAN Registers/Memory on
page 105.
occurrence/
frame b
b. Depends on the number of matching identifiers.
copy hidden buffer to receive
message buffer 17 0-1
update status from TX_RTR
to TX_ONCE_RTR 30-15
schedule a message for trans-
mission 20-1
VCC
to other modules
termination
CAN Bus Line
120
120
VCC
RS GND
BUS_L
BUS_H
TX
RX
REF
Transceiver Chip
GND
3
7
6
28
5
4
1
GND
CANTX
CANRX
CR16CAN
CORE BUS
Figure 72.External Transceiver Connection
(ISO-High-Speed)
Obsolete
117 www.national.com
The critical path derives from receiving a remote frame which
triggers the transmission of one or more data frames. There
are a minimum of four bit times in-between two consecutive
frames. These bit times start at the validation point of re-
ceived frame (reception of 6th EOF bit) and end at the earli-
est possible transmission start of the next frame, which is
after the third intermission bit at 100% burst bus load.
These four bit times have to be set in perspective with the
timing requirements of the CR16CAN.
The minimum duration of the four CAN bit times is deter-
mined by the following Bit Time Logic settings:
PSC = PSCmin = 2
TSEG1 = TSEG1min = 2
TSEG2 = TSEG2min = 1
bit time = Synch + Time Segment 1 + Time Segment 2
= (1 + 2 + 1) tq = 4 tq
= (4 tq x PSC) clock cycles
= (4 tq x 2) clock cycles = 8 clock cycles
For these minimum BTL settings, four CAN bit times take 32
clock cycles.
The following is an example that assumes typical case:
—minimum BTL settings
—reception and copy of a remote frame
—update of one buffer from TX_RTR
—schedule of one buffer from transmit
As outlined in Table39 the copy process, update and sched-
uling the next transmission gives a total of 17+3+2=22 clock
cycles. Therefore under these conditions there is no timing
restriction.
The following example assumes the worst case:
—minimum BTL settings
—reception and copy of a remote frame
—update of the 14 remaining buffers from TX_RTR
—schedule of one buffer for transmit
All these actions in total require 17 + 14 x 3 + 2 = 61 clock
cycles to be executed by CR16CAN. This leads to the limita-
tion of the Bit Time Logic of 61 / 4 = 15.25 clock cycles per
CAN bit as a minimum, resulting in the minimum clock fre-
quencies listed below (the frequency depends on the desired
baud rate and assumes the worst case scenario can occur in
the application).
Table40 gives examples for the minimum clock frequency in
order to ensure proper functionality at various CAN bus
speeds.
20.10.4 Bit Time Logic Calculation Examples
The calculation of the CAN bus clocks using CKI = 16MHz is
shown in the following examples. The desired baud rate for
both examples is 1Mbit/s.
Example 1
PSC = PSC[5:0] + 2 = 0 + 2 = 2
TSEG1 = TSEG1[3:0] + 1 = 3 + 1 = 4
TSEG2 = TSEG2[2:0] + 1 = 2 + 1 = 3
SJW = TSEG2 = 3
—sample point positioned at 62.5% of bit time
—bit time = 125ns x (1 + 4 + 3 ± 3) = (1 ± 0.375)µs
—busclock = 16MHz / (2 x (1 + 4 + 3)) = 1Mbit/s (nominal)
Example 2
PSC = PSC[5:0] + 1 = 2 + 2 = 4
TSEG1 = TSEG1[3:0] + 1 = 1 + 1 = 2
TSEG2 = TSEG2[2:0] + 1 = 0 + 1 = 1
SJW = TSEG2 = 1
•sample point positioned at 75% of bit time
•bit time = 250ns x (1 + 2 + 1 ± 1) = (1 ± 0.25)µs
•busclock = 16MHz / (2 x (1 + 4 + 3)) = 1Mbit/s (nominal)
20.10.5 Acceptance Filter Considerations
The CR16CAN provides two acceptance filter masks GMSK
and BMSK as described in Acceptance Filtering on page 96,
Global Mask Registers (GMSK — GMSKB and GMSKX) on
page 112 and Basic Mask Registers (BMSK — BMSKB and
BMSKX) on page 113. These masks allow filtering of up to 32
bits of the message, which includes the standard identifier,
the extended identifier as well as the frame control bits RTR,
SRR and IDE.
20.10.6 Remote Frames
Remote frames can be automatically processed by the
CR16CAN interface. However, to fully enable that feature,
the RTR/XRTR bits (for both standard and extended frames)
within the BMSK and/or GMSK register need to be set to
“don’t care”. This is because a remote frame with the RTR bit
being set to “1” should trigger the transmission of a data
frame with the RTR bit set to “0” and therefore the ID bits of
the received message need to pass through the acceptance
filter. The same applies to transmitting remote frames and
switching to receive the corresponding data frames.
Table 40Min. Clock Frequency Requirements
Baud Rate min. clock frequency
1Mbit/sec 15.25MHz
500kbit/sec 7.625MHz
250kbit/sec 3,81MHz
Obsolete
www.national.com 118
21.0 Analog Comparators
The Dual Analog Comparator (ACMP2) module contains two
independent analog comparators with all necessary control
logic. Each comparator unit compares the analog input volt-
ages applied to two input pins and determines which voltage
is higher. The comparison results can be placed on two out-
put pins and/or read by the software from a register.
Figure73 is a block diagram of the Dual Analog Comparator
module.
The two comparators are designated Comparator 1 (CMP1)
and Comparator 2 (CMP2). Each comparator has a positive
and a negative input, called CMP1P and CMP1N for Com-
parator 1 and CMP2P and CMP2N for Comparator 2. An op-
tional output, CMP1O for Comparator 1 or CMP2O for
Comparator 2, allows the external hardware to read the com-
parison results. If the positive input is greater than the nega-
tive input, the result is a logic 1. Otherwise, the result is a
logic 0. These same results are available to the software by
reading the CMPCTRL register. CMP1OP and CMP2OP are
the direct outputs of the analog comparator. These signals
are connected to the channels of the Multi-Wake-Up module.
21.1 ANALOG COMPARATOR CONTROL/
STATUS REGISTER (CMPCTRL)
The CMPCTRL register is a byte-wide, read/write register
that controls the comparator module and contains the com-
parison results. The control bits are read/write bits and the re-
sult bits are read-only bits. This register is cleared upon
reset. The register format is shown below.
CMP1RD Comparator 1 Read. This read-only bit con-
tains the output of Comparator 1 when the
comparator is enabled (CMP1EN=1).
CMP1RD is set to 1 when the voltage on
CMP1P is greater than the voltage on CMP1N.
This bit is always 0 when Comparator 1 is dis-
abled.
CMP2RD Comparator 2 Read. This read-only bit con-
tains the output of Comparator 2 when the
comparator is enabled (CMP2EN=1).
CMP2RD is set to 1 when the voltage on
CMP2P is greater than the voltage on CMP2N.
This bit is always 0 when Comparator 2 is dis-
abled.
CMP1EN Comparator 1 Enable. This read/write bit en-
ables (1) or disables (0) Comparator 1.
CMP2EN Comparator 2 Enable. This read/write bit en-
ables (1) or disables (0) Comparator 2.
CMP1OE Comparator 1 Output Enable. This read/write
bit, when set to 1, enables the use of the
CMP1O pin as the output of Comparator 1
when Comparator 1 is enabled (CMP1EN=1).
If Comparator 1 is disabled (CMP1EN=0), set-
ting the CMP1OE bit results in a logic 0 on the
CMP1O output pin.
CMP2OE Comparator 2 Output Enable. This read/write
bit, when set to 1, enables the use of the
CMP2O pin as the output of Comparator 2
when Comparator 2 is enabled (CMP2EN=1).
If Comparator 2 is disabled (CMP2EN=0), set-
ting the CMP2OE bit results in a logic 0 on the
CMP2O output pin.
21.2 ANALOG COMPARATOR USAGE
The comparator I/O pins are alternate functions of the Port L
pins. In order for a comparator to operate, its two input pins
must be configured to operate as inputs in the alternate func-
tion mode.
Using a comparator's output pin is optional. If it is to be used,
it must be configured to operate as an output in the alternate
function mode. The comparison result bits in the CMPCTRL
register are available to the CPU whether or not the output
pin is enabled.
The comparators uses DC current whenever they are en-
abled. Therefore, in order to reduce power consumption, it is
recommended that the comparators be disabled when they
are not needed, especially before entering any of the Power
Save modes.
7 6 5 4 3 2 1 0
Reserved CMP2OE CMP1OE CMP2EN CMP1EN CMP2RD CMP1RD
Figure 73.Dual Analog Comparator Block Diagram
+
_
CMP1
CMP1EN CMP1OE
+
_CMP2
CMP2EN CMP2OE
CONTROL + STATUS
CMP1P
CMP2P
CMP1N
CMP2N
CMP1O
CMP2O
CMP1OP
CMP2OP
Obsolete
119 www.national.com
22.0 A/D Converter
The A/D Converter (ADC) module is a 12-channel, multi-
plexed-input, analog-to-digital converter. The A/D Converter
receives an analog voltage on an input pin and converts that
voltage into an 8-bit digital value using successive approxi-
mation. The CPU can then read the result from a memory-
mapped register. The module supports four automated oper-
ating modes, providing single-channel or 4-channel scanned
operation in single-conversion or continuous mode.
Figure74 is a block diagram of the A/D Converter module.
The analog input signal is selected from the analog inputs us-
ing a 12-channel analog multiplexer. The input pins are alter-
nate functions of Port I.
A sample-and-hold circuit samples the analog voltage prior
to conversion and holds it stable throughout the conversion
process. A programmable initial delay period allows the sam-
pled voltage to stabilize before the conversion process be-
gins.
The input voltage range is from 0V to VREF (the A/D refer-
ence voltage). The device has a separate pin, VREF, for the
reference voltage.
A capacitor should be connected between the VREF and the
AVCC pin in order to minimize noise. The recommended val-
ue for this capacitor is about 0.47µF.
The internal analog-to-digital converter block is based on a
successive approximation algorithm, which compares the
sampled voltage against an internally generated sequence of
analog voltages. The result is a linear conversion of the ana-
log voltage to an unsigned 8-bit value ranging from 00 hex for
0.0 volts to FF hex for VREF.
The clock used by the converter block is generated by a clock
divider that scales down the system clock by a programma-
ble factor. The conversion algorithm requires ten A/D Con-
verter clock cycles, or 10 microseconds at the maximum
allowed A/D Converter clock rate of 2 MHz.
Conversion can start after the power supply is stable and AD-
CEN set for 30 µs.
The conversion results are stored in a 4-level data buffer. De-
pending on the operating mode, the buffer can hold the re-
sults of four successive conversions from a single channel or
four conversions from adjacent channels scanned in se-
quence.
22.1 OPERATING MODES
The A/D Converter can be configured to operate in any one
of four modes:
—Single channel, single conversion
—Single channel, continuous conversion
—4-channel scan, single conversion
—4-channel scan, continuous conversion
The configuration is set by the SCAN and CONT fields in the
ADC Control 2 Register (ADCCNT2), as indicated in
Table41. The A/D converter must be disabled when switch-
ing to a different mode.
22.1.1 Single Channel, Single Conversion Mode
In the single channel, single conversion mode, the A/D Con-
verter performs a single conversion using a specified chan-
nel.
The software starts a conversion by setting the START bit in
the ADCCNT2 register. Upon completion of the conversion,
the A/D Converter places the result in register ADDATA0,
clears the START bit, and sets the EOC (end of conversion)
bit in the ADCST register. If the A/D Converter interrupt is en-
abled, an interrupt to the CPU is generated at this time.
22.1.2 Single Channel, Continuous Conversion Mode
In the single channel, continuous conversion mode, the A/D
Converter performs conversions repeatedly using the same
specified channel.
The software starts a conversion sequence by setting the
START bit. The A/D Converter performs four A/D conver-
sions in sequence using the same channel, pausing only for
the programmable sampling delay time used in all conver-
sion operations. It loads the four results into the A/D data reg-
isters in sequence, starting with ADDATA0 and ending with
ADDATA3. After it loads all four registers, it sets the EOC
(end of conversion) bit. If the A/D Converter interrupt is en-
abled, an interrupt to the CPU is generated at this time.
The START bit remains set until cleared by the software. If
the software does not clear the START bit, the A/D Converter
continues performing conversions using the same input
channel, storing the results in ADDATA0 following ADDATA3.
To prevent an overrun error, the software must read the re-
sults from the data registers before the A/D Converter writes
the next result into ADDATA0 following ADDATA3.
When the software clears the START bit, the A/D Converter
first completes the conversion currently in progress, then
stops and sets the EOC bit. A 2-bit buffer pointer in the
ADCST register points to the register containing the final re-
sult.
22.1.3 4-Channel Scan, Single Conversion Mode
In the 4-channel scan, single conversion mode, the A/D Con-
verter performs four conversions using four adjacent input
channels.
The software starts the conversion sequence by setting the
START bit. The A/D Converter performs four A/D conver-
sions in sequence using four adjacent channels, starting with
the specified channel and pausing only for the programmable
sampling delay time. It loads the four results into the A/D data
registers in sequence, starting with ADDATA0 and ending
Table 41ADC Operation Modes
SCAN CONT Mode
00 0 Single Channel, Single Conversion
00 1 Single Channel, Continuous Conversion
01 0 4 Channels Scan, Single Conversion
01 1 4 Channel Scan, Continuous Conversion
Obsolete
www.national.com 120
with ADDATA3. After it loads all four registers, it clears the
START bit and sets the EOC (end of conversion) bit. If the A/
D Converter interrupt is enabled, an interrupt to the CPU is
generated at this time.
22.1.4 Channel Scan, Continuous Conversion Mode
In the 4-channel scan, continuous conversion mode, the A/D
Converter performs conversions repeatedly using four adja-
cent input channels.
The software starts conversion operations by setting the
START bit. The A/D Converter performs four A/D conver-
sions in sequence using four adjacent channels, starting with
the specified channel and pausing only for the programmable
sampling delay time. It loads the four results into the A/D data
registers in sequence, starting with ADDATA0 and ending
with ADDATA3. After it loads all four registers, it sets the EOC
(end of conversion) bit. If the A/D Converter interrupt is en-
abled, an interrupt to the CPU is generated at this time.
The START bit remains set until cleared by the software. If
the software does not clear the START bit, the A/D Converter
continues performing conversions, repeating the same se-
quence using the same four input channels and the same se-
quence of data registers. To prevent an overrun error, the
software must read the results from the data registers before
the A/D Converter writes the next result into ADDATA0.
When the software clears the START bit, the A/D Converter
first completes the 4-channel conversion sequence currently
in progress, then stops and sets the EOC bit.
22.2 A/D CONVERTER REGISTERS
The software controls the A/D Converter and reads the A/D
results by accessing the ADC registers. There are eight such
registers:
—ADC Status Register (ADCST)
—ADC Control 1 Register (ADCCNT1)
—ADC Control 2 Register (ADCCNT2)
—ADC Control 3 Register (ADCCNT3)
—ADC Data Registers (ADDATA0 through ADDATA3)
22.2.1 ADC Status Register (ADCST)
The ADCST register is a byte-wide register that indicates the
current status of the A/D Converter. One bit in this register,
the OVF flag bit, is cleared by writing a 1 to its bit position.
The other bits are read-only bits, so the values written to
them are ignored. Upon reset, the register is set to 30 hex.
The register format is shown below.
EOC End of Conversion. This read-only bit reports
the status of the most recent A/D Converter op-
eration. When cleared to 0, it indicates that the
conversion is not complete. When set to 1, it in-
dicates that the conversion is complete. The
hardware sets this bit when it places the con-
version results in the buffer and clears it when
any of the data registers are read.
BUSY ADC Busy. This read-only bit is set to 1 when
the A/D Converter is busy converting data and
is cleared to 0 when the A/D Converter is idle
or disabled.
OVF Overflow. The hardware sets this bit to 1 when
the A/D Converter finishes a conversion and at-
tempts to store the results in one of the data
registers (ADDATA0-ADDATA3) while the reg-
ister is full. When this happens, the A/D Con-
verter overwrites the data in the data register,
sets the OVF flag, and continues operating.
The OVF flag remains set until cleared by the
software. The software clears the flag by writ-
ing a 1 to it. Writing a 0 to this bit has no effect.
BUFPTR Buffer Pointer. This 2-bit, read-only field identi-
fies the data register that was most recently
written with new data:
00 = ADDATA0
01 = ADDATA1
10 = ADDATA2
11 = ADDATA3
Figure 74.A/D Converter Block Diagram
12:1
ANALOG
MUX SAMPLE
&
HOLD
CONFIGURATION
STATUS
&
CONTROL
DATA
BUFFER
CLOCK
DIVIDER
PERIPHERAL
BUS
CLK
CLK
VREF
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
ANALOG
TO
DIGITAL
CONVERTER
CH8
CH9
CH10
CH11
4
7 6 5 4 3 2 1 0
Reserved BUFPTR Reserved OVF BUSY EOC
Obsolete
121 www.national.com
This register is initialized to 11 when a new
conversion is started (when ADCCNT2.START
is changed from 0 to 1) and is automatically in-
cremented every time a result is written to buff-
ers ADDATA0-ADDATA3. The result is a four-
entry cyclic FIFO buffer, with BUFPTR pointing
to the last entry written by the A/D Converter.
22.2.2 ADC Control 1 Register (ADCCNT1)
The ADCCNT1 register is a byte-wide, read/write register
used to enable the A/D Converter and its interrupts, and also
to control the reference voltage source. When writing to this
register, all reserved bits must be written with 0 for the A/D
Converter to function properly. Changing any bits other than
ADCEN (bit 0) is not allowed while the A/D Converter is ac-
tive (ADCST.BUSY or ADCCNT2.START set). Upon reset,
all non-reserved bits are cleared to 0. The register format is
shown below.
ADCEN A/D Converter Enable. Setting this bit enables
the A/D Converter and allows a conversion to
be started by setting the start bit
(ADCCNT2.START). Clearing the ADCEN bit
disables the A/D Converter, terminates any
conversion in progress, and clears the ADC
status flags (ADCST.EOC, ADCST.BUSY,
ADCST.OVF, and ADCCNT2.START).
INTE Interrupt Enable. This bit enables (1) or dis-
ables (0) A/D Converter interrupts. If enabled,
and interrupt occurs at the end of a conversion
sequence or when the ADC data buffer is full,
depending on the operating mode.
All reserved bits must be written with 0 for ADC to operate
properly.
22.2.3 ADC Control 2 Register (ADCCNT2)
The ADCCNT2 register is a byte-wide, read/write register
used to specify the A/D Converter operating mode and to
start conversion operations. All register fields other than the
START bit should be changed only while the A/D Converter
is inactive (START=0). Data written to the SCAN and CONT
fields is ignored if the START bit is already set. Upon reset,
the non-reserved bits of this register are cleared to 0. The
register format is shown below.
CHANNEL Channel Select. This 4-bit field selects one of
the twelve analog input channels as follows:
0000 = ACH0
0001 = ACH1
0010 = ACH2
0011 = ACH3
0100 = ACH4
0101 = ACH5
0110 = ACH6
0111 = ACH7
1000 = ACH8
1001 = ACH9
1010 = ACH10
1011 = ACH11
11XX = reserved
CONT Continuous Conversion. When cleared to 0,
the A/D Converter stops operating upon com-
pletion of the programmed conversion cycle (a
single conversion or a sequence of four con-
versions on four channels). When set to 1, the
A/D Converter operates continuously by re-
peating the programmed conversion cycle.
SCAN Scan Mode. This 2-bit field selects the single-
conversion mode or 4-channel scan mode as
follows:
00 = single-conversion mode
01 = 4-channel scan mode
1X = reserved
START Start Conversion. The software sets this bit to
1 to start a conversion or a 4-channel conver-
sion cycle. In the “continuous” mode, this bit re-
mains set until cleared by the software. In the
“single” (non-continuous) mode, the hardware
clears this bit upon completion of the pro-
grammed conversion cycle. The software
should not attempt to set this bit while the A/D
Converter is busy (ADCST.BUSY=1).
22.2.4 ADC Control 3 Register (ADCCNT3)
The ADCCNT3 register is a byte-wide, read/write register
used to specify the analog sampling time delay and the di-
vide-by factor for generating the ADC clock. This register
should be written only when the A/D Converter is disabled
(ADCCNT1.ADCEN=0). Upon reset, the non-reserved bits of
the ADCCNT3 register are cleared to 0. The register format
is shown below.
CDIV Clock Divide. This 3-bit field sets the divide-by
factor for generating the A/D Converter clock
from the system clock. The frequency of the A/
D Converter clock is equal to the system clock
divided by the programmed factor. The result-
ing A/D Converter clock frequency must be
less than or equal to 2 MHz. The divide-by fac-
tor is defined as follows:
000 = divide by 1
001 = divide by 2
010 = divide by 4
011 = divide by 8
100 = divide by 16
101 = divide by 32
Other = reserved
DELAY Sampling Time Delay. This 3-bit field defines
the number of A/D Converter clock cycles of
delay from the time that the input channel is se-
lected until the analog voltage is sampled. The
programmed delay should be sufficient, depen-
dent on the source impedance, to allow the
sampled signal to reach its final level before the
conversion begins. The delay is defined as fol-
lows:
7 6 5 4 3 2 1 0
Reserved INTE Reserved ADCEN
7 6 5 4 3 2 1 0
START SCAN CONT CHANNEL
7 6 5 4 3 2 1 0
Reserved PWREN DELAY CDIV
Obsolete
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000 = 1 A/D Converter clock cycle
001 = 2 A/D Converter clock cycles
010 = 4 A/D Converter clock cycles
011 = 8 A/D Converter clock cycles
100 = 16 A/D Converter clock cycles
101 = 32 A/D Converter clock cycles
110 = 64 A/D Converter clock cycles
111 = reserved
PWREN Power Down Enable. controls the condition
when the ADC is powered down. When
PWREN is cleared (0), the ADC powers down
upon reset. When PWREN is set (1), the ADC
powers down when the ADCEN bit is low.
22.2.5 ADC Data Registers (ADDATA0-ADDATA3)
The four ADC Data Registers (ADDATA0 through ADDATA3)
are byte-wide, read/write registers that hold the conversion
results, which are stored sequentially starting with ADDATA0
and ending with ADDATA3. The results held in these regis-
ters are valid only after the ADCST.EOC flag is set. Upon re-
set, the contents of these registers are undefined.
The value read from a data register is a linear mapping of the
analog input voltage to an 8-bit value. The value 00 hex rep-
resents 0.0 volts and the value FF hex represents the refer-
ence voltage, VREF.
22.3 A/D CONVERTER PROGRAMMING
The software should set the A/D Converter configuration be-
fore it enables the A/D Converter module. The configuration
consists of the following settings:
—ADC clock rate: ADCCNT3.CDIV
—Sampling delay: ADCCNT3.DELAY
—Interrupt enable (if required): ADCCNT1.INTE
The ADC clock is created by scaling down the system clock.
The fastest allowable clock for the A/D Converter is 2 MHz.
Therefore, for the fastest possible operation of the A/D Con-
verter, use the smallest available divide-by factor that results
in a clock frequency of 1 MHz or lower. The available divide-
by factors are 1, 2, 4, 8, 16, and 32.
For example, if the system clock is 10 MHz, use a divide-by
factor of 16. In that case, the A/D Converter clock frequency
is 625 kHz, the clock period is 1.6 microseconds, and the A/
D conversion time is 16 microseconds (ten clock A/D Con-
verter clock cycles).
The programmable sampling time delay should be made
small for faster operation, but large enough to allow the input
voltage to settle. The internal resistance and capacitance of
the A/D Converter, together with the source resistance of the
device that drives the A/D input determine the charge-up time
required for the voltage to settle. Figure75 shows a schemat-
ic of the charge-up circuit. For the values of RAIN and CAIN,
see Section25.0.
Interrupts or polling can be used to read the A/D Converter
results. For interrupts, the A/D Converter interrupt must be
enabled by setting the ADCCNT1.INTE bit. The interrupt is
cleared automatically when any one of the data registers
(ADDATA0-ADDATA3) is read. For polling, the software
reads the ADCST.EOC bit to determine whether the conver-
sion sequence is completed.
Once the A/D Converter configuration has been set up, the
software can use the following procedure to perform an A/D
conversion sequence:
1. Enable the A/D Converter by setting the ADCCNT1.AD-
CEN bit and wait 30 µs before performing any conver-
sion.
2. Select the operating mode and channel by writing to the
SCAN, CONT, and CHANNEL fields of the ADCCNT2
register. At the same time, start the conversion by setting
the START bit in the same register.
3. Wait until the conversion is finished, either by polling or
using the A/D Converter interrupt.
4. Read the conversion results from the data registers,
ADDATA0 through ADDATA3 (or just ADDATA0 in the
single-channel, single-conversion mode).
5. In the continuous conversion modes, repeat Step 3 and
Step 4 for as long as samples are needed. Then stop the
A/D Converter by clearing either the START bit
(ADCCNT2.START) or the A/D Converter enable bit
(ADCCNT1.ADCEN).
To minimize power consumption, the A/D Converter should
be disabled when it is not needed, especially before entering
a Power Save mode.
Figure 75.Sample-and-Hold Charge-Up Schematic
A/D Converter
Analog
Multiplexer Sample &
Hold
RAIN
CAIN
Input
signal
RSOURCE
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23.0 Memory Map
The CompactRISC architecture supports a uniform linear ad-
dress space of 2 megabytes. The device implementation of
this architecture uses only the lowest 128K bytes of address
space, ranging from 0000 to 1FFFF hex. Table42 is a mem-
ory map showing the types of memory and peripherals that
occupy this memory space. Address ranges not listed in the
table are reserved and should not be read or written.
Table43 is a detailed memory map showing the specific
memory address of the memory, I/O ports, and registers. The
table shows the starting address, the size, and a brief de-
scription of each memory block and register. For detailed in-
formation on using these memory locations, see the
applicable sections in the data sheet.
All addresses not listed in the table are reserved and should
not be read or written. An attempt to access an unlisted ad-
dress will have unpredictable results.
Each byte-wide register occupies a single address and can
be accessed only in a byte-wide transaction. Each word-wide
register occupies two consecutive memory addresses and
can be accessed only in a word-wide transaction. Both the
byte-wide and word-wide registers reside at word boundaries
(even addresses). Thus, each byte-wide register uses only
the lowest eight bits of the internal data bus.
Most device registers are read/write registers. However,
some registers are read-only or write-only, as indicated in the
table. An attempt to read a write-only register or to write a
read-only register will have unpredictable results.
When the software writes to a register in which one or more
bits are reserved, it must write a zero to each reserved bit un-
less indicated otherwise in the description of the register.
Reading a reserved bit returns an undefined value.
Table 42Device Memory Map
Address
Range (hex) Description
0000-7FFF Flash Program Memorya
8000-BFFF Flash Program Memory (48K bytes)
C000-CBFF Static RAM (3K bytes)
E000-E5FF ISP Memory(1.5K bytes)
E800-EFFF Lower Endurance Flash EEPROM Data
Memory (2K bytes)
F000-F07F High Endurance Flash EEPROM Data
Memory (128 bytes)
F400-F7FF CAN buffers and registers (1K bytes)
F800-FAFF BIU Peripherals (768 bytes)
FB00-FB06 Port B registers
FB00-FBFF I/O Expansion + Ports PB & PC (256bytes)
FB10-FB16 Port C registers
FC00-FFFF Peripherals and other I/O Ports (1K bytes)
FC40-FC8A Clock, Power Management, and Wake-Up
registers
FCA0-FCA8 Port G registers
FCC0-FCC8 Port H registers
FF00-FF08 Port L registers
FD20-FD28 Port F registers
FE00-FE1E Interrupt Control Unit registers
FE40-FE4E USART 1 registers
FE60-FE66 MICROWIRE registers
FE80-FE8E USART 2 registers
FEC0-FECA ACCESS.bus registers
FEE0-FEE8 Port I registers
FF20-FF2A Timer and WATCHDOG registers
FF40-FF50 Multi-function Timer1 registers
FF60-FF70 Multi-function Timer2 registers
FF80-FFA4 Versatile Timer Unit registers
FFC0-FFD0 A/D Converter registers
FFE0-FFE0 Analog Comparator register
1C000-1FFFF Flash Program Memory (16K bytes)b
a. 32K ROM or Flash, size depends on device specifications.
Obsolete
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Table 43Device Detailed Memory Map
Register Name Size Register
Address
(hex) Access Type Contents
32K/48K 0000 Flash EEPROM Program Memory
3K C000 On-Chip RAM
2K E800 Low Endurance Flash EEPROM Data Memory
1.5K E000 ISP Memory
128 F000 High Endurance Flash EEPROM Data Memory
CMB0_CNTSTAT word F400 Read/Write CAN message buffer 0 Status Register
CMB0_TSTP word F402 Read/Write CAN message buffer 0 Time stamp Register
CMB0_DATA3 word F404 Read/Write CAN message buffer 0 Data 3 Register
CMB0_DATA2 word F406 Read/Write CAN message buffer 0 Data 2 Register
CMB0_DATA1 word F408 Read/Write CAN message buffer 0 Data 1 Register
CMB0_DATA0 word F40A Read/Write CAN message buffer 0 Data 0 Register
CMB0_ID0 word F40C Read/Write CAN message buffer 0 Identifier 0 Register
CMB0_ID1 word F40E Read/Write CAN message buffer 0 Identifier 1 Register
CMB1 8-word F410 Read/Write CAN message buffer 1 Register
CMB2 8-word F420 Read/Write CAN message buffer 2 Register
CMB3 8-word F430 Read/Write CAN message buffer 3 Register
CMB4 8-word F440 Read/Write CAN message buffer 4 Register
CMB5 8-word F450 Read/Write CAN message buffer 5 Register
CMB6 8-word F460 Read/Write CAN message buffer 6 Register
CMB7 8-word F470 Read/Write CAN message buffer 7 Register
CMB8 8-word F480 Read/Write CAN message buffer 8 Register
CMB9 8-word F490 Read/Write CAN message buffer 9 Register
CMB10 8-word F4A0 Read/Write CAN message buffer 10 Register
CMB11 8-word F4B0 Read/Write CAN message buffer 11 Register
CMB12 8-word F4C0 Read/Write CAN message buffer 12 Register
CMB13 8-word F4D0 Read/Write CAN message buffer 13 Register
CMB14 8-word F4E0 Read/Write CAN message buffer 14 Register
CGCR word F500 Read/Write CAN Global Configuration Register
CTIM word F502 Read/Write CAN Timing Register
GMSKX and GMSK word F504 Read/Write CAN Global Mask Registers
GMSKX and GMSKB word F508 Read/Write CAN Basic Mask Registers
CIEN word F50C Read/Write CAN Interrupt Enabled Register
CIPND word F50E Read/Write CAN Interrupt Pending Register
CICLR word F510 Read/Write CAN Interrupt Clear Register
CICEN word F512 Read/Write CAN Interrupt Code Enable Register
CSTPND word F514 Read/Write CAN Status Pending Register
CANEC word F516 Read/Write CAN Error Counter Register
CEDIAG word F518 Read/Write CAN Error Diagnostic Register
CTMR word F51A Read/Write CAN Timer Register
BCFG byte F900 Read/Write BIU Configuration Register
IOCFG word F902 Read/Write I/O Zone Configuration Register
SZCFG0 word F904 Read/Write Static Zone 0 Configuration Register
SZCFG1 word F906 Read/Write Static Zone 1 Configuration Register
MCFG byte F910 Read/Write Module Configuration Register
MSTAT byte F914 Read Only Module Status Register
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FLCTRL1 byte F930 Read/Write Flash EEPROM Program Memory Control Register 1
FLSEC byte F932 Read/Write Flash EEPROM Program Memory Security Register
ISPKEY byte F934 Read/Write ISP Memory Write Key Register
FLCTRL2 word F936 Read/Write Flash EEPROM Program Memory Control Register 2
DMCSR byte F940 Read/Write EEPROM Data Memory Control and Status Register
DMPSLR byte F942 Read/Write EEPROM Data Memory Prescaler Register
DMSTART byte F944 Read/Write Data Memory Start Time Reload Register
DMTRAN byte F946 Read/Write Data Memory Transition Time Reload Register
DMPROG byte F948 Read/Write Data Memory Programming Time Reload Register
DMERASE byte F94A Read/Write Data Memory Erase Time Reload Register
DMEND byte F94C Read/Write Data Memory End Time Reload Register
DMPCNT byte F94E Read/Write Data Memory Prescaler Count Register
DMCNT word F950 Read/Write Data Memory Timer Count Register
DMKEY byte F954 Read/Write EEPROM Data Memory Write Key Register
FLCSR byte F960 Read/Write Flash EEPROM Program Memory Control and Status
Register
FLPSLR byte F962 Read/Write Flash EEPROM Program Memory Prescaler Register
FLSTART byte F964 Read/Write Program Memory Start Time Reload Register
FLTRAN byte F966 Read/Write Program Memory Transition Time Reload Register
FLPROG byte F968 Read/Write Program Memory Programming Time Reload Register
FLERASE byte F96A Read/Write Program Memory Erase Time Reload Register
FLEND byte F96C Read/Write Program Memory End Time Reload Register
FLPCNT byte F96E Read/Write Program Memory Prescaler Count Reload Register
FLCNT1 byte F970 Read/Write Program Memory Timer Count Register 1
FLCNT2 byte F972 Read/Write Program Memory Timer Count Register 2
PGMKEY byte F974 Read/Write Flash EEPROM Program Memory Write Key Register
PBDIR byte FB00 Read/Write Port B Direction Register
PBDIN byte FB02 Read Only Port B Data Input Register
PBDOUT byte FB04 Read/Write Port B Data Output Register
PBWKPU byte FB06 Read/Write Port B Weak Pull-Up Register
PCDIR byte FB10 Read/Write Port C Direction Register
PCDIN byte FB12 Read Only Port C Data Input Register
PCDOUT byte FB14 Read/Write Port C Data Output Register
PCWKPU byte FB16 Read/Write Port C Weak Pull-Up Register
CRCTRL byte FC40 Read/Write Clock and Reset Control Register
PRSSC byte FC42 Read/Write Slow Clock Prescaler Register
PRSSC1 byte FC44 Read/Write Prescaler Slow Clock 1 Register
PMCSR byte FC60 Read/Write Power Management Control/Status Register
WKEDG word FC80 Read/Write Wake-Up Edge Detection Register
WKENA word FC82 Read/Write Wake-Up Enable Register
WKICT1 word FC84 Read/Write Wake-Up Interrupt Control Register 1
WKICTL2 word FC86 Read Set Wake-Up Interrupt Control Register 2
WKPND word FC88 Write Only Wake-Up Pending Register
WKPCL word FC8A Read/Write Wake-Up Pending Clear Register
PGALT byte FCA0 Read/Write Port G Alternate Function Register
Table 43Device Detailed Memory Map
Register Name Size Register
Address
(hex) Access Type Contents
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PGDIR byte FCA2 Read/Write Port G Direction Register
PGDIN byte FCA4 Read Only Port G Data Input Register
PGDOUT byte FCA6 Read/Write Port G Data Output Register
PGWKPU byte FCA8 Read/Write Port G Weak Pull-Up Register
PHALT byte FCC0 Read/Write Port H Alternate Function Register
PHDIR byte FCC2 Read/Write Port H Direction Register
PHDIN byte FCC4 Read Only Port H Data Input Register
PHDOUT byte FCC6 Read/Write Port H Data Output Register
PHWKUP byte FCC8 Read/Write Port H Weak Pull-Up Register
PFALT byte FD20 Read/Write Port F Alternate Function Register
PFDIR byte FD22 Read/Write Port F Direction Register
PFDIN byte FD24 Read Only Port F Data Input Register
PFDOUT byte FD26 Read/Write Port F Data Output Register
PFWKPU byte FD28 Read/Write Port F Weak Pull-Up Register
IVCT byte FE00 Read Only Interrupt Vector Register
NMISTAT byte FE02 Read Only NMI Status Register
EXNMI byte FE04 Read/Write External NMI Control/Status Register
ISTAT0 word FE0A Read Only Interrupt Status Register 0
ISTAT1 word FE0C Read Only Interrupt Status Register 1
IENAM0 word FE0E Read/Write Interrupt and Enable Mask Register 0
IENAM1 word FE10 Read/Write Interrupt and Enable Mask Register 1
IDBG word FE1A Read/Write Interrupt Debug Register
U1TBUF byte FE40 Read/Write USART 1 Transmit Data Buffer
U1RBUF byte FE42 Read Only USART 1 Receive Data Buffer
U1ICTRL byte FE44 Read/Write USART 1 Interrupt Control Register
U1STAT byte FE46 Read Only USART 1 Status Register
U1FRS byte FE48 Read/Write USART 1 Frame Select Register
U1MDSL byte FE4A Read/Write USART 1 Mode Select Register
U1BAUD byte FE4C Read/Write USART 1 Baud Rate Divisor Register
U1PSR byte FE4E Read/Write USART 1 Baud Rate Prescaler
MWDAT byte FE60 Read/Write MICROWIRE Data Register
MWCTL byte FE62 Read/Write MICROWIRE Control Register
MWSTAT word FE64 Read/Write MICROWIRE status Register
U2TBUF byte FE80 Read/Write USART 2 Transmit Data Buffer
U2RBUF byte FE82 Read Only USART 2 Receive Data Buffer
U2ICTRL byte FE84 Read/Write USART 2 Interrupt Control Register
U2STAT byte FE86 Read Only USART 2 Status Register
U2FRS byte FE88 Read/Write USART 2 Frame Select Register
U2MDSL byte FE8A Read/Write USART 2 Mode Select Register
ACBSDA byte FEC0 Read/Write ACB Serial Data Register
U2BAUD byte FE8C Read/Write USART 2 Baud Rate Divisor Register
U2PSR byte FE8E Read/Write USART 2 Baud Rate Prescaler
ACBST byte FEC2 Read/Write ACB Status Register
Table 43Device Detailed Memory Map
Register Name Size Register
Address
(hex) Access Type Contents
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ACBCST byte FEC4 Read/Write ACB Control Status Register
ACBCTL1 byte FEC6 Read/Write ACB Control 1 Register
ACBADDR byte FEC8 Read/Write ACB Own Address Register
ACBCTL2 byte FECA Read/Write ACB Control 2 Register
PIALT byte FEE0 Read/Write Port I Alternate Function Register
PIDIR byte FEE2 Read/Write Port I Direction Register
PIDIN byte FEE4 Read Only Port I Data Input Register
PIDOUT byte FEE6 Read/Write Port I Data Output Register
PIWKPU byte FEE8 Read/Write Port I Weak Pull-Up Register
PLALT byte FF00 Read/Write Port L Alternate Function Register
PLDIR byte FF02 Read/Write Port L Direction Register
PLDIN byte FF04 Read Only Port L Data Input Register
PLDOUT byte FF06 Read/Write Port L Data Output Register
PLWKPU byte FF08 Read/Write Port L Weak Pull-Up Register
TWCFG byte FF20 Read/Write Timer and WATCHDOG Configuration Register
TWCP byte FF22 Read/Write Timer and WATCHDOG Clock Prescaler Register
TWMT0 word FF24 Read/Write TWM Timer 0 Register
T0CSR byte FF26 Read/Write TWMT0 Control and Status Register
WDCNT byte FF28 Write Only WATCHDOG Count Register
WDSDM byte FF2A Write Only WATCHDOG Service Data Match Register
T1CNT1 word FF40 Read/Write T1 Timer/Counter I Register
T1CRA word FF42 Read/Write T1 Reload/Capture A Register
T1CRB word FF44 Read/Write T1 Reload/Capture B Register
T1CNT2 word FF46 Read/Write T1 Timer/Counter II Register
T1PRSC byte FF48 Read/Write T1 Clock Prescaler Register
T1CKC byte FF4A Read/Write T1 Clock Unit Control Register
T1CTRL byte FF4C Read/Write T1 Timer Mode Control Register
T1ICTL byte FF4E Read/Write T1 Timer Interrupt Control Register
T1ICLR byte FF50 Read/Write T1 Timer Interrupt Clear Register
T2CNT2 word FF60 Read/Write T2 Timer/Counter I Register
T2CRA word FF62 Read/Write T2 Reload/Capture A Register
T2CRB word FF64 Read/Write T2 Reload/Capture B Register
T2CNT2 word FF66 Read/Write T2 Timer/Counter II Register
T2PRSC byte FF68 Read/Write T2 Clock Prescaler Register
T2CKC byte FF6A Read/Write T2 Clock Unit Control Register
T2CTRL byte FF6C Read/Write T2 Timer Mode Control Register
T2ICTL byte FF6E Read/Write T2 Timer Interrupt Control Register
T2ICLR byte FF70 Read/Write T2 Timer Interrupt Clear Register
MODE word FF80 Read/Write Mode Control Register
IO1CTL word FF82 Read/Write I/O Control Register 1
IO2CTL word FF84 Read/Write I/O Control Register 2
INTCTL word FF86 Read/Write Interrupt Control Register
INTPND word FF88 Read/Write Interrupt Pending Register
CLK1PS word FF8A Read/Write Clock Prescaler Register 1
COUNT1 word FF8C Read/Write Counter Register 1
Table 43Device Detailed Memory Map
Register Name Size Register
Address
(hex) Access Type Contents
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PERCAP1 word FF8E Read/Write Period/Capture Register 1
DTYCAP1 word FF90 Read/Write Duty Cycle/Capture Register 1
COUNT2 word FF92 Read/Write Count Register 2
PERCAP2 word FF94 Read/Write Period/Capture Register 2
DTYCAP2 word FF96 Read/Write Duty Cycle/Capture Register 2
CLK2PS word FF98 Read/Write Clock Prescaler Register 2
COUNT3 word FF9A Read/Write Count Register 3
PERCAP3 word FF9C Read/Write Period/Capture Register 3
DTYCAP3 word FF9E Read/Write Duty Cycle/Capture Register 3
COUNT4 word FFA0 Read/Write Count Register 4
PERCAP4 word FFA2 Read/Write Period/Capture Register 4
DTYCAP4 word FFA4 Read/Write Duty Cycle/Capture Register 4
ADCST byte FFC0 Read/Write A/D Converter Status Register
ADCCNT1 byte FFC2 Read/Write A/D Converter Control 1 Register
ADCCNT2 byte FFC4 Read/Write A/D Converter Control 2 Register
ADCCNT3 byte FFC6 Read/Write A/D Converter Control 3 Register
ADDATA0 byte FFCA Read Only A/D Converter Data 0 Register
ADDATA1 byte FFCC Read Only A/D Converter Data 1 Register
ADDATA2 byte FFCE Read Only A/D Converter Data 2 Register
ADDATA3 byte FFD0 Read Only A/D Converter Data 3 Register
CMPCTRL byte FFE0 Read/Write Analog Comparator Control/Status Register
Table 43Device Detailed Memory Map
Register Name Size Register
Address
(hex) Access Type Contents
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24.0 Register Layouts
The following tables show the functions of the bit fields of the device registers. For more information on using these registers,
see the detailed description of the applicable function elsewhere in this data sheet.
24.1 REGISTER LAYOUT
CAN Memory
Registers 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
CMBn.ID1 XI28
ID10 XI27
ID9 XI26
ID8 XI25
ID7 XI24
ID6 XI23
ID5 XI22
ID4 XI21
ID3 XI20
ID2 XI19
ID1 XI18
ID0 SRR
RTR IDE XI17 XI16 XI15
CMBn.ID0 XI14 XI13 XI12 XI11 XI10 XI9 XI8 XI7 XI6 XI5 XI4 XI3 XI2 XI1 XI0 RTR
CMBn.DATA0 Data
1.7 Data
1.6 Data
1.5 Data
1.4 Data
1.3 Data
1.2 Data
1.1 Data
1.0 Data
2.7 Data
2.6 Data
2.5 Data
2.4 Data
2.3 Data
2.2 Data
2.1 Data
2.0
CMBn.DATA1 Data
3.7 Data
3.6 Data
3.5 Data
3.4 Data
3.3 Data
3.2 Data
3.1 Data
3.0 Data
4.7 Data
4.6 Data
4.5 Data
4.4 Data
4.3 Data
4.2 Data
4.1 Data
4.0
CMBn.DATA2 Data
5.7 Data
5.6 Data
5.5 Data
5.4 Data
5.3 Data
5.2 Data
5.1 Data
5.0 Data
6.7 Data
6.6 Data
6.5 Data
6.4 Data
6.3 Data
6.2 Data
6.1 Data
6.0
CMBn.DATA3 Data
7.7 Data
7.6 Data
7.5 Data
7.4 Data
7.3 Data
7.2 Data
7.1 Data
7.0 Data
8.7 Data
8.6 Data
8.5 Data
8.4 Data
8.3 Data
8.2 Data
8.1 Data
8.0
CMBn.TSTP TSTP15 TSTP14TSTP13 TSTP12TSTP11 TSTP10 TSTP9 TSTP8 TSTP7 TSTP6 TSTP5 TSTP4 TSTP3 TSTP2 TSTP1 TSTP0
CMBn.CNT-
STAT DLC3 DLC2 DLC1 DLC0 Reserved PRI3 PRI2 PRI1 PRI0 ST3 ST2 ST1 ST0
CAN
Control/
Status 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
CGCR Reserved EIT DIAGEN INTERNAL LOOPBACK IGNACK LO DDIR TSTPEN BUFFLOCK CRX CTX CANEN
CTIM PSC[6:0] SJW[1:0] TSEG1[3:0] TSEG2[2:0]
GMSKB GM[28:18] RTR IDE GM[17:15]
GMSKX GM[14:0] XRTR
BMSKB BM[28:18] RTR IDE BM[17:15]
BMSKX BM[14:0] XRTR
CIEN EIEN IEN[14:0]
CIPND EIPND IPND[14:0]
CICLR EICLR ICLR[14:0]
CICEN EICEN ICEN[14:0]
CSTPND Reserved NS[2:0] IRQ IST[3:0]
CANEC REC[7:0] TEC[7:0]
CEDIAG Reserve
dDRIVE MON CRC STUFF TXE EBID[5:0] EFID[3:0]
CTMR CTMR[15:0]
System
Configuration
Registers 7 6 5 4 3 2 1 0
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MCFG Reserved CLK2OE Reserved CLK1OE CLKOE Reserved
MSTAT Reserved PGMBUSY Reserved OENV1 OENV0
BIU Registers 15 12 11 10 9 8 7 6 5 4 3 2 1 0
BCFG Reserved EWR
IOCFG Reserved IPST Res BW Reserved HOLD WAIT
SZCFG0 Reserved FRE IPRE IPST Res BW Reserved HOLD WAIT
SZCFG1 Reserved FRE IPRE IPST Res BW Reserved HOLD WAIT
ISP Registers 15 13 12 10 9 8 76543210
FLCTRL1 Reserved BOOTAREA
FLCTRL2 EMPTY Reserved CODEAREA
FLSEC Reserved FROMWR FROMRD
ISPKEY Reserved ISPKYVAL
Flash Data
Memory
Registers 15 14 10 9 8 7 6 5 4 3 2 1 0
DMCSR Reserved ERASE DMBUSY ZEROWS Reserved
DMPSLR Reserved FTDIV
DMSTART Reserved FTSTART
DMTRAN Reserved FTTRAN
DMPROG Reserved FTPROG
DMERASE Reserved FTER
DMEND Reserved FTEND
DMPCNT Reserved FTPCNT
DMCNT Reserved FTCNT
DMKEY Reserved DMKEYVAL
Flash EEPROM Program
Memory Registers 76543210
FLCSR MERASE Reserved PMLFULL PMBUSY PMER Reserved
FLPSLR FTDIV
FLSTART FTSTART
FLTRAN FTTRAN
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FLPROG FTPROG
FLERASE FTER
FLEND FTEND
FLPCNT FTPCNT
FLCNT1 FTCNTL (0:7)
FLCNT2 Reserved FTCNTL (8:9)
PGMKEY PMKEYVAL
GPIO Registers 7 6 5 4 3 2 1 0
PxALT Px Pins Alternate Function Enable
PxDIR Px Port Direction
PxDIN Px Port Output Data
PxDOUT Px Port Input Data
PxWPU Px Port Weak Pull-up Enable
ICU31L Registers 15 12 11 8 76543210
IVCT Reserved 0 0 INTVECT
NMISTAT Reserved EXT
EXNMI Reserved ENLCK PIN EN
ISTAT0 IST(15:0)
ISTAT1 IST(31:16)
IENAM0 IENA(15:0)
IENAM1 IENA(31:16)
IDBG Reserved IRQVECT INTVECT
MIWU16
Registers 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
WKEDG WKED
WKENA WKEN
WKICTL1 WKINTR7 WKINTR6 WKINTR5 WKINTR4 WKINTR3 WKINTR2 WKINTR1 WKINTR0
WKICTL2 WKINTR15 WKINTR14 WKINTR13 WKINTR12 WKINTR11 WKINTR10 WKINTR9 WKINTR8
WKPND WKPD
WKPCL WKCL
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Dual Clock + Reset Registers 7 6 5 4 3 2 1 0
CRCTRL Reserved POR SCLK
PRSSC SCDIV
PRSSC1 SCDIV2 SCDIV1
Power Management Register 7 6 5 4 3 2 1 0
PMCSR OLFC OHFC WBPSM Reserved HALT IDLE DHF PSM
USART Registers 7 6 5 4 3 2 1 0
UnTBUF UnTBUF
UnRBUF UnRBUF
UnICTRL UnEEI UnERI UnETI Reserved UnRBF UnTBE
UnSTAT Reserved UnXMIP UnRB9 UnBKD UnERR UnDOE UnFE UnPE
UnFRS Reserved UnPEN UnPSEL UnXB9 UnSTP UnCHAR
UnMDSL Reserved UnCKS UnBRK UnATN UnMOD
UnBAUD UnDIV[7]: UnDIV[0]
UnPSR UnPSC UnDIV[10]: UnDIV[8]
MWSPI16
Registers 15 9 8 7 6 5 4 3 2 1 0
MWDAT MWDAT
MWCTL MCDV MIDL MSKM MEIW MEIR MEIO MECH MMOD MMNS MEN
MWSTAT Reserved MOVR MRBF MBSY
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ACB Registers 7 6 5 4 3 2 1 0
ACBSDA DATA
ACBST SLVSTP SDAST BER NEGACK STASTR NMATCH MASTER XMIT
ACBCST Reserved TGSCL TSDA GMATCH MATCH BB BUSY
ACBCTL1 STASTRE NMINTE GCMEN ACK Reserved INTEN STOP START
ACBADDR SAEN ADDR
ACBCTL2 SCLFRQ ENABLE
TIMER Registers 15 8 76543210
TnCNT1 TnCNT1
TnCRA TnCRA
TnCRB TnCRB
TnCNT2 TnCNT2
TnPRSC Reserved CLKPS
TnCKC Reserved C2CSEL C1CSEL
TnCTRL Reserved TnAOUT TnBEN TnAEN TnBEDG TnAEDG MDSEL
TnICTL TnDIEN TnCIEN TnBIEN TnAIEN TnDPND TnCPND TnBPND TnAPND
TnICLR Reserved TnDCLR TnCCLR TnBCLR TnACLR
Obsolete
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VTU
Registers 15 14 13 12 11 10 9876543210
MODE TMOD4 T8RUN T7RUN TMOD3 T6RUN T5RUN TMOD2 T4RUN T3RUN TMOD1 T2RUN T1RUN
IO1CTL P4POL C4EDG P3POL C3EDG P2POL C2EDG P1POL C1EDG
IO2CTL P8POL C8EDG P7POL C7EDG P6POL C6EDG P5POL C5EDG
INTCTL I4DEN I4CEN I4BEN I4AEN I3DEN I3CEN I3BEN I3AEN I2DEN I2CEN I2BEN I2AEN I1DEN I1CEN I1BEN I1AEN
INTPND I4DPD I4CPD I4BPD I4APD I3DPD I3CPD I3BPD I3APD I2DPD I2CPD I2BPD I2APD I1DPD I1CPD I1BPD I1APD
CLK1PS C2PRSC C1PRSC
COUNT1 CNT1
PERCAP1 PCAP1
DTYCAP1 DCAP1
COUNT2 CNT2
PERCAP2 PCAP2
DTYCAP2 DCAP2
CLK2PS C4PRSC C3PRSC
COUNT3 CNT3
PERCAP3 PCAP3
DTYCAP3 DCAP3
COUNT4 CNT4
PERCAP4 PCAP4
DTYCAP4 DCAP4
TWM Registers 15 8 7 6 5 4 3 2 1 0
TWCFG Reserved WDSDME WDCT0I LWDCNT LTWMT0 LTWCP LTWCFG
TWCP Reserved MDIV
TIMER0 PRESET
T0CSR Reserved T0INTE TC RST
WDCNT PRESET
WDSDM RSTDATA
Obsolete
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A/D Registers 7 6 5 4 3 2 1 0
ADCST Reserved BUFPTR Reserved OVF BUSY EOC
ADCCNT1 Reserved Reserved INTE Reserved ADCEN
ADCCNT2 START SCAN CONT CHANNEL
ADCCNT3 Reserved PWREN DELAY CDIV
ADDATA0 RESULT 1 DATA
ADDATA1 RESULT 2 DATA
ADDATA2 RESULT 3 DATA
ADDATA3 RESULT 4 DATA
Analog Comp. Registers 7 6 543210
CMPCTRL Reserved CMP2OE CMP1OE CMP2EN CMP1EN CMP2RD CMP1RD
Obsolete
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25.0 ELECTRICAL AND THERMAL CHARACTERISTICS
Absolute Maximum Ratings
If Military/Aerospace specified devices are required, please
contact the National Semiconductor Sales Office/Distributors
for availability and specifications. Note: Absolute maximum ratings indicate limits beyond
which damage to the device may occur. DC and AC electrical
specifications are not ensured when operating the device at
absolute maximum ratings. * The latch-up tolerance on Ac-
cess Bus pins 14 and 15 exceeds 150mA.
Thermal Characteristics
DC Electrical Characteristics: –40°C ≤ TA ≤ +85°C (also supports -40°C to +125°C)
Supply Voltage (VCC) 7V
Voltage at Any Pin * –0.6V to VCC +0.6V
ESD Protection Level 2 kV
(Human Body Model)
Total Current into VCC Pin (Source) 200 mA
Total Current out of GND Pin (Sink) 200 mA
Storage Temperature Range –65°C to +150°C
Characteristics Symbol Value Unit
Average junction temperature TJTA + (PD X ~JA)°C
Ambient temperature TAUser-determined °C
Package thermal resistance (junction-to-ambient)
80-pin quad flat pack (QFP) ~JA 49.8 °C/W
Total power dissipation1
PD
PINT + PI/O
or
K
TJ + 273°C
W
Device internal power
dissipation PINT IDD X VDD W
I/O pin power dissipation2PI/O User-determined W
A constant3KPD x (TA + 273°C) +
~ JA x PD2W, °C
1. This is an approximate value, neglecting PI/O.
2. For most applications PI/O << PINT and can be neglected.
3. K is a constant pertaining to the device. Solve for K with a known TA and a measured PD (at equilibrium). Use this value of K to solve for
PD and TJ iterntively for any value of TA.
Symbol Parameter Conditions Min Max Units
Operating Voltage 4.5 5.5 V
VIH Logical 1 CMOS Input Voltage (except ACB & clocks) 0.8Vcc Vcc + 0.5 V
VIL Logical 0 CMOS Input Voltage (except ACB & clocks) -0.5 0.2Vcc V
VIHACB SDA, SCL Logical 1 CMOS Input Voltage 0.7Vcc V
VILACB SDA, SCL Logical 0 CMOS Input Voltage 0.3Vcc V
Vxl Low Level Input Voltage OSC External X1 clock 00.2Vcc V
Vxh High Level Input Voltage OSC External X1 clock 0.5Vcc Vcc V
Vxl2 X2CKI Logical 0 Input Voltage External X2 clock 0.3 V
Vxh2 X2CKI Logical 1 Input Voltage External X2clock 1.2 V
Vhys Hysteresis Loop Width a0.1Vcc V
IOH Logical 1 CMOS Output Current VOH = 3.8V, Vcc=4.5V -1.6 mA
IOL Logical 0 CMOS Output Current VOL = 0.45V, Vcc=4.5V 1.6 mA
Obsolete
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A/D Converter Characteristics
VCC = 5V, TA = 25°C
IOLACB SDA, SCL Logical 0 CMOS Output Current VOL = 0.4V, Vcc=4.5V 3.0 mA
IOHW Weak Pull-up Current VOH = 3.8V, Vcc=4.5V -10 µA
IIL RESET pin Weak Pull-down Current VIL = 0.9V, Vcc=4.5V 0.4 µA
ILHigh Impedance Input Leakage Current 0V ≤ Vin ≤ Vcc - 2.0 2.0jµA
IO(Off) Output Leakage Current
(I/O pins in input mode) 0V ≤ Vout ≤ Vcc - 2.0 2.0jµA
Icca1 Digital Supply Current Active Mode bVcc= 5.5V 95 mA
Iccprog Digital Supply Current Active Mode cVcc= 5.5V 115 mA
Icca2 Digital Supply Current Active Mode dVcc = 5.5V 58 mA
Iccps Digital Supply Current Power Save Mode eVcc= 5.5V 9mA
Iccid Digital Supply Current Idle Mode fVcc = 5.5V 200 µA
Iccq Digital Supply Current Halt Mode fVcc = 5.5V 20kµA
Iacc Analog Supply Current Active Mode gVcc= 5.5V 3mA
a. Guaranteed by design
b. Run from internal memory, Iout=0mA, X1CKI=20MHz, not programming flash memory
c. Same conditions as Icca1 but programming or erasing one of the flash memory arrays
d. CPU executing an WAIT instruction, Iout=0mA, X1CKI=20MHz, peripherals not active
e. Running from internal memory, Iout=0mA, X1CKI=20MHz, X2CKI=32.768kHz
f. Iout=0mA, X1CKI=Vcc, X2CKI=32.768kHz
g. ADC and analog comparators enabled
j. IL adn IO are 2.0 µA at 85°C and 5.0 µA at 125°C
k. Iacq is 20 µA at 85°C and 50 µA at 125°C
Symbol Parameter Conditionsa
a. All parameters specified for fOSC =2 MHz, VDD = 5.0V ± 10% unless otherwise noted.
Min Typ Max Units
NIL Integral Errorb
b. Integral (Non-linearity) Error — The maximum difference between the best-fit straight line reference and the actual
conversion curves.
VREF = V
CC ±0.5 LSB
NDL Differential Errorc
c. Differential (Non-linearity) Error — The maximum difference between the best-fit step size of 1 LSB and any actual
step size.
VREF = V
CC ±1.0 LSB
VABSOLUTE Absolute Error VREF = V
CC ±1.5 LSB
VIN Input Voltage Range VREF < VCC - 0.1 0VREF V
VREFEX External Reference Voltage 3.0 VDD V
IVREF VREF input current VREF = 5V 1.2 mA
IAL Analog input leakage current VREF = V
CC ±1µA
RAIN Analog input resistanced
d. The resistance between the device input and the internal analog input capacitance.
200 Ω
CAIN Analog input capacitancee5pF
tADCCLK Conversion Clock period 500 ns
CREFEX External Vref bypass capacitance 0.47 µF
tACT First conversion after Vcc stable 30 µs
MMONOTON-
IC MONOTONICITYfGUARANTEED
Symbol Parameter Conditions Min Max Units
Obsolete
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e. The input signal is measured across the internal capacitance.
f. Conversion result never decreases with an increase in input voltage and has no missing codes.
Obsolete
139 www.national.com
Analog Comparator Characteristics
Flash EEPROM Program Memory Programming
Symbol Parameter Conditions Min Typ Max Units
VOS Input Offset Voltage Vcc = 5V,
0.4V ≤ VIN ≤ VCC – 1.5V ±25 mV
VCM Input Common Mode Voltage Range 0.4 VCC -1.5 V
ICS DC Supply Current per Comparator (When
Enabled) VCC=5.5V 250 µA
Response Time 1V Step / 100mV Overdrive 1µs
Symbol Parameter Conditions Min Max Units
tPWP Programming pulse width a
a. The programming pulse width is determined by the following equation:
tPWP
= Tclk x (FTDIV+1) x (FTPROG+1), where Tclk is the system clock period, FTDIV is the contents of the
FLPSLR register and FTPROG is the contents of the FLPROG register.
30 40 µs
tEWP Erase pulse widthb
b. The erase pulse width is determined by the following equation:
tEWP
= Tclk x (FTDIV+1) x 4 x (FTER+1), where Tclk is the system clock period, FTDIV is the contents of the
FLPSLR register and FTER is the contents of the FLERASE register.
1-ms
tSDP Charge pump power-up delayc
c. The program/erase start delay time is determined by the following equation:
tSDP = Tclk x (FTDIV+1) x (FTSTART+1), where Tclk is the system clock period, FTDIV is the contents of the
FLPSLR register and FTSTART is the contents of the FLSTART register.
10 -µs
tTTP Program/erase transition timed
d. The program/erase transition time is determined by the following equation:
tTTP = Tclk x (FTDIV+1) x (FTTRAN+1), where Tclk is the system clock period, FTDIV is the contents of the
FLPSLR register and FTTRAN is the contents of the FLTRAN register.
5-µs
tPAH Programming address hold, new address setup
time 2-clock
cycles
tPEP Charge pump enable hold time 1-clock
cycles
tEDP Charge pump power hold timee
e. The program/erase end delay time is determined by the following equation:
tEDP = Tclk x (FTDIV+1) x (FTEND+1), where T clk is the system clock period, FTDIV is the contents of the FLPSLR
register and FTEND is the contents of the FLEND register.
5µs
tCHVP Cumulative program high voltage period for each
row after erase.f
f. Cumulative program high voltage period for each row after erase tCHVP
is the accumulated duration a flash cell is
exposed to the programming voltage after the last erase cycle. It is the sum of all tHV after the last erase.
-25 ms
Data retention 100 -years
-100K cycles
Obsolete
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Flash EEPROM Data Programming
Flash EEPROM ISP-Memory Programming
Symbol Parameter Conditions Min Max Units
re-programming timea
a. One re-programming cycle involves one erase pulse followed by programming of four bytes.
1.32 -ms
tPWD Programming pulse width b
b. The programming pulse width is determined by the following equation:
tPWD = Tclk x (FTDIV+1) x (FTPROG+1), where Tclk is the system clock period, FTDIV is the contents of the
DMPSLR register and FTPROG is the contents of the DMPROG register.
30 40 µs
tEWD Erase pulse widthc
c. The erase pulse width is determined by the following equation:
tEWD = Tclk x (FTDIV+1) x 4 x (FTER+1), where Tclk is the system clock period, FTDIV is the contents of the
DMPSLR register and FTER is the contents of the DMERASE register.
1-ms
tSDD Charge pump power-up timed
d. The program/erase start delay time is determined by the following equation:
tSDD = Tclk x (FTDIV+1) x (FTSTART+1), where Tclk is the system clock period, FTDIV is the contents of the
DMPSLR register and FTSTART is the contents of the DMSTART register.
10 -µs
tTTD Program/erase transition timee
e. The program/erase transition time is determined by the following equation:
tTTD = Tclk x (FTDIV+1) x (FTTRAN+1), where T
clk is the system clock period, FTDIV is the contents of the
DMPSLR register and FTTRAN is the contents of the DMTRAN register.
5-µs
tPED Charge pump enable hold time 1-clock
cycles
tEDD Charge pump power hold timef
f. The program/erase end delay time is determined by the following equation:
tEDD = Tclk x (FTDIV+1) x (FTEND+1), where Tclk is the system clock period, FTDIV is the contents of the
DMPSLR register and FTEND is the contents of the DMEND register.
5-µs
Write/erase endurance (high endurance) 100,000 -cycles
Write/erase endurance (low endurance) 25,000 -cycles
Data retention 100 -years
Symbol Parameter Conditions Min Max Units
tPWI Programming pulse witha
a. Programming timing is controlled by the flash EEPROM data memory interface
30 40 µs
tEWI Erase pulse widthb
b. Erase timing is controlled by the flash EEPROM data memory interface
1-ms
Data retention 100 -years
-100K cycles
Obsolete
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Output Signal Levels
All output signals are powered by the digital supply (VCC).
Table44 summarizes the states of the output signals during
the reset state (when VCC power exists in the reset state)
and during the Power Save mode.
The RESET and NMI input pins are active during the Power
Save mode. In order to guarantee that the Power Save cur-
rent not exceed 1mA, these inputs must be driven to a volt-
age lower than 0.5V or higher than V
CC-0.5V. An input
voltage between 0.5V and (VCC-0.5V) may result in power
consumption exceeding 1 mA.
tSD tTT tPW tPW tPE tED
tPP
Row Select/
Start Charge
Pump
Select
Charge Pump/
Programming
Pulse
Figure 76.Flash EEPROM Memory Programming Timing
(Sample Sequence for Programming two Words into Flash EEPROM Program Memory
Enable
Programming
Voltage
Table 44Output Pins During Reset and Power-Save
Signals on a pin Reset state
(with Vcc) Power Save mode Comments
PF[0:7] TRI-STATE Previous state I/O ports will maintain their values when
entering power-save mode
PG[0:7] TRI-STATE Previous state
PI[0:7] TRI-STATE Previous state
PL[0:7] TRI-STATE Previous state
PB[0:7] TRI-STATE Previous state
PC[0:7] TRI-STATE Previous state
Obsolete
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25.0.1 Timing Waveforms
Figure 77.Clock Waveforms
ac-1
tCLKp
CLK
tCLKh tCLKl
tCLKf tCLKr
Output Valid Output Hold
Output
Signal
Input
Signal
Input Setup Input Hold
Control
Signal 1
Control
Signal 2
Output Active/Inactive time
Output Active/Inactive time
tX2h tX2l
X2
tX2p
tX1h tX1l
X1
tX1p
Obsolete
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Figure 78. ISE & NMI Signal Timing
Figure 79.Non-Power-On Reset
Figure 80.USART Asynchronous Mode Timing
Figure 81.USART Synchronous Mode Timing
CLK
ISE
NMI
tIh
tIs
tIh
tIs tIw
tIw
CLK
RESET tRST
CLK
TXDn
121212121212
tIS
tIH
RXDn
tCOv1 tCOv1
CKXn
TXDn
RXDn
tCLKX
tTXD
tRXS
tRXH
Obsolete
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Figure 82.Port Signals Timing
Figure 83.MICROWIRE Transaction Timing, Normal Mode, MIDL Bit = 0
CLK
BUZCLK
PORTS B, C (output)
121212121212
tCOv2 tCOv2
tIs
tIh
tCOv1
tOf
PORTS B, C (input)
tCOv1
msb
tMSKp
tMSKh tMSKl
tMDIs tMDIh
tMCSs
tMDOf
MSKn
Data In
MDIDOn
MCSn
lsb
lsb
tMDOf
tMDOv
tMDOh
msb
tMSKs tMSKhd
tMCSh
(Slave)
MDODIn
(slave)
(master) lsbmsb
tMSKd
Obsolete
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Figure 84.MICROWIRE Transaction Timing, Normal Mode, MIDL bit = 1
Figure 85.MICROWIRE Transaction Timing, Alternate Mode, MIDL bit = 0
msb
tMSKp
tMSKl tMSKh
tMDIs tMDIh
tMCSs
tMDOf
MSKn
Data In
MDIDOn
MCSn
lsb
tMDOf
tMDOv
tMDOh
tMSKs tMSKhd
tMCSh
(Slave)
MDODIn
(slave)
(master) msb
msb lsb
lsb
tMSKh tMSKl
tMDIs tMDIh
tMCSs
MSKn
Data In
MDIDOn
MCSn
tMSKs tMSKhd
tMCSh
(Slave)
tMSKp
msb lsb
tMDOf tMDOf
tMDOv
tMDOh
(Slave)
MDODIn
(Master) msb lsb
msb lsb
Obsolete
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Figure 86.MICROWIRE Transaction Timing, Alternate Mode, MIDL bit = 1
Figure 87.MICROWIRE Transaction Timing, Data Echoed to Output, Normal Mode, MIDLBit= 0, MECHBit= 1, Slave
tMSKp
tMSKl tMSKh
tMDIs tMDIh
tMCSs
tMDOf
MSKn
MDIDOn
MCSn
tMDOf
tMCSh
tMDOv
tMDOh
tMSKs tMSKhd
(Slave only)
lsbmsb
(Slave)
MDODIn
(Master)
msb lsb
msb lsb
tSKd
Data In
tMSKp
tMSKh tMSKl
tMDIh
tMCSs
tMDOnf
MSKn
MDODIn
MDIDOn
MCSn
DI lsb
tMDOf
DO msb
tMSKs tMSKhd
tMCSh
tMITOp
tMITOp
tMDIs
DI msb
(Slave)
(Slave) DO lsb
Obsolete
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Figure 88.ACB signals (SDA and SCL) Rise Time and Fall Timing
Figure 89.ACB Start and Stop Condition Timing
Figure 90.ACB Start Conditioning Timing
SDA
tSDAr
0.7VCC
0.3VCC
tSDAf
0.7VCC
0.3VCC
SCL
tSCLr
0.7VCC
0.3VCC
tSCLf
0.7VCC
0.3VCC
Note: In the timing tables the parameter name is added with an “o” for
output signal timing and “i” for input signal timing.
SDA
SCL
tCSTOs tBUF
tDLCs
tCSTRh
Start ConditionStop Condition
Note: In the timing tables the parameter name is added with an “o” for
output signal timing and “i” for input signal timing.
SDA
SCL
tCSTRs
tDHCs
Start Condition
tCSTRh
Note: In the timing tables the parameter name is added with an “o” for
output signal timing and “i” for input signal timing.
Obsolete
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Figure 91.ACB Data Bits Timing
Figure 92.Versatile-Timer-Unit Input Timing
Figure 93.Versatile-Timer-Unit Input Timing
CLK
TIOx
tTIOLtTIOH
CLK
TIOx
tTIOLtTIOH
Obsolete
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25.0.2 Timing Tables
Table 45Output Signals
Symbol Figure Description Reference Min (ns) Max (ns)
Tclk a77 CLK clock period R.E. CLK to next R.E. CLK 43.4 64000a
tCLKh 77 CLK high time At 2.0V
(Both Edges) 17.3
tCLKl 77 CLK low time At 0.8V
(Both Edges) 17.3
tCLKr 77 CLK rise time on R.E. CLK 0.8V to 2.0V 3
tCLKf 77 CLK fall time on F.E. CLK 2.0V to 0.8V 3
tCOv1
CMOS output valid
All signals with prop. delay from CLK
R.E.
After R.E. CLK 35
USART Output Signals
tTXD 84 TXDn output valid After R.E. CLKXn 35
MICROWIRE / SPI Output Signals
tMSKh 86 MICROWIRE Clock High At 2.0V (both edges) 80
tMSKl 86 MICROWIRE Clock Low At 0.8V (both edges) 80
tMSKp
86 MICROWIRE Clock Period MnIDL bit = 0: R.E. MSK to next R.E.
MSKn 200
87 MnIDL bit = 1: F.E. MSK to next F.E.
MSKn
tMSKd 86 MSK Leading Edge Delayed (master
only) Data Out Bit #7 Valid 0.5 tMSK 1.5 tMSK
tMDOf 86 MICROWIRE Data Float b
(slave only) After R.E. MCSn 56
tMDOh 86 MICROWIRE Data Out Hold Normal Mode: After F.E. MSK 0.0
Alternate Mode: After R.E. MSK
tMDOnf 90 MICROWIRE Data No Float (slave only) After F.E. MWCS 056
tMDOv 86 MICROWIRE Data Out Valid Normal Mode: After F.E. MSK 56
Alternate Mode: After R.E. MSK
tMITOp
MDODI to MDIDO
(slave only) Propagation Time
Value is the same in all clocking modes of
the MICROWIRE 56
90
CAN Output Signals
tCANTx CANTx output valid After R.E. CLKXn 13
ACCESS.bus Output Signals
tBUFo 89 Bus free time between Stop and Start
Condition tSCLhigho
tCSTOso 89 SCL setup time Before Stop Condition tSCLhigho
tCSTRho 89 SCL hold time After Start Condition tSCLhigho
tCSTRso 90 SCL setup time Before Start Condition tSCLhigho
tDHCso 90 Data High setup time Before SCL R.E. tSCLhigho
-tSDAro
tDLCso 89 Data Low setup time Before SCL R.E. tSCLhigho
-tSDAfo
tSCLfo 88 SCL signal Fall time 300c
Obsolete
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tSCLro 88 SCL signal Rise time - d
tSCLlowo 91 SCL low time After SCL F.E. K*tCLK -
1e
tSCLhigho 91 SCL high time After SCL R.E. K*tCLK -
1e
tSDAfo 88 SDA signal Fall time 300
tSDAro 88 SDA signal Rise time -
tSDAho 91 SDA hold time After SCL F.E. 7*tCLK -
tSCLfo
tSDAvo 91 SDA valid time After SCL F.E. 7*tCLK+
tRD
a. Tclk is the actual clock period of the CPU clock used in the system.
The value of Tclk is system dependent.
The maximum cycle time of 64000ns is for Power Save mode; in active mode, the maximum cycle time is limited to 250ns by
the high frequency oscillator.
b. Guaranteed by design, but not fully tested.
c. Assuming signal’s capacitance up to 400pF.
d. Depends on the signal’s capacitance and the pull-up value. Must be less than 1ms.
e. K is as defined in ACBCTL2.SCLFRQ.
Table 46Input Signal Requirements
Symbol Figure Description Reference Min (ns) Max (ns)
tX1p 77 X1 period R.E. X1 to next R.E. X1 40
tX1h 77 X1 high time, external clock At 2V level (Both Edges) 0.5 Tclk - 4
tX1l 77 X1 low time, external clock At 0.8V level (Both Edges) 0.5 Tclk - 4
tX2p 77 X2 period aR.E. X2 to next R.E. X2 10,000
tX2h 77 X2 high time, external clock At 2V level (both edges) 0.5 Tclk - 500
tX2l 77 X2 low time, external clock At 0.8V level (both edges) 0.5 Tclk - 500
tIs 81 Input setup time
ISE Before R.E. CLK 12
tIh 81 Input hold time
ISE, NMI, RXD1, RXD2 After R.E. CLK 0
tRST 82 Reset time Reset active to reset end 4Tclk
Input Signals
Input Pulse Width 1*Tclk+13
USART Input Signals
tIs 80 Input setup time
RXDn (asynchronous mode) Before R.E. CLK 12
tIh 80 Input hold time
RXDn (asynchronous mode) After R.E. CLK 0
tCLKX 81 CKXn input period
(synchronous mode) 200
tRXS 81 RDXn setup time
(synchronous mode) Before F.E. CKX in synchronous mode 4
tRXH 81 RDXn hold time
(synchronous mode) After F.E. CKX in synchronous mode 2
MICROWIRE / SPI Input Signals
tMSKh 83 MICROWIRE Clock High At 2.0V (both edges) 80
tMSKl 83 MICROWIRE Clock Low At 0.8V (both edges) 80
Table 45Output Signals
Symbol Figure Description Reference Min (ns) Max (ns)
Obsolete
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tMSKp 83 MICROWIRE Clock Period MnIDL bit = 0; R.E. MSK to next R.E. MSK 200
84 MIDL bit = 1; F.E. MSK to next F.E. MSK
tMSKh 83 MSK Hold (slave only) After MCS becomes inactive 40
tMSKs 83 MSK Setup (slave only) Before MCS becomes active 80
tMCSh 83 MCS Hold (slave only) MIDL bit = 0: After F.E. MSK 40
84 MIDL bit = 1: After R.E. MSK
tMCSs 83 MCS Setup (slave only) MIDL bit = 0: Before R.E. MSK 80
84 MIDL bit = 1: Before F.E. MSK
tMDIh
83 MICROWIRE Data In Hold (master) Normal Mode: After R.E. MSK 0
85 Alternate Mode: After F.E. MSK
83 MICROWIRE Data In Hold (slave) Normal Mode: After R.E. MSK 40
85 Alternate Mode: After F.E. MSK
tMDIs 83 MICROWIRE Data In Setup Normal Mode: Before R.E. MSK 80
85 Alternate Mode: Before F.E. MSK
CAN Input Signals
tIs CANRx Input setup time) Before R.E. CLK 12
tIh CANRx Input hold time After R.E. CLK 0
ACCESS.bus Input Signals
tBUFi 89 Bus free time between Stop and
Start Condition tSCLhigho
tCSTOsi 89 SCL setup time Before Stop Condition 8*tCLK - tSCLri
tCSTRhi 89 SCL hold time After Start Condition 8*tCLK - tSCLri
tCSTRsi 90 SCL setup time Before Start Condition 8*tCLK - tSCLri
tDHCsi 90 Data High setup time Before SCL R.E. 2*tCLK
tDLCsi 89 Data Low setup time Before SCL R.E. 2*tCLK
tSCLfi 88 SCL signal Rise time 300
tSCLri 88 SCL signal Fall time 1000
tSCLlowi 91 SCL low time After SCL F.E. 16*tCLK
tSCLhighi 91 SCL high time After SCL R.E. 16*tCLK
tSDAri 88 SDA signal Rise time 300
tSDAfi 88 SDA signal Fall time 1000
tSDAhi 91 SDA hold time After SCL F.E. 0
tSDAsi 91 SDA setup time Before SCL R.E. 2*tCLK
Multi-Function Timer Input Signals
tTAH 92 TnA High Time R.E. CLK TCLK+5
tTAL 92 TnA Low Time R.E. CLK TCLK+5
tTBH 92 TnB High Time R.E. CLK TCLK+5
tTBL 92 TnB Low Time R.E. CLK TCLK+5
Versatile Timer Input Signals
tTIOH 96 TIOx Input High Time RE CLK 1.5TCLK+5ns
tTIOL 96 TIOx Input Low Time RE CLK 1.5TCLK+5ns
a. Only when operating with an external square wave on X2CKI; otherwise a 32kHz crystal network must be used
between X2CKI and X2CKO. If the slow clock is internally generated from the fast clock, it may not exceed this
given limit.
Table 46Input Signal Requirements
Symbol Figure Description Reference Min (ns) Max (ns)
Obsolete
www.national.com 152
26.0 Appendix
The following document describes problems identified in the
CR16 modules.
26.1 CR16CAN
26.1.1 CR16CAN Problem Descriptions:
Under certain conditions it occurs that the CR16CAN module
receives a frame, sent by itself even though the loopback fea-
ture is disabled.
This condition consists of two parts, which both must be true
to cause this malfunction.
A) The first part is that a transmit buffer and at least one re-
ceive buffer are configured with the same identifier. Let's call
this identifier ID_RX_TX here. With regard to the receive
buffer, this means that the buffer identifier and the corre-
sponding filter masks are setup in a way that the buffer is able
to receive frames with the identifier ID_RX_TX.
B) The second part is that the CAN communication must take
place in the following sequence:
1. A message with the identifier ID_RX_TX from another
CAN node is received into the receive buffer.
2. A message with the identifier ID_RX_TX is sent by the
CR16CAN module immediately after the reception took
place (Note).
After this communication the frame sent by the CR16CAN
module will be copied into the next receive buffer available
for the identifier ID_RX_TX.
Note: If a frame with an identifier different to ID_RX_TX is
sent or received in between the steps 1 and 2, the problem
does not occur.
26.1.2 CR16CAN Problem Cause
When a frame is received into the hidden receive buffer, the
CR16CAN module scans through all CAN message buffers.
During this sequence all receive buffers (RX-buffers) capable
of receiving this frame are tagged (RX-tag). If the message
was received correctly the frame is copied into first tagged
buffer (lowest buffer number).
Every CAN node also monitors frames being transmitted in
order to switch from transmitter to receiver after a lost arbitra-
tion. In order to do this the CR16CAN module also receives
transmitted frames into the hidden receive buffer.
The scanning sequence is also applied to transmitted
frames. This means, the identifier in the hidden receive buffer
is compared with the RX-buffer identifiers. As the identifier is
the same as with the last receive scanning sequence, the
RX-tags will not be changed.
A CAN buffer receive tag is only updated in the following cas-
es:—A new scanning sequence has overwritten the old re-
ceive tags due to a different identifier mask under com-
parison.
—The CPU has changed the CAN buffer status in the
CNSTAT.ST-field to any value which disables the buff-
er to receive a message (e.g. RX_NOT_ACTIVE or
any TX-state)
—The CPU has changed the CAN buffer identifier.
Applied to the CAN communication sequence described
above, this means that the transmitted message, currently
present in the hidden receive buffer will be copied into the
same receive buffer and the message received from the oth-
er CAN node will be overwritten.
Example
Buffer Settings
Filter Masks:
GMSKB = 0x0000
GMSKX = 0x000F
Buffer configuration:
CAN Communication Sequence A:
(BUFFLOCK disabled)
1. Message sent from another CAN node received into
buffer 1.
Buffer 1 and buffer 2 are tagged for reception of this
message.
2. CPU reads out data from CAN buffer 1 and resets the
buffer state from RX_FULL to RX_READY (Note 1).
3. CAN buffer 0 sends a frame (status set to TX_ONCE).
4. Status of CAN buffer 1 changes to RX_FULL, because it
has received the message sent by buffer 0 (Note 2).
Note: 1. Step 2 does not need to be done. In case the buffer
1 status is not updated to RX_READY, the buffer status will
change from RX_FULL to RX_OVERRUN in step 4.
Note: 2. As BUFFLOCK is disabled, all messages with the
identifier ID_RX_TX will be copied into buffer 1. Buffer 2 does
not receive any message.
CAN Communication Sequence B:
(BUFFLOCK enabled)
1. Message sent from another CAN node received into
buffer 1. Buffer 1 is locked now.
Buffer 1 and buffer 2 are tagged for reception of this
message.
2. CAN buffer 0 sends a frame.
3. Status of CAN buffer 2 changes to RX_FULL, because it
has received the message sent by buffer 0.
CAN Communication Sequence C
(CR16CAN does NOT receive a frame sent by itself.)
CAN
Buffer
Number
CAN Buffer
Status Buffer
Identifier Identifier
Mask
0TX_NOT_ACTIVE 0x15555550 0x1555555X
1RX_READY 0x15555551 0x1555555X
2RX_READY 0x15555552 0x1555555X
3RX_READY 0x15555003 0x1555500X
X = don't care
Obsolete
153 www.national.com
1. Message sent from another CAN node received into
buffer 1.
Buffer 1 and buffer 2 are tagged for reception of this
message.
2. Message sent from another CAN node received into
buffer 3 (ID=0x15555003).
Only buffer 3 is now tagged for reception.
3. CAN buffer 0 sends a frame (status set to TX_ONCE).
4. Status of CAN buffer 1 and 2 remains RX_READY, be-
cause they have not received the message sent by buff-
er 0.
26.1.3 CR16CAN Problem Solutions
Reset receive buffer tags before transmitting a message
The receive tag of a CAN receive buffer is reset when the
CPU updates the buffer status in the CNSTAT.ST-field to any
value which disables the receive buffer. Therefore the user
should write the sequence RX_NOT_ACTIVE - RX_READY
to all receive buffers which have an identifier filter matching
the identifier of the frame to be sent next before the message
is sent.
Modified CAN Communication Sequence:
(BUFFLOCK disabled)
The same CAN buffer settings as described in also apply to
this example.
1. Message sent from another CAN node received into
buffer 1.
Buffer 1 and buffer 2 are tagged for reception of this
message.
2. CPU reads out data from CAN buffer 1 and resets the
buffer state from RX_FULL to RX_READY.
3. Write RX_NOT_ACTIVE to CNSTAT.ST-field of buffer 1
and buffer 2.
Buffer 1 and buffer 2 are NOT tagged for reception any-
more.
4. Write RX_READY to CNSTAT.ST-field of buffer 1 and
buffer 2.
5. CAN buffer 0 sends a frame (status set to TX_ONCE).
6. Status of CAN buffer 1 remains RX_READY, because it
has NOT received the message sent by buffer 0.
Advantage:
No receive buffer is overwritten by a message sent by the
same CR16CAN node.
Disadvantage:
The corresponding receive buffers must be disabled for a
short period of time. During this time, when the receive buff-
ers are in the RX_NOT_ACTIVE state, correct incoming
messages from other CAN nodes will get lost.
This method is more suitable compared to the method de-
scribed in Section, if the number of transmit buffers with
identifier ID_RX_TX is lower than the number of receive buff-
ers set up with the corresponding identifier mask.
Reset receive buffer tags after reception of a message
The receive tag of a CAN receive buffer is reset when the
CPU updates the buffer status in the CNSTAT.ST-field to any
value which disables the receive buffer. Therefore the user
should write the sequence RX_NOT_ACTIVE - RX_READY
to this receive buffer, which has received the latest message.
Modified CAN Communication Sequence:
In the CAN communication example described below, the
buffer 14 is set up as basic CAN path, which is able to receive
all standard frames. The buffers 1 to 13 cannot receive the
frame sent by buffer 0.
Filter Masks:
BMSKB = 0xFFF0
BMSKX = 0x0000
Buffer configuration:
1. Message sent from another CAN node received into
buffer 14.
Buffer 14 is tagged for reception of this message.
2. CPU reads out data from CAN buffer 14.
3. Write RX_NOT_ACTIVE to CNSTAT.ST-field of buffer
14.
Buffer 14 is NOT tagged for reception anymore.
4. Write RX_READY to CNSTAT.ST-field of buffer 14.
5. CAN buffer 0 sends a frame (status set to TX_ONCE).
6. Status of CAN buffer 14 remains RX_READY, because
it has NOT received the message sent by buffer 0.
Advantage:
No receive buffer is overwritten by a message sent by the
same CR16CAN node.
Disadvantage:
The corresponding receive buffers must be disabled for a
short period of time. During this time, when the receive buff-
ers are in the RX_NOT_ACTIVE state, correctly incoming
messages from other CAN nodes will get lost.
This method is more suitable compared to the method de-
scribed in Section, if the number of transmit buffers with
identifier ID_RX_TX is higher than the number of receive
buffers set up with the corresponding identifier mask. This is
the case if only the basic CAN path to buffer 14 is configured
to receive a range of identifiers, including the identifier
ID_RX_TX. All other buffers are configured with unique iden-
tifier filters.
Receive all frames and discard those, which were sent
by the same CR16CAN node.
Another approach to overcome this problem uses the Time
Stamp counter of the CR16CAN module to determine,
whether a message was sent and received at the same time.
This is the case when a transmitted frame is received by the
same CAN node.
CAN Buffer
Number CAN Buffer Status Buffer Identifier
0TX_NOT_ACTIVE any standard frame
14 RX_READY ID1.IDE bit = 1
Obsolete
www.national.com 154
When a frame was successfully sent by CR16CAN the con-
tents of the Time Stamp counter are captured into the Time
Stamp register (TSTP) of the transmit buffer during the ACK-
slot of the frame currently being sent. Also, when a message
is received, the TSTP-register of the receiving buffer is load-
ed with the Time Stamp counter value during the ACK-slot of
the CAN frame currently being received.
This means, in the case where a message is received in one
buffer, which was sent from another buffer of the same
CR16CAN node, the TSTP-register contents are equal after
this transaction.
A comparison of the two TSTP-register values can be insert-
ed into a "read from CAN receive buffer" software routine, to
distinguish whether the data received are from another CAN
node (valid) or from the same CAN node (invalid).
The flowchart below shows a possible implementation. The
same CAN buffer settings as described in Section also apply
to this example.
Modified CAN Receive Sequence:
Advantage:
None of the CAN receive buffers must be disabled at any
time.
Disadvantage:
The receive buffer contents are overwritten by an invalid
message sent from the same CR16CAN node.
26.2 8/16-BIT MICROWIRE/SPI (MWSPI16)
26.2.1 MWSPI16 Problem Description
According to the specification, the MSKn clock output in mas-
ter mode should have the value of the MnIDL bit of the
MWnCTL register, even when the module is disabled. How-
ever, the MSKn pin is enabled and the module is disabled.
thus, even if the MnIDL bit is set, the MSKn clock will change
to a low level as soon as the module is disabled. If any slave
is selected at this time, i will interpret this unwanted transition
as a shift clock.
26.2.2 MWSPI16 Problem Cause
Even if the module is disabled and the alternate function of
the MSKn pin is enabled, the module can still influence the
MSKn pin and drives the default value ‘0’.
26.2.3 MWSPI16 Problem Solutions
When the MSKn idle level of ‘1’ is to be used, the following
procedure should be followed when the module is disabled:
1. Set the MSKn pin to high level in the corresponding port
data output register.
2. Configure the MSKn pin to an output in the correspond-
ing port direction register.
3. Disable the alternate function of the MSKn pin in the cor-
responding port alternate function register.
4. Disable the MWSPI16 module.
26.3 TIMING AND WATCHDOG MODULE
26.3.1 Timing and WATCHDOG Module Problem
Description
The available window for a valid WATCHDOG service varies
with the TWM configuration and the operating mode of the
R16MCS9. Therefore it is not possible to generally provide
the limits for the maximum service window. However, the lim-
its for the minimum service window is guaranteed and should
be used.
26.3.2 Timing and WATCHDOG Module Problem
Cause
The timing and WATCHDOG module uses two different clock
signals for its operation, the slow system clock as well as the
fast system clock.
The slow system clock can either be generated by an exter-
nal 32 kHz quartz or it can be derived from the fast system
clock by means of a prescaler counter in the CLK2RES mod-
ules. The TWM can operate off a maximum slow system
clock of 100 kHz. The WATCHDOG counter (down-counter)
is either clocked directly by the slow system (T0IN) or it is
decremented every time the counter T0 underflows
(T0OUT).
The fast system clock is used for accesses to TWM registers,
which build the user interface of the TWM. These user inter-
face registers include all memory-mapped registers of the
TWM.
Message received
into Buffer 1
Time Stamp of
Buffer 1
=
Time Stamp of
Buffer 0
Read out Buffer 1 Data
Reset Buffer 1 Status to
RX_READY
Exit
Obsolete
155 www.national.com
Every time the user (CR16B core) writes to a TWM configu-
ration register or to the WATCHDOG Service Data Match
register, this “high speed operation” must be synchronized to
the internal TWM logic running at the slow clock rate. This
synchronization process takes a variable number of low
speed clock cycles, depending on the ratio between the low-
speed and the high-speed system clock and the phase shift
between the two clock signals. The more the two frequencies
differ from each other, the longer it takes the synchronization
process.
In other words, write operations to the TWM registers take a
certain number of low-speed clock cycles to show the de-
sired effects to the TWM logic.
This fact is especially critical for the write operation for the
WATCHDOG service, as it affects the allowed window for a
valid WATCHDOG service.
If the device runs in active mode, the synchronization pro-
cess can take up to four WATCHDOG counter clock cycles.
This limits the available WATCHDOG service to the window
shown in figure 94:
If the device runs in power save mode, the synchronization
process can take up to eight WATCHDOG counter clock cy- cles. This limits the available WATCHDOG service to the win-
dow shown in figure 95:
26.3.3 Timing and WATCHDOG Module Problem
Solutions
In order to guarantee a valid WATCHDOG service under all
circumstances, the WATCHDOG should only be serviced
within the guaranteed minimum valid window, as illustrated in
figure 94 and figure 95 in the previous section.
Figure 94.WATCHDOG Services Windows in Active Mode
Figure 95.WATCHDOG Services Windows in Power Save Mode
Obsolete
CR16HCS5/CR16HCS9/CR16MAR5/CR16MAS5 CR16MAS9/CR16MBR5/CR16MCS5/CR16MCS9 Family of 16-bit
CAN-enabled CompactRISC Microcontrollers
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied, and National reserves the right, at any time without notice, to change said circuitry or specifications.
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Obsolete
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