Features
•High Performance, Low Power AVR® 8-Bit Microcontroller
•Advanced RISC Architecture
– 123 Powerful Instructions – Most Single Clock Cycle Execution
– 32 x 8 General Purpose Working Registers
– Fully Static Operation
•Non-volatile Program and Data Memories
– 2/4/8K Byte of In-System Programmable Program Memory Flash
(ATtiny261/461/861)
Endurance: 10,000 Write/Erase Cycles
– 128/256/512 Bytes In-System Programmable EEPROM (ATtiny261/461/861)
Endurance: 100,000 Write/Erase Cycles
– 128/256/512 Bytes Internal SRAM (ATtiny261/461/861)
– Programming Lock for Self-Programming Flash Program and EEPROM Data
Security
•Peripheral Features
– 8/16-bit Timer/Counter with Prescaler
– 8/10-bit High Speed Timer/Counter with Separate Prescaler
3 High Frequency PWM Outputs with Separate Output Compare Registers
Programmable Dead Time Generator
– Universal Serial Interface with Start Condition Detector
– 10-bit ADC
11 Single Ended Channels
16 Differential ADC Channel Pairs
15 Differential ADC Channel Pairs with Programmable Gain (1x, 8x, 20x, 32x)
– Programmable Watchdog Timer with Separate On-chip Oscillator
– On-chip Analog Comparator
•Special Microcontroller Features
– debugWIRE On-chip Debug System
– In-System Programmable via SPI Port
– External and Internal Interrupt Sources
– Low Power Idle, ADC Noise Reduction, and Power-down Modes
– Enhanced Power-on Reset Circuit
– Programmable Brown-out Detection Circuit
– Internal Calibrated Oscillator
•I/O and Packages
– 16 Programmable I/O Lines
– 20-pin SOIC, 32-pad MLF and 20-lead TSSOP
•Operating Voltage:
– 2.7 - 5.5V for ATtiny261/461/861
•Speed Grade:
– ATtiny261/461/861: 0 - 8MHz at 2.7 - 5.5V, 0 - 16MHz at 4.5 - 5.5V
– Operating temperature: Automotive (–40°C to +125°C)
•Low Power Consumption
– Active Mode ATD On: 1MHz, 2.7V, 25°C: 300µA
– Power-down Mode no Watchdog: 2.7V, 25°C: 0.12µA
8-bit
Microcontroller
with 2/4/8K
Bytes In-System
Programmable
Flash
ATtiny261
ATtiny461
ATtiny861
Automotive
7753F–AVR–01/11
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1. Pin Configurations
Figure 1-1. Pinout ATtiny261/461/861
Note: The large center pad underneath the QFN/MLF package should be soldered to ground on the board to ensure good mechanical
stability.
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
(MOSI/DI/SDA/OC1A/PCINT8) PB0
(MISO/DO/OC1A/PCINT9) PB1
(SCK/USCK/SCL/OC1B/PCINT10) PB2
(OC1B/PCINT11) PB3
VCC
GND
(ADC7/OC1D/CLKI/XTAL1/PCINT12) PB4
(ADC8/OC1D/CLKO/XTAL2/PCINT13) PB5
(ADC9/INT0/T0/PCINT14) PB6
(ADC10/RESET/PCINT15) PB7
PA0 (ADC0/DI/SDA/PCINT0)
PA1 (ADC1/DO/PCINT1)
PA2 (ADC2/INT1/USCK/SCL/PCINT2)
PA3 (AREF/PCINT3)
AGND
AVCC
PA4 (ADC3/ICP0/PCINT4)
PA5 (ADC4/AIN2/PCINT5)
PA6 (ADC5/AIN0/PCINT6)
PA7 (ADC6/AIN1/PCINT7)
SOIC
1
2
3
4
5
6
7
8
24
23
22
21
20
19
18
17
32
31
30
29
28
27
26
25
9
10
11
12
13
14
15
16
NC
(OC1B/PCINT11) PB3
NC
VCC
GND
NC
(ADC7/OC1D/CLKI/XTAL1/PCINT12) PB4
(ADC8/OC1D/CLKO/XTAL2/PCINT13) PB5
NC
PA2 (ADC2/INT1/USCK/SCL/PCINT2)
PA3 (AREF/PCINT3)
AGND
NC
NC
AVCC
PA4 (ADC3/ICP0/PCINT4)
NC
(ADC9/INT0/T0/PCINT14) PB6
(ADC10/RESET/PCINT15) PB7
NC
(ADC6/AIN1/PCINT7) PA7
(ADC5/AIN0/PCINT6) PA6
(ADC4/AIN2/PCINT5) PA5
NC
PB2 (SCK/USCK/SCL/OC1B/PCINT10)
PB1 (MISO/DO/OC1A/PCINT9)
PB0 (MOSI/DI/SDA/OC1A/PCINT8)
NC
NC
NC
PA0 (ADC0/DI/SDA/PCINT0)
PA1 (ADC1/DO/PCINT1)
(OC1B/PCINT11)PB3
VCC
GND
QFN/MLF
QFN/MLF
1
20 19 18 17 16
678910
2
3
4
5
15
14
13
12
11
AGND
AVCC
(SCK/USCK/SCL/OC1B/PCINT10) PB2
(ADC7/OC1D/CLKI/XTAL1/PCINT12) PB4
PB1 (MISO/DO/OC1A/PCINT9)
PB0 (MOSI/DI/SDA/OC1A/PCINT8)
PA0 (ADC0/DI/SDA/PCINT0)
PA1 (ADC1/DO/PCINT1)
PA2 (ADC2/INT1/USCK/SCL/PCINT2)
PA3 (AREF/PCINT3)
PA4 (ADC3/ICP0/PCINT4)
PA5 (ADC4/AIN2/PCINT5)
(ADC5/AIN0/PCINT6) PA6
(ADC6/AIN1/PCINT7) PA7
(ADC10/RESET/PCINT15) PB7
(ADC9/INT0/T0/PCINT14) PB6
(ADC8/OC1D/CLKO/XTAL2/PCINT13) PB5
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1.1 Disclaimer
Typical values contained in this data sheet are based on simulations and characterization of
other AVR microcontrollers manufactured on the same process technology. Min and Max values
will be available after the device is characterized.
1.2 Automotive Quality Grade
The ATtiny261/461/861 have been developed and manufactured according to the most stringent
requirements of the international standard ISO-TS 16949. This data sheet contains limit values
extracted from the results of extensive characterization (Temperature and Voltage). The quality
and reliability of the ATtiny261/461/861 have been verified during regular product qualification as
per AEC-Q100 grade 1.
As indicated in the ordering information paragraph, the product is available in only one tempera-
ture grade, Table 1-1.
Table 1-1. Temperature Grade Identification for Automotive Products
Temperature
Temperature
Identifier Comments
–40; +125 Z Full Automotive Temperature Range
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2. Overview
The ATtiny261/461/861 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced
RISC architecture. By executing powerful instructions in a single clock cycle, the
ATtiny261/461/861 achieves throughputs approaching 1 MIPS per MHz allowing the system
designer to optimize power consumption versus processing speed.
2.1 Block Diagram
Figure 2-1. Block Diagram
Power
Supervision
POR/ BOD
and
RESET
Oscillator
Circuits/
Clock
Generation
Watchdog
Timer
Watchdog
Oscillator
Program
Logic
debugWIRE
AVR
CPU
EEPROM
DATA BUS
Flash
GND VCC
A/D Conv.
Timer/
Counter 0
Timer/
Counter 1
Analog
Comp.
Internal
Bandgap
USI
11
3
PORT B (8) PORT A (8)
SRAM
AVCC
GND
AREF
RESET
XTAL[1..2]
PB[0..7] PA[0..7]
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The AVR core combines a rich instruction set with 32 general purpose working registers. All the
32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent
registers to be accessed in one single instruction executed in one clock cycle. The resulting
architecture is more code efficient while achieving throughputs up to ten times faster than con-
ventional CISC microcontrollers.
The ATtiny261/461/861 provides the following features: 2/4/8K byte of In-System Programmable
Flash, 128/256/512 bytes EEPROM, 128/256/512 bytes SRAM, 6 general purpose I/O lines, 32
general purpose working registers, one 8-bit Timer/Counter with compare modes, one 8-bit high
speed Timer/Counter, Universal Serial Interface, Internal and External Interrupts, a 4-channel,
10-bit ADC, a programmable Watchdog Timer with internal Oscillator, and three software select-
able power saving modes. The Idle mode stops the CPU while allowing the SRAM,
Timer/Counter, ADC, Analog Comparator, and Interrupt system to continue functioning. The
Power-down mode saves the register contents, disabling all chip functions until the next Inter-
rupt or Hardware Reset. The ADC Noise Reduction mode stops the CPU and all I/O modules
except ADC, to minimize switching noise during ADC conversions.
The device is manufactured using Atmel®’s high density non-volatile memory technology. The
On-chip ISP Flash allows the Program memory to be re-programmed In-System through an SPI
serial interface, by a conventional non-volatile memory programmer or by an On-chip boot code
running on the AVR core.
The ATtiny261/461/861 AVR is supported with a full suite of program and system development
tools including: C Compilers, Macro Assemblers, Program Debugger/Simulators, In-Circuit Emu-
lators, and Evaluation kits.
2.2 Pin Descriptions
2.2.1 VCC
Supply voltage.
2.2.2 GND
Ground.
2.2.3 AVCC
Analog supply voltage.
2.2.4 AGND
Analog ground.
2.2.5 Port A (PA7..PA0)
Port A is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port A output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port A pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port A pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port A also serves the functions of various special features of the ATtiny261/461/861 as listed
on page 66.
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2.2.6 Port B (PB7..PB0)
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port B output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port B pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port B also serves the functions of various special features of the ATtiny261/461/861 as listed
on page 63.
2.2.7 RESET
Reset input. A low level on this pin for longer than the minimum pulse length will generate a
reset, even if the clock is not running. The minimum pulse length is given in Table 23-3 on page
191. Shorter pulses are not guaranteed to generate a reset.
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3. Resources
A comprehensive set of development tools, application notes and datasheets are available for
download on http://www.atmel.com/avr.
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4. About Code Examples
This documentation contains simple code examples that briefly show how to use various parts of
the device. These code examples assume that the part specific header file is included before
compilation. Be aware that not all C compiler vendors include bit definitions in the header files
and interrupt handling in C is compiler dependent. Please confirm with the C compiler documen-
tation for more details.
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5. AVR CPU Core
5.1 Overview
This section discusses the AVR core architecture in general. The main function of the CPU core
is to ensure correct program execution. The CPU must therefore be able to access memories,
perform calculations, control peripherals, and handle interrupts.
Figure 5-1. Block Diagram of the AVR Architecture
In order to maximize performance and parallelism, the AVR uses a Harvard architecture – with
separate memories and buses for program and data. Instructions in the Program memory are
executed with a single level pipelining. While one instruction is being executed, the next instruc-
tion is pre-fetched from the Program memory. This concept enables instructions to be executed
in every clock cycle. The Program memory is In-System Reprogrammable Flash memory.
Status and
Control
Interrupt
Unit
32 x 8
General
Purpose
Registers
ALU
Data Bus 8-bit
Data
SRAM
Watchdog
Timer
Instruction
Register
Instruction
Decoder
Analog
Comparator
EEPROM
I/O Lines
I/O Module n
Control Lines
Direct Addressing
Indirect Addressing
I/O Module 2
I/O Module 1
Program
Counter
Flash
Program
Memory
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The fast-access Register File contains 32 x 8-bit general purpose working registers with a single
clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU) operation. In a typ-
ical ALU operation, two operands are output from the Register File, the operation is executed,
and the result is stored back in the Register File – in one clock cycle.
Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data
Space addressing – enabling efficient address calculations. One of the these address pointers
can also be used as an address pointer for look up tables in Flash Program memory. These
added function registers are the 16-bit X-, Y-, and Z-register, described later in this section.
The ALU supports arithmetic and logic operations between registers or between a constant and
a register. Single register operations can also be executed in the ALU. After an arithmetic opera-
tion, the Status Register is updated to reflect information about the result of the operation.
Program flow is provided by conditional and unconditional jump and call instructions, able to
directly address the whole address space. Most AVR instructions have a single 16-bit word for-
mat. Most AVR instructions are 16-bit wide. There are also 32-bit instructions.
During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the
Stack. The Stack is effectively allocated in the general data SRAM, and consequently the Stack
size is only limited by the total SRAM size and the usage of the SRAM. All user programs must
initialize the SP in the Reset routine (before subroutines or interrupts are executed). The Stack
Pointer (SP) is read/write accessible in the I/O space. The data SRAM can easily be accessed
through the five different addressing modes supported in the AVR architecture.
The memory spaces in the AVR architecture are all linear and regular memory maps.
A flexible interrupt module has its control registers in the I/O space with an additional Global
Interrupt Enable bit in the Status Register. All interrupts have a separate Interrupt Vector in the
Interrupt Vector table. The interrupts have priority in accordance with their Interrupt Vector posi-
tion. The lower the Interrupt Vector address, the higher the priority.
The I/O memory space contains 64 addresses for CPU peripheral functions as Control Regis-
ters, SPI, and other I/O functions. The I/O memory can be accessed directly, or as the Data
Space locations following those of the Register File, 0x20 - 0x5F.
5.2 ALU – Arithmetic Logic Unit
The high-performance AVR ALU operates in direct connection with all the 32 general purpose
working registers. Within a single clock cycle, arithmetic operations between general purpose
registers or between a register and an immediate are executed. The ALU operations are divided
into three main categories – arithmetic, logical, and bit-functions. Some implementations of the
architecture also provide a powerful multiplier supporting both signed/unsigned multiplication
and fractional format. See the “Instruction Set” section for a detailed description.
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5.3 Status Register
The Status Register contains information about the result of the most recently executed arithme-
tic instruction. This information can be used for altering program flow in order to perform
conditional operations. Note that the Status Register is updated after all ALU operations, as
specified in the Instruction Set Reference. This will in many cases remove the need for using the
dedicated compare instructions, resulting in faster and more compact code. The Status Register
is not automatically stored when entering an interrupt routine and restored when returning from
an interrupt. This must be handled by software.
5.3.1 SREG – AVR Status Register
The AVR Status Register – SREG – is defined as:
• Bit 7 – I: Global Interrupt Enable
The Global Interrupt Enable bit must be set for the interrupts to be enabled. The individual inter-
rupt enable control is then performed in separate control registers. If the Global Interrupt Enable
Register is cleared, none of the interrupts are enabled independent of the individual interrupt
enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is set by
the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared by
the application with the SEI and CLI instructions, as described in the instruction set reference.
• Bit 6 – T: Bit Copy Storage
The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or desti-
nation for the operated bit. A bit from a register in the Register File can be copied into T by the
BST instruction, and a bit in T can be copied into a bit in a register in the Register File by the
BLD instruction.
• Bit 5 – H: Half Carry Flag
The Half Carry Flag H indicates a Half Carry in some arithmetic operations. Half Carry is useful
in BCD arithmetic. See the “Instruction Set Description” for detailed information.
• Bit 4 – S: Sign Bit, S = N ⊕ V
The S-bit is always an exclusive or between the Negative Flag N and the Two’s Complement
Overflow Flag V. See the “Instruction Set Description” for detailed information.
• Bit 3 – V: Two’s Complement Overflow Flag
The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See the
“Instruction Set Description” for detailed information.
• Bit 2 – N: Negative Flag
The Negative Flag N indicates a negative result in an arithmetic or logic operation. See the
“Instruction Set Description” for detailed information.
• Bit 1 – Z: Zero Flag
The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction
Set Description” for detailed information.
Bit 76543210
0x3F (0x5F) I T H S V N Z C SREG
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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ATtiny261/ATtiny461/ATtiny861
• Bit 0 – C: Carry Flag
The Carry Flag C indicates a carry in an arithmetic or logic operation. See the “Instruction Set
Description” for detailed information.
5.4 General Purpose Register File
The Register File is optimized for the AVR Enhanced RISC instruction set. In order to achieve
the required performance and flexibility, the following input/output schemes are supported by the
Register File:
• One 8-bit output operand and one 8-bit result input
• Two 8-bit output operands and one 8-bit result input
• Two 8-bit output operands and one 16-bit result input
• One 16-bit output operand and one 16-bit result input
Figure 5-2 shows the structure of the 32 general purpose working registers in the CPU.
Figure 5-2. AVR CPU General Purpose Working Registers
Most of the instructions operating on the Register File have direct access to all registers, and
most of them are single cycle instructions.
As shown in Figure 5-2, each register is also assigned a Data memory address, mapping them
directly into the first 32 locations of the user Data Space. Although not being physically imple-
mented as SRAM locations, this memory organization provides great flexibility in access of the
registers, as the X-, Y- and Z-pointer registers can be set to index any register in the file.
7 0 Addr.
R0 0x00
R1 0x01
R2 0x02
…
R13 0x0D
General R14 0x0E
Purpose R15 0x0F
Working R16 0x10
Registers R17 0x11
…
R26 0x1A X-register Low Byte
R27 0x1B X-register High Byte
R28 0x1C Y-register Low Byte
R29 0x1D Y-register High Byte
R30 0x1E Z-register Low Byte
R31 0x1F Z-register High Byte
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5.4.1 The X-register, Y-register, and Z-register
The registers R26..R31 have some added functions to their general purpose usage. These reg-
isters are 16-bit address pointers for indirect addressing of the data space. The three indirect
address registers X, Y, and Z are defined as described in Figure 5-3 on page 13.
Figure 5-3. The X-, Y-, and Z-registers
In the different addressing modes these address registers have functions as fixed displacement,
automatic increment, and automatic decrement (see the instruction set reference for details).
5.5 Stack Pointer
The Stack is mainly used for storing temporary data, for storing local variables and for storing
return addresses after interrupts and subroutine calls. The Stack Pointer Register always points
to the top of the Stack. Note that the Stack is implemented as growing from higher memory loca-
tions to lower memory locations. This implies that a Stack PUSH command decreases the Stack
Pointer.
The Stack Pointer points to the data SRAM Stack area where the Subroutine and Interrupt
Stacks are located. This Stack space in the data SRAM must be defined by the program before
any subroutine calls are executed or interrupts are enabled. The Stack Pointer must be set to
point above 0x60. The Stack Pointer is decremented by one when data is pushed onto the Stack
with the PUSH instruction, and it is decremented by two when the return address is pushed onto
the Stack with subroutine call or interrupt. The Stack Pointer is incremented by one when data is
popped from the Stack with the POP instruction, and it is incremented by two when data is
popped from the Stack with return from subroutine RET or return from interrupt RETI.
The AVR Stack Pointer is implemented as two 8-bit registers in the I/O space. The number of
bits actually used is implementation dependent. Note that the data space in some implementa-
tions of the AVR architecture is so small that only SPL is needed. In this case, the SPH Register
will not be present
15 XH XL 0
X-register 7 0 7 0
R27 (0x1B) R26 (0x1A)
15 YH YL 0
Y-register 7 0 7 0
R29 (0x1D) R28 (0x1C)
15 ZH ZL 0
Z-register 7 0 7 0
R31 (0x1F) R30 (0x1E)
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5.5.1 SPH and SPL – Stack Pointer Register
5.6 Instruction Execution Timing
This section describes the general access timing concepts for instruction execution. The AVR
CPU is driven by the CPU clock clkCPU, directly generated from the selected clock source for the
chip. No internal clock division is used.
Figure 5-4 shows the parallel instruction fetches and instruction executions enabled by the Har-
vard architecture and the fast access Register File concept. This is the basic pipelining concept
to obtain up to 1 MIPS per MHz with the corresponding unique results for functions per cost,
functions per clocks, and functions per power-unit.
Figure 5-4. The Parallel Instruction Fetches and Instruction Executions
Figure 5-5 shows the internal timing concept for the Register File. In a single clock cycle an ALU
operation using two register operands is executed, and the result is stored back to the destina-
tion register.
Figure 5-5. Single Cycle ALU Operation
Bit 1514131211109 8
0x3E (0x5E) SP15 SP14 SP13 SP12 SP11 SP10 SP9 SP8 SPH
0x3D (0x5D) SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SPL
76543210
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND
RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND
clkCPU
1st Instruction Fetch
1st Instruction Execute
2nd Instruction Fetch
T1 T2 T3 T4
2nd Instruction Execute
3rd Instruction Fetch
3rd Instruction Execute
4th Instruction Fetch
clk
CPU
T1
Register Operands Fetch
Result Write Back
ALU Operation Execute
Total Execution Time
T2 T3 T4
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5.7 Reset and Interrupt Handling
The AVR provides several different interrupt sources. These interrupts and the separate Reset
Vector each have a separate Program Vector in the Program memory space. All interrupts are
assigned individual enable bits which must be written logic one together with the Global Interrupt
Enable bit in the Status Register in order to enable the interrupt.
The lowest addresses in the Program memory space are by default defined as the Reset and
Interrupt Vectors. The complete list of vectors is shown in “Interrupts” on page 50. The list also
determines the priority levels of the different interrupts. The lower the address the higher is the
priority level. RESET has the highest priority, and next is INT0 – the External Interrupt Request
0.
When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts are dis-
abled. The user software can write logic one to the I-bit to enable nested interrupts. All enabled
interrupts can then interrupt the current interrupt routine. The I-bit is automatically set when a
Return from Interrupt instruction – RETI – is executed.
There are basically two types of interrupts. The first type is triggered by an event that sets the
Interrupt Flag. For these interrupts, the Program Counter is vectored to the actual Interrupt Vec-
tor in order to execute the interrupt handling routine, and hardware clears the corresponding
Interrupt Flag. Interrupt Flags can also be cleared by writing a logic one to the flag bit position(s)
to be cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is
cleared, the Interrupt Flag will be set and remembered until the interrupt is enabled, or the flag is
cleared by software. Similarly, if one or more interrupt conditions occur while the Global Interrupt
Enable bit is cleared, the corresponding Interrupt Flag(s) will be set and remembered until the
Global Interrupt Enable bit is set, and will then be executed by order of priority.
The second type of interrupts will trigger as long as the interrupt condition is present. These
interrupts do not necessarily have Interrupt Flags. If the interrupt condition disappears before the
interrupt is enabled, the interrupt will not be triggered.
When the AVR exits from an interrupt, it will always return to the main program and execute one
more instruction before any pending interrupt is served.
Note that the Status Register is not automatically stored when entering an interrupt routine, nor
restored when returning from an interrupt routine. This must be handled by software.
When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled.
No interrupt will be executed after the CLI instruction, even if it occurs simultaneously with the
CLI instruction. The following example shows how this can be used to avoid interrupts during the
timed EEPROM write sequence.
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When using the SEI instruction to enable interrupts, the instruction following SEI will be exe-
cuted before any pending interrupts, as shown in this example.
5.7.1 Interrupt Response Time
The interrupt execution response for all the enabled AVR interrupts is four clock cycles mini-
mum. After four clock cycles the Program Vector address for the actual interrupt handling routine
is executed. During this four clock cycle period, the Program Counter is pushed onto the Stack.
The vector is normally a jump to the interrupt routine, and this jump takes three clock cycles. If
an interrupt occurs during execution of a multi-cycle instruction, this instruction is completed
before the interrupt is served. If an interrupt occurs when the MCU is in sleep mode, the interrupt
execution response time is increased by four clock cycles. This increase comes in addition to the
start-up time from the selected sleep mode.
A return from an interrupt handling routine takes four clock cycles. During these four clock
cycles, the Program Counter (two bytes) is popped back from the Stack, the Stack Pointer is
incremented by two, and the I-bit in SREG is set.
Assembly Code Example
in r16, SREG ; store SREG value
cli ; disable interrupts during timed sequence
sbi EECR, EEMPE ; start EEPROM write
sbi EECR, EEPE
out SREG, r16 ; restore SREG value (I-bit)
C Code Example
char cSREG;
cSREG = SREG; /* store SREG value */
/* disable interrupts during timed sequence */
_CLI();
EECR |= (1<<EEMPE); /* start EEPROM write */
EECR |= (1<<EEPE);
SREG = cSREG; /* restore SREG value (I-bit) */
Assembly Code Example
sei ; set Global Interrupt Enable
sleep; enter sleep, waiting for interrupt
; note: will enter sleep before any pending
; interrupt(s)
C Code Example
_SEI(); /* set Global Interrupt Enable */
_SLEEP(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */
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6. AVR Memories
This section describes the different memories in the ATtiny261/461/861. The AVR architecture
has two main memory spaces, the Data memory and the Program memory space. In addition,
the ATtiny261/461/861 features an EEPROM Memory for data storage. All three memory
spaces are linear and regular.
6.1 In-System Re-programmable Flash Program Memory
The ATtiny261/461/861 contains 2/4/8K byte On-chip In-System Reprogrammable Flash mem-
ory for program storage. Since all AVR instructions are 16 or 32 bits wide, the Flash is organized
as 1024/2048/4096 x 16.
The Flash memory has an endurance of at least 10,000 write/erase cycles. The
ATtiny261/461/861 Program Counter (PC) is 10/11/12 bits wide, thus addressing the
1024/2048/4096 Program memory locations. “Memory Programming” on page 172 contains a
detailed description on Flash data serial downloading using the SPI pins.
Constant tables can be allocated within the entire Program memory address space (see the
LPM – Load Program memory instruction description).
Timing diagrams for instruction fetch and execution are presented in “Instruction Execution Tim-
ing” on page 14.
Figure 6-1. Program Memory Map
6.2 SRAM Data Memory
Figure 6-2 shows how the ATtiny261/461/861 SRAM Memory is organized.
The lower 224/352/608 Data memory locations address both the Register File, the I/O memory
and the internal data SRAM. The first 32 locations address the Register File, the next 64 loca-
tions the standard I/O memory, and the last 128/256/512 locations address the internal data
SRAM.
The five different addressing modes for the Data memory cover: Direct, Indirect with Displace-
ment, Indirect, Indirect with Pre-decrement, and Indirect with Post-increment. In the Register
File, registers R26 to R31 feature the indirect addressing pointer registers.
The direct addressing reaches the entire data space.
The Indirect with Displacement mode reaches 63 address locations from the base address given
by the Y- or Z-register.
0x0000
0x03FF/0x07FF/0x0FFF
Program Memory
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When using register indirect addressing modes with automatic pre-decrement and post-incre-
ment, the address registers X, Y, and Z are decremented or incremented.
The 32 general purpose working registers, 64 I/O Registers, and the 128/256/512 bytes of inter-
nal data SRAM in the ATtiny261/461/861 are all accessible through all these addressing modes.
The Register File is described in “General Purpose Register File” on page 12.
Figure 6-2. Data Memory Map
6.2.1 Data Memory Access Times
This section describes the general access timing concepts for internal memory access. The
internal data SRAM access is performed in two clkCPU cycles as described in Figure 6-3.
Figure 6-3. On-chip Data SRAM Access Cycles
6.3 EEPROM Data Memory
The ATtiny261/461/861 contains 128/256/512 bytes of data EEPROM memory. It is organized
as a separate data space, in which single bytes can be read and written. The EEPROM has an
endurance of at least 100,000 write/erase cycles. The access between the EEPROM and the
CPU is described in the following, specifying the EEPROM Address Registers, the EEPROM
Data Register, and the EEPROM Control Register. For a detailed description of Serial data
downloading to the EEPROM, see page 184.
Data Memory
0x0000 - 0x001F
0x0020 - 0x005F
0x0060
0x0DF/0x15F/0x25F
32 Registers
64 I/O Registers
Internal SRAM
(128/256/512 x 8)
clk
CPU
T1
Data
Data
RD
WR
Address validCompute Address
Next Instruction
Write
Read
Memory Access Instruction
A
ddress
T2 T3
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6.3.1 EEPROM Read/Write Access
The EEPROM Access Registers are accessible in the I/O space.
The write access times for the EEPROM are given in Table 6-1. A self-timing function, however,
lets the user software detect when the next byte can be written. If the user code contains instruc-
tions that write the EEPROM, some precautions must be taken. In heavily filtered power
supplies, VCC is likely to rise or fall slowly on Power-up/down. This causes the device for some
period of time to run at a voltage lower than specified as minimum for the clock frequency used.
See “Preventing EEPROM Corruption” on page 21 for details on how to avoid problems in these
situations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed.
Refer to “Atomic Byte Programming” on page 19 and “Split Byte Programming” on page 19 for
details on this.
When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is
executed. When the EEPROM is written, the CPU is halted for two clock cycles before the next
instruction is executed.
6.3.2 Atomic Byte Programming
Using Atomic Byte Programming is the simplest mode. When writing a byte to the EEPROM, the
user must write the address into the EEARL Register and data into EEDR Register. If the
EEPMn bits are zero, writing EEPE (within four cycles after EEMPE is written) will trigger the
erase/write operation. Both the erase and write cycle are done in one operation and the total
programming time is given in Table 1. The EEPE bit remains set until the erase and write opera-
tions are completed. While the device is busy with programming, it is not possible to do any
other EEPROM operations.
6.3.3 Split Byte Programming
It is possible to split the erase and write cycle in two different operations. This may be useful if
the system requires short access time for some limited period of time (typically if the power sup-
ply voltage falls). In order to take advantage of this method, it is required that the locations to be
written have been erased before the write operation. But since the erase and write operations
are split, it is possible to do the erase operations when the system allows doing time-critical
operations (typically after Power-up).
6.3.4 Erase
To erase a byte, the address must be written to EEAR. If the EEPMn bits are 0b01, writing the
EEPE (within four cycles after EEMPE is written) will trigger the erase operation only (program-
ming time is given in Table 1). The EEPE bit remains set until the erase operation completes.
While the device is busy programming, it is not possible to do any other EEPROM operations.
6.3.5 Write
To write a location, the user must write the address into EEAR and the data into EEDR. If the
EEPMn bits are 0b10, writing the EEPE (within four cycles after EEMPE is written) will trigger
the write operation only (programming time is given in Table 1). The EEPE bit remains set until
the write operation completes. If the location to be written has not been erased before write, the
data that is stored must be considered as lost. While the device is busy with programming, it is
not possible to do any other EEPROM operations.
The calibrated Oscillator is used to time the EEPROM accesses. Make sure the Oscillator fre-
quency is within the requirements described in “OSCCAL – Oscillator Calibration Register” on
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page 32.
The following code examples show one assembly and one C function for erase, write, or atomic
write of the EEPROM. The examples assume that interrupts are controlled (e.g., by disabling
interrupts globally) so that no interrupts will occur during execution of these functions.
Assembly Code Example
EEPROM_write:
; Wait for completion of previous write
sbic EECR,EEPE
rjmp EEPROM_write
; Set Programming mode
ldi r16, (0<<EEPM1)|(0<<EEPM0)
out EECR, r16
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Write data (r16) to data register
out EEDR, r16
; Write logical one to EEMPE
sbi EECR,EEMPE
; Start eeprom write by setting EEPE
sbi EECR,EEPE
ret
C Code Example
void EEPROM_write(unsigned char ucAddress, unsigned char ucData)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set Programming mode */
EECR = (0<<EEPM1)|(0<<EEPM0);
/* Set up address and data registers */
EEAR = ucAddress;
EEDR = ucData;
/* Write logical one to EEMPE */
EECR |= (1<<EEMPE);
/* Start eeprom write by setting EEPE */
EECR |= (1<<EEPE);
}
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The next code examples show assembly and C functions for reading the EEPROM. The exam-
ples assume that interrupts are controlled so that no interrupts will occur during execution of
these functions.
6.3.6 Preventing EEPROM Corruption
During periods of low VCC, the EEPROM data can be corrupted because the supply voltage is
too low for the CPU and the EEPROM to operate properly. These issues are the same as for
board level systems using EEPROM, and the same design solutions should be applied.
An EEPROM data corruption can be caused by two situations when the voltage is too low. First,
a regular write sequence to the EEPROM requires a minimum voltage to operate correctly. Sec-
ondly, the CPU itself can execute instructions incorrectly, if the supply voltage is too low.
EEPROM data corruption can easily be avoided by following this design recommendation:
Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This can
be done by enabling the internal Brown-out Detector (BOD). If the detection level of the internal
BOD does not match the needed detection level, an external low VCC reset protection circuit can
be used. If a reset occurs while a write operation is in progress, the write operation will be com-
pleted provided that the power supply voltage is sufficient.
Assembly Code Example
EEPROM_read:
; Wait for completion of previous write
sbic EECR,EEPE
rjmp EEPROM_read
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Start eeprom read by writing EERE
sbi EECR,EERE
; Read data from data register
in r16,EEDR
ret
C Code Example
unsigned char EEPROM_read(unsigned char ucAddress)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set up address register */
EEAR = ucAddress;
/* Start eeprom read by writing EERE */
EECR |= (1<<EERE);
/* Return data from data register */
return EEDR;
}
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6.4 I/O Memory
The I/O space definition of the ATtiny261/461/861 is shown in “Register Summary” on page 208.
All ATtiny261/461/861 I/Os and peripherals are placed in the I/O space. All I/O locations may be
accessed by the LD/LDS/LDD and ST/STS/STD instructions, transferring data between the 32
general purpose working registers and the I/O space. I/O Registers within the address range
0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these registers, the
value of single bits can be checked by using the SBIS and SBIC instructions. Refer to the
instruction set section for more details. When using the I/O specific commands IN and OUT, the
I/O addresses 0x00 - 0x3F must be used. When addressing I/O Registers as data space using
LD and ST instructions, 0x20 must be added to these addresses.
For compatibility with future devices, reserved bits should be written to zero if accessed.
Reserved I/O memory addresses should never be written.
Some of the Status Flags are cleared by writing a logical one to them. Note that, the CBI and
SBI instructions will only operate on the specified bit, and can therefore be used on registers
containing such Status Flags. The CBI and SBI instructions work with registers 0x00 to 0x1F
only.
The I/O and Peripherals Control Registers are explained in later sections.
6.4.1 General Purpose I/O Registers
The ATtiny261/461/861 contains three General Purpose I/O Registers. These registers can be
used for storing any information, and they are particularly useful for storing global variables and
Status Flags. General Purpose I/O Registers within the address range 0x00 - 0x1F are directly
bit-accessible using the SBI, CBI, SBIS, and SBIC instructions.
6.5 Register Description
6.5.1 EEARH and EEARL – EEPROM Address Register
• Bit 7:1 – Res6:0: Reserved Bits
These bits are reserved for future use and will always read as 0 in ATtiny261/461/861.
• Bits 8:0 – EEAR8:0: EEPROM Address
The EEPROM Address Registers – EEARH and EEARL – specifies the high EEPROM address
in the 128/256/512 bytes EEPROM space. The EEPROM data bytes are addressed linearly
between 0 and 127/255/511. The initial value of EEAR is undefined. A proper value must be writ-
ten before the EEPROM may be accessed.
Bit 76543210
0x1F (0x3F) -------EEAR8EEARH
0x1E (0x3E) EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEARL
Bit 76543210
Read/Write RRRRRRRR/W
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value0000000X
Initial ValueXXXXXXXX
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6.5.2 EEDR – EEPROM Data Register
• Bits 7:0 – EEDR7:0: EEPROM Data
For the EEPROM write operation the EEDR Register contains the data to be written to the
EEPROM in the address given by the EEAR Register. For the EEPROM read operation, the
EEDR contains the data read out from the EEPROM at the address given by EEAR.
6.5.3 EECR – EEPROM Control Register
• Bit 7 – Res: Reserved Bit
This bit is reserved for future use and will always read as 0 in ATtiny261/461/861. For compati-
bility with future AVR devices, always write this bit to zero. After reading, mask out this bit.
• Bit 6 – Res: Reserved Bit
This bit is reserved in the ATtiny261/461/861 and will always read as zero.
• Bits 5, 4 – EEPM1 and EEPM0: EEPROM Programming Mode Bits
The EEPROM Programming mode bits setting defines which programming action that will be
triggered when writing EEPE. It is possible to program data in one atomic operation (erase the
old value and program the new value) or to split the Erase and Write operations in two different
operations. The Programming times for the different modes are shown in Table 6-1. While EEPE
is set, any write to EEPMn will be ignored. During reset, the EEPMn bits will be reset to 0b00
unless the EEPROM is busy programming.
• Bit 3 – EERIE: EEPROM Ready Interrupt Enable
Writing EERIE to one enables the EEPROM Ready Interrupt if the I-bit in SREG is set. Writing
EERIE to zero disables the interrupt. The EEPROM Ready Interrupt generates a constant inter-
rupt when Non-volatile memory is ready for programming.
Bit 76543210
0x1D (0x3D) EEDR7 EEDR6 EEDR5 EEDR4 EEDR3 EEDR2 EEDR1 EEDR0 EEDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x1C (0x3C) – – EEPM1 EEPM0 EERIE EEMPE EEPE EERE EECR
Read/Write R R R/W R/W R/W R/W R/W R/W
Initial Value 0 0 X X 0 0 X 0
Table 6-1. EEPROM Mode Bits
EEPM1 EEPM0
Programming
Time Operation
0 0 3.4 ms Erase and Write in one operation (Atomic Operation)
0 1 1.8 ms Erase Only
1 0 1.8 ms Write Only
1 1 – Reserved for future use
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• Bit 2 – EEMPE: EEPROM Master Program Enable
The EEMPE bit determines whether writing EEPE to one will have effect or not.
When EEMPE is set, setting EEPE within four clock cycles will program the EEPROM at the
selected address. If EEMPE is zero, setting EEPE will have no effect. When EEMPE has been
written to one by software, hardware clears the bit to zero after four clock cycles.
• Bit 1 – EEPE: EEPROM Program Enable
The EEPROM Program Enable Signal EEPE is the programming enable signal to the EEPROM.
When EEPE is written, the EEPROM will be programmed according to the EEPMn bits setting.
The EEMPE bit must be written to one before a logical one is written to EEPE, otherwise no
EEPROM write takes place. When the write access time has elapsed, the EEPE bit is cleared by
hardware. When EEPE has been set, the CPU is halted for two cycles before the next instruction
is executed.
• Bit 0 – EERE: EEPROM Read Enable
The EEPROM Read Enable Signal – EERE – is the read strobe to the EEPROM. When the cor-
rect address is set up in the EEAR Register, the EERE bit must be written to one to trigger the
EEPROM read. The EEPROM read access takes one instruction, and the requested data is
available immediately. When the EEPROM is read, the CPU is halted for four cycles before the
next instruction is executed. The user should poll the EEPE bit before starting the read opera-
tion. If a write operation is in progress, it is neither possible to read the EEPROM, nor to change
the EEAR Register.
6.5.4 GPIOR2 – General Purpose I/O Register 2
6.5.5 GPIOR1 – General Purpose I/O Register 1
6.5.6 GPIOR0 – General Purpose I/O Register 0
Bit 76543210
0x0C (0x2C) MSB LSB GPIOR2
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
0x0B (0x2B) MSB LSB GPIOR1
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
0x0A (0x2A) MSB LSB GPIOR0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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7. System Clock and Clock Options
7.1 Clock Systems and their Distribution
Figure 7-1 presents the principal clock systems in the AVR and their distribution. All of the clocks
need not be active at a given time. In order to reduce power consumption, the clocks to modules
not being used can be halted by using different sleep modes, as described in “Power Manage-
ment and Sleep Modes” on page 35. The clock systems are detailed below.
Figure 7-1. Clock Distribution
7.1.1 CPU Clock – clkCPU
The CPU clock is routed to parts of the system concerned with operation of the AVR core.
Examples of such modules are the General Purpose Register File, the Status Register and the
Data memory holding the Stack Pointer. Halting the CPU clock inhibits the core from performing
general operations and calculations.
7.1.2 I/O Clock – clkI/O
The I/O clock is used by the majority of the I/O modules, like Timer/Counter. The I/O clock is
also used by the External Interrupt module, but note that some external interrupts are detected
by asynchronous logic, allowing such interrupts to be detected even if the I/O clock is halted.
General I/O
Module
Flash and
EEPROM
PLL
Oscillator
Calibrated RC
Oscillator
Low Frequency
Crystal Oscillator
Crystal
Oscillator
Watchdog
Oscillator
System Clock
Prescaler
General I/O
Modules
AVR Clock
Control Unit
ADC
External Clock
CPU Core
Source Clock
Watchdog Clock
RAM
Reset Logic Watchdog Timer
clkI/O
clkCPU
clkADC
clkFLASH
Clock
Multiplexer
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7.1.3 Flash Clock – clkFLASH
The Flash clock controls operation of the Flash interface. The Flash clock is usually active simul-
taneously with the CPU clock.
7.1.4 ADC Clock – clkADC
The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O clocks
in order to reduce noise generated by digital circuitry. This gives more accurate ADC conversion
results.
7.1.5 Internal PLL for Fast Peripheral Clock Generation - clkPCK
The internal PLL in ATtiny261/461/861 generates a clock frequency that is 8x multiplied from a
source input. By default, the PLL uses the output of the internal 8.0 MHz RC oscillator as source.
Alternatively, if the LSM bit of the PLLCSR is set the PLL will use the output of the RC oscillator
divided by two. Thus the output of the PLL, the fast peripheral clock is 64 MHz. The fast periph-
eral clock, or a clock prescaled from that, can be selected as the clock source for
Timer/Counter1or as a system clock. See Figure 7-2. The frequency of the fast peripheral clock
is divided by two when LSM of PLLCSR is set, resulting in a clock frequency of 32 MHz. Note,
that LSM can not be set if PLLCLK is used as a system clock.
Figure 7-2. PCK Clocking System
The PLL is locked on the RC oscillator and adjusting the RC oscillator via OSCCAL register will
adjust the fast peripheral clock at the same time. However, even if the RC oscillator is taken to a
higher frequency than 8 MHz, the fast peripheral clock frequency saturates at 85 MHz (worst
case) and remains oscillating at the maximum frequency. It should be noted that the PLL in this
case is not locked any longer with the RC oscillator clock. Therefore, it is recommended not to
take the OSCCAL adjustments to a higher frequency than 8 MHz in order to keep the PLL in the
correct operating range.
The internal PLL is enabled when:
• The PLLE bit of the PLLCSR register is set.
• The CKSEL fuse are programmed to ‘0001’.
The PLLCSR bit PLOCK is set when PLL is locked.
Both internal RC oscillator and PLL are switched off in power down and stand-by sleep modes.
8.0MHz
Oscillator
4MHz
8MHz
16MHz
8MHz
64/32MHz
Oscillators
Lock
Detector
PLL
8x
1/2
1/4
OSCCAL LSM PLLE CKSEL3:0 CLKPS3:0
PLOCK
PCK
SYSTEM
CLOCK
XTAL1
XTAL2
Prescaler
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7.2 Clock Sources
The device has the following clock source options, selectable by Flash Fuse bits as shown
below. The clock from the selected source is input to the AVR clock generator, and routed to the
appropriate modules.
Note: 1. For all fuses “1” means unprogrammed while “0” means programmed.
The various choices for each clocking option is given in the following sections. When the CPU
wakes up from Power-down or Power-save, the selected clock source is used to time the
start-up, ensuring stable Oscillator operation before instruction execution starts. When the CPU
starts from reset, there is an additional delay allowing the power to reach a stable level before
commencing normal operation. The Watchdog Oscillator is used for timing this real-time part of
the start-up time. The number of WDT Oscillator cycles used for each time-out is shown in Table
7-2.
7.3 Default Clock Source
The device is shipped with CKSEL = “0010”, SUT = “10”, and CKDIV8 programmed. The default
clock source setting is therefore the Internal RC Oscillator running at 8 MHz with longest start-up
time and an initial system clock prescaling of 8. This default setting ensures that all users can
make their desired clock source setting using an In-System or High-voltage Programmer.
Table 7-1. Device Clocking Options Select(1) vs. PB4 and PB5 Functionality
Device Clocking Option CKSEL3..0 PB4 PB5
External Clock 0000 XTAL1 I/O
PLL Clock 0001 I/O I/O
Calibrated Internal RC Oscillator 8.0 MHz 0010 I/O I/O
Watchdog Oscillator 128 kHz 0011 I/O I/O
External Low-Frequency Crystal 01xx XTAL1 XTAL2
External Crystal/Ceramic Resonator (0.4 - 0.9 MHz) 1000 XTAL1 XTAL2
External Crystal/Ceramic Resonator (0.4 - 0.9 MHz) 1001 XTAL1 XTAL2
External Crystal/Ceramic Resonator (0.9 - 3.0 MHz) 1010 XTAL1 XTAL2
External Crystal/Ceramic Resonator (0.9 - 3.0 MHz) 1011 XTAL1 XTAL2
External Crystal/Ceramic Resonator (3.0 - 8.0 MHz) 1100 XTAL1 XTAL2
External Crystal/Ceramic Resonator (3.0 - 8.0 MHz) 1101 XTAL1 XTAL2
External Crystal/Ceramic Resonator (8.0 - 16.0 MHz) 1110 XTAL1 XTAL2
External Crystal/Ceramic Resonator (8.0 - 16.0 MHz) 1111 XTAL1 XTAL2
Table 7-2. Number of Watchdog Oscillator Cycles
Typ Time-out Number of Cycles
4 ms 512
64 ms 8K (8,192)
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7.4 External Clock
To drive the device from an external clock source, CLKI should be driven as shown in Figure
7-3. To run the device on an external clock, the CKSEL Fuses must be programmed to “0000”.
Figure 7-3. External Clock Drive Configuration
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 7-3.
Note that the System Clock Prescaler can be used to implement run-time changes of the internal
clock frequency while still ensuring stable operation. Refer to “System Clock Prescaler” on page
32 for details.
7.5 High Frequency PLL Clock - PLLCLK
There is an internal PLL that provides nominally 64 MHz clock rate locked to the RC Oscillator
for the use of the Peripheral Timer/Counter1 and for the system clock source. When selected as
a system clock source, by programming the CKSEL fuses to ‘0001’, it is divided by four like
shown in Table 7-4. When this clock source is selected, start-up times are determined by the
SUT fuses as shown in Table 7-5. See also “PCK Clocking System” on page 26.
Table 7-3. Start-up Times for the External Clock Selection
SUT1..0
Start-up Time from
Power-down and Power-save
Additional Delay from
Reset Recommended Usage
00 6 CK 14CK BOD enabled
01 6 CK 14CK + 4 ms Fast rising power
10 6 CK 14CK + 64 ms Slowly rising power
11 Reserved
Table 7-4. PLLCK Operating Modes
CKSEL3..0 Nominal Frequency
0001 16 MHz
Table 7-5. Start-up Times for the PLLCK
SUT1..0
Start-up Time from Power
Down
Additional Delay from
Power-On-Reset (VCC = 5.0V) Recommended usage
00 14CK + 1K (1024) + 4 ms 4 ms BOD enabled
01 14CK + 16K (16384) + 4 ms 4 ms Fast rising power
10 14CK + 1K (1024) + 64 ms 4 ms Slowly rising power
11 14CK + 16K (16384) + 64 ms 4 ms Slowly rising power
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7.6 Calibrated Internal RC Oscillator
By default, the Internal RC Oscillator provides an approximate 8.0 MHz clock. Though voltage
and temperature dependent, this clock can be very accurately calibrated by the user. See Table
23-1 on page 190 and “Internal Oscillator Speed” on page 207 for more details. The device is
shipped with the CKDIV8 Fuse programmed. See “System Clock Prescaler” on page 32 for
more details.
This clock may be selected as the system clock by programming the CKSEL Fuses as shown in
Table 7-6 on page 29. If selected, it will operate with no external components. During reset,
hardware loads the pre-programmed calibration value into the OSCCAL Register and thereby
automatically calibrates the RC Oscillator. The accuracy of this calibration is shown as Factory
calibration in Table 23-1 on page 190.
By changing the OSCCAL register from SW, see “OSCCAL – Oscillator Calibration Register” on
page 32, it is possible to get a higher calibration accuracy than by using the factory calibration.
The accuracy of this calibration is shown as User calibration in Table 23-1 on page 190.
When this Oscillator is used as the chip clock, the Watchdog Oscillator will still be used for the
Watchdog Timer and for the Reset Time-out. For more information on the pre-programmed cali-
bration value, see the section “Calibration Byte” on page 174.
Notes: 1. The device is shipped with this option selected.
2. If 8 MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8
Fuse can be programmed in order to divide the internal frequency by 8.
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 7-7 on page 29.
Note: 1. The device is shipped with this option selected.
Table 7-6. Internal Calibrated RC Oscillator Operating Modes(1)(2)
Frequency Range (MHz) CKSEL3..0
7.84 - 8.16 0010
Table 7-7. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
SUT1..0
Start-up Time
from Power-down
Additional Delay from
Reset (VCC = 5.0V) Recommended Usage
00 6 CK 14CK BOD enabled
01 6 CK 14CK + 4 ms Fast rising power
10(1) 6 CK 14CK + 64 ms Slowly rising power
11 Reserved
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7.7 128 kHz Internal Oscillator
The 128 kHz internal Oscillator is a low power Oscillator providing a clock of 128 kHz. The fre-
quency is nominal at 3V and 25°C. This clock may be select as the system clock by
programming the CKSEL Fuses to “0011”.
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 7-8.
7.8 Low-frequency Crystal Oscillator
To use a 32.768 kHz watch crystal as the clock source for the device, the low-frequency crystal
oscillator must be selected by setting CKSEL fuses to ‘0100’. The crystal should be connected
as shown in Figure 7-4. Refer to the 32 kHz Crystal Oscillator Application Note for details on
oscillator operation and how to choose appropriate values for C1 and C2.
When this oscillator is selected, start-up times are determined by the SUT fuses as shown in
Table 7-9.
Notes: 1. These options should only be used if frequency stability at start-up is not important for the
application.
7.9 Crystal Oscillator
XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be con-
figured for use as an On-chip Oscillator, as shown in Figure 7-4. Either a quartz crystal or a
ceramic resonator may be used.
C1 and C2 should always be equal for both crystals and resonators. The optimal value of the
capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and the
electromagnetic noise of the environment. Some initial guidelines for choosing capacitors for
use with crystals are given in Table 7-10. For ceramic resonators, the capacitor values given by
the manufacturer should be used.
Table 7-8. Start-up Times for the 128 kHz Internal Oscillator
SUT1..0
Start-up Time from
Power-down and Power-save
Additional Delay from
Reset Recommended Usage
00 6 CK 14CK BOD enabled
01 6 CK 14CK + 4 ms Fast rising power
10 6 CK 14CK + 64 ms Slowly rising power
11 Reserved
Table 7-9. Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
SUT1..0
Start-up Time from Power
Down and Power Save
Additional Delay from
Reset (VCC = 5.0V) Recommended usage
00 1K (1024) CK(1) 4 ms Fast rising power or BOD enabled
01 1K (1024) CK(1) 64 ms Slowly rising power
10 32K (32768) CK 64 ms Stable frequency at start-up
11 Reserved
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Figure 7-4. Crystal Oscillator Connections
The Oscillator can operate in three different modes, each optimized for a specific frequency
range. The operating mode is selected by the fuses CKSEL3..1 as shown in Table 7-10.
Notes: 1. This option should not be used with crystals, only with ceramic resonators.
The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in Table
7-11.
Table 7-10. Crystal Oscillator Operating Modes
CKSEL3..1 Frequency Range (MHz)
Recommended Range for Capacitors C1 and C2
for Use with Crystals (pF)
100(1) 0.4 - 0.9 –
101 0.9 - 3.0 12 - 22
110 3.0 - 8.0 12 - 22
111 8.0 - 12 - 22
Table 7-11. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0 SUT1..0
Start-up Time from
Power-down and
Power-save
Additional Delay from
Reset
(VCC = 5.0V) Recommended Usage
0 00 258 CK(1) 14CK + 4.1 ms Ceramic resonator, fast
rising power
0 01 258 CK(1) 14CK + 65 ms Ceramic resonator, slowly
rising power
0 10 1K (1024) CK(2) 14CK Ceramic resonator, BOD
enabled
0 11 1K (1024)CK(2) 14CK + 4.1 ms Ceramic resonator, fast
rising power
1 00 1K (1024)CK(2) 14CK + 65 ms Ceramic resonator, slowly
rising power
1 01 16K (16384) CK 14CK Crystal Oscillator, BOD
enabled
1 10 16K (16384) CK 14CK + 4.1 ms Crystal Oscillator, fast rising
power
1 11 16K (16384) CK 14CK + 65 ms Crystal Oscillator, slowly
rising power
Notes: 1. These options should only be used when not operating close to the maximum frequency of
the device, and only if frequency stability at start-up is not important for the application. These
options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure frequency stability
at start-up. They can also be used with crystals when not operating close to the maximum fre-
quency of the device, and if frequency stability at start-up is not important for the application.
C2
XTAL2
XTAL1
GND
C1
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7.10 Clock Output Buffer
The device can output the system clock on the CLKO pin. To enable the output, the CKOUT
Fuse has to be programmed. This mode is suitable when the chip clock is used to drive other cir-
cuits on the system. Note that the clock will not be output during reset and the normal operation
of I/O pin will be overridden when the fuse is programmed. Any clock source, including the inter-
nal RC Oscillator, can be selected when the clock is output on CLKO. If the System Clock
Prescaler is used, it is the divided system clock that is output.
7.11 System Clock Prescaler
The ATtiny261/461/861 system clock can be divided by setting the Clock Prescale Register –
CLKPR. This feature can be used to decrease power consumption when the requirement for
processing power is low. This can be used with all clock source options, and it will affect the
clock frequency of the CPU and all synchronous peripherals. clkI/O, clkADC, clkCPU, and clkFLASH
are divided by a factor as shown in Table 7-12.
7.11.1 Switching Time
When switching between prescaler settings, the System Clock Prescaler ensures that no
glitches occur in the clock system and that no intermediate frequency is higher than neither the
clock frequency corresponding to the previous setting, nor the clock frequency corresponding to
the new setting.
The ripple counter that implements the prescaler runs at the frequency of the undivided clock,
which may be faster than the CPU’s clock frequency. Hence, it is not possible to determine the
state of the prescaler – even if it were readable, and the exact time it takes to switch from one
clock division to another cannot be exactly predicted.
From the time the CLKPS values are written, it takes between T1 + T2 and T1 + 2*T2 before the
new clock frequency is active. In this interval, 2 active clock edges are produced. Here, T1 is the
previous clock period, and T2 is the period corresponding to the new prescaler setting.
7.12 Register Description
7.12.1 OSCCAL – Oscillator Calibration Register
• Bits 7:0 – CAL7:0: Oscillator Calibration Value
The Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator to
remove process variations from the oscillator frequency. A pre-programmed calibration value is
automatically written to this register during chip reset, giving the Factory calibrated frequency as
specified in Table 23-1 on page 190.
The application software can write this register to change the oscillator frequency. The oscillator
can be calibrated to frequencies as specified in Table 23-1 on page 190. Calibration outside that
range is not guaranteed.
Note that this oscillator is used to time EEPROM and Flash write accesses, and these write
times will be affected accordingly. If the EEPROM or Flash are written, do not calibrate to more
than 8.8 MHz. Otherwise, the EEPROM or Flash write may fail.
Bit 76543210
0x31 (0x51) CAL7 CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 OSCCAL
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value Device Specific Calibration Value
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The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0 gives the
lowest frequency range, setting this bit to 1 gives the highest frequency range. The two fre-
quency ranges are overlapping, in other words a setting of OSCCAL = 0x7F gives a higher
frequency than OSCCAL = 0x80.
The CAL6..0 bits are used to tune the frequency within the selected range. A setting of 0x00
gives the lowest frequency in that range, and a setting of 0x7F gives the highest frequency in the
range.
7.12.2 CLKPR – Clock Prescale Register
• Bit 7 – CLKPCE: Clock Prescaler Change Enable
The CLKPCE bit must be written to logic one to enable change of the CLKPS bits. The CLKPCE
bit is only updated when the other bits in CLKPR are simultaneously written to zero. CLKPCE is
cleared by hardware four cycles after it is written or when the CLKPS bits are written. Rewriting
the CLKPCE bit within this time-out period does neither extend the time-out period, nor clear the
CLKPCE bit.
• Bits 6:4 – Res: Reserved Bits
These bits are reserved bits in the ATtiny261/461/861 and will always read as zero.
• Bits 3:0 – CLKPS3:0: Clock Prescaler Select Bits 3 - 0
These bits define the division factor between the selected clock source and the internal system
clock. These bits can be written run-time to vary the clock frequency to suit the application
requirements.
As the divider divides the master clock input to the MCU, the speed of all synchronous peripher-
als is reduced when a division factor is used. The division factors are given in Table 7-12.
To avoid unintentional changes of clock frequency, a special write procedure must be followed
to change the CLKPS bits:
1. Write the Clock Prescaler Change Enable (CLKPCE) bit to one and all other bits in
CLKPR to zero.
2. Within four cycles, write the desired value to CLKPS while writing a zero to CLKPCE.
Interrupts must be disabled when changing prescaler setting to make sure the write procedure is
not interrupted.
The CKDIV8 Fuse determines the initial value of the CLKPS bits. If CKDIV8 is unprogrammed,
the CLKPS bits will be reset to “0000”. If CKDIV8 is programmed, CLKPS bits are reset to
“0011”, giving a division factor of eight at start up. This feature should be used if the selected
clock source has a higher frequency than the maximum frequency of the device at the present
operating conditions. Note that any value can be written to the CLKPS bits regardless of the
CKDIV8 Fuse setting. The Application software must ensure that a sufficient division factor is
chosen if the selected clock source has a higher frequency than the maximum frequency of the
device at the present operating conditions. The device is shipped with the CKDIV8 Fuse
programmed.
Bit 7 6543210
0x28 (0x48) CLKPCE – – – CLKPS3 CLKPS2 CLKPS1 CLKPS0 CLKPR
Read/Write R/W R R R R/W R/W R/W R/W
Initial Value 0 0 0 0 See Bit Description
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Table 7-12. Clock Prescaler Select
CLKPS3 CLKPS2 CLKPS1 CLKPS0 Clock Division Factor
0000 1
0001 2
0010 4
0011 8
0100 16
0101 32
0110 64
0111 128
1000 256
1001 Reserved
1010 Reserved
1011 Reserved
1100 Reserved
1101 Reserved
1110 Reserved
1111 Reserved
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8. Power Management and Sleep Modes
The high performance and industry leading code efficiency makes the AVR microcontrollers an
ideal choice for low power applications.
Sleep modes enable the application to shut down unused modules in the MCU, thereby saving
power. The AVR provides various sleep modes allowing the user to tailor the power consump-
tion to the application’s requirements.
8.1 Sleep Modes
Figure 7-1 on page 25 presents the different clock systems in the ATtiny261/461/861, and their
distribution. The figure is helpful in selecting an appropriate sleep mode. Table 8-1 shows the
different sleep modes and their wake up sources.
Note: 1. For INT0 and INT1, only level interrupt.
To enter any of the three sleep modes, the SE bit in MCUCR must be written to logic one and a
SLEEP instruction must be executed. The SM1..0 bits in the MCUCR Register select which
sleep mode (Idle, ADC Noise Reduction, Power-down, or Standby) will be activated by the
SLEEP instruction. See Table 8-2 for a summary.
If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU wakes up. The MCU
is then halted for four cycles in addition to the start-up time, executes the interrupt routine, and
resumes execution from the instruction following SLEEP. The contents of the Register File and
SRAM are unaltered when the device wakes up from sleep. If a reset occurs during sleep mode,
the MCU wakes up and executes from the Reset Vector.
8.2 Idle Mode
When the SM1..0 bits are written to 00, the SLEEP instruction makes the MCU enter Idle mode,
stopping the CPU but allowing Analog Comparator, ADC, Timer/Counter, Watchdog, and the
interrupt system to continue operating. This sleep mode basically halts clkCPU and clkFLASH, while
allowing the other clocks to run.
Idle mode enables the MCU to wake up from external triggered interrupts as well as internal
ones like the Timer Overflow. If wake-up from the Analog Comparator interrupt is not required,
the Analog Comparator can be powered down by setting the ACD bit in the Analog Comparator
Control and Status Register – ACSR. This will reduce power consumption in Idle mode. If the
ADC is enabled, a conversion starts automatically when this mode is entered.
Table 8-1. Active Clock Domains and Wake-up Sources in the Different Sleep Modes
Active Clock Domains Oscillators Wake-up Sources
Sleep Mode
clkCPU
clkFLASH
clkIO
clkADC
clkPCK
Main Clock
Source Enabled
INT0, INT1 and
Pin Change
SPM/EEPROM
Ready
ADC
WDT
USI
Other I/O
Idle X X X X X X XXXX
ADC Noise
Reduction XXX
(1) X XXX
Power-down X(1) XX
Standby X(1) XX
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8.3 ADC Noise Reduction Mode
When the SM1..0 bits are written to 01, the SLEEP instruction makes the MCU enter ADC Noise
Reduction mode, stopping the CPU but allowing the ADC, the external interrupts, and the
Watchdog to continue operating (if enabled). This sleep mode halts clkI/O, clkCPU, and clkFLASH,
while allowing the other clocks to run.
This improves the noise environment for the ADC, enabling higher resolution measurements. If
the ADC is enabled, a conversion starts automatically when this mode is entered. Apart form the
ADC Conversion Complete interrupt, only an External Reset, a Watchdog Reset, a Brown-out
Reset, an SPM/EEPROM ready interrupt, an external level interrupt on INT0 or a pin change
interrupt can wake up the MCU from ADC Noise Reduction mode.
8.4 Power-down Mode
When the SM1..0 bits are written to 10, the SLEEP instruction makes the MCU enter
Power-down mode. In this mode, the Oscillator is stopped, while the external interrupts, and the
Watchdog continue operating (if enabled). Only an External Reset, a Watchdog Reset, a
Brown-out Reset, an external level interrupt on INT0, or a pin change interrupt can wake up the
MCU. This sleep mode halts all generated clocks, allowing operation of asynchronous modules
only.
Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed
level must be held for some time to wake up the MCU. Refer to “External Interrupts” on page 52
for details.
8.5 Standby Mode
When the SM1..0 bits are written to 11 and an external crystal/resonator clock option is selected,
the SLEEP instruction makes the MCU enter Standby mode. This mode is identical to
Power-down with the exception that the Oscillator is kept running. From Standby mode, the
device wakes up in six clock cycles.
8.6 Power Reduction Register
The Power Reduction Register (PRR), see “PRR – Power Reduction Register” on page 38, pro-
vides a method to stop the clock to individual peripherals to reduce power consumption. The
current state of the peripheral is frozen and the I/O registers can not be read or written.
Resources used by the peripheral when stopping the clock will remain occupied, hence the
peripheral should in most cases be disabled before stopping the clock. Waking up a module,
which is done by clearing the bit in PRR, puts the module in the same state as before shutdown.
Module shutdown can be used in Idle mode and Active mode to significantly reduce the overall
power consumption. See “Supply Current of I/O modules” on page 200 for examples. In all other
sleep modes, the clock is already stopped.
8.7 Minimizing Power Consumption
There are several issues to consider when trying to minimize the power consumption in an AVR
controlled system. In general, sleep modes should be used as much as possible, and the sleep
mode should be selected so that as few as possible of the device’s functions are operating. All
functions not needed should be disabled. In particular, the following modules may need special
consideration when trying to achieve the lowest possible power consumption.
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8.7.1 Analog to Digital Converter
If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be dis-
abled before entering any sleep mode. When the ADC is turned off and on again, the next
conversion will be an extended conversion. Refer to “ADC – Analog to Digital Converter” on
page 144 for details on ADC operation.
8.7.2 Analog Comparator
When entering Idle mode, the Analog Comparator should be disabled if not used. When entering
ADC Noise Reduction mode, the Analog Comparator should be disabled. In the other sleep
modes, the Analog Comparator is automatically disabled. However, if the Analog Comparator is
set up to use the Internal Voltage Reference as input, the Analog Comparator should be dis-
abled in all sleep modes. Otherwise, the Internal Voltage Reference will be enabled,
independent of sleep mode. Refer to “AC – Analog Comparator” on page 140 for details on how
to configure the Analog Comparator.
8.7.3 Brown-out Detector
If the Brown-out Detector is not needed in the application, this module should be turned off. If the
Brown-out Detector is enabled by the BODLEVEL Fuses, it will be enabled in all sleep modes,
and hence, always consume power. In the deeper sleep modes, this will contribute significantly
to the total current consumption. Refer to “Brown-out Detection” on page 43 for details on how to
configure the Brown-out Detector.
8.7.4 Internal Voltage Reference
The Internal Voltage Reference will be enabled when needed by the Brown-out Detection, the
Analog Comparator or the ADC. If these modules are disabled as described in the sections
above, the internal voltage reference will be disabled and it will not be consuming power. When
turned on again, the user must allow the reference to start up before the output is used. If the
reference is kept on in sleep mode, the output can be used immediately. Refer to “Internal Volt-
age Reference” on page 44 for details on the start-up time.
8.7.5 Watchdog Timer
If the Watchdog Timer is not needed in the application, this module should be turned off. If the
Watchdog Timer is enabled, it will be enabled in all sleep modes, and hence, always consume
power. In the deeper sleep modes, this will contribute significantly to the total current consump-
tion. Refer to “Watchdog Timer” on page 44 for details on how to configure the Watchdog Timer.
8.7.6 Port Pins
When entering a sleep mode, all port pins should be configured to use minimum power. The
most important thing is then to ensure that no pins drive resistive loads. In sleep modes where
both the I/O clock (clkI/O) and the ADC clock (clkADC) are stopped, the input buffers of the device
will be disabled. This ensures that no power is consumed by the input logic when not needed. In
some cases, the input logic is needed for detecting wake-up conditions, and it will then be
enabled. Refer to the section “Digital Input Enable and Sleep Modes” on page 59 for details on
which pins are enabled. If the input buffer is enabled and the input signal is left floating or has an
analog signal level close to VCC/2, the input buffer will use excessive power.
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For analog input pins, the digital input buffer should be disabled at all times. An analog signal
level close to VCC/2 on an input pin can cause significant current even in active mode. Digital
input buffers can be disabled by writing to the Digital Input Disable Registers (DIDR0, DIDR1).
Refer to “DIDR0 – Digital Input Disable Register 0” on page 164 or “DIDR1 – Digital Input Dis-
able Register 1” on page 164 for details.
8.8 Register Description
8.8.1 MCUCR – MCU Control Register
The MCU Control Register contains control bits for power management.
• Bit 5 – SE: Sleep Enable
The SE bit must be written to logic one to make the MCU enter the sleep mode when the SLEEP
instruction is executed. To avoid the MCU entering the sleep mode unless it is the programmer’s
purpose, it is recommended to write the Sleep Enable (SE) bit to one just before the execution of
the SLEEP instruction and to clear it immediately after waking up.
• Bits 4, 3 – SM1:0: Sleep Mode Select Bits 2..0
These bits select between the three available sleep modes as shown in Table 8-2.
• Bit 2 – Res: Reserved Bit
This bit is a reserved ed bit in the ATtiny261/461/861 and will always read as zero.
8.8.2 PRR – Power Reduction Register
• Bits 7, 6, 5, 4- Res: Reserved Bits
These bits are reserved bits in the ATtiny261/461/861 and will always read as zero.
Bit 76543210
0x35 (0x55) –PUD SE SM1 SM0 — ISC01 ISC00 MCUCR
Read/Write R R/W R/W R/W R/W R R/W R/W
Initial Value00000000
Table 8-2. Sleep Mode Select
SM1 SM0 Sleep Mode
00Idle
0 1 ADC Noise Reduction
1 0 Power-down
1 1 Standby
Bit 76543 2 10
0x36 (0x56) – - - - PRTIM1 PRTIM0 PRUSI PRADC PRR
Read/Write R R R R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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• Bit 3- PRTIM1: Power Reduction Timer/Counter1
Writing a logic one to this bit shuts down the Timer/Counter1 module. When the Timer/Counter1
is enabled, operation will continue like before the shutdown.
• Bit 2- PRTIM0: Power Reduction Timer/Counter0
Writing a logic one to this bit shuts down the Timer/Counter0 module. When the Timer/Counter0
is enabled, operation will continue like before the shutdown.
• Bit 1 - PRUSI: Power Reduction USI
Writing a logic one to this bit shuts down the USI by stopping the clock to the module. When
waking up the USI again, the USI should be re initialized to ensure proper operation.
• Bit 0 - PRADC: Power Reduction ADC
Writing a logic one to this bit shuts down the ADC. The ADC must be disabled before shut down.
Also Analog Comparator needs this clock.
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9. System Control and Reset
9.0.1 Resetting the AVR
During reset, all I/O Registers are set to their initial values, and the program starts execution
from the Reset Vector. The instruction placed at the Reset Vector must be a RJMP – Relative
Jump – instruction to the reset handling routine. If the program never enables an interrupt
source, the Interrupt Vectors are not used, and regular program code can be placed at these
locations. The circuit diagram in Figure 9-1 shows the reset logic. “System and Reset Character-
istics” on page 191 defines the electrical parameters of the reset circuitry.
The I/O ports of the AVR are immediately reset to their initial state when a reset source goes
active. This does not require any clock source to be running.
After all reset sources have gone inactive, a delay counter is invoked, stretching the internal
reset. This allows the power to reach a stable level before normal operation starts. The time-out
period of the delay counter is defined by the user through the SUT and CKSEL Fuses. The dif-
ferent selections for the delay period are presented in “Clock Sources” on page 27.
9.0.2 Reset Sources
The ATtiny261/461/861 has four sources of reset:
• Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset
threshold (VPOT).
• External Reset. The MCU is reset when a low level is present on the RESET pin for longer
than the minimum pulse length.
• Watchdog Reset. The MCU is reset when the Watchdog Timer period expires and the
Watchdog is enabled.
• Brown-out Reset. The MCU is reset when the supply voltage VCC is below the Brown-out
Reset threshold (VBOT) and the Brown-out Detector is enabled.
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Figure 9-1. Reset Logic
9.0.3 Power-on Reset
A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level
is defined in “System and Reset Characteristics” on page 191. The POR is activated whenever
VCC is below the detection level. The POR circuit can be used to trigger the Start-up Reset, as
well as to detect a failure in supply voltage.
A Power-on Reset (POR) circuit ensures that the device is reset from Power-on. Reaching the
Power-on Reset threshold voltage invokes the delay counter, which determines how long the
device is kept in RESET after VCC rise. The RESET signal is activated again, without any delay,
when VCC decreases below the detection level.
Power-on Reset
Circuit
Brown-out
Reset Circuit
MCU Status
Register (MCUSR)
Reset Circuit
Pull-up Resistor
BODLEVEL [1..0]
SQ
R
DATA BUS
CK
SUT [1:0]
CKSEL [3:0]
COUNTER RESET
INTERNAL RESET
TIMEOUT
Spike
Filter
RESET
VCC
Delay Counters
Watchdog
Timer
Watchdog
Oscillator
Clock
Generator
PORF
BORF
WDRF
EXTRF
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Figure 9-2. MCU Start-up, RESET Tied to VCC
Figure 9-3. MCU Start-up, RESET Extended Externally
Table 9-1. Power On Reset Specifications
Note: 1. Before rising, the supply has to be between VPORMIN and VPORMAX to ensure a Reset.
9.0.4 External Reset
An External Reset is generated by a low level on the RESET pin if enabled. Reset pulses longer
than the minimum pulse width (see “System and Reset Characteristics” on page 191) will gener-
ate a reset, even if the clock is not running. Shorter pulses are not guaranteed to generate a
reset. When the applied signal reaches the Reset Threshold Voltage – VRST – on its positive
edge, the delay counter starts the MCU after the Time-out period – tTOUT – has expired.
Symbol Parameter Min Typ Max Unit
VPOT
Power-on Reset Threshold Voltage (rising) 1.1 1.4 1.7 V
Power-on Reset Threshold Voltage (falling)(1) 0.8 1.3 1.6 V
VPORMAX VCC Max. start voltage to ensure internal
Power-on Reset signal 0.4 V
VPORMIN VCC Min. start voltage to ensure internal
Power-on Reset signal -0.1 V
VCCRR VCC Rise Rate to ensure Power-on Reset 0.01 V/ms
VRST RESET Pin Threshold Voltage 0.1 VCC 0.9VCC V
VCC
INTERNAL
RESET
TIME-OUT
RESET
VPORMAX
VPORMIN
VRST
tTOUT
VCCRR
VCC
INTERNAL
RESET
TIME-OUT
RESET
VPOT
VRST
tTOUT
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Figure 9-4. External Reset During Operation
9.0.5 Brown-out Detection
ATtiny261/461/861 has an On-chip Brown-out Detection (BOD) circuit for monitoring the VCC
level during operation by comparing it to a fixed trigger level. The trigger level for the BOD can
be selected by the BODLEVEL Fuses. The trigger level has a hysteresis to ensure spike free
Brown-out Detection. The hysteresis on the detection level should be interpreted as VBOT+ =
VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.
When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in Figure
9-5), the Brown-out Reset is immediately activated. When VCC increases above the trigger level
(VBOT+ in Figure 9-5), the delay counter starts the MCU after the Time-out period tTOUT has
expired.
The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level for lon-
ger than tBOD given in “System and Reset Characteristics” on page 191.
Figure 9-5. Brown-out Reset During Operation
9.0.6 Watchdog Reset
When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On
the falling edge of this pulse, the delay timer starts counting the Time-out period tTOUT. Refer to
page 44 for details on operation of the Watchdog Timer.
tTOUT
RESET
VCC
INTERNAL
RESET
TIME-OUT
VRST
VBOT-
VBOT+
tTOUT
VCC
RESET
INTERNAL
RESET
TIME-OUT
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Figure 9-6. Watchdog Reset During Operation
9.1 Internal Voltage Reference
ATtiny261/461/861 features an internal bandgap reference. This reference is used for Brown-out
Detection, and it can be used as an input to the Analog Comparator or the ADC.
9.1.1 Voltage Reference Enable Signals and Start-up Time
The voltage reference has a start-up time that may influence the way it should be used. The
start-up time is given in “System and Reset Characteristics” on page 191. To save power, the
reference is not always turned on. The reference is on during the following situations:
1. When the BOD is enabled (by programming the BODLEVEL [2..0] Fuse bits).
2. When the bandgap reference is connected to the Analog Comparator (by setting the
ACBG bit in ACSR).
3. When the ADC is enabled.
Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user
must always allow the reference to start up before the output from the Analog Comparator or
ADC is used. To reduce power consumption in Power-down mode, the user can avoid the three
conditions above to ensure that the reference is turned off before entering Power-down mode.
9.2 Watchdog Timer
The Watchdog Timer is clocked from an On-chip Oscillator which runs at 128 kHz. By controlling
the Watchdog Timer prescaler, the Watchdog Reset interval can be adjusted as shown in Table
9-4 on page 48. The WDR – Watchdog Reset – instruction resets the Watchdog Timer. The
Watchdog Timer is also reset when it is disabled and when a Chip Reset occurs. Ten different
clock cycle periods can be selected to determine the reset period. If the reset period expires
without another Watchdog Reset, the ATtiny261/461/861 resets and executes from the Reset
Vector. For timing details on the Watchdog Reset, refer to Table 9-4 on page 48.
The Watchdog Timer can also be configured to generate an interrupt instead of a reset. This can
be very helpful when using the Watchdog to wake-up from Power-down.
To prevent unintentional disabling of the Watchdog or unintentional change of time-out period,
two different safety levels are selected by the fuse WDTON as shown in Table 9-2. Refer to
“Timed Sequences for Changing the Configuration of the Watchdog Timer” on page 45 for
details.
VCC
INTERNAL
RESET
WDT
TIME-OUT
RESET
TIME-OUT
RESET
tTOUT
1 CK Cycle
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Figure 9-7. Watchdog Timer
9.3 Timed Sequences for Changing the Configuration of the Watchdog Timer
The sequence for changing configuration differs slightly between the two safety levels. Separate
procedures are described for each level.
9.3.1 Safety Level 1
In this mode, the Watchdog Timer is initially disabled, but can be enabled by writing the WDE bit
to one without any restriction. A timed sequence is needed when disabling an enabled Watch-
dog Timer. To disable an enabled Watchdog Timer, the following procedure must be followed:
1. In the same operation, write a logic one to WDCE and WDE. A logic one must be written
to WDE regardless of the previous value of the WDE bit.
2. Within the next four clock cycles, in the same operation, write the WDE and WDP bits as
desired, but with the WDCE bit cleared.
9.3.2 Safety Level 2
In this mode, the Watchdog Timer is always enabled, and the WDE bit will always read as one. A
timed sequence is needed when changing the Watchdog Time-out period. To change the
Watchdog Time-out, the following procedure must be followed:
1. In the same operation, write a logical one to WDCE and WDE. Even though the WDE
always is set, the WDE must be written to one to start the timed sequence.
2. Within the next four clock cycles, in the same operation, write the WDP bits as desired,
but with the WDCE bit cleared. The value written to the WDE bit is irrelevant.
Table 9-2. WDT Configuration as a Function of the Fuse Settings of WDTON
WDTON
Safety
Level
WDT Initial
State
How to Disable the
WDT
How to Change
Time-out
Unprogrammed 1 Disabled Timed sequence No limitations
Programmed 2 Enabled Always enabled Timed sequence
OSC/2K
OSC/4K
OSC/8K
OSC/16K
OSC/32K
OSC/64K
OSC/128K
OSC/256K
OSC/512K
OSC/1024K
Watchdog
Prescaler
MCU RESET
WDP0
WATCHDOG
RESET
WDP1
WDP2
WDP3
WDE
128kHz
Oscillator
MUX
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9.4 Register Description
9.4.1 MCUSR – MCU Status Register
The MCU Status Register provides information on which reset source caused an MCU Reset.
• Bits 7:4 – Res: Reserved Bits
These bits are reserved bits in the ATtiny261/461/861 and will always read as zero.
• Bit 3 – WDRF: Watchdog Reset Flag
This bit is set if a Watchdog Reset occurs. The bit is reset by a Power-on Reset, or by writing a
logic zero to the flag.
• Bit 2 – BORF: Brown-out Reset Flag
This bit is set if a Brown-out Reset occurs. The bit is reset by a Power-on Reset, or by writing a
logic zero to the flag.
• Bit 1 – EXTRF: External Reset Flag
This bit is set if an External Reset occurs. The bit is reset by a Power-on Reset, or by writing a
logic zero to the flag.
• Bit 0 – PORF: Power-on Reset Flag
This bit is set if a Power-on Reset occurs. The bit is reset only by writing a logic zero to the flag.
To make use of the Reset Flags to identify a reset condition, the user should read and then reset
the MCUSR as early as possible in the program. If the register is cleared before another reset
occurs, the source of the reset can be found by examining the Reset Flags.
9.4.2 WDTCR – Watchdog Timer Control Register
• Bit 7 – WDIF: Watchdog Timeout Interrupt Flag
This bit is set when a time-out occurs in the Watchdog Timer and the Watchdog Timer is config-
ured for interrupt. WDIF is cleared by hardware when executing the corresponding interrupt
handling vector. Alternatively, WDIF is cleared by writing a logic one to the flag. When the I-bit in
SREG and WDIE are set, the Watchdog Time-out Interrupt is executed.
• Bit 6 – WDIE: Watchdog Timeout Interrupt Enable
When this bit is written to one, WDE is cleared, and the I-bit in the Status Register is set, the
Watchdog Time-out Interrupt is enabled. In this mode the corresponding interrupt is executed
instead of a reset if a timeout in the Watchdog Timer occurs.
If WDE is set, WDIE is automatically cleared by hardware when a time-out occurs. This is useful
for keeping the Watchdog Reset security while using the interrupt. After the WDIE bit is cleared,
Bit 76543210
0x34 (0x54) – – – – WDRF BORF EXTRF PORF MCUSR
Read/Write R R R R R/W R/W R/W R/W
Initial Value 0 0 0 0 See Bit Description
Bit 76543210
0x21 (0x41) WDIF WDIE WDP3 WDCE WDE WDP2 WDP1 WDP0 WDTCR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value0000X000
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the next time-out will generate a reset. To avoid the Watchdog Reset, WDIE must be set after
each interrupt.
• Bit 4 – WDCE: Watchdog Change Enable
This bit must be set when the WDE bit is written to logic zero. Otherwise, the Watchdog will not
be disabled. Once written to one, hardware will clear this bit after four clock cycles. Refer to the
description of the WDE bit for a Watchdog disable procedure. This bit must also be set when
changing the prescaler bits. See “Timed Sequences for Changing the Configuration of the
Watchdog Timer” on page 45.
• Bit 3 – WDE: Watchdog Enable
When the WDE is written to logic one, the Watchdog Timer is enabled, and if the WDE is written
to logic zero, the Watchdog Timer function is disabled. WDE can only be cleared if the WDCE bit
has logic level one. To disable an enabled Watchdog Timer, the following procedure must be
followed:
1. In the same operation, write a logic one to WDCE and WDE. A logic one must be written
to WDE even though it is set to one before the disable operation starts.
2. Within the next four clock cycles, write a logic 0 to WDE. This disables the Watchdog.
In safety level 2, it is not possible to disable the Watchdog Timer, even with the algorithm
described above. See “Timed Sequences for Changing the Configuration of the Watchdog
Timer” on page 45.
In safety level 1, WDE is overridden by WDRF in MCUSR. See “MCUSR – MCU Status Regis-
ter” on page 46 for description of WDRF. This means that WDE is always set when WDRF is set.
To clear WDE, WDRF must be cleared before disabling the Watchdog with the procedure
described above. This feature ensures multiple resets during conditions causing failure, and a
safe start-up after the failure.
Note: If the watchdog timer is not going to be used in the application, it is important to go through a
watchdog disable procedure in the initialization of the device. If the Watchdog is accidentally
enabled, for example by a runaway pointer or brown-out condition, the device will be reset, which
in turn will lead to a new watchdog reset. To avoid this situation, the application software should
always clear the WDRF flag and the WDE control bit in the initialization routine.
• Bits 5, 2:0 – WDP3..0: Watchdog Timer Prescaler 3, 2, 1, and 0
The WDP3..0 bits determine the Watchdog Timer prescaling when the Watchdog Timer is
enabled. The different prescaling values and their corresponding Timeout Periods are shown in
Table 9-4 on page 48.
Table 9-3. Watchdog Timer Configuration
WDE WDIE Watchdog Timer State Action on Time-out
0 0 Stopped None
0 1 Running Interrupt
1 0 Running Reset
1 1 Running Interrupt
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Notes: 1. If selecting a reserved code WDT time-out is selected to be one of the legal selections.
Table 9-4. Watchdog Timer Prescale Select
WDP3 WDP2 WDP1 WDP0
Number of WDT Oscillator
Cycles
Typical Time-out at
VCC = 5.0V
0000 2K (2048) cycles 16 ms
0001 4K (4096) cycles 32 ms
0010 8K (8192) cycles 64 ms
0011 16K (16384) cycles 0.125 s
0100 32K (32764) cycles 0.25 s
0101 64K (65536) cycles 0.5 s
0110 128K (131072) cycles 1.0 s
0111 256K (262144) cycles 2.0 s
1000 512K (524288) cycles 4.0 s
10011024K (1048576) cycles 8.0 s
1010
Reserved(1)
1011
1100
1101
1110
1111
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The following code example shows one assembly and one C function for turning off the WDT.
The example assumes that interrupts are controlled (e.g., by disabling interrupts globally) so that
no interrupts will occur during execution of these functions.
Note: 1. The example code assumes that the part specific header file is included.
Assembly Code Example(1)
WDT_off:
WDR
; Clear WDRF in MCUSR
ldi r16, (0<<WDRF)
out MCUSR, r16
; Write logical one to WDCE and WDE
; Keep old prescaler setting to prevent unintentional Watchdog Reset
in r16, WDTCR
ori r16, (1<<WDCE)|(1<<WDE)
out WDTCR, r16
; Turn off WDT
ldi r16, (0<<WDE)
out WDTCR, r16
ret
C Code Example(1)
void WDT_off(void)
{
_WDR();
/* Clear WDRF in MCUSR */
MCUSR = 0x00
/* Write logical one to WDCE and WDE */
WDTCR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCR = 0x00;
}
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10. Interrupts
This section describes the specifics of the interrupt handling as performed in ATtiny261/461/861.
For a general explanation of the AVR interrupt handling, refer to “Reset and Interrupt Handling”
on page 15.
10.1 Interrupt Vectors in ATtiny261/461/861
If the program never enables an interrupt source, the Interrupt Vectors are not used, and regular
program code can be placed at these locations. The most typical and general program setup for
the Reset and Interrupt Vector Addresses in ATtiny261/461/861 is:
Table 10-1. Reset and Interrupt Vectors
Vector
No.
Program
Address Source Interrupt Definition
1 0x0000 RESET External Pin, Power-on Reset, Brown-out
Reset, Watchdog Reset
2 0x0001 INT0 External Interrupt Request 0
3 0x0002 PCINT Pin Change Interrupt Request
4 0x0003 TIMER1_COMPA Timer/Counter1 Compare Match A
5 0x0004 TIMER1_COMPB Timer/Counter1 Compare Match B
6 0x0005 TIMER1_OVF Timer/Counter1 Overflow
7 0x0006 TIMER0_OVF Timer/Counter0 Overflow
8 0x0007 USI_START USI Start
9 0x0008 USI_OVF USI Overflow
10 0x0009 EE_RDY EEPROM Ready
11 0x000A ANA_COMP Analog Comparator
12 0x000B ADC ADC Conversion Complete
13 0x000C WDT Watchdog Time-out
14 0x000D INT1 External Interrupt Request 1
15 0x000E TIMER0_COMPA Timer/Counter0 Compare Match A
16 0x000F TIMER0_COMPB Timer/Counter0 Compare Match B
17 0x0010 TIMER0_CAPT Timer/Counter1 Capture Event
18 0x0011 TIMER1_COMPD Timer/Counter1 Compare Match D
19 0x0012 FAULT_PROTECTION Timer/Counter1 Fault Protection
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Address Labels Code Comments
0x0000 rjmp RESET ; Reset Handler
0x0001 rjmp EXT_INT0 ; IRQ0 Handler
0x0002 rjmp PCINT ; PCINT Handler
0x0003 rjmp TIM1_COMPA ; Timer1 CompareA Handler
0x0004 rjmp TIM1_COMPB ; Timer1 CompareB Handler
0x0005 rjmp TIM1_OVF ; Timer1 Overflow Handler
0x0006 rjmp TIM0_OVF ; Timer0 Overflow Handler
0x0007 rjmp USI_START ; USI Start Handler
0x0008 rjmp USI_OVF ; USI Overflow Handler
0x0009 rjmp EE_RDY ; EEPROM Ready Handler
0x000A rjmp ANA_COMP ; Analog Comparator Handler
0x000B rjmp ADC ; ADC Conversion Handler
0x000C rjmp WDT ; WDT Interrupt Handler
0x000D rjmp EXT_INT1 ; IRQ1 Handler
0x000E rjmp TIM0_COMPA ; Timer0 CompareA Handler
0x000F rjmp TIM0_COMPB ; Timer0 CompareB Handler
0x0010 rjmp TIM0_CAPT ; Timer0 Capture Event Handler
0x0011 rjmp TIM1_COMPD ; Timer1 CompareD Handler
0x0012 rjmp FAULT_PROTECTION ; Timer1 Fault Protection
0x0013 RESET: ldi r16, low(RAMEND) ; Main program start
0x0014 ldi r17, high(RAMEND); Tiny861 have also SPH
0x0015 out SPL, r16 ; Set Stack Pointer to top of RAM
0x0016 out SPH, r17 ; Tiny861 have also SPH
0x0017 sei ; Enable interrupts
0x0018 <instr> xxx
... ... ... ...
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11. External Interrupts
The External Interrupts are triggered by the INT0 or INT1 pin or any of the PCINT15..0 pins.
Observe that, if enabled, the interrupts will trigger even if the INT0, INT1 or PCINT15..0 pins are
configured as outputs. This feature provides a way of generating a software interrupt. Pin
change interrupts PCI will trigger if any enabled PCINT15..0 pin toggles. The PCMSK Register
control which pins contribute to the pin change interrupts. Pin change interrupts on PCINT15..0
are detected asynchronously. This implies that these interrupts can be used for waking the part
also from sleep modes other than Idle mode.
The INT0 and INT1 interrupts can be triggered by a falling or rising edge or a low level. This is
set up as indicated in the specification for the MCU Control Register – MCUCR. When the INT0
interrupt is enabled and is configured as level triggered, the interrupt will trigger as long as the
pin is held low. Note that recognition of falling or rising edge interrupts on INT0 or INT1 requires
the presence of an I/O clock, described in “Clock Systems and their Distribution” on page 25.
Low level interrupt on INT0 is detected asynchronously. This implies that this interrupt can be
used for waking the part also from sleep modes other than Idle mode. The I/O clock is halted in
all sleep modes except Idle mode.
Note that if a level triggered interrupt is used for wake-up from Power-down, the required level
must be held long enough for the MCU to complete the wake-up to trigger the level interrupt. If
the level disappears before the end of the Start-up Time, the MCU will still wake up, but no inter-
rupt will be generated. The start-up time is defined by the SUT and CKSEL Fuses as described
in “System Clock and Clock Options” on page 25.
11.1 Register Description
11.1.1 MCUCR – MCU Control Register
The MCU Register contains control bits for interrupt sense control.
• Bits 1, 0 – ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0
The External Interrupt 0 is activated by the external pin INT0 or INT1 if the SREG I-flag and the
corresponding interrupt mask are set. The level and edges on the external INT0 or INT1 pin that
activate the interrupt are defined in Table 11-1. The value on the INT0 or INT1 pin is sampled
before detecting edges. If edge or toggle interrupt is selected, pulses that last longer than one
clock period will generate an interrupt. Shorter pulses are not guaranteed to generate an inter-
rupt. If low level interrupt is selected, the low level must be held until the completion of the
currently executing instruction to generate an interrupt.
Bit 76543210
0x35 (0x55) –PUD SE SM1 SM0 – ISC01 ISC00 MCUCR
Read/WriteR R/WR/WR/WR/WR R/WR/W
Initial Value00000000
Table 11-1. Interrupt 0 Sense Control
ISC01 ISC00 Description
0 0 The low level of INT0 or INT1 generates an interrupt request.
0 1 Any logical change on INT0 or INT1 generates an interrupt request.
1 0 The falling edge of INT0 or INT1 generates an interrupt request.
1 1 The rising edge of INT0 or INT1 generates an interrupt request.
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11.1.2 GIMSK – General Interrupt Mask Register
• Bit 7 – INT1: External Interrupt Request 1 Enable
When the INT1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the exter-
nal pin interrupt is enabled. The Interrupt Sense Control0 bits 1/0 (ISC01 and ISC00) in the MCU
Control Register (MCUCR) define whether the external interrupt is activated on rising and/or fall-
ing edge of the INT1 pin or level sensed. Activity on the pin will cause an interrupt request even
if INT1 is configured as an output. The corresponding interrupt of External Interrupt Request 1 is
executed from the INT1 Interrupt Vector.
• Bit 6 – INT0: External Interrupt Request 0 Enable
When the INT0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the exter-
nal pin interrupt is enabled. The Interrupt Sense Control0 bits 1/0 (ISC01 and ISC00) in the MCU
Control Register (MCUCR) define whether the external interrupt is activated on rising and/or fall-
ing edge of the INT0 pin or level sensed. Activity on the pin will cause an interrupt request even
if INT0 is configured as an output. The corresponding interrupt of External Interrupt Request 0 is
executed from the INT0 Interrupt Vector.
• Bit 5 – PCIE1: Pin Change Interrupt Enable
When the PCIE1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin
change interrupt is enabled. Any change on any enabled PCINT7..0 or PCINT15..12 pin will
cause an interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed
from the PCI Interrupt Vector. PCINT7..0 and PCINT15..12 pins are enabled individually by the
PCMSK0 and PCMSK1 Register.
• Bit 4 – PCIE0: Pin Change Interrupt Enable
When the PCIE0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin
change interrupt is enabled. Any change on any enabled PCINT11..8 pin will cause an interrupt.
The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI Interrupt
Vector. PCINT11..8 pins are enabled individually by the PCMSK1 Register.
• Bits 3..0 – Res: Reserved Bits
These bits are reserved bits in the ATtiny261/461/861 and will always read as zero.
11.1.3 GIFR – General Interrupt Flag Register
• Bit 7– INTF1: External Interrupt Flag 1
When an edge or logic change on the INT1 pin triggers an interrupt request, INTF1 becomes set
(one). If the I-bit in SREG and the INT1 bit in GIMSK are set (one), the MCU will jump to the cor-
responding Interrupt Vector. The flag is cleared when the interrupt routine is executed.
Alternatively, the flag can be cleared by writing a logical one to it. This flag is always cleared
when INT1 is configured as a level interrupt.
Bit 76543210
0x3B (0x5B) INT1 INT0 PCIE1 PCIE0 – – – – GIMSK
Read/Write R/W R/W R/W R/w R R R R
Initial Value00000000
Bit 76543210
0x3A (0x5A) INT1INTF0PCIF–––––GIFR
Read/WriteR/WR/WR/WRRRRR
Initial Value00000000
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• Bit 6 – INTF0: External Interrupt Flag 0
When an edge or logic change on the INT0 pin triggers an interrupt request, INTF0 becomes set
(one). If the I-bit in SREG and the INT0 bit in GIMSK are set (one), the MCU will jump to the cor-
responding Interrupt Vector. The flag is cleared when the interrupt routine is executed.
Alternatively, the flag can be cleared by writing a logical one to it. This flag is always cleared
when INT0 is configured as a level interrupt.
• Bit 5 – PCIF: Pin Change Interrupt Flag
When a logic change on any PCINT15 pin triggers an interrupt request, PCIF becomes set
(one). If the I-bit in SREG and the PCIE bit in GIMSK are set (one), the MCU will jump to the cor-
responding Interrupt Vector. The flag is cleared when the interrupt routine is executed.
Alternatively, the flag can be cleared by writing a logical one to it.
• Bits 4:0 – Res: Reserved Bits
These bits are reserved bits in the ATtiny261/461/861 and will always read as zero.
11.1.4 PCMSK0 – Pin Change Mask Register A
• Bits 7:0 – PCINT7:0: Pin Change Enable Mask 7..0
Each PCINT7:0 bit selects whether pin change interrupt is enabled on the corresponding I/O pin.
If PCINT7:0 is set and the PCIE1 bit in GIMSK is set, pin change interrupt is enabled on the cor-
responding I/O pin. If PCINT7..0 is cleared, pin change interrupt on the corresponding I/O pin is
disabled.
11.1.5 PCMSK1 – Pin Change Mask Register B
• Bits 7:0 – PCINT15:8: Pin Change Enable Mask 15..8
Each PCINT15:8 bit selects whether pin change interrupt is enabled on the corresponding I/O
pin. If PCINT11:8 is set and the PCIE0 bit in GIMSK is set, pin change interrupt is enabled on
the corresponding I/O pin, and if PCINT15:12 is set and the PCIE1 bit in GIMSK is set, pin
change interrupt is enabled on the corresponding I/O pin. If PCINT15:8 is cleared, pin change
interrupt on the corresponding I/O pin is disabled.
Bit 76543210
0x23 (0x43) PCINT7 PCINT6 PCINT5 PCINT4 PCINT3 PCINT2 PCINT1 PCINT0 PCMSK0
Read/WriteR/WR/WR/WR/w R/WR/WR/WR/W
Initial Value11001000
Bit 76543210
0x22 (0x42) PCINT15 PCINT14 PCINT13 PCINT12 PCINT11 PCINT10 PCINT9 PCINT8 PCMSK1
Read/Write R/W R/W R/W R/w R/W R/W R/W R/W
Initial Value11111111
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12. I/O Ports
12.1 Overview
All AVR ports have true Read-Modify-Write functionality when used as general digital I/O ports.
This means that the direction of one port pin can be changed without unintentionally changing
the direction of any other pin with the SBI and CBI instructions. The same applies when chang-
ing drive value (if configured as output) or enabling/disabling of pull-up resistors (if configured as
input). Each output buffer has symmetrical drive characteristics with both high sink and source
capability. The pin driver is strong enough to drive LED displays directly. All port pins have indi-
vidually selectable pull-up resistors with a supply-voltage invariant resistance. All I/O pins have
protection diodes to both VCC and Ground as indicated in Figure 12-1. Refer to “Electrical Char-
acteristics” on page 188 for a complete list of parameters.
Figure 12-1. I/O Pin Equivalent Schematic
All registers and bit references in this section are written in general form. A lower case “x” repre-
sents the numbering letter for the port, and a lower case “n” represents the bit number. However,
when using the register or bit defines in a program, the precise form must be used. For example,
PORTB3 for bit no. 3 in Port B, here documented generally as PORTxn. The physical I/O Regis-
ters and bit locations are listed in “Register Description” on page 69.
Three I/O memory address locations are allocated for each port, one each for the Data Register
– PORTx, Data Direction Register – DDRx, and the Port Input Pins – PINx. The Port Input Pins
I/O location is read only, while the Data Register and the Data Direction Register are read/write.
However, writing a logic one to a bit in the PINx Register, will result in a toggle in the correspond-
ing bit in the Data Register. In addition, the Pull-up Disable – PUD bit in MCUCR disables the
pull-up function for all pins in all ports when set.
Using the I/O port as General Digital I/O is described in “Ports as General Digital I/O” on page
56. Most port pins are multiplexed with alternate functions for the peripheral features on the
device. How each alternate function interferes with the port pin is described in “Alternate Port
Functions” on page 60. Refer to the individual module sections for a full description of the alter-
nate functions.
Note that enabling the alternate function of some of the port pins does not affect the use of the
other pins in the port as general digital I/O.
Cpin
Rpu
Pxn
Logic
See Figure
”General Digital I/O”
for Details
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12.2 Ports as General Digital I/O
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 12-2 shows a func-
tional description of one I/O-port pin, here generically called Pxn.
Figure 12-2. General Digital I/O(1)
Note: 1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O,
SLEEP, and PUD are common to all ports.
12.2.1 Configuring the Pin
Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in “Register
Description” on page 69, the DDxn bits are accessed at the DDRx I/O address, the PORTxn bits
at the PORTx I/O address, and the PINxn bits at the PINx I/O address.
The DDxn bit in the DDRx Register selects the direction of this pin. If DDxn is written logic one,
Pxn is configured as an output pin. If DDxn is written logic zero, Pxn is configured as an input
pin.
D
0
1
Q
WRx
RRx
WPx
Pxn
CLR
RESET
Synchronizer
DATA BUS
PORTxn
Q
Q
L
D
Q
QD
Q
PINxn
RESET
RPx
WDx: WRITE DDRx
WRx:
WPx:
RPx:
RRx: READ PORTx REGISTER
READ PORTx PIN
WRITE PORTx REGISTER
RDx:
WRITE PORTx
READ DDRx
PUD: PULLUP DISABLE
CLKI/O:
SLEEP:
I/O CLOCK
SLEEP CONTROL
RDx
CLKI/O
PUD
WDx
SLEEP
D
QCLR
DDxn
Q
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If PORTxn is written logic one when the pin is configured as an input pin, the pull-up resistor is
activated. To switch the pull-up resistor off, PORTxn has to be written logic zero or the pin has to
be configured as an output pin. The port pins are tri-stated when reset condition becomes active,
even if no clocks are running.
If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven
high (one). If PORTxn is written logic zero when the pin is configured as an output pin, the port
pin is driven low (zero).
12.2.2 Toggling the Pin
Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn.
Note that the SBI instruction can be used to toggle one single bit in a port.
12.2.3 Switching Between Input and Output
When switching between tri-state ({DDxn, PORTxn} = 0b00) and output high ({DDxn, PORTxn}
= 0b11), an intermediate state with either pull-up enabled {DDxn, PORTxn} = 0b01) or output
low ({DDxn, PORTxn} = 0b10) must occur. Normally, the pull-up enabled state is fully accept-
able, as a high-impedent environment will not notice the difference between a strong high driver
and a pull-up. If this is not the case, the PUD bit in the MCUCR Register can be set to disable all
pull-ups in all ports.
Switching between input with pull-up and output low generates the same problem. The user
must use either the tri-state ({DDxn, PORTxn} = 0b00) or the output high state ({DDxn, PORTxn}
= 0b10) as an intermediate step.
Table 12-1 summarizes the control signals for the pin value.
12.2.4 Reading the Pin Value
Independent of the setting of Data Direction bit DDxn, the port pin can be read through the
PINxn Register bit. As shown in Figure 12-2, the PINxn Register bit and the preceding latch con-
stitute a synchronizer. This is needed to avoid metastability if the physical pin changes value
near the edge of the internal clock, but it also introduces a delay. Figure 12-3 shows a timing dia-
gram of the synchronization when reading an externally applied pin value. The maximum and
minimum propagation delays are denoted tpd,max and tpd,min respectively.
Table 12-1. Port Pin Configurations
DDxn PORTxn
PUD
(in MCUCR) I/O Pull-up Comment
0 0 X Input No Tri-state (Hi-Z)
0 1 0 Input Yes Pxn will source current if ext. pulled low.
0 1 1 Input No Tri-state (Hi-Z)
1 0 X Output No Output Low (Sink)
1 1 X Output No Output High (Source)
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Figure 12-3. Synchronization when Reading an Externally Applied Pin value
Consider the clock period starting shortly after the first falling edge of the system clock. The latch
is closed when the clock is low, and goes transparent when the clock is high, as indicated by the
shaded region of the “SYNC LATCH” signal. The signal value is latched when the system clock
goes low. It is clocked into the PINxn Register at the succeeding positive clock edge. As indi-
cated by the two arrows tpd, max and tpd, min, a single signal transition on the pin will be
delayed between ½ and 1½ system clock period depending upon the time of assertion.
When reading back a software assigned pin value, a nop instruction must be inserted as indi-
cated in Figure 12-4. The out instruction sets the “SYNC LATCH” signal at the positive edge of
the clock. In this case, the delay tpd through the synchronizer is one system clock period.
Figure 12-4. Synchronization when Reading a Software Assigned Pin Value
The following code example shows how to set port B pins 0 and 1 high, 2 and 3 low, and define
the port pins from 4 to 5 as input with a pull-up assigned to port pin 4. The resulting pin values
are read back again, but as previously discussed, a nop instruction is included to be able to read
back the value recently assigned to some of the pins.
tpd,max
tpd,min
0xFF0x00
XXX in r17, PINxXXX
INSTRUCTIONS
SYNC LATCH
r17
PINxn
SYSTEM CLK
tpd
0xFF
0xFF
0x00
nop in r17, PINxout PORTx, r16
INSTRUCTIONS
SYNC LATCH
r16
r17
PINxn
SYSTEM CLK
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Note: 1. For the assembly program, two temporary registers are used to minimize the time from
pull-ups are set on pins 0, 1 and 4, until the direction bits are correctly set, defining bit 2 and 3
as low and redefining bits 0 and 1 as strong high drivers.
12.2.5 Digital Input Enable and Sleep Modes
As shown in Figure 12-2, the digital input signal can be clamped to ground at the input of the
schmitt-trigger. The signal denoted SLEEP in the figure, is set by the MCU Sleep Controller in
Power-down mode, Power-save mode, and Standby mode to avoid high power consumption if
some input signals are left floating, or have an analog signal level close to VCC/2.
SLEEP is overridden for port pins enabled as external interrupt pins. If the external interrupt
request is not enabled, SLEEP is active also for these pins. SLEEP is also overridden by various
other alternate functions as described in “Alternate Port Functions” on page 60.
If a logic high level (“one”) is present on an asynchronous external interrupt pin configured as
“Interrupt on Rising Edge, Falling Edge, or Any Logic Change on Pin” while the external interrupt
is not enabled, the corresponding External Interrupt Flag will be set when resuming from the
above mentioned Sleep mode, as the clamping in these sleep mode produces the requested
logic change.
Assembly Code Example(1)
...
; Define pull-ups and set outputs high
; Define directions for port pins
ldi r16,(1<<PB4)|(1<<PB1)|(1<<PB0)
ldi r17,(1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0)
out PORTB,r16
out DDRB,r17
; Insert nop for synchronization
nop
; Read port pins
in r16,PINB
...
C Code Example
unsigned char i;
...
/* Define pull-ups and set outputs high */
/* Define directions for port pins */
PORTB = (1<<PB4)|(1<<PB1)|(1<<PB0);
DDRB = (1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0);
/* Insert nop for synchronization*/
_NOP();
/* Read port pins */
i = PINB;
...
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12.2.6 Unconnected Pins
If some pins are unused, it is recommended to ensure that these pins have a defined level. Even
though most of the digital inputs are disabled in the deep sleep modes as described above, float-
ing inputs should be avoided to reduce current consumption in all other modes where the digital
inputs are enabled (Reset, Active mode and Idle mode).
The simplest method to ensure a defined level of an unused pin, is to enable the internal pull-up.
In this case, the pull-up will be disabled during reset. If low power consumption during reset is
important, it is recommended to use an external pull-up or pull-down. Connecting unused pins
directly to VCC or GND is not recommended, since this may cause excessive currents if the pin is
accidentally configured as an output.
12.3 Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. Figure 12-5
shows how the port pin control signals from the simplified Figure 12-2 can be overridden by
alternate functions. The overriding signals may not be present in all port pins, but the figure
serves as a generic description applicable to all port pins in the AVR microcontroller family.
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Figure 12-5. Alternate Port Functions(1)
Note: 1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O,
SLEEP, and PUD are common to all ports. All other signals are unique for each pin.
D
0
1
Q
WRx
RRx
WPx
PTOExn
Pnx
CLR
CLR CLR
RESET
Synchronizer
DATA BUS
PORTxn
Q
0
1
Q
L
D
Q
QD
Q
PINxn
0
1
RESET
RPx
Pxn PULL-UP OVERRIDE ENABLE
Pxn PULL-UP OVERRIDE VALUE
PUD: PULL-UP DISABLEPUOExn:
Pxn PORT VALUE OVERRIDE VALUEPVOVxn:
Pxn PORT VALUE OVERRIDE ENABLEPVOExn:
Pxn DATA DIRECTION OVERRIDE ENABLE
Pxn DATA DIRECTION OVERRIDE VALUE
DDOExn:
DDOVxn:
SLEEP CONTROLSLEEP:
Pxn, PORT TOGGLE OVERRIDE ENABLEPTOExn:
Pxn DIGITAL INPUT ENABLE OVERRIDE VALUEDIEOVxn:
Pxn DIGITAL INPUT ENABLE OVERRIDE ENABLEDIEOExn:
I/O CLOCK
RDx:
RPx:
WRITE PINx
WRx:
ANALOG INPUT/OUTPUT PIN n ON PORTx
DIGITAL INPUT PIN n ON PORTx
RRx: READ PORTx REGISTER
WPx:
WRITE PORTx
AIOxn:
DIxn:
READ PORTx PIN
WDx:
READ DDRx
WRITE DDRxPUOVxn:
RDx
CLKI/O
DIxn
AIOxn
CLK:I/O
DIEOVxn
DIEOExn
PVOExn
DDOExn
PVOVxn
0
1
PUOExn
PUOVxn
0
1DDOVxn
SLEEP
PUD
WDx
D
QCLR
DDxn
Q
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Table 12-2 summarizes the function of the overriding signals. The pin and port indexes from Fig-
ure 12-5 are not shown in the succeeding tables. The overriding signals are generated internally
in the modules having the alternate function.
The following subsections shortly describe the alternate functions for each port, and relate the
overriding signals to the alternate function. Refer to the alternate function description for further
details.
Table 12-2. Generic Description of Overriding Signals for Alternate Functions
Signal Name Full Name Description
PUOE Pull-up Override
Enable
If this signal is set, the pull-up enable is controlled by the PUOV
signal. If this signal is cleared, the pull-up is enabled when
{DDxn, PORTxn, PUD} = 0b010.
PUOV Pull-up Override
Value
If PUOE is set, the pull-up is enabled/disabled when PUOV is
set/cleared, regardless of the setting of the DDxn, PORTxn,
and PUD Register bits.
DDOE Data Direction
Override Enable
If this signal is set, the Output Driver Enable is controlled by the
DDOV signal. If this signal is cleared, the Output driver is
enabled by the DDxn Register bit.
DDOV Data Direction
Override Value
If DDOE is set, the Output Driver is enabled/disabled when
DDOV is set/cleared, regardless of the setting of the DDxn
Register bit.
PVOE Port Value
Override Enable
If this signal is set and the Output Driver is enabled, the port
value is controlled by the PVOV signal. If PVOE is cleared, and
the Output Driver is enabled, the port Value is controlled by the
PORTxn Register bit.
PVOV Port Value
Override Value
If PVOE is set, the port value is set to PVOV, regardless of the
setting of the PORTxn Register bit.
PTOE Port Toggle
Override Enable If PTOE is set, the PORTxn Register bit is inverted.
DIEOE
Digital Input
Enable Override
Enable
If this bit is set, the Digital Input Enable is controlled by the
DIEOV signal. If this signal is cleared, the Digital Input Enable is
determined by MCU state (Normal mode, sleep mode).
DIEOV
Digital Input
Enable Override
Value
If DIEOE is set, the Digital Input is enabled/disabled when
DIEOV is set/cleared, regardless of the MCU state (Normal
mode, sleep mode).
DI Digital Input
This is the Digital Input to alternate functions. In the figure, the
signal is connected to the output of the schmitt-trigger but
before the synchronizer. Unless the Digital Input is used as a
clock source, the module with the alternate function will use its
own synchronizer.
AIO Analog
Input/Output
This is the Analog Input/Output to/from alternate functions. The
signal is connected directly to the pad, and can be used
bi-directionally.
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12.3.1 Alternate Functions of Port B
The Port B pins with alternate function are shown in Table 12-3.
The alternate pin configuration is as follows:
• Port B, Bit 7 - RESET/ dW/ ADC10/ PCINT15
RESET, Reset pin: When the RSTDISBL Fuse is programmed, this pin functions as a normal I/O
pin, and the part will have to rely on Power-on Reset and Brown-out Reset as its reset sources.
When the RSTDISBL Fuse is unprogrammed, the reset circuitry is connected to the pin, and the
pin can not be used as an I/O pin.
If PB7 is used as a reset pin, DDB7, PORTB7 and PINB7 will all read 0.
dW: When the debugWIRE Enable (DWEN) Fuse is programmed and Lock bits are unpro-
grammed, the RESET port pin is configured as a wire-AND (open-drain) bi-directional I/O pin
with pull-up enabled and becomes the communication gateway between target and emulator.
ADC10: ADC input Channel 10. Note that ADC input channel 10 uses analog power.
PCINT15: Pin Change Interrupt source 15.
• Port B, Bit 6 - ADC9/ T0/ INT0/ PCINT14
ADC9: ADC input Channel 9. Note that ADC input channel 9 uses analog power.
T0: Timer/Counter0 counter source.
INT0: The PB6 pin can serve as an External Interrupt source 0.
PCINT14: Pin Change Interrupt source 14.
• Port B, Bit 5 - XTAL2/ CLKO/ ADC8/ PCINT13
XTAL2: Chip clock Oscillator pin 2. Used as clock pin for crystal Oscillator or Low-frequency
crystal Oscillator. When used as a clock pin, the pin can not be used as an I/O pin.
CLKO: The divided system clock can be output on the PB5 pin, if the CKOUT Fuse is pro-
grammed, regardless of the PORTB5 and DDB5 settings. It will also be output during reset.
OC1D Output Compare Match output: The PB5 pin can serve as an external output for the
Timer/Counter1 Compare Match D when configured as an output (DDA1 set). The OC1D pin is
also the output pin for the PWM mode timer function.
Table 12-3. Port B Pins Alternate Functions
Port Pin Alternate Function
PB7 RESET / dW / ADC10 / PCINT15
PB6 ADC9 / T0 / INT0 / PCINT14
PB5 XTAL2 / CLKO / OC1D / ADC8 / PCINT13
PB4 XTAL1 / CLKI / OC1D / ADC7 / PCINT12
PB3 OC1B / PCINT11
PB2 SCK / USCK / SCL / OC1B /PCINT10
PB1 MISO / DO / OC1A / PCINT9
PB0 MOSI / DI / SDA / OC1A / PCINT8
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ADC8: ADC input Channel 8. Note that ADC input channel 8 uses analog power.
PCINT13: Pin Change Interrupt source 13.
• Port B, Bit 4 - XTAL1/ CLKI/ OC1B/ ADC7/ PCINT12
XTAL1/CLKI: Chip clock Oscillator pin 1. Used for all chip clock sources except internal cali-
brated RC Oscillator. When used as a clock pin, the pin can not be used as an I/O pin.
OC1D: Inverted Output Compare Match output: The PB4 pin can serve as an external output for
the Timer/Counter1 Compare Match D when configured as an output (DDA0 set). The OC1D pin
is also the inverted output pin for the PWM mode timer function.
ADC7: ADC input Channel 7. Note that ADC input channel 7 uses analog power.
PCINT12: Pin Change Interrupt source 12.
• Port B, Bit 3 - OC1B/ PCINT11
OC1B, Output Compare Match output: The PB3 pin can serve as an external output for the
Timer/Counter1 Compare Match B. The PB3 pin has to be configured as an output (DDB3 set
(one)) to serve this function. The OC1B pin is also the output pin for the PWM mode timer
function.
PCINT11: Pin Change Interrupt source 11.
• Port B, Bit 2 - SCK/ USCK/ SCL/ OC1B/ PCINT10
SCK: Master Clock output, Slave Clock input pin for SPI channel. When the SPI is enabled as a
Slave, this pin is configured as an input regardless of the setting of DDB2. When the SPI is
enabled as a Master, the data direction of this pin is controlled by DDB2. When the pin is forced
by the SPI to be an input, the pull-up can still be controlled by the PORTB2 bit.
USCK: Three-wire mode Universal Serial Interface Clock.
SCL: Two-wire mode Serial Clock for USI Two-wire mode.
OC1B: Inverted Output Compare Match output: The PB2 pin can serve as an external output for
the Timer/Counter1 Compare Match B when configured as an output (DDB2 set). The OC1B pin
is also the inverted output pin for the PWM mode timer function.
PCINT10: Pin Change Interrupt source 10.
• Port B, Bit 1 - MISO/ DO/ OC1A/ PCINT9
MISO: Master Data input, Slave Data output pin for SPI channel. When the SPI is enabled as a
Master, this pin is configured as an input regardless of the setting of DDB1. When the SPI is
enabled as a Slave, the data direction of this pin is controlled by DDB1. When the pin is forced
by the SPI to be an input, the pull-up can still be controlled by the PORTB1 bit.
DO: Three-wire mode Universal Serial Interface Data output. Three-wire mode Data output over-
rides PORTB1 value and it is driven to the port when data direction bit DDB1 is set (one).
PORTB1 still enables the pull-up, if the direction is input and PORTB1 is set (one).
OC1A: Output Compare Match output: The PB1 pin can serve as an external output for the
Timer/Counter1 Compare Match B when configured as an output (DDB1 set). The OC1A pin is
also the output pin for the PWM mode timer function.
PCINT9: Pin Change Interrupt source 9.
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• Port B, Bit 0 - MOSI/ DI/ SDA/ OC1A/ PCINT8
MOSI: SPI Master Data output, Slave Data input for SPI channel. When the SPI is enabled as a
Slave, this pin is configured as an input regardless of the setting of DDB0. When the SPI is
enabled as a Master, the data direction of this pin is controlled by DDB0. When the pin is forced
by the SPI to be an input, the pull-up can still be controlled by the PORTB0 bit.
DI: Data Input in USI Three-wire mode. USI Three-wire mode does not override normal port
functions, so pin must be configure as an input for DI function.
SDA: Two-wire mode Serial Interface Data.
OC1A: Inverted Output Compare Match output: The PB0 pin can serve as an external output for
the Timer/Counter1 Compare Match B when configured as an output (DDB0 set). The OC1A pin
is also the inverted output pin for the PWM mode timer function.
PCINT8: Pin Change Interrupt source 8.
Table 12-4 and Table 12-5 relate the alternate functions of Port B to the overriding signals
shown in Figure 12-5 on page 61.
Note: 1. 1 when the Fuse is “0” (Programmed).
Table 12-4. Overriding Signals for Alternate Functions in PB7..PB4
Signal
Name
PB7/RESET/dW/
ADC10/PCINT15
PB6/ADC9/T0/INT0/
PCINT14
PB5/XTAL2/CLKO/
OC1D/ADC8/PCINT13(1) PB4/XTAL1/OC1D/
ADC7/PCINT12(1)
PUOE RSTDISBL(1) •
DWEN(1) 0 INTRC • EXTCLK INTRC
PUOV 1 0 0 0
DDOE RSTDISBL(1) •
DWEN(1) 0 INTRC • EXTCLK INTRC
DDOV debugWire Transmit 0 0 0
PVOE 0 0 OC1D Enable OC1D Enable
PVOV 0 0 OC1D OC1D
PTOE 0 0 0 0
DIEOE 0 RSTDISBL + (PCINT5
• PCIE + ADC9D)
INTRC • EXTCLK + PCINT4 •
PCIE + ADC8D
INTRC + PCINT12
• PCIE + ADC7D
DIEOV ADC10D ADC9D (INTRC • EXTCLK) + ADC8D INTRC • ADC7D
DI PCINT15 T0/INT0/PCINT14 PCINT13 PCINT12
AIO RESET / ADC10 ADC9 XTAL2, ADC8 XTAL1, ADC7
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Note: 1. INTRC means that one of the internal RC Oscillators are selected (by the CKSEL fuses),
EXTCK means that external clock is selected (by the CKSEL fuses).
12.3.2 Alternate Functions of Port A
The Port A pins with alternate function are shown in Table 12-6.
The alternate pin configuration is as follows:
• Port A, Bit 7- ADC6/AIN0/PCINT7
ADC6: Analog to Digital Converter, Channel 6.
AIN0: Analog Comparator Input. Configure the port pin as input with the internal pull-up switched
off to avoid the digital port function from interfering with the function of the Analog Comparator.
PCINT7: Pin Change Interrupt source 8.
Table 12-5. Overriding Signals for Alternate Functions in PB3..PB0
Signal
Name
PB3/OC1B/
PCINT11
PB2/SCK/USCK/SCL/
OC1B/PCINT10
PB1/MISO/DO/OC1A/
PCINT9
PB0/MOSI/DI/SDA/
OC1A/PCINT8
PUOE 0 0 0 0
PUOV 0 0 0 0
DDOE 0 USI_TWO_WIRE • USIPOS 0USI_TWO_WIRE •
USIPOS
DDOV 0 (USI_SCL_HOLD +
PORTB2) • DDB2 • USIPOS 0(SDA + PORTB0) •
DDB0 • USIPOS
PVOE OC1B Enable OC1B Enable + USIPOS •
USI_TWO_WIRE • DDB2
OC1A Enable + USIPOS
• USI_THREE_WIRE
OC1A Enable +
(USI_TWO_WIRE •
DDB0 • USIPOS)
PVOV OC1B OC1B OC1A + (DO • USIPOS)OC1A
PTOE 0 USITC • USIPOS 00
DIEOE PCINT11 • PCIE PCINT10 • PCIE + USISIE •
USIPOS PCINT9 • PCIE PCINT8 • PCIE +
(USISIE • USIPOS)
DIEOV 0 0 0 0
DI PCINT11 USCK/SCL/PCINT10 PCINT9 DI/SDA/PCINT8
AIO
Table 12-6. Port B Pins Alternate Functions
Port Pin Alternate Function
PA7 ADC6 / AIN0 / PCINT7
PA6 ADC5 / AIN1 / PCINT6
PA5 ADC4 / AIN2 / PCINT5
PA4 ADC3 /ICP0/ PCINT4
PA3 AREF / PCINT3
PA2 ADC2 / INT1 / USCK / SCL / PCINT2
PA1 ADC1 / DO / PCINT1
PA0 ADC0 / DI / SDA / PCINT0
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• Port A, Bit 6 - ADC5/AIN1/PCINT6
ADC5: Analog to Digital Converter, Channel 5.
AIN1: Analog Comparator Input. Configure the port pin as input with the internal pull-up switched
off to avoid the digital port function from interfering with the function of the Analog Comparator.
PCINT6: Pin Change Interrupt source 6.
• Port A, Bit 5 - ADC4/AIN2/PCINT5
ADC4: Analog to Digital Converter, Channel 4.
AIN2: Analog Comparator Input. Configure the port pin as input with the internal pull-up switched
off to avoid the digital port function from interfering with the function of the Analog Comparator.
PCINT5: Pin Change Interrupt source 5.
• Port A, Bit 4 - ADC3/ICP0/PCINT4
ADC3: Analog to Digital Converter, Channel 3.
ICP0: Timer/Counter0 Input Capture Pin.
PCINT4: Pin Change Interrupt source 4.
• Port A, Bit 3 - AREF/PCINT3
AREF: External analog reference for ADC. Pull-up and output driver are disabled on PA3 when
the pin is used as an external reference or internal voltage reference with external capacitor at
the AREF pin.
PCINT3: Pin Change Interrupt source 3.
• Port A, Bit 2 - ADC2/INT1/USCK/SCL/PCINT2
ADC2: Analog to Digital Converter, Channel 2.
INT1: The PA2 pin can serve as an External Interrupt source 1.
USCK: Three-wire mode Universal Serial Interface Clock.
SCL: Two-wire mode Serial Clock for USI Two-wire mode.
PCINT2: Pin Change Interrupt source 2.
• Port A, Bit 1 - ADC1/DO/PCINT1
ADC1: Analog to Digital Converter, Channel 1.
DO: Three-wire mode Universal Serial Interface Data output. Three-wire mode Data output over-
rides PORTA1 value and it is driven to the port when data direction bit DDA1 is set. PORTA1 still
enables the pull-up, if the direction is input and PORTA1 is set.
PCINT1: Pin Change Interrupt source 1.
• Port A, Bit 0 - ADC0/DI/SDA/PCINT0
ADC0: Analog to Digital Converter, Channel 0.
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DI: Data Input in USI Three-wire mode. USI Three-wire mode does not override normal port
functions, so pin must be configure as an input for DI function.
SDA: Two-wire mode Serial Interface Data.
PCINT0: Pin Change Interrupt source 0.
Table 12-7 and Table 12-8 relate the alternate functions of Port A to the overriding signals
shown in Figure 12-5 on page 61.
Table 12-7. Overriding Signals for Alternate Functions in PA7..PA4
Signal
Name
PA7/ADC6/AIN0/
PCINT7
PA6/ADC5/AIN1/
PCINT6
PA5/ADC4/AIN2/
PCINT5
PA4/ADC3/ICP0/
PCINT4
PUOE0000
PUOV0000
DDOE0000
DDOV0000
PVOE0000
PVOV0000
PTOE0000
DIEOE PCINT7 • PCIE +
ADC6D
PCINT6 • PCIE +
ADC5D
PCINT5 • PCIE +
ADC4D
PCINT4 • PCIE +
ADC3D
DIEOV ADC6D ADC5D ADC4D ADC3D
DI PCINT7 PCINT6 PCINT5 ICP0/PCINT4
AIO ADC6, AIN0 ADC5, AIN1 ADC4, AIN2 ADC3
Table 12-8. Overriding Signals for Alternate Functions in PA3..PA0
Signal
Name
PA3/AREF/
PCINT3
PA2/ADC2/INT1/
USCK/SCL/PCINT2
PA1/ADC1/DO/
PCINT1
PA0/ADC0/DI/SDA/
PCINT0
PUOE 0 0 0 0
PUOV 0 0 0 0
DDOE 0 USI_TWO_WIRE • USIPOS 0USI_TWO_WIRE •
USIPOS
DDOV 0 (USI_SCL_HOLD +
PORTB2) • DDB2 • USIPOS 0(SDA + PORTB0) •
DDRB0 • USIPOS
PVOE 0 USI_TWO_WIRE • DDRB2 USI_THREE_WIRE
• USIPOS
USI_TWO_WIRE •
DDRB0 • USIPOS
PVOV 0 0 DO • USIPOS 0
PTOE 0 USI_PTOE • USIPOS 0 0
DIEOE PCINT3 • PCIE PCINT2 • PCIE + INT1 +
ADC2D + USISIE • USIPOS
PCINT1 • PCIE +
ADC1D
PCINT0 • PCIE + ADC0D
+ USISIE • USIPOS
DIEOV 0 ADC2D ADC1D ADC0D
DI PCINT3 USCK/SCL/INT1/ PCINT2 PCINT1 DI/SDA/PCINT0
AIO AREF ADC2 ADC1 ADC0
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12.4 Register Description
12.4.1 MCUCR – MCU Control Register
• Bit 6 – PUD: Pull-up Disable
When this bit is written to one, the pull-ups in the I/O ports are disabled even if the DDxn and
PORTxn Registers are configured to enable the pull-ups ({DDxn, PORTxn} = 0b01). See “Con-
figuring the Pin” on page 56 for more details about this feature.
12.4.2 PORTA – Port A Data Register
12.4.3 DDRA – Port A Data Direction Register
12.4.4 PINA – Port A Input Pins Address
12.4.5 PORTB – Port B Data Register
12.4.6 DDRB – Port B Data Direction Register
12.4.7 PINB – Port B Input Pins Address
Bit 7 6 5 4 3 2 1 0
0x35 (0x55) -PUDSE SM1 SM0 -ISC01 ISC00 MCUCR
Read/Write R R/W R/W R/W R/W R R R
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
0x1B (0x3B) PORTA7 PORTA6 PORTA5 PORTA4 PORTA3 PORTA2 PORTA1 PORTA0 PORTA
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x1A (0x3A) DDA7 DDA6 DDA5 DDA4 DDA3 DDA2 DDA1 DDA0 DDRA
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x19 (0x39) PINA7 PINA6 PINA5 PINA4 PINA3 PINA2 PINA1 PINA0 PINA
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A
Bit 76543210
0x18 (0x38) PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 PORTB
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
0x17 (0x37) DDB7 DDB6 DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 DDRB
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x16 (0x36) PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 PINB
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A
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13. Timer/Counter0 Prescaler
The Timer/Counter can be clocked directly by the system clock (by setting the CSn2:0 = 1). This
provides the fastest operation, with a maximum Timer/Counter clock frequency equal to system
clock frequency (fCLK_I/O). Alternatively, one of four taps from the prescaler can be used as a
clock source. The prescaled clock has a frequency of either fCLK_I/O/8, fCLK_I/O/64, fCLK_I/O/256, or
fCLK_I/O/1024. See Table 13-1 on page 72 for details.
13.0.1 Prescaler Reset
The prescaler is free running, i.e., operates independently of the Clock Select logic of the
Timer/Counter. Since the prescaler is not affected by the Timer/Counter’s clock select, the state
of the prescaler will have implications for situations where a prescaled clock is used. One exam-
ple of prescaling artifacts occurs when the timer is enabled and clocked by the prescaler (6 >
CSn2:0 > 1). The number of system clock cycles from when the timer is enabled to the first count
occurs can be from 1 to N+1 system clock cycles, where N equals the prescaler divisor (8, 64,
256, or 1024). It is possible to use the Prescaler Reset for synchronizing the Timer/Counter to
program execution.
13.0.2 External Clock Source
An external clock source applied to the T0 pin can be used as Timer/Counter clock (clkT0). The
T0 pin is sampled once every system clock cycle by the pin synchronization logic. The synchro-
nized (sampled) signal is then passed through the edge detector. Figure 13-1 shows a functional
equivalent block diagram of the T0 synchronization and edge detector logic. The registers are
clocked at the positive edge of the internal system clock (clkI/O). The latch is transparent in the
high period of the internal system clock.
The edge detector generates one clkT0 pulse for each positive (CSn2:0 = 7) or negative (CSn2:0
= 6) edge it detects. See Table 13-1 on page 72 for details.
Figure 13-1. T0 Pin Sampling
The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system clock cycles
from an edge has been applied to the T0 pin to the counter is updated.
Enabling and disabling of the clock input must be done when T0 has been stable for at least one
system clock cycle, otherwise it is a risk that a false Timer/Counter clock pulse is generated.
Each half period of the external clock applied must be longer than one system clock cycle to
ensure correct sampling. The external clock must be guaranteed to have less than half the sys-
tem clock frequency (fExtClk < fclk_I/O/2) given a 50/50% duty cycle. Since the edge detector uses
sampling, the maximum frequency of an external clock it can detect is half the sampling fre-
quency (Nyquist sampling theorem).
Tn
Synchronization Edge Detector
Tn_sync
(To Clock
Select Logic)
Q
LE
D QD QD
clkI/O
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However, due to variation of the system clock frequency and duty cycle caused by Oscillator
source (crystal, resonator, and capacitors) tolerances, it is recommended that maximum fre-
quency of an external clock source is less than fclk_I/O/2.5.
An external clock source can not be prescaled.
Figure 13-2. Prescaler for Timer/Counter0
Note: 1. The synchronization logic on the input pins (T0) is shown in Figure 13-1.
13.1 Register Description
13.1.1 TCCR0B – Timer/Counter0 Control Register B
• Bit 4 – TSM: Timer/Counter Synchronization Mode
Writing the TSM bit to one activates the Timer/Counter Synchronization mode. In this mode, the
value that is written to the PSR0 bit is kept, hence keeping the Prescaler Reset signal asserted.
This ensures that the Timer/Counter is halted and can be configured without the risk of advanc-
ing during configuration. When the TSM bit is written to zero, the PSR0 bit is cleared by
hardware, and the Timer/Counter start counting.
• Bit 3 – PSR0: Prescaler Reset Timer/Counter0
When this bit is one, the Timer/Counter0 prescaler will be Reset. This bit is normally cleared
immediately by hardware, except if the TSM bit is set.
• Bits 2, 1, 0 – CS02, CS01, CS00: Clock Select0, Bit 2, 1, and 0
The Clock Select0 bits 2, 1, and 0 define the prescaling source of Timer0.
Timer/Counter Clock Source
clkI/O
PSR10
T0
10-bit T/C Prescaler
0
CS00
CK/8
CK/64
CK/256
CK/1024
CS01
CS02
Synchronization
Clear
clkT0
Bit 76543210
0x33 (0x53) --- TSM PSR0 CS02 CS01 CS01 TCCR0B
Read/Write R R R R/W R/W R/W R/W R/W
Initial Value00000000
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If external pin modes are used for the Timer/Counter0, transitions on the T0 pin will clock the
counter even if the pin is configured as an output. This feature allows software control of the
counting.
Table 13-1. Clock Select Bit Description
CS02 CS01 CS00 Description
0 0 0 No clock source (Timer/Counter stopped)
001clk
I/O/(No prescaling)
010clk
I/O/8 (From prescaler)
011clk
I/O/64 (From prescaler)
100clk
I/O/256 (From prescaler)
101clk
I/O/1024 (From prescaler)
1 1 0 External clock source on T0 pin. Clock on falling edge.
1 1 1 External clock source on T0 pin. Clock on rising edge.
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14. Timer/Counter0
14.1 Features •Clear Timer on Compare Match (Auto Reload)
•Input Capture unit
•Four Independent Interrupt Sources (TOV0, OCF0A, OCF0B, ICF0)
•8-bit Mode with Two Independent Output Compare Units
•16-bit Mode with One Independent Output Compare Unit
14.2 Overview
Timer/Counter0 is a general purpose 8-/16-bit Timer/Counter module, with two/one Output Com-
pare units and Input Capture feature.
The Timer/Counter0 general operation is described in 8-/16-bit mode. A simplified block diagram
of the 8-/16-bit Timer/Counter is shown in Figure 14-1. For the actual placement of I/O pins, refer
to “Pinout ATtiny261/461/861” on page 2. CPU accessible I/O Registers, including I/O bits and
I/O pins, are shown in bold. The device-specific I/O Register and bit locations are listed in the
“Register Description” on page 85.
Figure 14-1. 8-/16-bit Timer/Counter Block Diagram
Control Logic
TCNTnL
Fixed TOP value
TCNTnH
Timer/Counter
Count
Clear
Direction
clkTn
OCRnAOCRnB
==
TCCRnA TCCRnB
Edge
Detector
(from Prescaler)
Clock Select
TOP
TOVn (Int. Req.)
OCnA (Int. Req.)
(From Analog
Comparator Output)
OCnB (Int. Req.)
ICFn (Int. Req.)
Tn
Edge
Detector
Noise
Canceler
DATA BUS
=
ICPn
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14.2.1 Registers
The Timer/Counter0 Low Byte Register (TCNT0L) and Output Compare Registers (OCR0A and
OCR0B) are 8-bit registers. Interrupt request (abbreviated to Int.Req. in Figure 14-1) signals are
all visible in the Timer Interrupt Flag Register (TIFR). All interrupts are individually masked with
the Timer Interrupt Mask Register (TIMSK). TIFR and TIMSK are not shown in the figure.
In 16-bit mode the Timer/Counter consists one more 8-bit register, the Timer/Counter0 High
Byte Register (TCNT0H). Furthermore, there is only one Output Compare Unit in 16-bit mode as
the two Output Compare Registers, OCR0A and OCR0B, are combined to one 16-bit Output
Compare Register.
OCR0A contains the low byte of the word and OCR0B contains the high byte of the word. When
accessing 16-bit registers, special procedures described in section “Accessing Registers in
16-bit Mode” on page 81 must be followed.
14.2.2 Definitions
Many register and bit references in this section are written in general form. A lower case “n”
replaces the Timer/Counter number, in this case 0. A lower case “x” replaces the Output Com-
pare Unit, in this case Compare Unit A or Compare Unit B. However, when using the register or
bit defines in a program, the precise form must be used, i.e., TCNT0L for accessing
Timer/Counter0 counter value and so on.
The definitions in Table 14-1 are also used extensively throughout the document.
14.3 Timer/Counter Clock Sources
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on
the T0 pin. The Clock Select logic is controlled by the Clock Select (CS02:0) bits located in the
Timer/Counter Control Register 0 B (TCCR0B), and controls which clock source and edge the
Timer/Counter uses to increment its value. The Timer/Counter is inactive when no clock source
is selected. The output from the Clock Select logic is referred to as the timer clock (clkT0). For
details on clock sources and prescaler, see “Timer/Counter0 Prescaler” on page 70.
14.4 Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure
14-3 shows a block diagram of the counter and its surroundings.
Table 14-1. Definitions
BOTTOM The counter reaches the BOTTOM when it becomes 0.
MAX The counter reaches its MAXimum when it becomes 0xFF (decimal 255) in 8-bit mode or
0xFFFF (decimal 65535) in 16-bit mode.
TOP
The counter reaches the TOP when it becomes equal to the highest value in the count
sequence. The TOP value can be assigned to be the fixed value 0xFF/0xFFFF (MAX) or the
value stored in the OCR0A Register.
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Table 14-2. Counter Unit Block Diagram
Signal description (internal signals):
count Increment or decrement TCNT0 by 1.
clkTnTimer/Counter clock, referred to as clkT0 in the following.
top Signalize that TCNT0 has reached maximum value.
The counter is incremented at each timer clock (clkT0) until it passes its TOP value and then
restarts from BOTTOM. The counting sequence is determined by the setting of the CTC0 bit
located in the Timer/Counter Control Register (TCCR0A). For more details about counting
sequences, see “Modes of Operation” on page 75. clkT0 can be generated from an external or
internal clock source, selected by the Clock Select bits (CS02:0). When no clock source is
selected (CS02:0 = 0) the timer is stopped. However, the TCNT0 value can be accessed by the
CPU, regardless of whether clkT0 is present or not. A CPU write overrides (has priority over) all
counter clear or count operations. The Timer/Counter Overflow Flag (TOV0) is set when the
counter reaches the maximum value and it can be used for generating a CPU interrupt.
14.5 Modes of Operation
The mode of operation is defined by the Timer/Counter Width (TCW0), Input Capture Enable
(ICEN0) and Wave Generation Mode (CTC0) bits in “TCCR0A – Timer/Counter0 Control Regis-
ter A” on page 85. Table 14-3 shows the different Modes of Operation.
Top
TOVn
(Int. Req.)
DATA BUS
Control LogicTCNTn
clk
Tn
Count
Edge
Detector
(From Prescaler)
Clock Select
Tn
Table 14-3. Modes of operation
Mode ICEN0 TCW0 CTC0 Mode of Operation TOP Value Update of OCRx at TOV Flag Set on
0000Normal 8-bit Mode 0xFF ImmediateMAX (0xFF)
10018-bit CTC OCR0A ImmediateMAX (0xFF)
2 0 1 X 16-bit Mode 0xFFFF Immediate MAX (0xFFFF)
3 1 0 X 8-bit Input Capture Mode 0xFF Immediate MAX (0xFF)
4 1 1 X 16-bit Input Capture Mode 0xFFFF Immediate MAX (0xFFFF)
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14.5.1 Normal 8-bit Mode
In the Normal 8-bit mode, see Table 14-3 on page 75, the counter (TCNT0L) is incrementing
until it overruns when it passes its maximum 8-bit value (MAX = 0xFF) and then restarts from the
bottom (0x00). The Overflow Flag (TOV0) will be set in the same timer clock cycle as the
TCNT0L becomes zero. The TOV0 Flag in this case behaves like a ninth bit, except that it is only
set, not cleared. However, combined with the timer overflow interrupt that automatically clears
the TOV0 Flag, the timer resolution can be increased by software. There are no special cases to
consider in the Normal 8-bit mode, a new counter value can be written anytime. The Output
Compare Unit can be used to generate interrupts at some given time.
14.5.2 Clear Timer on Compare Match (CTC) 8-bit Mode
In Clear Timer on Compare or CTC mode, see Table 14-3 on page 75, the OCR0A Register is
used to manipulate the counter resolution. In CTC mode the counter is cleared to zero when the
counter value (TCNT0) matches the OCR0A. The OCR0A defines the top value for the counter,
hence also its resolution. This mode allows greater control of the Compare Match output fre-
quency. It also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 14-2. The counter value (TCNT0)
increases until a Compare Match occurs between TCNT0 and OCR0A, and then counter
(TCNT0) is cleared.
Figure 14-2. CTC Mode, Timing Diagram
An interrupt can be generated each time the counter value reaches the TOP value by using the
OCF0A Flag. If the interrupt is enabled, the interrupt handler routine can be used for updating
the TOP value. However, changing TOP to a value close to BOTTOM when the counter is run-
ning with none or a low prescaler value must be done with care since the CTC mode does not
have the double buffering feature. If the new value written to OCR0A is lower than the current
value of TCNT0, the counter will miss the Compare Match. The counter will then have to count to
its maximum value (0xFF) and wrap around starting at 0x00 before the Compare Match can
occur. As for the Normal mode of operation, the TOV0 Flag is set in the same timer clock cycle
that the counter counts from MAX to 0x00.
14.5.3 16-bit Mode
In 16-bit mode, see Table 14-3 on page 75, the counter (TCNT0H/L) is a incrementing until it
overruns when it passes its maximum 16-bit value (MAX = 0xFFFF) and then restarts from the
bottom (0x0000). The Overflow Flag (TOV0) will be set in the same timer clock cycle as the
TCNT0H/L becomes zero. The TOV0 Flag in this case behaves like a 17th bit, except that it is
only set, not cleared. However, combined with the timer overflow interrupt that automatically
clears the TOV0 Flag, the timer resolution can be increased by software.
12
TCNTn
Period 3
OCnx Interrupt
Flag Set
4
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There are no special cases to consider in the Normal mode, a new counter value can be written
anytime. The Output Compare Unit can be used to generate interrupts at some given time.
14.5.4 8-bit Input Capture Mode
The Timer/Counter0 can also be used in an 8-bit Input Capture mode, see Table 14-3 on page
75 for bit settings. For full description, see the section “Input Capture Unit” on page 77.
14.5.5 16-bit Input Capture Mode
The Timer/Counter0 can also be used in a 16-bit Input Capture mode, see Table 14-3 on page
75 for bit settings. For full description, see the section “Input Capture Unit” on page 77.
14.6 Input Capture Unit
The Timer/Counter incorporates an Input Capture unit that can capture external events and give
them a time-stamp indicating time of occurrence. The external signal indicating an event, or mul-
tiple events, can be applied via the ICP0 pin or alternatively, via the analog-comparator unit. The
time-stamps can then be used to calculate frequency, duty-cycle, and other features of the sig-
nal applied. Alternatively the time-stamps can be used for creating a log of the events.
The Input Capture unit is illustrated by the block diagram shown in Figure 14-3. The elements of
the block diagram that are not directly a part of the Input Capture unit are gray shaded.
Figure 14-3. Input Capture Unit Block Diagram
ICF0 (Int. Req.)
OCR0A (8-bit)OCR0B (8-bit)
ICR0 (16-bit Register)
TEMP (8-bit)
TCNT0L (8-bit)TCNT0H (8-bit)
TCNT0 (16-bit Counter)
DATA BUS (8-bit)
Noise
Canceler
Analog
Comparator Edge
Detector
ICNC0ACIC0*ACO*
WRITE
+
-
ICES0
ICP0
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The Output Compare Register OCR0A is a dual-purpose register that is also used as an 8-bit
Input Capture Register ICR0. In 16-bit Input Capture mode the Output Compare Register
OCR0B serves as the high byte of the Input Capture Register ICR0. In 8-bit Input Capture mode
the Output Compare Register OCR0B is free to be used as a normal Output Compare Register,
but in 16-bit Input Capture mode the Output Compare Unit cannot be used as there are no free
Output Compare Register(s). Even though the Input Capture register is called ICR0 in this sec-
tion, it is referring to the Output Compare Register(s).
When a change of the logic level (an event) occurs on the Input Capture pin (ICP0), alternatively
on the Analog Comparator output (ACO), and this change confirms to the setting of the edge
detector, a capture will be triggered. When a capture is triggered, the value of the counter
(TCNT0) is written to the Input Capture Register (ICR0). The Input Capture Flag (ICF0) is set at
the same system clock as the TCNT0 value is copied into Input Capture Register. If enabled
(TICIE0=1), the Input Capture Flag generates an Input Capture interrupt. The ICF0 flag is auto-
matically cleared when the interrupt is executed. Alternatively the ICF0 flag can be cleared by
software by writing a logical one to its I/O bit location.
14.6.1 Input Capture Trigger Source
The default trigger source for the Input Capture unit is the Input Capture pin (ICP0).
Timer/Counter0 can alternatively use the Analog Comparator output as trigger source for the
Input Capture unit. The Analog Comparator is selected as trigger source by setting the Analog
Comparator Input Capture Enable (ACIC0) bit in the Timer/Counter Control Register A
(TCCR0A). Be aware that changing trigger source can trigger a capture. The Input Capture Flag
must therefore be cleared after the change.
Both the Input Capture pin (ICP0) and the Analog Comparator output (ACO) inputs are sampled
using the same technique as for the T0 pin (Figure 13-1 on page 72). The edge detector is also
identical. However, when the noise canceler is enabled, additional logic is inserted before the
edge detector, which increases the delay by four system clock cycles. An Input Capture can also
be triggered by software by controlling the port of the ICP0 pin.
14.6.2 Noise Canceler
The noise canceler improves noise immunity by using a simple digital filtering scheme. The
noise canceler input is monitored over four samples, and all four must be equal for changing the
output that in turn is used by the edge detector.
The noise canceler is enabled by setting the Input Capture Noise Canceler (ICNC0) bit in
Timer/Counter Control Register B (TCCR0B). When enabled the noise canceler introduces addi-
tional four system clock cycles of delay from a change applied to the input, to the update of the
ICR0 Register. The noise canceler uses the system clock and is therefore not affected by the
prescaler.
14.6.3 Using the Input Capture Unit
The main challenge when using the Input Capture unit is to assign enough processor capacity
for handling the incoming events. The time between two events is critical. If the processor has
not read the captured value in the ICR0 Register before the next event occurs, the ICR0 will be
overwritten with a new value. In this case the result of the capture will be incorrect.
When using the Input Capture interrupt, the ICR0 Register should be read as early in the inter-
rupt handler routine as possible. The maximum interrupt response time is dependent on the
maximum number of clock cycles it takes to handle any of the other interrupt requests.
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Measurement of an external signal’s duty cycle requires that the trigger edge is changed after
each capture. Changing the edge sensing must be done as early as possible after the ICR0
Register has been read. After a change of the edge, the Input Capture Flag (ICF0) must be
cleared by software (writing a logical one to the I/O bit location). For measuring frequency only,
the trigger edge change is not required (if an interrupt handler is used).
14.7 Output Compare Unit
The comparator continuously compares Timer/Counter (TCNT0) with the Output Compare Reg-
isters (OCR0A and OCR0B), and whenever the Timer/Counter equals to the Output Compare
Registers, the comparator signals a match. A match will set the Output Compare Flag at the next
timer clock cycle. In 8-bit mode the match can set either the Output Compare Flag OCF0A or
OCF0B, but in 16-bit mode the match can set only the Output Compare Flag OCF0A as there is
only one Output Compare Unit. If the corresponding interrupt is enabled, the Output Compare
Flag generates an Output Compare interrupt. The Output Compare Flag is automatically cleared
when the interrupt is executed.
Alternatively, the flag can be cleared by software by writing a logical one to its I/O bit location.
Figure 14-4 shows a block diagram of the Output Compare unit.
Figure 14-4. Output Compare Unit, Block Diagram
14.7.1 Compare Match Blocking by TCNT0 Write
All CPU write operations to the TCNT0H/L Register will block any Compare Match that occur in
the next timer clock cycle, even when the timer is stopped. This feature allows OCR0A/B to be
initialized to the same value as TCNT0 without triggering an interrupt when the Timer/Counter
clock is enabled.
14.7.2 Using the Output Compare Unit
Since writing TCNT0H/L will block all Compare Matches for one timer clock cycle, there are risks
involved when changing TCNT0H/L when using the Output Compare Unit, independently of
whether the Timer/Counter is running or not. If the value written to TCNT0H/L equals the
OCR0A/B value, the Compare Match will be missed.
14.8 Timer/Counter Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkT0) is therefore shown as a
clock enable signal in the following figures. The figures include information on when Interrupt
Flags are set. Figure 14-5 contains timing data for basic Timer/Counter operation. The figure
shows the count sequence close to the MAX value.
OCFnx (Int. Req.)
= (8/16-bit Comparator)
OCRnx TCNTn
DATA BUS
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Figure 14-5. Timer/Counter Timing Diagram, no Prescaling
Figure 14-6 shows the same timing data, but with the prescaler enabled.
Figure 14-6. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
Figure 14-7 shows the setting of OCF0A and OCF0B in Normal mode.
Figure 14-7. Timer/Counter Timing Diagram, Setting of OCF0x, with Prescaler (fclk_I/O/8)
shows the setting of OCF0A and the clearing of TCNT0 in CTC mode.
MAX - 1
clkI/O
(clkI/O/1)
TCNTn
TOVn
clkTn
MAX BOTTOM BOTTOM + 1
MAX - 1
clkI/O
(clkI/O/8)
TCNTn
TOVn
clkTn
MAX BOTTOM BOTTOM + 1
OCRnx - 1
clkI/O
(clkI/O/8)
TCNTn
OCRnx
OCFnx
clkTn
OCRnx OCRnx + 1
OCRnx Value
OCRnx + 2
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Figure 14-8. Timer/Counter Timing Diagram, CTC mode, with Prescaler (fclk_I/O/8)
14.9 Accessing Registers in 16-bit Mode
In 16-bit mode (the TCW0 bit is set to one) the TCNT0H/L and OCR0A/B or TCNT0L/H and
OCR0B/A are 16-bit registers that can be accessed by the AVR CPU via the 8-bit data bus. The
16-bit register must be byte accessed using two read or write operations. The 16-bit
Timer/Counter has a single 8-bit register for temporary storing of the high byte of the 16-bit
access. The same temporary register is shared between all 16-bit registers. Accessing the low
byte triggers the 16-bit read or write operation. When the low byte of a 16-bit register is written
by the CPU, the high byte stored in the temporary register, and the low byte written are both cop-
ied into the 16-bit register in the same clock cycle. When the low byte of a 16-bit register is read
by the CPU, the high byte of the 16-bit register is copied into the temporary register in the same
clock cycle as the low byte is read.
There is one exception in the temporary register usage. In the Output Compare mode the 16-bit
Output Compare Register OCR0A/B is read without the temporary register, because the Output
Compare Register contains a fixed value that is only changed by CPU access. However, in
16-bit Input Capture mode the ICR0 register formed by the OCR0A and OCR0B registers must
be accessed with the temporary register.
To do a 16-bit write, the high byte must be written before the low byte. For a 16-bit read, the low
byte must be read before the high byte.
TOP - 1
clkPCK
(clkPCK/8)
TCNTn
(CTC)
OCRnx
OCFnx
clkTn
TOP BOTTOM
TOP
BOTTOM + 1
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The following code examples show how to access the 16-bit timer registers assuming that no
interrupts updates the temporary register. The same principle can be used directly for accessing
the OCR0A/B registers.
Note: 1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example returns the TCNT0H/L value in the r17:r16 register pair.
It is important to notice that accessing 16-bit registers are atomic operations. If an interrupt
occurs between the two instructions accessing the 16-bit register, and the interrupt code
updates the temporary register by accessing the same or any other of the 16-bit timer registers,
then the result of the access outside the interrupt will be corrupted. Therefore, when both the
main code and the interrupt code update the temporary register, the main code must disable the
interrupts during the 16-bit access.
Assembly Code Example
...
; Set TCNT0 to 0x01FF
ldi r17,0x01
ldi r16,0xFF
out TCNT0H,r17
out TCNT0L,r16
; Read TCNT0 into r17:r16
in r16,TCNT0L
in r17,TCNT0H
...
C Code Example
unsigned int i;
...
/* Set TCNT0 to 0x01FF */
TCNT0H = 0x01;
TCNT0L = 0xff;
/* Read TCNT0 into i */
i = TCNT0L;
i |= ((unsigned int)TCNT0H << 8);
...
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The following code examples show how to do an atomic read of the TCNT0 register contents.
Reading any of the OCR0 register can be done by using the same principle.
Note: 1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example returns the TCNT0H/L value in the r17:r16 register pair.
Assembly Code Example
TIM0_ReadTCNT0:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Read TCNT0 into r17:r16
in r16,TCNT0L
in r17,TCNT0H
; Restore global interrupt flag
out SREG,r18
ret
C Code Example
unsigned int TIM0_ReadTCNT0( void )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Read TCNT0 into i */
i = TCNT0L;
i |= ((unsigned int)TCNT0H << 8);
/* Restore global interrupt flag */
SREG = sreg;
return i;
}
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The following code examples show how to do an atomic write of the TCNT0H/L register con-
tents. Writing any of the OCR0A/B registers can be done by using the same principle.
Note: 1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example requires that the r17:r16 register pair contains the value to be writ-
ten to TCNT0H/L.
14.9.1 Reusing the temporary high byte register
If writing to more than one 16-bit register where the high byte is the same for all registers written,
then the high byte only needs to be written once. However, note that the same rule of atomic
operation described previously also applies in this case.
Assembly Code Example
TIM0_WriteTCNT0:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Set TCNT0 to r17:r16
out TCNT0H,r17
out TCNT0L,r16
; Restore global interrupt flag
out SREG,r18
ret
C Code Example
void TIM0_WriteTCNT0( unsigned int i )
{
unsigned char sreg;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Set TCNT0 to i */
TCNT0H = (i >> 8);
TCNT0L = (unsigned char)i;
/* Restore global interrupt flag */
SREG = sreg;
}
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14.10 Register Description
14.10.1 TCCR0A – Timer/Counter0 Control Register A
• Bit 7– TCW0: Timer/Counter0 Width
When this bit is written to one 16-bit mode is selected as described Figure 14-5 on page 80.
Timer/Counter0 width is set to 16-bits and the Output Compare Registers OCR0A and OCR0B
are combined to form one 16-bit Output Compare Register. Because the 16-bit registers
TCNT0H/L and OCR0B/A are accessed by the AVR CPU via the 8-bit data bus, special proce-
dures must be followed. These procedures are described in section “Accessing Registers in
16-bit Mode” on page 81.
• Bit 6– ICEN0: Input Capture Mode Enable
When this bit is written to one, the Input Capture Mode is enabled.
• Bit 5 – ICNC0: Input Capture Noise Canceler
Setting this bit activates the Input Capture Noise Canceler. When the noise canceler is acti-
vated, the input from the Input Capture Pin (ICP0) is filtered. The filter function requires four
successive equal valued samples of the ICP0 pin for changing its output. The Input Capture is
therefore delayed by four System Clock cycles when the noise canceler is enabled.
• Bit 4 – ICES0: Input Capture Edge Select
This bit selects which edge on the Input Capture Pin (ICP0) that is used to trigger a capture
event. When the ICES0 bit is written to zero, a falling (negative) edge is used as trigger, and
when the ICES0 bit is written to one, a rising (positive) edge will trigger the capture. When a cap-
ture is triggered according to the ICES0 setting, the counter value is copied into the Input
Capture Register. The event will also set the Input Capture Flag (ICF0), and this can be used to
cause an Input Capture Interrupt, if this interrupt is enabled.
• Bit 3 - ACIC0: Analog Comparator Input Capture Enable
When written logic one, this bit enables the input capture function in Timer/Counter0 to be trig-
gered by the Analog Comparator. The comparator output is in this case directly connected to the
input capture front-end logic, making the comparator utilize the noise canceler and edge select
features of the Timer/Counter0 Input Capture interrupt. When written logic zero, no connection
between the Analog Comparator and the input capture function exists. To make the comparator
trigger the Timer/Counter0 Input Capture interrupt, the TICIE0 bit in the Timer Interrupt Mask
Register (TIMSK) must be set.
• Bits 2:1 – Res: Reserved Bits
These bits are reserved bits in the ATtiny261/461/861 and will always read as zero.
• Bit 0 – CTC0: Waveform Generation Mode
This bit controls the counting sequence of the counter, the source for maximum (TOP) counter
value, see Figure 14-5 on page 80.
Bit 76543210
0x15 (0x35) TCW0 ICEN0 ICNC0 ICES0 ACIC0 – – CTC0 TCCR0A
Read/Write R/W R/W R/W R/W R/W R R R/W
Initial Value00000000
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Modes of operation supported by the Timer/Counter unit are: Normal mode (counter) and Clear
Timer on Compare Match (CTC) mode (see “Modes of Operation” on page 75).
14.10.2 TCNT0L – Timer/Counter0 Register Low Byte
The Timer/Counter0 Register Low Byte, TCNT0L, gives direct access, both for read and write
operations, to the Timer/Counter unit 8-bit counter. Writing to the TCNT0L Register blocks (dis-
ables) the Compare Match on the following timer clock. Modifying the counter (TCNT0L) while
the counter is running, introduces a risk of missing a Compare Match between TCNT0L and the
OCR0x Registers. In 16-bit mode the TCNT0L register contains the lower part of the 16-bit
Timer/Counter0 Register.
14.10.3 TCNT0H – Timer/Counter0 Register High Byte
When 16-bit mode is selected (the TCW0 bit is set to one) the Timer/Counter Register TCNT0H
combined to the Timer/Counter Register TCNT0L gives direct access, both for read and write
operations, to the Timer/Counter unit 16-bit counter. To ensure that both the high and low bytes
are read and written simultaneously when the CPU accesses these registers, the access is per-
formed using an 8-bit temporary high byte register (TEMP). This temporary register is shared by
all the other 16-bit registers. See “Accessing Registers in 16-bit Mode” on page 81
14.10.4 OCR0A – Timer/Counter0 Output Compare Register A
The Output Compare Register A contains an 8-bit value that is continuously compared with the
counter value (TCNT0L). A match can be used to generate an Output Compare interrupt.
In 16-bit mode the OCR0A register contains the low byte of the 16-bit Output Compare Register.
To ensure that both the high and the low bytes are written simultaneously when the CPU writes
to these registers, the access is performed using an 8-bit temporary high byte register (TEMP).
This temporary register is shared by all the other 16-bit registers. See “Accessing Registers in
16-bit Mode” on page 81.
14.10.5 OCR0B – Timer/Counter0 Output Compare Register B
The Output Compare Register B contains an 8-bit value that is continuously compared with the
counter value (TCNT0L in 8-bit mode and TCNTH in 16-bit mode). A match can be used to gen-
erate an Output Compare interrupt.
Bit 76543210
0x32 (0x52) TCNT0L[7:0] TCNT0L
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x14 (0x34) TCNT0H[7:0] TCNT0H
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x13 (0x33) OCR0A[7:0] OCR0A
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x12 (0x32) OCR0B[7:0] OCR0B
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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In 16-bit mode the OCR0B register contains the high byte of the 16-bit Output Compare Regis-
ter. To ensure that both the high and the low bytes are written simultaneously when the CPU
writes to these registers, the access is performed using an 8-bit temporary high byte register
(TEMP). This temporary register is shared by all the other 16-bit registers. See “Accessing Reg-
isters in 16-bit Mode” on page 81.
14.10.6 TIMSK – Timer/Counter0 Interrupt Mask Register
• Bit 4 – OCIE0A: Timer/Counter0 Output Compare Match A Interrupt Enable
When the OCIE0A bit is written to one, and the I-bit in the Status Register is set, the
Timer/Counter0 Compare Match A interrupt is enabled. The corresponding interrupt is executed
if a Compare Match in Timer/Counter0 occurs, i.e., when the OCF0A bit is set in the
Timer/Counter 0 Interrupt Flag Register – TIFR0.
• Bit 3 – OCIE0B: Timer/Counter Output Compare Match B Interrupt Enable
When the OCIE0B bit is written to one, and the I-bit in the Status Register is set, the
Timer/Counter Compare Match B interrupt is enabled. The corresponding interrupt is executed if
a Compare Match in Timer/Counter occurs, i.e., when the OCF0B bit is set in the Timer/Counter
Interrupt Flag Register – TIFR0.
• Bit 1 – TOIE0: Timer/Counter0 Overflow Interrupt Enable
When the TOIE0 bit is written to one, and the I-bit in the Status Register is set, the
Timer/Counter0 Overflow interrupt is enabled. The corresponding interrupt is executed if an
overflow in Timer/Counter0 occurs, i.e., when the TOV0 bit is set in the Timer/Counter 0 Inter-
rupt Flag Register – TIFR0.
• Bit 0 – TICIE0: Timer/Counter0, Input Capture Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter1 Input Capture interrupt is enabled. The corresponding Interrupt
Vector (See “Interrupts” on page 50.) is executed when the ICF0 flag, located in TIFR, is set.
Bit 76543210
0x39 (0x59) OCIE1D OCIE1A OCIE1B OCIE0A OCIE0B TOIE1 TOIE0 TICIE0 TIMSK
Read/Write R/W R/W R/W R/W R/W R/W R/W R
Initial Value00000000
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14.10.7 TIFR – Timer/Counter0 Interrupt Flag Register
• Bit 4– OCF0A: Output Compare Flag 0 A
The OCF0A bit is set when a Compare Match occurs between the Timer/Counter0 and the data
in OCR0A – Output Compare Register0. OCF0A is cleared by hardware when executing the cor-
responding interrupt handling vector. Alternatively, OCF0A is cleared by writing a logic one to
the flag. When the I-bit in SREG, OCIE0A (Timer/Counter0 Compare Match Interrupt Enable),
and OCF0A are set, the Timer/Counter0 Compare Match Interrupt is executed.
The OCF0A is also set in 16-bit mode when a Compare Match occurs between the Timer/Coun-
ter and 16-bit data in OCR0B/A. The OCF0A is not set in Input Capture mode when the Output
Compare Register OCR0A is used as an Input Capture Register.
• Bit 3 – OCF0B: Output Compare Flag 0 B
The OCF0B bit is set when a Compare Match occurs between the Timer/Counter and the data in
OCR0B – Output Compare Register0 B. OCF0B is cleared by hardware when executing the cor-
responding interrupt handling vector. Alternatively, OCF0B is cleared by writing a logic one to
the flag. When the I-bit in SREG, OCIE0B (Timer/Counter Compare B Match Interrupt Enable),
and OCF0B are set, the Timer/Counter Compare Match Interrupt is executed.
The OCF0B is not set in 16-bit Output Compare mode when the Output Compare Register
OCR0B is used as the high byte of the 16-bit Output Compare Register or in 16-bit Input Cap-
ture mode when the Output Compare Register OCR0B is used as the high byte of the Input
Capture Register.
• Bit 1 – TOV0: Timer/Counter0 Overflow Flag
The bit TOV0 is set when an overflow occurs in Timer/Counter0. TOV0 is cleared by hardware
when executing the corresponding interrupt handling vector. Alternatively, TOV0 is cleared by
writing a logic one to the flag. When the SREG I-bit, TOIE0 (Timer/Counter0 Overflow Interrupt
Enable), and TOV0 are set, the Timer/Counter0 Overflow interrupt is executed.
• Bits 0 – ICF0: Timer/Counter0, Input Capture Flag
This flag is set when a capture event occurs on the ICP0 pin. When the Input Capture Register
(ICR0) is set to be used as the TOP value, the ICF0 flag is set when the counter reaches the
TOP value.
ICF0 is automatically cleared when the Input Capture Interrupt Vector is executed. Alternatively,
ICF0 can be cleared by writing a logic one to its bit location.
Bit 76543210
0x38 (0x58) OCF1D OCF1A OCF1B OCF0A OCF0B TOV1 TOV0 ICF0 TIFR
Read/Write R/W R/W R/W R/W R/W R/W R/W R
Initial Value00000000
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15. Timer/Counter1 Prescaler
Figure 15-1 shows the Timer/Counter1 prescaler that supports two clocking modes, a synchro-
nous clocking mode and an asynchronous clocking mode. The synchronous clocking mode uses
the system clock (CK) as a clock timebase and asynchronous mode uses the fast peripheral
clock (PCK) as a clock time base. The PCKE bit from the PLLCSR register enables the asyn-
chronous mode when it is set (‘1’).
Figure 15-1. Timer/Counter1 Prescaler
In the asynchronous clocking mode the clock selections are from PCK to PCK/16384 and stop,
and in the synchronous clocking mode the clock selections are from CK to CK/16384 and stop.
The clock options are described in Table 15-1 on page 91 and the Timer/Counter1 Control Reg-
ister, TCCR1B.
The frequency of the fast peripheral clock is 64 MHz or 32 MHz in Low Speed mode (the LSM bit
in PLLCSR register is set to one). The Low Speed Mode is recommended to use when the sup-
ply voltage below 2.7 volts are used.
15.0.1 Prescaler Reset
Setting the PSR1 bit in TCCR1B register resets the prescaler. It is possible to use the Prescaler
Reset for synchronizing the Timer/Counter to program execution.
15.0.2 Prescaler Initialization for Asynchronous Mode
To change Timer/Counter1 to the asynchronous mode follow the procedure below:
1. Enable PLL.
2. Wait 100 µs for PLL to stabilize.
3. Poll the PLOCK bit until it is set.
4. Set the PCKE bit in the PLLCSR register which enables the asynchronous mode.
14-bit
T/C Prescaler
Timer/Counter1 Count Enable
T1CK
PSR1
PCK64/32MHz
CK
PCKE
0
CS10
CS11
CS12
CS13
T1CK/8
T1CK/4
T1CK/2
T1CK
T1CK/16
T1CK/32
T1CK/64
T1CK/128
T1CK/256
T1CK/512
T1CK/1024
T1CK/2048
T1CK/4096
T1CK/8192
T1CK/16384
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15.1 Register Description
15.1.1 PLLCSR – PLL Control and Status Register
• Bit 7- LSM: Low Speed Mode
The Low Speed mode is set, if the LSM bit is written to one. Then the fast peripheral clock is
scaled down to 32 MHz. The Low Speed Mode must be set, if the supply voltage is below 2.7
volts, because the Timer/Counter1 is not running fast enough on low voltage levels. It is recom-
mended that the Timer/Counter1 is stopped whenever the LSM bit is changed.
Note, that LSM can not be set if PLLCLK is used as a system clock.
• Bit 6:3- Res: Reserved Bits
These bits are reserved bits in the ATtiny261/461/861 and always read as zero.
• Bit 2- PCKE: PCK Enable
The PCKE bit change the Timer/Counter1 clock source. When it is set, the asynchronous clock
mode is enabled and fast 64 MHz (or 32 MHz in Low Speed Mode) PCK clock is used as a
Timer/Counter1 clock source. If this bit is cleared, the synchronous clock mode is enabled, and
system clock CK is used as Timer/Counter1 clock source. It is safe to set this bit only when the
PLL is locked i.e the PLOCK bit is 1. Note that the PCKE bit can be set only, if the PLL has been
enabled earlier. The PLL is enabled when the CKSEL fuse has been programmed to 0x0001
(the PLL clock mode is selected) or the PLLE bit has been set to one.
• Bit 1- PLLE: PLL Enable
When the PLLE is set, the PLL is started and if needed internal RC-oscillator is started as a PLL
reference clock. If PLL is selected as a system clock source the value for this bit is always 1.
• Bit 0- PLOCK: PLL Lock Detector
When the PLOCK bit is set, the PLL is locked to the reference clock. The PLOCK bit should be
ignored during initial PLL lock-in sequence when PLL frequency overshoots and undershoots,
before reaching steady state. The steady state is obtained within 100 µs. After PLL lock-in it is
recommended to check the PLOCK bit before enabling PCK for Timer/Counter1.
15.1.2 TCCR1B – Timer/Counter1 Control Register B
• Bit 7 - Res: Reserved Bit
• Bit 6 - PSR1: Prescaler Reset Timer/Counter1
Bit 76543210
0x29 (0x49)LSM----PCKEPLLEPLOCKPLLCSR
Read/WriteR/WRRRRR/WR/WR
Initial value0000000/10
Bit 76543210
0x2F (0x4F) - PSR1 DTPS11 DTPS10 CS13 CS12 CS11 CS10 TCCR1B
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value00000000
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When this bit is set (one), the Timer/Counter prescaler (TCNT1 is unaffected) will be reset. The
bit will be cleared by hardware after the operation is performed. Writing a zero to this bit will have
no effect. This bit will always read as zero.
• Bits 3:0 - CS13, CS12, CS11, CS10: Clock Select Bits 3, 2, 1, and 0
The Clock Select bits 3, 2, 1, and 0 define the prescaling source of Timer/Counter1.
The Stop condition provides a Timer Enable/Disable function.
Table 15-1. Timer/Counter1 Prescale Select
CS13 CS12 CS11 CS10
Asynchronous
Clocking Mode
Synchronous
Clocking Mode
0 0 0 0 T/C1 stopped T/C1 stopped
0001PCK CK
0010PCK/2CK/2
0011PCK/4CK/4
0100PCK/8CK/8
0101PCK/16CK/16
0110PCK/32CK/32
0111PCK/64CK/64
1000PCK/128CK/128
1001PCK/256CK/256
1010PCK/512CK/512
1011PCK/1024CK/1024
1100PCK/2048CK/2048
1101PCK/4096CK/4096
1110PCK/8192CK/8192
1 1 1 1 PCK/16384 CK/16384
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16. Timer/Counter1
16.1 Features •10/8-Bit Accuracy
•Three Independent Output Compare Units
•Clear Timer on Compare Match (Auto Reload)
•Glitch Free, Phase and Frequency Correct Pulse Width Modulator (PWM)
•Variable PWM Period
•Independent Dead Time Generators for each PWM channels
•Five Independent Interrupt Sources (TOV1, OCF1A, OCD1B, OCF1D, FPF1)
•High Speed Asynchronous and Synchronous Clocking Modes
•Separate Prescaler Unit
16.2 Overview
Timer/Counter1 is a general purpose high speed Timer/Counter module, with three independent
Output Compare Units, and with PWM support.
The Timer/Counter1 features a high resolution and a high accuracy usage with the lower presca-
ling opportunities. It can also support three accurate and high speed Pulse Width Modulators
using clock speeds up to 64 MHz. In PWM mode Timer/Counter1 and the output compare regis-
ters serve as triple stand-alone PWMs with non-overlapping non-inverted and inverted outputs.
Similarly, the high prescaling opportunities make this unit useful for lower speed functions or
exact timing functions with infrequent actions. A simplified block diagram of the Timer/Counter1
is shown in Figure 16-1. For actual placement of the I/O pins, refer to “Pinout
ATtiny261/461/861” on page 2. The device-specific I/O register and bit locations are listed in the
“Register Description” on page 115.
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Figure 16-1. Timer/Counter1 Block Diagram
16.2.1 Speed
The maximum speed of the Timer/Counter1 is 64 MHz. However, if a supply voltage below 2.7
volts is used, it is recommended to use the Low Speed Mode (LSM), because the
Timer/Counter1 is not running fast enough on low voltage levels. In the Low Speed Mode the
fast peripheral clock is scaled down to 32 MHz. For more details about the Low Speed Mode,
see “PLLCSR – PLL Control and Status Register” on page 90.
16.2.2 Accuracy
The Timer/Counter1 is a 10-bit Timer/Counter module that can alternatively be used as an 8-bit
Timer/Counter. The Timer/Counter1 registers are basically 8-bit registers, but on top of that
there is a 2-bit High Byte Register (TC1H) that can be used as a common temporary buffer to
access the two MSBs of the 10-bit Timer/Counter1 registers by the AVR CPU via the 8-bit data
bus, if the 10-bit accuracy is used. Whereas, if the two MSBs of the 10-bit registers are written to
zero the Timer/Counter1 is working as an 8-bit Timer/Counter. When reading the low byte of any
8-bit register the two MSBs are written to the TC1H register, and when writing the low byte of
any 8-bit register the two MSBs are written from the TC1H register. Special procedures must be
followed when accessing the 10-bit Timer/Counter1 values via the 8-bit data bus. These proce-
dures are described in the section “Accessing 10-Bit Registers” on page 112.
T/C Control
Register A (TCCR1A)
Dead Time Generator
OCW1D
OCW1B
OCW1A
CLEAR
DIRECTION
COUNT
CLK
TOV1 OCF1A OCF1B OCF1D OC1A OC1A OC1B OC1B OC1D OC1D Fault_Protection
COM1A1
TOIE1
OCIE1A
OCIE1B
OCIE1D
TOV1
OVF1A
OCF1B
FPIE1
FPF1
OCF1D
COM1A0
COM1B1
COM1B0
FOC1A
FOC1B
PWM1A
PWM1B
10-Bit Comparator 10-Bit Comparator 10-Bit Comparator
8-Bit Data Bus
10-Bit Comparator
Dead Time GeneratorDead Time Generator
Timer/Counter1 Control Logic
T/C Int. Flag
Register (TIFR)
T/C Int. Mask
Register (TIMSK)
10-Bit Output
Compare Register A
Timer/Counter1
(TCNT1)
T/C Control
Register C (TCCR1C)
COM1A1
COM1A0
COM1B1
COM1B0
COM1D1
COM1D0
FOC1D
PWM1D
T/C Control
Register D (TCCR1D)
FPIE1
FPEN1OC10E5
OC10E4
OC10E3
OC10E2
OC10E1
OC10E0
FPNC1
FPES1
FPAC1
FPF1
WGM11
WGM10
T/C Control
Register D (TCCR1E)
T/C Control
Register B (TCCR1B)
PSR1
PSR!
PSR1
CS13
CS12
CS11
CS10
10-Bit Output
Compare Register B
10-Bit Output
Compare Register C
10-Bit Output
Compare Register D
8-Bit Output Compare
Register A (OCR1A)
8-Bit Output Compare
Register B (OCR1B)
8-Bit Output Compare
Register C (OCR1C)
8-Bit Output Compare
Register D (OCR1D)
2-Bit High Byte
Register (TC1H)
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16.2.3 Registers
The Timer/Counter (TCNT1) and Output Compare Registers (OCR1A, OCR1B, OCR1C and
OCR1D) are 8-bit registers that are used as a data source to be compared with the TCNT1 con-
tents. The OCR1A, OCR1B and OCR1D registers determine the action on the OC1A, OC1B and
OC1D pins and they can also generate the compare match interrupts. The OCR1C holds the
Timer/Counter TOP value, i.e. the clear on compare match value. The Timer/Counter1 High
Byte Register (TC1H) is a 2-bit register that is used as a common temporary buffer to access the
MSB bits of the Timer/Counter1 registers, if the 10-bit accuracy is used.
Interrupt request (overflow TOV1, and compare matches OCF1A, OCF1B, OCF1D and fault pro-
tection FPF1) signals are visible in the Timer Interrupt Flag Register (TIFR) and Timer/Counter1
Control Register D (TCCR1D). The interrupts are individually masked with the Timer Interrupt
Mask Register (TIMSK) and the FPIE1 bit in the Timer/Counter1 Control Register D (TCCR1D).
Control signals are found in the Timer/Counter Control Registers TCCR1A, TCCR1B, TCCR1C,
TCCR1D and TCCR1E.
16.2.4 Synchronization
In asynchronous clocking mode the Timer/Counter1 and the prescaler allow running the CPU
from any clock source while the prescaler is operating on the fast peripheral clock (PCK) having
frequency of 64 MHz (or 32 MHz in Low Speed Mode). This is possible because there is a syn-
chronization boundary between the CPU clock domain and the fast peripheral clock domain.
Figure 16-2 shows Timer/Counter 1 synchronization register block diagram and describes syn-
chronization delays in between registers. Note that all clock gating details are not shown in the
figure.
The Timer/Counter1 register values go through the internal synchronization registers, which
cause the input synchronization delay, before affecting the counter operation. The registers
TCCR1A, TCCR1B, TCCR1C, TCCR1D, OCR1A, OCR1B, OCR1C and OCR1D can be read
back right after writing the register. The read back values are delayed for the Timer/Counter1
(TCNT1) register, Timer/Counter1 High Byte Register (TC1H) and flags (OCF1A, OCF1B,
OCF1D and TOV1), because of the input and output synchronization.
The system clock frequency must be lower than half of the PCK frequency, because the syn-
chronization mechanism of the asynchronous Timer/Counter1 needs at least two edges of the
PCK when the system clock is high. If the frequency of the system clock is too high, it is a risk
that data or control values are lost.
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Figure 16-2. Timer/Counter1 Synchronization Register Block Diagram
16.2.5 Definitions
Many register and bit references in this section are written in general form. A lower case “n”
replaces the Timer/Counter number, in this case 0. A lower case “x” replaces the Output Com-
pare Unit, in this case Compare Unit A, B, C or D. However, when using the register or bit
defines in a program, the precise form must be used, i.e., TCNT1 for accessing Timer/Counter1
counter value and so on. The definitions in Table 16-1 are used extensively throughout the
document.
OCR1A
IO Registers Timer/Counter1
8-Bit Data Bus
Input Synchronization
Registers
Output Synchronization
Registers
OCR1B
OCR1C
OCR1D
TCCR1A
TCCR1B
TCCR1C
TCCR1D
TCNT1
TC1H
OCF1A
OCF1B
OCF1D
TOV1
S
A
OCR1A_SI
OCR1B_SI
OCR1C_SI
OCR1D_SI
TCCR1A_SI
TCNT1
TCCR1B_SI
TCCR1C_SI
TCCR1D_SI
TCNT1_SI
TC1H_SI
OCF1A_SI
OCF1B_SI
OCF1D_SI
TOV1_SI
1/2 CK Delay 1/2 CK Delay1 CK Delay 1 CK Delay
TCNT1_SO TCNT1
TC1H
OCF1A
OCF1B
OCF1D
TOV1
PCKE
CK
PCK
SYNC
MODE
ASYNC
MODE
TC1H_SO
OCF1A_SO
OCF1B_SO
OCF1D_SO
TOV1_SO
~1/2 CK Delay ~1/2 CK Delay1 PCK Delay 1 PCK Delay
S
A
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16.3 Counter Unit
The main part of the Timer/Counter1 is the programmable bi-directional counter unit. Figure 16-3
shows a block diagram of the counter and its surroundings.
Figure 16-3. Counter Unit Block Diagram
Signal description (internal signals):
count TCNT1 increment or decrement enable.
direction Select between increment and decrement.
clear Clear TCNT1 (set all bits to zero).
clkTnTimer/Counter clock, referred to as clkT1 in the following.
top Signalize that TCNT1 has reached maximum value.
bottom Signalize that TCNT1 has reached minimum value (zero).
Depending of the mode of operation used, the counter is cleared, incremented, or decremented
at each timer clock (clkT1). The timer clock is generated from an synchronous system clock or an
asynchronous PLL clock using the Clock Select bits (CS13:0) and the PCK Enable bit (PCKE).
When no clock source is selected (CS13:0 = 0) the timer is stopped. However, the TCNT1 value
can be accessed by the CPU, regardless of whether clkT1 is present or not. A CPU write over-
rides (has priority over) all counter clear or count operations.
The counting sequence of the Timer/Counter1 is determined by the setting of the WGM10 and
PWM1x bits located in the Timer/Counter1 Control Registers (TCCR1A, TCCR1C and
TCCR1D). For more details about advanced counting sequences and waveform generation, see
“Modes of Operation” on page 102. The Timer/Counter Overflow Flag (TOV1) is set according to
the mode of operation selected by the PWM1x and WGM10 bits. The Overflow Flag can be used
for generating a CPU interrupt.
Table 16-1. Definitions
BOTTOM The counter reaches the BOTTOM when it becomes 0.
MAX The counter reaches its MAXimum value when it becomes 0x3FF (decimal 1023).
TOP The counter reaches the TOP value (stored in the OCR1C) when it becomes equal to the
highest value in the count sequence. The TOP has a value 0x0FF as default after reset.
topbottom
TOV1
DATA BUS
Control Logic
TCNT1
clkT1
count
Timer/Counter1 Count Enable
(from Prescaler)
PCKE
PCK
CK
clear
direction
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16.3.1 Counter Initialization for Asynchronous Mode
To change Timer/Counter1 to the asynchronous mode follow the procedure below:
1. Enable PLL.
2. Wait 100 µs for PLL to stabilize.
3. Poll the PLOCK bit until it is set.
4. Set the PCKE bit in the PLLCSR register which enables the asynchronous mode.
16.4 Output Compare Unit
The comparator continuously compares TCNT1 with the Output Compare Registers (OCR1A,
OCR1B, OCR1C and OCR1D). Whenever TCNT1 equals to the Output Compare Register, the
comparator signals a match. A match will set the Output Compare Flag (OCF1A, OCF1B or
OCF1D) at the next timer clock cycle. If the corresponding interrupt is enabled, the Output Com-
pare Flag generates an Output Compare interrupt. The Output Compare Flag is automatically
cleared when the interrupt is executed. Alternatively, the flag can be cleared by software by writ-
ing a logical one to its I/O bit location. The Waveform Generator uses the match signal to
generate an output according to operating mode set by the PWM1x, WGM10 and Compare Out-
put mode (COM1x1:0) bits. The top and bottom signals are used by the Waveform Generator for
handling the special cases of the extreme values in some modes of operation (See “Modes of
Operation” on page 102.). Figure 16-4 shows a block diagram of the Output Compare unit.
Figure 16-4. Output Compare Unit, Block Diagram
The OCR1x Registers are double buffered when using any of the Pulse Width Modulation
(PWM) modes. For the normal mode of operation, the double buffering is disabled. The double
buffering synchronizes the update of the OCR1x Compare Registers to either top or bottom of
the counting sequence. The synchronization prevents the occurrence of odd-length, non-sym-
metrical PWM pulses, thereby making the output glitch-free. See Figure 16-5 for an example.
OCFnx (Int. Req.)
= (10-bit Comparator)
10-BIT OCRnx
TCnH TCNTnOCRnx
Waveform Generator
10-BIT TCNTn
TOP PWMnx
WGM10
COMnX1:0
BOTTOM
FOCn
OCWnx
8-BIT DATA BUS
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During the time between the write and the update operation, a read from OCR1A, OCR1B,
OCR1C or OCR1D will read the contents of the temporary location. This means that the most
recently written value always will read out of OCR1A, OCR1B, OCR1C or OCR1D.
Figure 16-5. Effects of Unsynchronized OCR Latching
16.4.1 Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced by
writing a one to the Force Output Compare (FOC1x) bit. Forcing Compare Match will not set the
OCF1x Flag or reload/clear the timer, but the Waveform Output (OCW1x) will be updated as if a
real Compare Match had occurred (the COM1x1:0 bits settings define whether the Waveform
Output (OCW1x) is set, cleared or toggled).
16.4.2 Compare Match Blocking by TCNT1 Write
All CPU write operations to the TCNT1 Register will block any Compare Match that occur in the
next timer clock cycle, even when the timer is stopped. This feature allows OCR1x to be initial-
ized to the same value as TCNT1 without triggering an interrupt when the Timer/Counter clock is
enabled.
16.4.3 Using the Output Compare Unit
Since writing TCNT1 in any mode of operation will block all Compare Matches for one timer
clock cycle, there are risks involved when changing TCNT1 when using the Output Compare
Unit, independently of whether the Timer/Counter is running or not. If the value written to TCNT1
equals the OCR1x value, the Compare Match will be missed, resulting in incorrect waveform
generation. Similarly, do not write the TCNT1 value equal to BOTTOM when the counter is
down-counting.
The setup of the Waveform Output (OCW1x) should be performed before setting the Data Direc-
tion Register for the port pin to output. The easiest way of setting the OCW1x value is to use the
Force Output Compare (FOC1x) strobe bits in Normal mode. The OC1x keeps its value even
when changing between Waveform Generation modes.
Be aware that the COM1x1:0 bits are not double buffered together with the compare value.
Changing the COM1x1:0 bits will take effect immediately.
Compare Value changes
Compare Value changes
Counter Value
Glitch
Synchronized WFnx Latch
Unsynchronized WFnx Latch
Compare Value
Output Compare
Waveform OCWnx
Counter Value
Compare Value
Output Compare
Waveform OCWnx
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16.5 Dead Time Generator
The Dead Time Generator is provided for the Timer/Counter1 PWM output pairs to allow driving
external power control switches safely. The Dead Time Generator is a separate block that can
be used to insert dead times (non-overlapping times) for the Timer/Counter1 complementary
output pairs OC1x and OC1x when the PWM mode is enabled and the COM1x1:0 bits are set to
“01”. The sharing of tasks is as follows: the Waveform Generator generates the Waveform Out-
put (OCW1x) and the Dead Time Generator generates the non-overlapping PWM output pair
from the Waveform Output. Three Dead Time Generators are provided, one for each PWM out-
put. The non-overlap time is adjustable and the PWM output and it’s complementary output are
adjusted separately, and independently for both PWM outputs.
Figure 16-6. Output Compare Unit, Block Diagram
The Dead Time Generation is based on the 4-bit down counters that count the dead time, as
shown in Figure 16-7. There is a dedicated prescaler in front of the Dead Time Generator that
can divide the Timer/Counter1 clock (PCK or CK) by 1, 2, 4 or 8. This provides for large range of
dead times that can be generated. The prescaler is controlled by two control bits DTPS11..10.
The block has also a rising and falling edge detector that is used to start the dead time counting
period. Depending on the edge, one of the transitions on the rising edges, OC1x or OC1x is
delayed until the counter has counted to zero. The comparator is used to compare the counter
with zero and stop the dead time insertion when zero has been reached. The counter is loaded
with a 4-bit DT1H or DT1L value from DT1 I/O register, depending on the edge of the Waveform
Output (OCW1x) when the dead time insertion is started. The Output Compare Output are
delayed by one timer clock cycle at minimum from the Waveform Output when the Dead Time is
adjusted to zero. The outputs OC1x and OC1x are inverted, if the PWM Inversion Mode bit
PWM1X is set. This will also cause both outputs to be high during the dead time.
Figure 16-7. Dead Time Generator
Waveform Generator
OCnx
pin
OCnx
pin
top
bottom
FOCn
PWMnx WGM10 COMnx
OCWnx
OCnx
OCnx
CK or PCK
CLOCK
Dead Time Generator
DTPSn DTnH DTnL
Dead Time
Prescaler Clock Control
OCWnx
DTPSn
DTnH
DTnL
CK or PCK
CLOCK
TCCRnB Register DTn I/O Register
4 Bit Counter
Comparator
PWM1X
OCnx
OCnx
PWM1X
DATA BUS (8-bit)
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The length of the counting period is user adjustable by selecting the dead time prescaler setting
by using the DTPS11:10 control bits, and selecting then the dead time value in I/O register DT1.
The DT1 register consists of two 4-bit fields, DT1H and DT1L that control the dead time periods
of the PWM output and its' complementary output separately in terms of the number of pres-
caled dead time generator clock cycles. Thus the rising edge of OC1x and OC1x can have
different dead time periods as the tnon-overlap / rising edge is adjusted by the 4-bit DT1H value and the
tnon-overlap / falling edge is adjusted by the 4-bit DT1L value.
Figure 16-8. The Complementary Output Pair, COM1x1:0 = 1
16.6 Compare Match Output Unit
The Compare Output Mode (COM1x1:0) bits have two functions. The Waveform Generator uses
the COM1x1:0 bits for defining the inverted or non-inverted Waveform Output (OCW1x) at the
next Compare Match. Also, the COM1x1:0 bits control the OC1x and OC1x pin output source.
Figure 16-9 shows a simplified schematic of the logic affected by the COM1x1:0 bit setting. The
I/O Registers, I/O bits, and I/O pins in the figure are shown in bold. Only the parts of the general
I/O Port Control Registers (DDR and PORT) that are affected by the COM1x1:0 bits are shown.
In Normal Mode (non-PWM) the Dead Time Generator is disabled and it is working like a syn-
chronizer: the Output Compare (OC1x) is delayed from the Waveform Output (OCW1x) by one
timer clock cycle. Whereas in Fast PWM Mode and in Phase and Frequency Correct PWM
Mode when the COM1x1:0 bits are set to “01” both the non-inverted and the inverted Output
Compare output are generated, and an user programmable Dead Time delay is inserted for
these complementary output pairs (OC1x and OC1x). The functionality in PWM modes is similar
to Normal mode when any other COM1x1:0 bit setup is used. When referring to the OC1x state,
the reference is for the Output Compare output (OC1x) from the Dead Time Generator, not the
OC1x pin. If a system reset occur, the OC1x is reset to “0”.
The general I/O port function is overridden by the Output Compare (OC1x / OC1x) from the
Dead Time Generator if either of the COM1x1:0 bits are set. However, the OC1x pin direction
(input or output) is still controlled by the Data Direction Register (DDR) for the port pin. The Data
Direction Register bit for the OC1x and OC1x pins (DDR_OC1x and DDR_OC1x) must be set as
output before the OC1x and OC1x values are visible on the pin. The port override function is
independent of the Output Compare mode.
The design of the Output Compare Pin Configuration logic allows initialization of the OC1x state
before the output is enabled. Note that some COM1x1:0 bit settings are reserved for certain
modes of operation. For Output Compare Pin Configurations refer to Table 16-2 on page 103,
Table 16-3 on page 105, Table 16-4 on page 107, and Table 16-5 on page 109.
OCWnx
OCnx
OCnx
(COMnx = 1)
t
non-overlap/rising edge
t
non-overlap/falling edge
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Figure 16-9. Compare Match Output Unit, Schematic
1
0
0
1
0
1
0
1
QD
clkTn
clkI/O
Dead Time
Generator A
PORTB0
DDRB0
OCW1A
WGM11
OC1OE3:2
COM1B1:0
WGM11
OC1OE5:4
COM1D1:0
WGM11
OC1OE3:2
COM1A1:0
OC1A
OC1A
Q
Q
Q
D
QD
Output Compare
Pin Configuration
OC1A
PIN
PORTB1
DDRB1
clkTn
OCW1B OC1B
OC1B
Dead Time
Generator B
Q
Q
QD
QD
PORTB2
DDRB2
QD
QD
DATA BUS
DDRB3
QD
QD
PORTB4
DDRB4
QD
QD
PORTB5
DDRB5
QD
OC1A
PIN
OC1B
PIN
OC1B
PIN
OC1D
PIN
OC1D
PIN
0
1
2
0
1
0
1
Output Compare
Pin Configuration
0
1
clkTn
OCW1D OC1D
OC1D
Dead Time
Generator B
Q
Q
0
1
2
0
1
0
1
Output Compare
Pin Configuration
PORTB3
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16.6.1 Compare Output Mode and Waveform Generation
The Waveform Generator uses the COM1x1:0 bits differently in Normal mode and PWM modes.
For all modes, setting the COM1x1:0 = 0 tells the Waveform Generator that no action on the
OCW1x Output is to be performed on the next Compare Match. For compare output actions in
the non-PWM modes refer to Table 16-6 on page 115. For fast PWM mode, refer to Table 16-7
on page 115, and for the Phase and Frequency Correct PWM refer to Table 16-8 on page 116.
A change of the COM1x1:0 bits state will have effect at the first Compare Match after the bits are
written. For non-PWM modes, the action can be forced to have immediate effect by using the
FOC1x strobe bits.
16.7 Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is
defined by the combination of the Waveform Generation mode (bits PWM1x and WGM10) and
Compare Output mode (COM1x1:0) bits. The Compare Output mode bits do not affect the
counting sequence, while the Waveform Generation mode bits do. The COM1x1:0 bits control
whether the PWM output generated should be inverted, non-inverted or complementary. For
non-PWM modes the COM1x1:0 bits control whether the output should be set, cleared, or tog-
gled at a Compare Match.
16.7.1 Normal Mode
The simplest mode of operation is the Normal mode (PWM1x = 0), the counter counts from
BOTTOM to TOP (defined as OCR1C) then restarts from BOTTOM. The OCR1C defines the
TOP value for the counter, hence also its resolution, and allows control of the Compare Match
output frequency. In toggle Compare Output Mode the Waveform Output (OCW1x) is toggled at
Compare Match between TCNT1 and OCR1x. In non-inverting Compare Output Mode the
Waveform Output is cleared on the Compare Match. In inverting Compare Output Mode the
Waveform Output is set on Compare Match.
The timing diagram for the Normal mode is shown in Figure 16-10. The counter value (TCNT1)
that is shown as a histogram in the timing diagram is incremented until the counter value
matches the TOP value. The counter is then cleared at the following clock cycle The diagram
includes the Waveform Output (OCW1x) in toggle Compare Mode. The small horizontal line
marks on the TCNT1 slopes represent Compare Matches between OCR1x and TCNT1.
Figure 16-10. Normal Mode, Timing Diagram
12
TCNTn
OCWnx
(COMnx=1)
Period 3
TOVn Interrupt Flag Set
4
OCnx Interrupt Flag Set
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The Timer/Counter Overflow Flag (TOV1) is set in the same clock cycle as the TCNT1 becomes
zero. The TOV1 Flag in this case behaves like a 11th bit, except that it is only set, not cleared.
However, combined with the timer overflow interrupt, that automatically clears the TOV1 Flag,
the timer resolution can be increased by software. There are no special cases to consider in the
Normal mode, a new counter value can be written anytime.
The Output Compare Unit can be used to generate interrupts at some given time. Using the Out-
put Compare to generate waveforms in Normal mode is not recommended, since this will
occupy too much of the CPU time. For generating a waveform, the OCW1x output can be set to
toggle its logical level on each Compare Match by setting the Compare Output mode bits to tog-
gle mode (COM1x1:0 = 1). The OC1x value will not be visible on the port pin unless the data
direction for the pin is set to output. The waveform generated will have a maximum frequency of
fOC1x = fclkT1/4 when OCR1C is set to zero. The waveform frequency is defined by the following
equation:
Resolution shows how many bit is required to express the value in the OCR1C register. It is cal-
culated by following equation:
ResolutionPWM = log2(OCR1C + 1).
The Output Compare Pin configurations in Normal Mode are described in Table 16-2.
16.7.2 Fast PWM Mode
The fast Pulse Width Modulation or fast PWM mode (PWM1x = 1 and WGM10 = 0) provides a
high frequency PWM waveform generation option. The fast PWM differs from the other PWM
option by its single-slope operation. The counter counts from BOTTOM to TOP (defined as
OCR1C) then restarts from BOTTOM. In non-inverting Compare Output mode the Waveform
Output (OCW1x) is cleared on the Compare Match between TCNT1 and OCR1x and set at
BOTTOM. In inverting Compare Output mode, the Waveform Output is set on Compare Match
and cleared at BOTTOM. In complementary Compare Output mode the Waveform Output is
cleared on the Compare Match and set at BOTTOM.
Due to the single-slope operation, the operating frequency of the fast PWM mode can be twice
as high as the Phase and Frequency Correct PWM mode that use dual-slope operation. This
high frequency makes the fast PWM mode well suited for power regulation, rectification, and
DAC applications. High frequency allows physically small sized external components (coils,
capacitors), and therefore reduces total system cost.
The timing diagram for the fast PWM mode is shown in Figure 16-11. The counter is incre-
mented until the counter value matches the TOP value. The counter is then cleared at the
following timer clock cycle. The TCNT1 value is in the timing diagram shown as a histogram for
illustrating the single-slope operation.
Table 16-2. Output Compare Pin Configurations in Normal Mode
COM1x1 COM1x0 OC1x Pin OC1x Pin
0 0 Disconnected Disconnected
0 1 Disconnected OC1x
1 0 Disconnected OC1x
1 1 Disconnected OC1x
fOC1xfclkT1
21OCR1C+()⋅
-------------------------------------------=
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The diagram includes the Waveform Output in non-inverted and inverted Compare Output
modes. The small horizontal line marks on the TCNT1 slopes represent Compare Matches
between OCR1x and TCNT1.
Figure 16-11. Fast PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches TOP. If the inter-
rupt is enabled, the interrupt handler routine can be used for updating the compare value.
In fast PWM mode, the compare unit allows generation of PWM waveforms on the OC1x pins.
Setting the COM1x1:0 bits to two will produce a non-inverted PWM and setting the COM1x1:0 to
three will produce an inverted PWM output. Setting the COM1x1:0 bits to one will enable com-
plementary Compare Output mode and produce both the non-inverted (OC1x) and inverted
output (OC1x). The actual value will only be visible on the port pin if the data direction for the
port pin is set as output. The PWM waveform is generated by setting (or clearing) the Waveform
Output (OCW1x) at the Compare Match between OCR1x and TCNT1, and clearing (or setting)
the Waveform Output at the timer clock cycle the counter is cleared (changes from TOP to
BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
The N variable represents the number of steps in single-slope operation. The value of N equals
either to the TOP value.
The extreme values for the OCR1C Register represents special cases when generating a PWM
waveform output in the fast PWM mode. If the OCR1C is set equal to BOTTOM, the output will
be a narrow spike for each MAX+1 timer clock cycle. Setting the OCR1C equal to MAX will result
in a constantly high or low output (depending on the polarity of the output set by the COM1x1:0
bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by set-
ting the Waveform Output (OCW1x) to toggle its logical level on each Compare Match
(COM1x1:0 = 1). The waveform generated will have a maximum frequency of fOC1 = fclkT1/4 when
OCR1C is set to three.
1234567
TCNTn
OCWnx
(COMnx1:0 = 2)
OCWnx
(COMnx1:0 = 3)
Period
OCRnx Update and
TOVn Interrupt Flag Set
OCRnx Interrupt Flag Set
fOCnxPWM fclkT1
N
-------------=
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The general I/O port function is overridden by the Output Compare value (OC1x / OC1x) from
the Dead Time Generator, if either of the COM1x1:0 bits are set and the Data Direction Register
bits for the OC1X and OC1X pins are set as an output. If the COM1x1:0 bits are cleared, the
actual value from the port register will be visible on the port pin. The Output Compare Pin config-
urations are described in Table 16-3.
16.7.3 Phase and Frequency Correct PWM Mode
The Phase and Frequency Correct PWM Mode (PWMx = 1 and WGM10 = 1) provides a high
resolution Phase and Frequency Correct PWM waveform generation option. The Phase and
Frequency Correct PWM mode is based on a dual-slope operation. The counter counts repeat-
edly from BOTTOM to TOP (defined as OCR1C) and then from TOP to BOTTOM. In
non-inverting Compare Output Mode the Waveform Output (OCW1x) is cleared on the Compare
Match between TCNT1 and OCR1x while upcounting, and set on the Compare Match while
down-counting. In inverting Output Compare mode, the operation is inverted. In complementary
Compare Output Mode, the Waveform Output is cleared on the Compare Match and set at BOT-
TOM. The dual-slope operation has lower maximum operation frequency than single slope
operation. However, due to the symmetric feature of the dual-slope PWM modes, these modes
are preferred for motor control applications.
The timing diagram for the Phase and Frequency Correct PWM mode is shown on Figure 16-12
in which the TCNT1 value is shown as a histogram for illustrating the dual-slope operation. The
counter is incremented until the counter value matches TOP. When the counter reaches TOP, it
changes the count direction. The TCNT1 value will be equal to TOP for one timer clock cycle.
The diagram includes the Waveform Output (OCW1x) in non-inverted and inverted Compare
Output Mode. The small horizontal line marks on the TCNT1 slopes represent Compare
Matches between OCR1x and TCNT1.
Table 16-3. Output Compare Pin Configurations in Fast PWM Mode
COM1x1 COM1x0 OC1x Pin OC1x Pin
0 0 Disconnected Disconnected
01OC1x OC1x
1 0 Disconnected OC1x
1 1 Disconnected OC1x
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Figure 16-12. Phase and Frequency Correct PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches BOTTOM. The
Interrupt Flag can be used to generate an interrupt each time the counter reaches the BOTTOM
value.
In the Phase and Frequency Correct PWM mode, the compare unit allows generation of PWM
waveforms on the OC1x pins. Setting the COM1x1:0 bits to two will produce a non-inverted
PWM and setting the COM1x1:0 to three will produce an inverted PWM output. Setting the
COM1A1:0 bits to one will enable complementary Compare Output mode and produce both the
non-inverted (OC1x) and inverted output (OC1x). The actual values will only be visible on the
port pin if the data direction for the port pin is set as output. The PWM waveform is generated by
clearing (or setting) the Waveform Output (OCW1x) at the Compare Match between OCR1x and
TCNT1 when the counter increments, and setting (or clearing) the Waveform Output at Compare
Match when the counter decrements. The PWM frequency for the output when using the Phase
and Frequency Correct PWM can be calculated by the following equation:
The N variable represents the number of steps in dual-slope operation. The value of N equals to
the TOP value.
The extreme values for the OCR1C Register represent special cases when generating a PWM
waveform output in the Phase and Frequency Correct PWM mode. If the OCR1C is set equal to
BOTTOM, the output will be continuously low and if set equal to MAX the output will be continu-
ously high for non-inverted PWM mode. For inverted PWM the output will have the opposite
logic values.
The general I/O port function is overridden by the Output Compare value (OC1x / OC1x) from
the Dead Time Generator, if either of the COM1x1:0 bits are set and the Data Direction Register
bits for the OC1X and OC1X pins are set as an output. If the COM1x1:0 bits are cleared, the
actual value from the port register will be visible on the port pin. The configurations of the Output
Compare Pins are described in Table 16-4.
123
OCRnx Update and
TOVn Interrupt Flag Set
OCRnx Interrupt Flag Set
TCNTn
OCWnx
(COMnx = 2)
OCWnx
(COMnx = 3)
Period
fOCnxPCPWM fclkT1
N
-------------=
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16.7.4 PWM6 Mode
The PWM6 Mode (PWM1A = 1, WGM11 = 1 and WGM10 = x) provide PWM waveform genera-
tion option e.g. for controlling Brushless DC (BLDC) motors. In the PWM6 Mode the OCR1A
Register controls all six Output Compare waveforms as the same Waveform Output (OCW1A)
from the Waveform Generator is used for generating all waveforms. The PWM6 Mode also pro-
vides an Output Compare Override Enable Register (OC1OE) that can be used with an instant
response for disabling or enabling the Output Compare pins. If the Output Compare Override
Enable bit is cleared, the actual value from the port register will be visible on the port pin.
The PWM6 Mode provides two counter operation modes, a single-slope operation and a
dual-slope operation. If the single-slope operation is selected (the WGM10 bit is set to 0), the
counter counts from BOTTOM to TOP (defined as OCR1C) then restart from BOTTOM like in
Fast PWM Mode. The PWM waveform is generated by setting (or clearing) the Waveform Out-
put (OCW1A) at the Compare Match between OCR1A and TCNT1, and clearing (or setting) the
Waveform Output at the timer clock cycle the counter is cleared (changes from TOP to BOT-
TOM). The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches the TOP
and, if the interrupt is enabled, the interrupt handler routine can be used for updating the com-
pare value.
Whereas, if the dual-slope operation is selected (the WGM10 bit is set to 1), the counter counts
repeatedly from BOTTOM to TOP (defined as OCR1C) and then from TOP to BOTTOM like in
Phase and Frequency Correct PWM Mode. The PWM waveform is generated by setting (or
clearing) the Waveform Output (OCW1A) at the Compare Match between OCR1A and TCNT1
when the counter increments, and clearing (or setting) the Waveform Output at the he Compare
Match between OCR1A and TCNT1 when the counter decrements. The Timer/Counter Overflow
Flag (TOV1) is set each time the counter reaches the BOTTOM and, if the interrupt is enabled,
the interrupt handler routine can be used for updating the compare value.
The timing diagram for the PWM6 Mode in single-slope operation (WGM11 = 0) when the
COM1A1:0 bits are set to “10” is shown in Figure 16-13. The counter is incremented until the
counter value matches the TOP value. The counter is then cleared at the following timer clock
cycle. The TCNT1 value is in the timing diagram shown as a histogram for illustrating the sin-
gle-slope operation. The timing diagram includes Output Compare pins OC1A and OC1A, and
the corresponding Output Compare Override Enable bits (OC1OE1..OC1OE0).
Table 16-4. Output Compare pin configurations in Phase and Frequency Correct PWM Mode
COM1x1 COM1x0 OC1x Pin OC1x Pin
0 0 Disconnected Disconnected
01OC1x OC1x
1 0 Disconnected OC1x
1 1 Disconnected OC1x
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Figure 16-13. PWM6 Mode, Single-slope Operation, Timing Diagram
The general I/O port function is overridden by the Output Compare value (OC1x / OC1x) from
the Dead Time Generator if either of the COM1x1:0 bits are set. The Output Compare pins can
also be overridden by the Output Compare Override Enable bits OC1OE5..OC1OE0. If an Over-
ride Enable bit is cleared, the actual value from the port register will be visible on the port pin
and, if the Override Enable bit is set, the Output Compare pin is allowed to be connected on the
port pin. The Output Compare Pin configurations are described in Table 16-5.
TCNT1
OCW1A
OC1OE0
OC1OE1
OC1OE3
OC1OE4
OC1OE5
OC1OE2
OC1A Pin
OC1A Pin
OC1B Pin
OC1B Pin
OC1D Pin
OC1D Pin
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16.8 Timer/Counter Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkT1) is therefore shown as a
clock enable signal in the following figures. The figures include information on when Interrupt
Flags are set.
Figure 16-14 contains timing data for basic Timer/Counter operation. The figure shows the count
sequence close to the MAX value in all modes other than Phase and Frequency Correct PWM
Mode. Figure 16-15 shows the same timing data, but with the prescaler enabled, in all modes
other than Phase and Frequency Correct PWM Mode. Figure 16-16 shows the setting of
OCF1A, OCF1B and OCF1D in all modes, and Figure 16-17 shows the setting of TOV1 in
Phase and Frequency Correct PWM Mode.
Figure 16-14. Timer/Counter Timing Diagram, no Prescaling
Table 16-5. Output Compare Pin configurations in PWM6 Mode
COM1A1 COM1A0 OC1A Pin (PB0) OC1A Pin (PB1)
0 0 Disconnected Disconnected
01OC1A
• OC1OE0 OC1A • OC1OE1
10OC1A • OC1OE0 OC1A • OC1OE1
11OC1A • OC1OE0 OC1A • OC1OE1
COM1B1 COM1B0 OC1B Pin (PB2) OC1B Pin (PB3)
0 0 Disconnected Disconnected
01OC1A • OC1OE2 OC1A • OC1OE3
10OC1A • OC1OE2 OC1A • OC1OE3
11OC1A • OC1OE2 OC1A • OC1OE3
COM1D1 COM1D0 OC1D Pin (PB4) OC1D Pin (PB5)
0 0 Disconnected Disconnected
01OC1A • OC1OE4 OC1A • OC1OE5
10OC1A • OC1OE4 OC1A • OC1OE5
11OC1A • OC1OE4 OC1A • OC1OE5
TOP - 1
clkPCK
(clkPCK/1)
TCNTn
TOVn
clkTn
TOP BOTTOM BOTTOM + 1
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Figure 16-15. Timer/Counter Timing Diagram, with Prescaler (fclkT1/8)
Figure 16-16. Timer/Counter Timing Diagram, Setting of OCF1x, with Prescaler (fclkT1/8)
Figure 16-17. Timer/Counter Timing Diagram, with Prescaler (fclkT1/8)
TOP - 1
clkPCK
(clkPCK/8)
TCNTn
TOVn
clkTn
TOP BOTTOM BOTTOM + 1
OCRnx - 1
clkPCK
(clkPCK/8)
TCNTn
OCRnx
OCFnx
clkTn
OCRnx OCRnx + 1
OCRnx Value
OCRnx + 2
BOTTOM - 1
clkPCK
(clkPCK/8)
TCNTn
TOVn
clkTn
BOTTOM + 1 BOTTOM BOTTOM + 1
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16.9 Fault Protection Unit
The Timer/Counter1 incorporates a Fault Protection unit that can disable the PWM output pins, if
an external event is triggered. The external signal indicating an event can be applied via the
external interrupt INT0 pin or alternatively, via the analog-comparator unit. The Fault Protection
unit is illustrated by the block diagram shown in Figure 16-18. The elements of the block diagram
that are not directly a part of the Fault Protection unit are gray shaded.
Figure 16-18. Fault Protection Unit Block Diagram
When the Fault Protection mode is enabled by the Fault Protection Enable (FPEN1) bit and a
change of the logic level (an event) occurs on the external interrupt pin (INT0), alternatively on
the Analog Comparator output (ACO), and this change confirms to the setting of the edge detec-
tor, a Fault Protection mode will be triggered. When a Fault Protection is triggered, the COM1x
bits are cleared, Output Comparators are disconnected from the PWM output pins and the
PORTB register bits are connected on the PWM output pins. The Fault Protection Enable
(FPEN1) is automatically cleared at the same system clock as the COM1nx bits are cleared. If
the Fault Protection Interrupt Enable bit (FPIE1) is set, a Fault Protection interrupt is generated
and the FPEN1 bit is cleared. Alternatively the FPEN1 bit can be polled by software to figure out
when the Timer/Counter has entered to Fault Protection mode.
16.9.1 Fault Protection Trigger Source
The main trigger source for the Fault Protection unit is the external interrupt pin (INT0). Alterna-
tively the Analog Comparator output can be used as trigger source for the Fault Protection unit.
The Analog Comparator is selected as trigger source by setting the Fault Protection Analog
Comparator (FPAC1) bit in the Timer/Counter1 Control Register (TCCR1D). Be aware that
changing trigger source can trigger a Fault Protection mode. Therefore it is recommended to
clear the FPF1 flag after changing trigger source, setting edge detector or enabling the Fault
Protection.
Both the external interrupt pin (INT0) and the Analog Comparator output (ACO) inputs are sam-
pled using the same technique as for the T0 pin (Figure 13-1 on page 70). The edge detector is
also identical. However, when the noise canceler is enabled, additional logic is inserted before
the edge detector, which increases the delay by four system clock cycles. An Input Capture can
also be triggered by software by controlling the port of the INT0 pin.
16.9.2 Noise Canceler
The noise canceler improves noise immunity by using a simple digital filtering scheme. The
noise canceler input is monitored over four samples, and all four must be equal for changing the
output that in turn is used by the edge detector. The noise canceler is enabled by setting the
Fault Protection Noise Canceler (FPNC1) bit in Timer/Counter1 Control Register D (TCCR1D).
When enabled the noise canceler introduces additional four system clock cycles of delay from a
change applied to the input. The noise canceler uses the system clock and is therefore not
affected by the prescaler.
Fault_Protection (Int. Req.)
Noise
Canceler
Analog
Comparator Edge
Detector Timer/Counter1
FPNC1FPAC1ACO*
+
-
FPES1 FPEN1
INT0
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16.10 Accessing 10-Bit Registers
If 10-bit values are written to the TCNT1 and OCR1A/B/C/D registers, the 10-bit registers can be
byte accessed by the AVR CPU via the 8-bit data bus using two read or write operations. The
10-bit registers have a common 2-bit Timer/Counter1 High Byte Register (TC1H) that is used for
temporary storing of the two MSBs of the 10-bit access. The same TC1H register is shared
between all 10-bit registers. Accessing the low byte triggers the 10-bit read or write operation.
When the low byte of a 10-bit register is written by the CPU, the high byte stored in the TC1H
register, and the low byte written are both copied into the 10-bit register in the same clock cycle.
When the low byte of a 10-bit register is read by the CPU, the high byte of the 10-bit register is
copied into the TC1H register in the same clock cycle as the low byte is read.
To do a 10-bit write, the high byte must be written to the TC1H register before the low byte is
written. For a 10-bit read, the low byte must be read before the high byte.
The following code examples show how to access the 10-bit timer registers assuming that no
interrupts updates the TC1H register. The same principle can be used directly for accessing the
OCR1A/B/C/D registers.
Note: 1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example returns the TCNT1 value in the r17:r16 register pair.
Assembly Code Example
...
; Set TCNT1 to 0x01FF
ldi r17,0x01
ldi r16,0xFF
out TC1H,r17
out TCNT1,r16
; Read TCNT1 into r17:r16
in r16,TCNT1
in r17,TC1H
...
C Code Example
unsigned int i;
...
/* Set TCNT1 to 0x01FF */
TC1H = 0x01;
TCNT1 = 0xFF;
/* Read TCNT1 into i */
i = TCNT1;
i |= ((unsigned int)TC1H << 8);
...
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It is important to notice that accessing 10-bit registers are atomic operations. If an interrupt
occurs between the two instructions accessing the 10-bit register, and the interrupt code
updates the TC1H register by accessing the same or any other of the 10-bit timer registers, then
the result of the access outside the interrupt will be corrupted. Therefore, when both the main
code and the interrupt code update the TC1H register, the main code must disable the interrupts
during the 16-bit access.
The following code examples show how to do an atomic read of the TCNT1 register contents.
Reading any of the OCR1A/B/C/D registers can be done by using the same principle.
Note: 1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example returns the TCNT1 value in the r17:r16 register pair.
Assembly Code Example
TIM1_ReadTCNT1:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Read TCNT1 into r17:r16
in r16,TCNT1
in r17,TC1H
; Restore global interrupt flag
out SREG,r18
ret
C Code Example
unsigned int TIM1_ReadTCNT1( void )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Read TCNT1 into i */
i = TCNT1;
i |= ((unsigned int)TC1H << 8);
/* Restore global interrupt flag
SREG = sreg;
return i;
}
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The following code examples show how to do an atomic write of the TCNT1 register contents.
Writing any of the OCR1A/B/C/D registers can be done by using the same principle.
Note: 1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example requires that the r17:r16 register pair contains the value to be writ-
ten to TCNT1.
16.10.1 Reusing the temporary high byte register
If writing to more than one 10-bit register where the high byte is the same for all registers written,
then the high byte only needs to be written once. However, note that the same rule of atomic
operation described previously also applies in this case.
Assembly Code Example
TIM1_WriteTCNT1:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Set TCNT1 to r17:r16
out TC1H,r17
out TCNT1,r16
; Restore global interrupt flag
out SREG,r18
ret
C Code Example
void TIM1_WriteTCNT1( unsigned int i )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Set TCNT1 to i */
TC1H = (i >> 8);
TCNT1 = (unsigned char)i;
/* Restore global interrupt flag */
SREG = sreg;
}
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16.11 Register Description
16.11.1 TCCR1A – Timer/Counter1 Control Register A
• Bits 7,6 - COM1A1, COM1A0: Comparator A Output Mode, Bits 1 and 0
These bits control the behavior of the Waveform Output (OCW1A) and the connection of the
Output Compare pin (OC1A). If one or both of the COM1A1:0 bits are set, the OC1A output
overrides the normal port functionality of the I/O pin it is connected to. The complementary
OC1B output is connected only in PWM modes when the COM1A1:0 bits are set to “01”. Note
that the Data Direction Register (DDR) bit corresponding to the OC1A and OC1A pins must be
set in order to enable the output driver.
The function of the COM1A1:0 bits depends on the PWM1A, WGM10 and WGM11 bit settings.
Table 16-6 shows the COM1A1:0 bit functionality when the PWM1A bit is set to Normal Mode
(non-PWM).
Table 16-7 shows the COM1A1:0 bit functionality when the PWM1A, WGM10 and WGM11 bits
are set to fast PWM mode.
Bit 76543210
0x30 (0x50) COM1A1 COM1A0 COM1B1 COM1B0 FOC1A FOC1B PWM1A PWM1B TCCR1A
Read/Write R/W R/W R/W R/W W W R/W R/W
Initial value00000000
Table 16-6. Compare Output Mode, Normal Mode (non-PWM)
COM1A1..0 OCW1A Behavior OC1A Pin OC1A Pin
00 Normal port operation. Disconnected Disconnected
01 Toggle on Compare Match. Connected Disconnected
10 Clear on Compare Match. Connected Disconnected
11 Set on Compare Match. Connected Disconnected
Table 16-7. Compare Output Mode, Fast PWM Mode
COM1A1..0 OCW1A Behavior OC1A OC1A
00 Normal port operation. Disconnected Disconnected
01 Cleared on Compare Match.
Set when TCNT1 = 0x000. Connected Connected
10 Cleared on Compare Match.
Set when TCNT1 = 0x000. Connected Disconnected
11 Set on Compare Match.
Cleared when TCNT1 = 0x000. Connected Disconnected
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Table 16-8 shows the COM1A1:0 bit functionality when the PWM1A, WGM10 and WGM11 bits
are set to Phase and Frequency Correct PWM Mode.
Table 16-9 shows the COM1A1:0 bit functionality when the PWM1A, WGM10 and WGM11 bits
are set to single-slope PWM6 Mode. In the PWM6 Mode the same Waveform Output (OCW1A)
is used for generating all waveforms and the Output Compare values OC1A and OC1A are con-
nected on the all OC1x and OC1x pins as described below.
Table 16-10 shows the COM1A1:0 bit functionality when the PWM1A, WGM10 and WGM11 bits
are set to dual-slope PWM6 Mode.I
• Bits 5,4 - COM1B1, COM1B0: Comparator B Output Mode, Bits 1 and 0
These bits control the Behavior of the Waveform Output (OCW1B) and the connection of the
Output Compare pin (OC1B). If one or both of the COM1B1:0 bits are set, the OC1B output
overrides the normal port functionality of the I/O pin it is connected to. The complementary
OC1B output is connected only in PWM modes when the COM1B1:0 bits are set to “01”.
Table 16-8. Compare Output Mode, Phase and Frequency Correct PWM Mode
COM1A1..0 OCW1A Behavior OC1A Pin OC1A Pin
00 Normal port operation. Disconnected Disconnected
01 Cleared on Compare Match when up-counting.
Set on Compare Match when down-counting. Connected Connected
10 Cleared on Compare Match when up-counting.
Set on Compare Match when down-counting. Connected Disconnected
11 Set on Compare Match when up-counting.
Cleared on Compare Match when down-counting. Connected Disconnected
Table 16-9. Compare Output Mode, Single-Slope PWM6 Mode
COM1A1..0 OCW1A Behavior OC1x Pin OC1x Pin
00 Normal port operation. Disconnected Disconnected
01 Cleared on Compare Match.
Set when TCNT1 = 0x000. OC1A OC1A
10 Cleared on Compare Match.
Set when TCNT1 = 0x000. OC1A OC1A
11 Set on Compare Match.
Cleared when TCNT1 = 0x000. OC1A OC1A
Table 16-10. Compare Output Mode, Dual-Slope PWM6 Mode
COM1A1..0 OCW1A Behavior OC1x Pin OC1x Pin
00 Normal port operation. Disconnected Disconnected
01 Cleared on Compare Match when up-counting.
Set on Compare Match when down-counting. OC1A OC1A
10 Cleared on Compare Match when up-counting.
Set on Compare Match when down-counting. OC1A OC1A
11 Set on Compare Match when up-counting.
Cleared on Compare Match when down-counting. OC1A OC1A
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Note that the Data Direction Register (DDR) bit corresponding to the OC1B pin must be set in
order to enable the output driver.
The function of the COM1B1:0 bits depends on the PWM1B and WGM10 bit settings. Table
16-11 shows the COM1B1:0 bit functionality when the PWM1B bit is set to Normal Mode
(non-PWM).
Table 16-12 shows the COM1B1:0 bit functionality when the PWM1B and WGM10 bits are set to
Fast PWM Mode.
Table 16-13 shows the COM1B1:0 bit functionality when the PWM1B and WGM10 bits are set to
Phase and Frequency Correct PWM Mode.
• Bit 3 - FOC1A: Force Output Compare Match 1A
The FOC1A bit is only active when the PWM1A bit specify a non-PWM mode.
Writing a logical one to this bit forces a change in the Waveform Output (OCW1A) and the Out-
put Compare pin (OC1A) according to the values already set in COM1A1 and COM1A0. If
COM1A1 and COM1A0 written in the same cycle as FOC1A, the new settings will be used. The
Force Output Compare bit can be used to change the output pin value regardless of the timer
value.
Table 16-11. Compare Output Mode, Normal Mode (non-PWM)
COM1B1..0 OCW1B Behavior OC1B Pin OC1B Pin
00 Normal port operation. Disconnected Disconnected
01 Toggle on Compare Match. Connected Disconnected
10 Clear on Compare Match. Connected Disconnected
11 Set on Compare Match. Connected Disconnected
Table 16-12. Compare Output Mode, Fast PWM Mode
COM1B1..0 OCW1B Behavior OC1B Pin OC1B Pin
00 Normal port operation. Disconnected Disconnected
01 Cleared on Compare Match.
Set when TCNT1 = 0x000. Connected Connected
10 Cleared on Compare Match.
Set when TCNT1 = 0x000. Connected Disconnected
11 Set on Compare Match.
Cleared when TCNT1 = 0x000. Connected Disconnected
Table 16-13. Compare Output Mode, Phase and Frequency Correct PWM Mode
COM1B1..0 OCW1B Behavior OC1B Pin OC1B Pin
00 Normal port operation. Disconnected Disconnected
01 Cleared on Compare Match when up-counting.
Set on Compare Match when down-counting. Connected Connected
10 Cleared on Compare Match when up-counting.
Set on Compare Match when down-counting. Connected Disconnected
11 Set on Compare Match when up-counting.
Cleared on Compare Match when down-counting. Connected Disconnected
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The automatic action programmed in COM1A1 and COM1A0 takes place as if a compare match
had occurred, but no interrupt is generated. The FOC1A bit is always read as zero.
• Bit 2 - FOC1B: Force Output Compare Match 1B
The FOC1B bit is only active when the PWM1B bit specify a non-PWM mode.
Writing a logical one to this bit forces a change in the Waveform Output (OCW1B) and the Out-
put Compare pin (OC1B) according to the values already set in COM1B1 and COM1B0. If
COM1B1 and COM1B0 written in the same cycle as FOC1B, the new settings will be used. The
Force Output Compare bit can be used to change the output pin value regardless of the timer
value. The automatic action programmed in COM1B1 and COM1B0 takes place as if a compare
match had occurred, but no interrupt is generated.
The FOC1B bit is always read as zero.
• Bit 1 - PWM1A: Pulse Width Modulator A Enable
When set (one) this bit enables PWM mode based on comparator OCR1A
• Bit 0 - PWM1B: Pulse Width Modulator B Enable
When set (one) this bit enables PWM mode based on comparator OCR1B.
16.11.2 TCCR1B – Timer/Counter1 Control Register B
• Bit 7 - PWM1X: PWM Inversion Mode
When this bit is set (one), the PWM Inversion Mode is selected and the Dead Time Generator
outputs, OC1x and OC1x are inverted.
• Bit 6 - PSR1: Prescaler Reset Timer/Counter1
When this bit is set (one), the Timer/Counter1 prescaler (TCNT1 is unaffected) will be reset. The
bit will be cleared by hardware after the operation is performed. Writing a zero to this bit will have
no effect. This bit will always read as zero.
• Bits 5,4 - DTPS11, DTPS10: Dead Time Prescaler Bits
The Timer/Counter1 Control Register B is a 8-bit read/write register.
The dedicated Dead Time prescaler in front of the Dead Time Generator can divide the
Timer/Counter1 clock (PCK or CK) by 1, 2, 4 or 8 providing a large range of dead times that can
be generated. The Dead Time prescaler is controlled by two bits DTPS11 and DTPS10 from the
Dead Time Prescaler register. These bits define the division factor of the Dead Time prescaler.
The division factors are given in Table 16-14.
Bit 76543210
0x2F (0x4F) PWM1X PSR1 DTPS11 DTPS10 CS13 CS12 CS11 CS10 TCCR1B
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value00000000
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• Bits 3.. 0 - CS13, CS12, CS11, CS10: Clock Select Bits 3, 2, 1, and 0
The Clock Select bits 3, 2, 1, and 0 define the prescaling source of Timer/Counter1.
The Stop condition provides a Timer Enable/Disable function.
16.11.3 TCCR1C – Timer/Counter1 Control Register C
• Bits 7,6 - COM1A1S, COM1A0S: Comparator A Output Mode, Bits 1 and 0
These bits are the shadow bits of the COM1A1 and COM1A0 bits that are described in the sec-
tion “TCCR1A – Timer/Counter1 Control Register A” on page 115.
Table 16-14. Division factors of the Dead Time prescaler
DTPS11 DTPS10 Prescaler divides the T/C1 clock by
0 0 1x (no division)
012x
104x
118x
Table 16-15. Timer/Counter1 Prescaler Select
CS13 CS12 CS11 CS10 Asynchronous Clocking Mode Synchronous Clocking Mode
0000T/C1 stopped T/C1 stopped
0001PCK CK
0010PCK/2 CK/2
0011PCK/4 CK/4
0100PCK/8 CK/8
0101PCK/16 CK/16
0110PCK/32 CK/32
0111PCK/64 CK/64
1000PCK/128 CK/128
1001PCK/256 CK/256
1010PCK/512 CK/512
1011PCK/1024 CK/1024
1100PCK/2048 CK/2048
1101PCK/4096 CK/4096
1110PCK/8192 CK/8192
1111PCK/16384 CK/16384
Bit 76543210
0x27 (0x47) COM1A1S COM1A0S COM1B1S COM1B0S COM1D1 COM1D0 FOC1D PWM1D TCCR1C
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value 00000000
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• Bits 5,4 - COM1B1S, COM1B0S: Comparator B Output Mode, Bits 1 and 0
These bits are the shadow bits of the COM1A1 and COM1A0 bits that are described in the sec-
tion “TCCR1A – Timer/Counter1 Control Register A” on page 115.
• Bits 3,2 - COM1D1, COM1D0: Comparator D Output Mode, Bits 1 and 0
These bits control the Behavior of the Waveform Output (OCW1D) and the connection of the
Output Compare pin (OC1D). If one or both of the COM1D1:0 bits are set, the OC1D output
overrides the normal port functionality of the I/O pin it is connected to. The complementary
OC1D output is connected only in PWM modes when the COM1D1:0 bits are set to “01”. Note
that the Data Direction Register (DDR) bit corresponding to the OC1D pin must be set in order to
enable the output driver.
The function of the COM1D1:0 bits depends on the PWM1D and WGM10 bit settings. Table
16-16 shows the COM1D1:0 bit functionality when the PWM1D bit is set to a Normal Mode
(non-PWM).
Table 16-17 shows the COM1D1:0 bit functionality when the PWM1D and WGM10 bits are set
to Fast PWM Mode.
Table 16-18 on page 121 shows the COM1D1:0 bit functionality when the PWM1D and WGM10
bits are set to Phase and Frequency Correct PWM Mode.
Table 16-16. Compare Output Mode, Normal Mode (non-PWM)
COM1D1..0 OCW1D Behavior OC1D Pin OC1D Pin
00 Normal port operation. Disconnected Disconnected
01 Toggle on Compare Match. Connected Disconnected
10 Clear on Compare Match. Connected Disconnected
11 Set on Compare Match. Connected Disconnected
Table 16-17. Compare Output Mode, Fast PWM Mode
COM1D1..0 OCW1D Behavior OC1D Pin OC1D Pin
00 Normal port operation. Disconnected Disconnected
01 Cleared on Compare Match.
Set when TCNT1 = 0x000. Connected Connected
10 Cleared on Compare Match.
Set when TCNT1 = 0x000. Connected Disconnected
11 Set on Compare Match.
Clear when TCNT1 = 0x000. Connected Disconnected
121
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ATtiny261/ATtiny461/ATtiny861
• Bit 1 - FOC1D: Force Output Compare Match 1D
The FOC1D bit is only active when the PWM1D bit specify a non-PWM mode.
Writing a logical one to this bit forces a change in the Waveform Output (OCW1D) and the Out-
put Compare pin (OC1D) according to the values already set in COM1D1 and COM1D0. If
COM1D1 and COM1D0 written in the same cycle as FOC1D, the new settings will be used. The
Force Output Compare bit can be used to change the output pin value regardless of the timer
value. The automatic action programmed in COM1D1 and COM1D0 takes place as if a compare
match had occurred, but no interrupt is generated. The FOC1D bit is always read as zero.
• Bit 0 - PWM1D: Pulse Width Modulator D Enable
When set (one) this bit enables PWM mode based on comparator OCR1D.
16.11.4 TCCR1D – Timer/Counter1 Control Register D
• Bit 7 - FPIE1: Fault Protection Interrupt Enable
Setting this bit (to one) enables the Fault Protection Interrupt.
• Bit 6– FPEN1: Fault Protection Mode Enable
Setting this bit (to one) activates the Fault Protection Mode.
• Bit 5 – FPNC1: Fault Protection Noise Canceler
Setting this bit activates the Fault Protection Noise Canceler. When the noise canceler is acti-
vated, the input from the Fault Protection Pin (INT0) is filtered. The filter function requires four
successive equal valued samples of the INT0 pin for changing its output. The Fault Protection is
therefore delayed by four Oscillator cycles when the noise canceler is enabled.
• Bit 4 – FPES1: Fault Protection Edge Select
This bit selects which edge on the Fault Protection pin (INT0) is used to trigger a fault event.
When the FPES1 bit is written to zero, a falling (negative) edge is used as trigger, and when the
FPES1 bit is written to one, a rising (positive) edge will trigger the fault.
Table 16-18. Compare Output Mode, Phase and Frequency Correct PWM Mode
COM1D1..0 OCW1D Behavior OC1D Pin OC1D Pin
00 Normal port operation. Disconnected Disconnected
01 Cleared on Compare Match when up-counting.
Set on Compare Match when down-counting. Connected Connected
10 Cleared on Compare Match when up-counting.
Set on Compare Match when down-counting. Connected Disconnected
11 Set on Compare Match when up-counting.
Cleared on Compare Match when down-counting. Connected Disconnected
Bit 76543210
0x26 (0x46) FPIE1 FPEN1 FPNC1 FPES1 FPAC1 FPF1 WGM11 WGM10 TCCR1D
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value 00000000
122
7753F–AVR–01/11
ATtiny261/ATtiny461/ATtiny861
• Bit 3 - FPAC1: Fault Protection Analog Comparator Enable
When written logic one, this bit enables the Fault Protection function in Timer/Counter1 to be
triggered by the Analog Comparator. The comparator output is in this case directly connected to
the Fault Protection front-end logic, making the comparator utilize the noise canceler and edge
select features of the Timer/Counter1 Fault Protection interrupt. When written logic zero, no con-
nection between the Analog Comparator and the Fault Protection function exists. To make the
comparator trigger the Timer/Counter1 Fault Protection interrupt, the FPIE1 bit in the
Timer/Counter1 Control Register D (TCCR1D) must be set.
• Bit 2- FPF1: Fault Protection Interrupt Flag
When the FPIE1 bit is set (one), the Fault Protection Interrupt is enabled. Activity on the pin will
cause an interrupt request even, if the Fault Protection pin is configured as an output. The corre-
sponding interrupt of Fault Protection Interrupt Request is executed from the Fault Protection
Interrupt Vector. The bit FPF1 is cleared by hardware when executing the corresponding inter-
rupt handling vector. Alternatively, FPF1 is cleared after a synchronization clock cycle by writing
a logical one to the flag. When the SREG I-bit, FPIE1 and FPF1 are set, the Fault Interrupt is
executed.
• Bits 1:0 - WGM11, WGM10: Waveform Generation Mode Bits
This bit associated with the PWMx bits control the counting sequence of the counter, the source
for type of waveform generation to be used, see Table 16-19. Modes of operation supported by
the Timer/Counter1 are: Normal mode (counter), Fast PWM Mode, Phase and Frequency Cor-
rect PWM and PWM6 Modes.
16.11.5 TCCR1E – Timer/Counter1 Control Register E
• Bits 7:6 - Res: Reserved Bits
These bits are reserved bits in the ATtiny261/461/861 and always reads as zero.
• Bits 5:0 – OC1OE5:OC1OE0: Output Compare Override Enable Bits
These bits are the Output Compare Override Enable bits that are used to connect or disconnect
the Output Compare Pins in PWM6 Modes with an instant response on the corresponding Out-
put Compare Pins.
Table 16-19. Waveform Generation Mode Bit Description
PWM1x WGM11..10 Timer/Counter Mode of Operation TOP
Update of
OCR1x at
TOV1 Flag
Set on
0 xx Normal OCR1C Immediate TOP
1 00 Fast PWM OCR1C TOP TOP
1 01 Phase and Frequency Correct PWM OCR1C BOTTOM BOTTOM
1 10 PWM6 / Single-slope OCR1C TOP TOP
1 11 PWM6 / Dual-slope OCR1C BOTTOM BOTTOM
Bit 76543210
0x00 (0x20) - - OC1OE5 OC1OE4 OC1OE3 OC1OE2 OC1OE1 OC1OE0 TCCR1E
Read/Write R R R/W R/W R/W R/W R/W R/W
Initial value 00000000
123
7753F–AVR–01/11
ATtiny261/ATtiny461/ATtiny861
The actual value from the port register will be visible on the port pin, when the Output Compare
Override Enable Bit is cleared. Table 16-20 shows the Output Compare Override Enable Bits
and their corresponding Output Compare pins.
16.11.6 TCNT1 – Timer/Counter1
This 8-bit register contains the value of Timer/Counter1.
The Timer/Counter1 is realized as a 10-bit up/down counter with read and write access. Due to
synchronization of the CPU, Timer/Counter1 data written into Timer/Counter1 is delayed by one
and half CPU clock cycles in synchronous mode and at most one CPU clock cycles for asyn-
chronous mode. When a 10-bit accuracy is preferred, special procedures must be followed for
accessing the 10-bit TCNT1 register via the 8-bit AVR data bus. These procedures are
described in section “Accessing 10-Bit Registers” on page 112. Alternatively the Timer/Counter1
can be used as an 8-bit Timer/Counter. Note that the Timer/Counter1 always starts counting up
after writing the TCNT1 register.
16.11.7 TC1H – Timer/Counter1 High Byte
The temporary Timer/Counter1 register is an 2-bit read/write register.
• Bits 7:2 - Res: Reserved Bits
These bits are reserved bits in the ATtiny261/461/861 and always reads as zero.
• Bits 1:0 - TC19, TC18: Two MSB bits of the 10-bit accesses
If 10-bit accuracy is used, the Timer/Counter1 High Byte Register (TC1H) is used for temporary
storing the MSB bits (TC19, TC18) of the 10-bit accesses. The same TC1H register is shared
between all 10-bit registers within the Timer/Counter1. Note that special procedures must be fol-
lowed when accessing the 10-bit TCNT1 register via the 8-bit AVR data bus. These procedures
are described in section “Accessing 10-Bit Registers” on page 112.
Table 16-20. Output Compare Override Enable Bits vs. Output Compare Pins
OC1OE0 OC1OE1 OC1OE2 OC1OE3 OC1OE4 OC1OE5
OC1A (PB0) OC1A (PB1) OC1B (PB2) OC1B (PB3) OC1D (PB4) OC1D (PB5)
Bit 76543210
0x2E (0x4E) MSB LSB TCNT1
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value00000000
Bit 76543210
0x25 (0x45) ------TC19TC18TC1H
Read/WriteRRRRRRR/WR/W
Initial value00000000
124
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ATtiny261/ATtiny461/ATtiny861
16.11.8 OCR1A – Timer/Counter1 Output Compare Register A
The output compare register A is an 8-bit read/write register.
The Timer/Counter Output Compare Register A contains data to be continuously compared with
Timer/Counter1. Actions on compare matches are specified in TCCR1A. A compare match does
only occur if Timer/Counter1 counts to the OCR1A value. A software write that sets TCNT1 and
OCR1A to the same value does not generate a compare match.
A compare match will set the compare interrupt flag OCF1A after a synchronization delay follow-
ing the compare event.
Note that, if 10-bit accuracy is used special procedures must be followed when accessing the
internal 10-bit Output Compare Registers via the 8-bit AVR data bus. These procedures are
described in section “Accessing 10-Bit Registers” on page 112.
16.11.9 OCR1B – Timer/Counter1 Output Compare Register B
The output compare register B is an 8-bit read/write register.
The Timer/Counter Output Compare Register B contains data to be continuously compared with
Timer/Counter1. Actions on compare matches are specified in TCCR1. A compare match does
only occur if Timer/Counter1 counts to the OCR1B value. A software write that sets TCNT1 and
OCR1B to the same value does not generate a compare match.
A compare match will set the compare interrupt flag OCF1B after a synchronization delay follow-
ing the compare event.
Note that, if 10-bit accuracy is used special procedures must be followed when accessing the
internal 10-bit Output Compare Registers via the 8-bit AVR data bus. These procedures are
described in section “Accessing 10-Bit Registers” on page 112.
16.11.10 OCR1C – Timer/Counter1 Output Compare Register C
The output compare register C is an 8-bit read/write register.
The Timer/Counter Output Compare Register C contains data to be continuously compared with
Timer/Counter1, and a compare match will clear TCNT1. This register has the same function in
Normal mode and PWM modes.
Bit 76543210
0x2D (0x4D) MSB LSB OCR1A
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value00000000
Bit 76543210
0x2C (0x4C) MSB LSB OCR1B
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value00000000
Bit 76543210
0x2B (0x4B) MSB LSB OCR1C
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value11111111
125
7753F–AVR–01/11
ATtiny261/ATtiny461/ATtiny861
Note that, if a smaller value than three is written to the Output Compare Register C, the value is
automatically replaced by three as it is a minimum value allowed to be written to this register.
Note that, if 10-bit accuracy is used special procedures must be followed when accessing the
internal 10-bit Output Compare Registers via the 8-bit AVR data bus. These procedures are
described in section “Accessing 10-Bit Registers” on page 112.
16.11.11 OCR1D – Timer/Counter1 Output Compare Register D
The output compare register D is an 8-bit read/write register.
The Timer/Counter Output Compare Register D contains data to be continuously compared with
Timer/Counter1. Actions on compare matches are specified in TCCR1A. A compare match does
only occur if Timer/Counter1 counts to the OCR1D value. A software write that sets TCNT1 and
OCR1D to the same value does not generate a compare match.
A compare match will set the compare interrupt flag OCF1D after a synchronization delay follow-
ing the compare event.
Note that, if 10-bit accuracy is used special procedures must be followed when accessing the
internal 10-bit Output Compare Registers via the 8-bit AVR data bus. These procedures are
described in section “Accessing 10-Bit Registers” on page 112.
16.11.12 TIMSK – Timer/Counter1 Interrupt Mask Register
• Bit 7- OCIE1D: Timer/Counter1 Output Compare Interrupt Enable
When the OCIE1D bit is set (one) and the I-bit in the Status Register is set (one), the
Timer/Counter1 Compare MatchD, interrupt is enabled. The corresponding interrupt at vector
$010 is executed if a compare matchD occurs. The Compare Flag in Timer/Counter1 is set (one)
in the Timer/Counter Interrupt Flag Register.
• Bit 6 - OCIE1A: Timer/Counter1 Output Compare Interrupt Enable
When the OCIE1A bit is set (one) and the I-bit in the Status Register is set (one), the
Timer/Counter1 Compare MatchA, interrupt is enabled. The corresponding interrupt at vector
$003 is executed if a compare matchA occurs. The Compare Flag in Timer/Counter1 is set (one)
in the Timer/Counter Interrupt Flag Register.
• Bit 5 - OCIE1B: Timer/Counter1 Output Compare Interrupt Enable
When the OCIE1B bit is set (one) and the I-bit in the Status Register is set (one), the
Timer/Counter1 Compare MatchB, interrupt is enabled. The corresponding interrupt at vector
$009 is executed if a compare matchB occurs. The Compare Flag in Timer/Counter1 is set (one)
in the Timer/Counter Interrupt Flag Register.
Bit 76543210
0x2A (0x4A) MSB LSB OCR1D
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value00000000
Bit 76543210
0x39 (0x59) OCIE1D OCIE1A OCIE1B OCIE0A OCIE0B TOIE1 TOIE0 TICIE0 TIMSK
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value00000000
126
7753F–AVR–01/11
ATtiny261/ATtiny461/ATtiny861
• Bit 2 - TOIE1: Timer/Counter1 Overflow Interrupt Enable
When the TOIE1 bit is set (one) and the I-bit in the Status Register is set (one), the
Timer/Counter1 Overflow interrupt is enabled. The corresponding interrupt (at vector $004) is
executed if an overflow in Timer/Counter1 occurs. The Overflow Flag (Timer1) is set (one) in the
Timer/Counter Interrupt Flag Register - TIFR.
16.11.13 TIFR – Timer/Counter1 Interrupt Flag Register
• Bit 7- OCF1D: Output Compare Flag 1D
The OCF1D bit is set (one) when compare match occurs between Timer/Counter1 and the data
value in OCR1D - Output Compare Register 1D. OCF1D is cleared by hardware when executing
the corresponding interrupt handling vector. Alternatively, OCF1D is cleared, after synchroniza-
tion clock cycle, by writing a logic one to the flag. When the I-bit in SREG, OCIE1D, and OCF1D
are set (one), the Timer/Counter1 D compare match interrupt is executed.
• Bit 6 - OCF1A: Output Compare Flag 1A
The OCF1A bit is set (one) when compare match occurs between Timer/Counter1 and the data
value in OCR1A - Output Compare Register 1A. OCF1A is cleared by hardware when executing
the corresponding interrupt handling vector. Alternatively, OCF1A is cleared, after synchroniza-
tion clock cycle, by writing a logic one to the flag. When the I-bit in SREG, OCIE1A, and OCF1A
are set (one), the Timer/Counter1 A compare match interrupt is executed.
• Bit 5 - OCF1B: Output Compare Flag 1B
The OCF1B bit is set (one) when compare match occurs between Timer/Counter1 and the data
value in OCR1B - Output Compare Register 1A. OCF1B is cleared by hardware when executing
the corresponding interrupt handling vector. Alternatively, OCF1B is cleared, after synchroniza-
tion clock cycle, by writing a logic one to the flag. When the I-bit in SREG, OCIE1B, and OCF1B
are set (one), the Timer/Counter1 B compare match interrupt is executed.
• Bit 2 - TOV1: Timer/Counter1 Overflow Flag
In Normal Mode and Fast PWM Mode the TOV1 bit is set (one) each time the counter reaches
TOP at the same clock cycle when the counter is reset to BOTTOM. In Phase and Frequency
Correct PWM Mode the TOV1 bit is set (one) each time the counter reaches BOTTOM at the
same clock cycle when zero is clocked to the counter.
The bit TOV1 is cleared by hardware when executing the corresponding interrupt handling vec-
tor. Alternatively, TOV1 is cleared, after synchronization clock cycle, by writing a logical one to
the flag. When the SREG I-bit, and TOIE1 (Timer/Counter1 Overflow Interrupt Enable), and
TOV1 are set (one), the Timer/Counter1 Overflow interrupt is executed.
Bit 76543210
0x38 (0x58) OCF1D OCF1A OCF1B OCF0A OCF0B TOV1 TOV0 ICF0 TIFR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value00000000
127
7753F–AVR–01/11
ATtiny261/ATtiny461/ATtiny861
16.11.14 DT1 – Timer/Counter1 Dead Time Value
The dead time value register is an 8-bit read/write register.
The dead time delay of all Timer/Counter1 channels are adjusted by the dead time value regis-
ter, DT1. The register consists of two fields, DT1H3..0 and DT1L3..0, one for each
complementary output. Therefore a different dead time delay can be adjusted for the rising edge
of OC1x and the rising edge of OC1x.
• Bits 7:4- DT1H3:DT1H0: Dead Time Value for OC1x Output
The dead time value for the OC1x output. The dead time delay is set as a number of the pres-
caled timer/counter clocks. The minimum dead time is zero and the maximum dead time is the
prescaled time/counter clock period multiplied by 15.
• Bits 3:0- DT1L3:DT1L0: Dead Time Value for OC1x Output
The dead time value for the OC1x output. The dead time delay is set as a number of the pres-
caled timer/counter clocks. The minimum dead time is zero and the maximum dead time is the
prescaled time/counter clock period multiplied by 15.
Bit 76543210
0x24 (0x44) DT1H3 DT1H2 DT1H1 DT1H0 DT1L3 DT1L2 DT1L1 DT1L0 DT1
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value 00000000
128
7753F–AVR–01/11
ATtiny261/ATtiny461/ATtiny861
17. USI – Universal Serial Interface
17.1 Features •Two-wire Synchronous Data Transfer (Master or Slave)
•Three-wire Synchronous Data Transfer (Master or Slave)
•Data Received Interrupt
•Wakeup from Idle Mode
•In Two-wire Mode: Wake-up from All Sleep Modes, Including Power-down Mode
•Two-wire Start Condition Detector with Interrupt Capability
17.2 Overview
The Universal Serial Interface, or USI, provides the basic hardware resources needed for serial
communication. Combined with a minimum of control software, the USI allows significantly
higher transfer rates and uses less code space than solutions based on software only. Interrupts
are included to minimize the processor load.
A simplified block diagram of the USI is shown on Figure 17-1. For the actual placement of I/O
pins, refer to “Pinout ATtiny261/461/861” on page 2. CPU accessible I/O Registers, including I/O
bits and I/O pins, are shown in bold. The device-specific I/O Register and bit locations are listed
in the “Register Descriptions” on page 135.
Figure 17-1. Universal Serial Interface, Block Diagram
Q
3
2
1
0
LE
2
USIDR
D
TIM0 COMP
USCK/ SCL
Two-wire Clock
Control Unit
CLOCK
HOLD
DATA BUS
[1]
Bit0
Bit7
USISIF
USIOIF
USIPF
USIDC
USIBR
USISR
4-bit Counter
DI/ SDA
DO (Output only)
(Input/ Open Drain))
(Input/ Open Drain))
3
2
1
0
1
0
USISIE
USIOIE
USIWM1
USIWM0
USICS1
USICS0
USICLK
USITC
USICR
129
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ATtiny261/ATtiny461/ATtiny861
The 8-bit USI Data Register is directly accessible via the data bus and contains the incoming
and outgoing data. The register has no buffering so the data must be read as quickly as possible
to ensure that no data is lost. The USI Data Register is a serial shift register and the most signif-
icant bit that is the output of the serial shift register is connected to one of two output pins
depending of the wire mode configuration. A transparent latch is inserted between the USI Data
Register Output and output pin, which delays the change of data output to the opposite clock
edge of the data input sampling. The serial input is always sampled from the Data Input (DI) pin
independent of the configuration.
The 4-bit counter can be both read and written via the data bus, and can generate an overflow
interrupt. Both the USI Data Register and the counter are clocked simultaneously by the same
clock source. This allows the counter to count the number of bits received or transmitted and
generate an interrupt when the transfer is complete. Note that when an external clock source is
selected the counter counts both clock edges. In this case the counter counts the number of
edges, and not the number of bits. The clock can be selected from three different sources: The
USCK pin, Timer/Counter0 Compare Match or from software.
The Two-wire clock control unit can generate an interrupt when a start condition is detected on
the Two-wire bus. It can also generate wait states by holding the clock pin low after a start con-
dition is detected, or after the counter overflows.
17.3 Functional Descriptions
17.3.1 Three-wire Mode
The USI Three-wire mode is compliant to the Serial Peripheral Interface (SPI) mode 0 and 1, but
does not have the slave select (SS) pin functionality. However, this feature can be implemented
in software if necessary. Pin names used by this mode are: DI, DO, and USCK.
Figure 17-2. Three-wire Mode Operation, Simplified Diagram
Bit7
DI
USCK
USCK
DO
PORTxn
SLAVE
Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
Bit7
DI
DO
MASTER
Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
130
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ATtiny261/ATtiny461/ATtiny861
Figure 17-2 shows two USI units operating in Three-wire mode, one as Master and one as
Slave. The two USI Data Register are interconnected in such way that after eight USCK clocks,
the data in each register are interchanged. The same clock also increments the USI’s 4-bit coun-
ter. The Counter Overflow (interrupt) Flag, or USIOIF, can therefore be used to determine when
a transfer is completed. The clock is generated by the Master device software by toggling the
USCK pin via the PORT Register or by writing a one to the USITC bit in USICR.
Figure 17-3. Three-wire Mode, Timing Diagram
The Three-wire mode timing is shown in Figure 17-3. At the top of the figure is a USCK cycle ref-
erence. One bit is shifted into the USI Data Register (USIDR) for each of these cycles. The
USCK timing is shown for both external clock modes. In External Clock mode 0 (USICS0 = 0), DI
is sampled at positive edges, and DO is changed (Data Register is shifted by one) at negative
edges. External Clock mode 1 (USICS0 = 1) uses the opposite edges versus mode 0, i.e., sam-
ples data at negative and changes the output at positive edges. The USI clock modes
corresponds to the SPI data mode 0 and 1.
Referring to the timing diagram (Figure 17-3.), a bus transfer involves the following steps:
1. The Slave device and Master device sets up its data output and, depending on the proto-
col used, enables its output driver (mark A and B). The output is set up by writing the
data to be transmitted to the USI Data Register. Enabling of the output is done by setting
the corresponding bit in the port Data Direction Register. Note that point A and B does
not have any specific order, but both must be at least one half USCK cycle before point C
where the data is sampled. This must be done to ensure that the data setup requirement
is satisfied. The 4-bit counter is reset to zero.
2. The Master generates a clock pulse by software toggling the USCK line twice (C and D).
The bit value on the slave and master’s data input (DI) pin is sampled by the USI on the
first edge (C), and the data output is changed on the opposite edge (D). The 4-bit counter
will count both edges.
3. Step 2. is repeated eight times for a complete register (byte) transfer.
4. After eight clock pulses (i.e., 16 clock edges) the counter will overflow and indicate that
the transfer is completed. The data bytes transferred must now be processed before a
new transfer can be initiated. The overflow interrupt will wake up the processor if it is set
to Idle mode. Depending of the protocol used the slave device can now set its output to
high impedance.
12
6MSB 54321LSB
345678
6MSB
CYCLE
(Reference)
USCK
USCK
54321LSB
A B C D E
DI
DO
131
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ATtiny261/ATtiny461/ATtiny861
17.3.2 SPI Master Operation Example
The following code demonstrates how to use the USI module as a SPI Master:
SPITransfer:
sts USIDR,r16
ldi r16,(1<<USIOIF)
sts USISR,r16
ldi r16,(1<<USIWM0)|(1<<USICS1)|(1<<USICLK)|(1<<USITC)
SPITransfer_loop:
sts USICR,r16
lds r16, USISR
sbrs r16, USIOIF
rjmp SPITransfer_loop
lds r16,USIDR
ret
The code is size optimized using only eight instructions (+ ret). The code example assumes that
the DO and USCK pins are enabled as output in the DDRA or DDRB Register. The value stored
in register r16 prior to the function is called is transferred to the Slave device, and when the
transfer is completed the data received from the Slave is stored back into the r16 Register.
The second and third instructions clears the USI Counter Overflow Flag and the USI counter
value. The fourth and fifth instruction set Three-wire mode, positive edge Shift Register clock,
count at USITC strobe, and toggle USCK. The loop is repeated 16 times.
The following code demonstrates how to use the USI module as a SPI Master with maximum
speed (fsck = fck/4):
SPITransfer_Fast:
sts USIDR,r16
ldi r16,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)
ldi r17,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)|(1<<USICLK)
sts USICR,r16 ; MSB
sts USICR,r17
sts USICR,r16
sts USICR,r17
sts USICR,r16
sts USICR,r17
sts USICR,r16
sts USICR,r17
sts USICR,r16
sts USICR,r17
sts USICR,r16
sts USICR,r17
sts USICR,r16
sts USICR,r17
sts USICR,r16; LSB
sts USICR,r17
lds r16,USIDR
ret
132
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ATtiny261/ATtiny461/ATtiny861
17.3.3 SPI Slave Operation Example
The following code demonstrates how to use the USI module as a SPI Slave:
init:
ldi r16,(1<<USIWM0)|(1<<USICS1)
sts USICR,r16
...
SlaveSPITransfer:
sts USIDR,r16
ldi r16,(1<<USIOIF)
sts USISR,r16
SlaveSPITransfer_loop:
lds r16, USISR
sbrs r16, USIOIF
rjmp SlaveSPITransfer_loop
lds r16,USIDR
ret
The code is size optimized using only eight instructions (+ ret). The code example assumes that
the DO is configured as output and USCK pin is configured as input in the DDR Register. The
value stored in register r16 prior to the function is called is transferred to the master device, and
when the transfer is completed the data received from the Master is stored back into the r16
Register.
Note that the first two instructions is for initialization only and needs only to be executed
once.These instructions sets Three-wire mode and positive edge USI Data Register clock. The
loop is repeated until the USI Counter Overflow Flag is set.
17.3.4 Two-wire Mode
The USI Two-wire mode is compliant to the Inter IC (TWI) bus protocol, but without slew rate lim-
iting on outputs and input noise filtering. Pin names used by this mode are SCL and SDA.
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Figure 17-4. Two-wire Mode Operation, Simplified Diagram
Figure 17-4 shows two USI units operating in Two-wire mode, one as Master and one as Slave.
It is only the physical layer that is shown since the system operation is highly dependent of the
communication scheme used. The main differences between the Master and Slave operation at
this level, is the serial clock generation which is always done by the Master, and only the Slave
uses the clock control unit. Clock generation must be implemented in software, but the shift
operation is done automatically by both devices. Note that only clocking on negative edge for
shifting data is of practical use in this mode. The slave can insert wait states at start or end of
transfer by forcing the SCL clock low. This means that the Master must always check if the SCL
line was actually released after it has generated a positive edge.
Since the clock also increments the counter, a counter overflow can be used to indicate that the
transfer is completed. The clock is generated by the master by toggling the USCK pin via the
PORT Register.
The data direction is not given by the physical layer. A protocol, like the one used by the
TWI-bus, must be implemented to control the data flow.
Figure 17-5. Two-wire Mode, Typical Timing Diagram
Bit7
SDA
SCL
HOLD
SCL
SLAVE
Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
Two-wire
Clock
Control Unit
VCC
Bit7
SDA
SCL
MASTER
Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
PORTxn
1 to 7 8
SADDRESS R/W ACK DATA ACK ACKDATA
1 to 8 9 1 to 8 99
A B C D E F
SDA
SCL
P
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Referring to the timing diagram (Figure 17-5.), a bus transfer involves the following steps:
1. The a start condition is generated by the Master by forcing the SDA low line while the
SCL line is high (A). SDA can be forced low either by writing a zero to bit 7 of the Shift
Register, or by setting the corresponding bit in the PORT Register to zero. Note that the
USI Data Register bit must be set to one for the output to be enabled. The slave device’s
start detector logic (Figure 17-6.) detects the start condition and sets the USISIF Flag.
The flag can generate an interrupt if necessary.
2. In addition, the start detector will hold the SCL line low after the Master has forced an
negative edge on this line (B). This allows the Slave to wake up from sleep or complete
its other tasks before setting up the USI Data Register to receive the address. This is
done by clearing the start condition flag and reset the counter.
3. The Master set the first bit to be transferred and releases the SCL line (C). The Slave
samples the data and shift it into the USI Data Register at the positive edge of the SCL
clock.
4. After eight bits are transferred containing slave address and data direction (read or
write), the Slave counter overflows and the SCL line is forced low (D). If the slave is not
the one the Master has addressed, it releases the SCL line and waits for a new start
condition.
5. If the Slave is addressed it holds the SDA line low during the acknowledgment cycle
before holding the SCL line low again (i.e., the Counter Register must be set to 14 before
releasing SCL at (D)). Depending of the R/W bit the Master or Slave enables its output. If
the bit is set, a master read operation is in progress (i.e., the slave drives the SDA line)
The slave can hold the SCL line low after the acknowledge (E).
6. Multiple bytes can now be transmitted, all in same direction, until a stop condition is given
by the Master (F). Or a new start condition is given.
If the Slave is not able to receive more data it does not acknowledge the data byte it has last
received. When the Master does a read operation it must terminate the operation by force the
acknowledge bit low after the last byte transmitted.
Figure 17-6. Start Condition Detector, Logic Diagram
17.3.5 Start Condition Detector
The start condition detector is shown in Figure 17-6. The SDA line is delayed (in the range of 50
to 300 ns) to ensure valid sampling of the SCL line. The start condition detector is only enabled
in Two-wire mode.
The start condition detector is working asynchronously and can therefore wake up the processor
from the Power-down sleep mode. However, the protocol used might have restrictions on the
SCL hold time. Therefore, when using this feature in this case the Oscillator start-up time set by
the CKSEL Fuses (see “Clock Systems and their Distribution” on page 25) must also be taken
into the consideration. Refer to the USISIF bit description on page 136 for further details.
Q
SDA
SCL
Write (USISIF)
D
CLR
QD
USISIF
CLOCK
HOLD
CLR
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17.4 Alternative USI Usage
When the USI unit is not used for serial communication, it can be set up to do alternative tasks
due to its flexible design.
17.4.1 Half-duplex Asynchronous Data Transfer
By utilizing the USI Data Register in Three-wire mode, it is possible to implement a more com-
pact and higher performance UART than by software only.
17.4.2 4-bit Counter
The 4-bit counter can be used as a stand-alone counter with overflow interrupt. Note that if the
counter is clocked externally, both clock edges will generate an increment.
17.4.3 12-bit Timer/Counter
Combining the USI 4-bit counter and Timer/Counter0 allows them to be used as a 12-bit
counter.
17.4.4 Edge Triggered External Interrupt
By setting the counter to maximum value (F) it can function as an additional external interrupt.
The Overflow Flag and Interrupt Enable bit are then used for the external interrupt. This feature
is selected by the USICS1 bit.
17.4.5 Software Interrupt
The counter overflow interrupt can be used as a software interrupt triggered by a clock strobe.
17.5 Register Descriptions
17.5.1 USIDR – USI Data Register
When accessing the USI Data Register (USIDR) the Serial Register can be accessed directly. If
a serial clock occurs at the same cycle the register is written, the register will contain the value
written and no shift is performed. A (left) shift operation is performed depending of the
USICS1..0 bits setting. The shift operation can be controlled by an external clock edge, by a
Timer/Counter0 Compare Match, or directly by software using the USICLK strobe bit. Note that
even when no wire mode is selected (USIWM1..0 = 0) both the external data input (DI/SDA) and
the external clock input (USCK/SCL) can still be used by the USI Data Register.
The output pin in use, DO or SDA depending on the wire mode, is connected via the output latch
to the most significant bit (bit 7) of the Data Register. The output latch is open (transparent) dur-
ing the first half of a serial clock cycle when an external clock source is selected (USICS1 = 1),
and constantly open when an internal clock source is used (USICS1 = 0). The output will be
changed immediately when a new MSB written as long as the latch is open. The latch ensures
that data input is sampled and data output is changed on opposite clock edges.
Note that the corresponding Data Direction Register to the pin must be set to one for enabling
data output from the USI Data Register.
Bit 7654 3210
0x0F (0x2F) MSB LSB USIDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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17.5.2 USIBR – USI Buffer Register
The content of the Serial Register is loaded to the USI Buffer Register when the transfer is com-
pleted, and instead of accessing the USI Data Register (the Serial Register) the USI Data Buffer
can be accessed when the CPU reads the received data. This gives the CPU time to handle
other program tasks too as the controlling of the USI is not so timing critical. The USI flags as set
same as when reading the USIDR register.
17.5.3 USISR – USI Status Register
The Status Register contains Interrupt Flags, line Status Flags and the counter value.
• Bit 7 – USISIF: Start Condition Interrupt Flag
When Two-wire mode is selected, the USISIF Flag is set (to one) when a start condition is
detected. When output disable mode or Three-wire mode is selected and (USICSx = 0b11 &
USICLK = 0) or (USICS = 0b10 & USICLK = 0), any edge on the SCK pin sets the flag.
An interrupt will be generated when the flag is set while the USISIE bit in USICR and the Global
Interrupt Enable Flag are set. The flag will only be cleared by writing a logical one to the USISIF
bit. Clearing this bit will release the start detection hold of USCL in Two-wire mode.
A start condition interrupt will wakeup the processor from all sleep modes.
• Bit 6 – USIOIF: Counter Overflow Interrupt Flag
This flag is set (one) when the 4-bit counter overflows (i.e., at the transition from 15 to 0). An
interrupt will be generated when the flag is set while the USIOIE bit in USICR and the Global
Interrupt Enable Flag are set. The flag will only be cleared if a one is written to the USIOIF bit.
Clearing this bit will release the counter overflow hold of SCL in Two-wire mode.
A counter overflow interrupt will wake up the processor from Idle sleep mode.
• Bit 5 – USIPF: Stop Condition Flag
When Two-wire mode is selected, the USIPF Flag is set (one) when a stop condition is detected.
The flag is cleared by writing a one to this bit. Note that this is not an Interrupt Flag. This signal is
useful when implementing Two-wire bus master arbitration.
• Bit 4 – USIDC: Data Output Collision
This bit is logical one when bit 7 in the USI Data Register differs from the physical pin value. The
flag is only valid when Two-wire mode is used. This signal is useful when implementing
Two-wire bus master arbitration.
• Bits 3:0 – USICNT3..0: Counter Value
These bits reflect the current 4-bit counter value. The 4-bit counter value can directly be read or
written by the CPU.
Bit 7 6 5 4 3 2 1 0
0x10 (0x30) MSB LSB USIBR
Read/Write R R R R R R R R
Initial Value 0 0 0 0 0 0 0 0
Bit 7654 3 2 1 0
0x0E (0x2E) USISIF USIOIF USIPF USIDC USICNT3 USICNT2 USICNT1 USICNT0 USISR
Read/Write R/W R/W R/W R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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The 4-bit counter increments by one for each clock generated either by the external clock edge
detector, by a Timer/Counter0 Compare Match, or by software using USICLK or USITC strobe
bits. The clock source depends of the setting of the USICS1..0 bits. For external clock operation
a special feature is added that allows the clock to be generated by writing to the USITC strobe
bit. This feature is enabled by write a one to the USICLK bit while setting an external clock
source (USICS1 = 1).
Note that even when no wire mode is selected (USIWM1..0 = 0) the external clock input
(USCK/SCL) are can still be used by the counter.
17.5.4 USICR – USI Control Register
The Control Register includes interrupt enable control, wire mode setting, Clock Select setting,
and clock strobe.
• Bit 7 – USISIE: Start Condition Interrupt Enable
Setting this bit to one enables the Start Condition detector interrupt. If there is a pending inter-
rupt when the USISIE and the Global Interrupt Enable Flag is set to one, this will immediately be
executed. Refer to the USISIF bit description on page 136 for further details.
• Bit 6 – USIOIE: Counter Overflow Interrupt Enable
Setting this bit to one enables the Counter Overflow interrupt. If there is a pending interrupt when
the USIOIE and the Global Interrupt Enable Flag is set to one, this will immediately be executed.
Refer to the USIOIF bit description on page 136 for further details.
• Bit 5:4 – USIWM1:0: Wire Mode
These bits set the type of wire mode to be used. Basically only the function of the outputs are
affected by these bits. Data and clock inputs are not affected by the mode selected and will
always have the same function. The counter and USI Data Register can therefore be clocked
externally, and data input sampled, even when outputs are disabled. The relations between
USIWM1:0 and the USI operation is summarized in Table 17-1.
Bit 7 6 5 4 3 2 1 0
0x0D (0x2D) USISIE USIOIE USIWM1 USIWM0 USICS1 USICS0 USICLK USITC USICR
Read/Write R/W R/W R/W R/W R/W R/W W W
Initial Value 0 0 0 0 0 0 0 0
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Note: 1. The DI and USCK pins are renamed to Serial Data (SDA) and Serial Clock (SCL) respectively
to avoid confusion between the modes of operation.
• Bit 3:2 – USICS1:0: Clock Source Select
These bits set the clock source for the USI Data Register and counter. The data output latch
ensures that the output is changed at the opposite edge of the sampling of the data input
(DI/SDA) when using external clock source (USCK/SCL). When software strobe or
Timer/Counter0 Compare Match clock option is selected, the output latch is transparent and
therefore the output is changed immediately. Clearing the USICS1:0 bits enables software
strobe option. When using this option, writing a one to the USICLK bit clocks both the USI Data
Register and the counter. For external clock source (USICS1 = 1), the USICLK bit is no longer
used as a strobe, but selects between external clocking and software clocking by the USITC
strobe bit.
Table 17-2 on page 139 shows the relationship between the USICS1..0 and USICLK setting and
clock source used for the USI Data Register and the 4-bit counter.
Table 17-1. Relations between USIWM1..0 and the USI Operation
USIWM1 USIWM0 Description
0 0 Outputs, clock hold, and start detector disabled. Port pins operates as normal.
01
Three-wire mode. Uses DO, DI, and USCK pins.
The Data Output (DO) pin overrides the corresponding bit in the PORT Register in
this mode. However, the corresponding DDR bit still controls the data direction.
When the port pin is set as input the pins pull-up is controlled by the PORT bit.
The Data Input (DI) and Serial Clock (USCK) pins do not affect the normal port
operation. When operating as master, clock pulses are software generated by
toggling the PORT Register, while the data direction is set to output. The USITC
bit in the USICR Register can be used for this purpose.
10
Two-wire mode. Uses SDA (DI) and SCL (USCK) pins(1).
The Serial Data (SDA) and the Serial Clock (SCL) pins are bi-directional and uses
open-collector output drives. The output drivers are enabled by setting the
corresponding bit for SDA and SCL in the DDR Register.
When the output driver is enabled for the SDA pin, the output driver will force the
line SDA low if the output of the USI Data Register or the corresponding bit in the
PORT Register is zero. Otherwise the SDA line will not be driven (i.e., it is
released). When the SCL pin output driver is enabled the SCL line will be forced
low if the corresponding bit in the PORT Register is zero, or by the start detector.
Otherwise the SCL line will not be driven.
The SCL line is held low when a start detector detects a start condition and the
output is enabled. Clearing the Start Condition Flag (USISIF) releases the line.
The SDA and SCL pin inputs is not affected by enabling this mode. Pull-ups on the
SDA and SCL port pin are disabled in Two-wire mode.
11
Two-wire mode. Uses SDA and SCL pins.
Same operation as for the Two-wire mode described above, except that the SCL
line is also held low when a counter overflow occurs, and is held low until the
Counter Overflow Flag (USIOIF) is cleared.
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• Bit 1 – USICLK: Clock Strobe
Writing a one to this bit location strobes the USI Data Register to shift one step and the counter
to increment by one, provided that the USICS1..0 bits are set to zero and by doing so the soft-
ware clock strobe option is selected. The output will change immediately when the clock strobe
is executed, i.e., in the same instruction cycle. The value shifted into the USI Data Register is
sampled the previous instruction cycle. The bit will be read as zero.
When an external clock source is selected (USICS1 = 1), the USICLK function is changed from
a clock strobe to a Clock Select Register. Setting the USICLK bit in this case will select the
USITC strobe bit as clock source for the 4-bit counter (see Table 17-2).
• Bit 0 – USITC: Toggle Clock Port Pin
Writing a one to this bit location toggles the USCK/SCL value either from 0 to 1, or from 1 to 0.
The toggling is independent of the setting in the Data Direction Register, but if the PORT value is
to be shown on the pin the DDB2 must be set as output (to one). This feature allows easy clock
generation when implementing master devices. The bit will be read as zero.
When an external clock source is selected (USICS1 = 1) and the USICLK bit is set to one, writ-
ing to the USITC strobe bit will directly clock the 4-bit counter. This allows an early detection of
when the transfer is done when operating as a master device.
17.5.5 USIPP – USI Pin Position
• Bits 7:1 – Res: Reserved Bits
These bits are reserved bits in the ATtiny261/461/861 and always reads as zero.
• Bit 0 – USIPOS: USI Pin Position
Setting this bit to one changes the USI pin position. As default pins PB2..PB0 are used for the
USI pin functions, but when writing this bit to one the USIPOS bit is set the USI pin functions are
on pins PA2..PA0.
Table 17-2. Relations between the USICS1..0 and USICLK Setting
USICS1 USICS0 USICLK
USI Data Register Clock
Source 4-bit Counter Clock Source
0 0 0 No Clock No Clock
001
Software clock strobe
(USICLK)
Software clock strobe
(USICLK)
01X
Timer/Counter0 Compare
Match
Timer/Counter0 Compare
Match
1 0 0 External, positive edge External, both edges
1 1 0 External, negative edge External, both edges
1 0 1 External, positive edge Software clock strobe (USITC)
1 1 1 External, negative edge Software clock strobe (USITC)
Bit 76543210
0x11 (0x31) -------USIPOSUSIPP
Read/WriteRRRRRRRR/W
Initial Value00000000
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18. AC – Analog Comparator
The Analog Comparator compares the input values on the selectable positive pin (AIN0, AIN1 or
AIN2) and selectable negative pin (AIN0, AIN1 or AIN2). When the voltage on the positive pin is
higher than the voltage on the negative pin, the Analog Comparator output, ACO, is set. The
comparator can trigger a separate interrupt, exclusive to the Analog Comparator. The user can
select Interrupt triggering on comparator output rise, fall or toggle. A block diagram of the com-
parator and its surrounding logic is shown in Figure 18-1.
Figure 18-1. Analog Comparator Block Diagram(2)
Notes: 1. See Table 18-2 on page 142.
2. Refer to Figure 1-1 on page 2 and Table 12.3.2 on page 66 for Analog Comparator pin
placement.
18.1 Register Description
18.1.1 ACSRA – Analog Comparator Control and Status Register A
• Bit 7 – ACD: Analog Comparator Disable
When this bit is written logic one, the power to the Analog Comparator is switched off. This bit
can be set at any time to turn off the Analog Comparator. This will reduce power consumption in
Active and Idle mode. When changing the ACD bit, the Analog Comparator Interrupt must be
disabled by clearing the ACIE bit in ACSRA. Otherwise an interrupt can occur when the bit is
changed.
Bandgap
Reference
Interrupt
Select
AIN0
VCC
ACIS1
HSEL
HLEV
ADC Multiplexer
Output(1)
ACIS0ACIS0
ACO
ACIE
Analog
Comparator
IRQ
ACI
ACBG
ACM2..1
ACME
ADEN
ACD
+
-
MUX
AIN1
AIN2
Bit 76543210
0x08 (0x28) ACD ACBG ACO ACI ACIE ACME ACIS1 ACIS0 ACSRA
Read/Write R/W R/W R R/W R/W R/W R/W R/W
Initial Value00N/A00000
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• Bit 6 – ACBG: Analog Comparator Bandgap Select
When this bit is set an internal 1.1V reference voltage replaces the positive input to the Analog
Comparator. The selection of the internal voltage reference is done by writing the REFS2..0 bits
in ADMUX register. When this bit is cleared, AIN0, AIN1 or AIN2 depending on the ACM2..0 bits
is applied to the positive input of the analog comparator.
• Bit 5 – ACO: Analog Comparator Output
The output of the Analog Comparator is synchronized and then directly connected to ACO. The
synchronization introduces a delay of 1 - 2 clock cycles.
• Bit 4 – ACI: Analog Comparator Interrupt Flag
This bit is set by hardware when a comparator output event triggers the interrupt mode defined
by ACIS1 and ACIS0. The Analog Comparator interrupt routine is executed if the ACIE bit is set
and the I-bit in SREG is set. ACI is cleared by hardware when executing the corresponding inter-
rupt handling vector. Alternatively, ACI is cleared by writing a logic one to the flag.
• Bit 3 – ACIE: Analog Comparator Interrupt Enable
When the ACIE bit is written logic one and the I-bit in the Status Register is set, the Analog Com-
parator interrupt is activated. When written logic zero, the interrupt is disabled.
• Bit 2 – ACME: Analog Comparator Multiplexer Enable
When this bit is written logic one and the ADC is switched off (ADEN in ADCSRA is zero), the
ADC multiplexer selects the negative input to the Analog Comparator. When this bit is written
logic zero, AIN1 is applied to the negative input of the Analog Comparator. For a detailed
description of this bit, see “Analog Comparator Multiplexed Input” on page 142.
• Bits 1, 0 – ACIS1, ACIS0: Analog Comparator Interrupt Mode Select
These bits determine which comparator events that trigger the Analog Comparator interrupt. The
different settings are shown in Table 18-1.
When changing the ACIS1/ACIS0 bits, the Analog Comparator Interrupt must be disabled by
clearing its Interrupt Enable bit in the ACSR Register. Otherwise an interrupt can occur when the
bits are changed.
Table 18-1. ACIS1/ACIS0 Settings
ACIS1 ACIS0 Interrupt Mode
0 0 Comparator Interrupt on Output Toggle.
01Reserved
1 0 Comparator Interrupt on Falling Output Edge.
1 1 Comparator Interrupt on Rising Output Edge.
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18.2 Analog Comparator Multiplexed Input
When the Analog to Digital Converter (ADC) is configured as single ended input channel, it is
possible to select any of the ADC10..0 pins to replace the negative input to the Analog Compar-
ator. The ADC multiplexer is used to select this input, and consequently, the ADC must be
switched off to utilize this feature. If the Analog Comparator Multiplexer Enable bit (ACME in
ADCSRB) is set and the ADC is switched off (ADEN in ADCSRA is zero), MUX5..0 in ADMUX
select the input pin to replace the negative input to the Analog Comparator, as shown in Table
18-2. If ACME is cleared or ADEN is set, either AIN0, AIN1 or AIN2 is applied to the negative
input to the Analog Comparator.
Table 18-2. Analog Comparator Multiplexed Input
ACME ADEN MUX5..0 ACM2..0 Positive Input Negative Input
0 x xxxxxx 000 AIN0 AIN1
0 x xxxxxx 001 AIN0 AIN2
0 x xxxxxx 010 AIN1 AIN0
0 x xxxxxx 011 AIN1 AIN2
0 x xxxxxx 100 AIN2 AIN0
0 x xxxxxx 101,110,111 AIN2 AIN1
1 1 xxxxxx 000 AIN0 AIN1
1 0 000000 000 AIN0 ADC0
1 0 000000 01x AIN1 ADC0
1 0 000000 1xx AIN2 ADC0
1 0 000001 000 AIN0 ADC1
1 0 000001 01x AIN1 ADC1
1 0 000001 1xx AIN2 ADC1
1 0 000010 000 AIN0 ADC2
1 0 000010 01x AIN1 ADC2
1 0 000010 1xx AIN2 ADC2
1 0 000011 000 AIN0 ADC3
1 0 000011 01x AIN1 ADC3
1 0 000011 1xx AIN2 ADC3
1 0 000100 000 AIN0 ADC4
1 0 000100 01x AIN1 ADC4
1 0 000100 1xx AIN2 ADC4
1 0 000101 000 AIN0 ADC5
1 0 000101 01x AIN1 ADC5
1 0 000101 1xx AIN2 ADC5
1 0 000110 000 AIN0 ADC6
1 0 000110 01x AIN1 ADC6
1 0 000110 1xx AIN2 ADC6
1 0 000111 000 AIN0 ADC7
1 0 000111 01x AIN1 ADC7
1 0 000111 1xx AIN2 ADC7
1 0 001000 000 AIN0 ADC8
1 0 001000 01x AIN1 ADC8
1 0 001000 1xx AIN2 ADC8
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18.2.1 ACSRB – Analog Comparator Control and Status Register B
• Bit 7 – HSEL: Hysteresis Select
When this bit is written logic one, the hysteresis of the Analog Comparator is switched on. The
hysteresis level is selected by the HLEV bit.
• Bit 6 – HLEV: Hysteresis Level
When the hysteresis is enabled by the HSEL bit, the Hysteresis Level, HLEV, bit selects the hys-
teresis level that is either 20mV (HLEV=0) or 50mV (HLEV=1).
• Bit 2:0 – ACM2:ACM0: Analog Comparator Multiplexer
The Analog Comparator multiplexer bits select the positive and negative input pins of the Analog
Comparator. The different settings are shown in Table 18-2.
1 0 001001 000 AIN0 ADC9
1 0 001001 01x AIN1 ADC9
1 0 001001 1xx AIN2 ADC9
1 0 001010 000 AIN0 ADC10
1 0 001010 01x AIN1 ADC10
1 0 001010 1xx AIN2 ADC10
Table 18-2. Analog Comparator Multiplexed Input (Continued)
ACME ADEN MUX5..0 ACM2..0 Positive Input Negative Input
Bit 76543210
0x09 (0x29) HSEL HLEV --- ACM2 ACM1 ACM0 ACSRB
Read/Write R/W R/W R R R R/W R/W R/W
Initial Value00N/A00000
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19. ADC – Analog to Digital Converter
19.1 Features •10-bit Resolution
•1.0 LSB Integral Non-linearity
•± 2 LSB Absolute Accuracy
•65 - 260 µs Conversion Time
•Up to 15 kSPS at Maximum Resolution
•11 Multiplexed Single Ended Input Channels
•16 Differential input pairs
•15 Differential input pairs with selectable gain
•Temperature sensor input channel
•Optional Left Adjustment for ADC Result Readout
•0 - VCC ADC Input Voltage Range
•Selectable 1.1V / 2.56V ADC Voltage Reference
•Free Running or Single Conversion Mode
•ADC Start Conversion by Auto Triggering on Interrupt Sources
•Interrupt on ADC Conversion Complete
•Sleep Mode Noise Cancel
•Unipolar/ Bipolar Input Mode
•Input Polarity Reversal Mode
19.2 Overview
The ATtiny261/461/861 features a 10-bit successive approximation ADC. The ADC is connected
to a 11-channel Analog Multiplexer which allows 16 differential voltage input combinations and
11 single-ended voltage inputs constructed from the pins PA7..PA0 or PB7..PB4. The differential
input is equipped with a programmable gain stage, providing amplification steps of 1x, 8x, 20x or
32x on the differential input voltage before the A/D conversion. The single-ended voltage inputs
refer to 0V (GND).
The ADC contains a Sample and Hold circuit which ensures that the input voltage to the ADC is
held at a constant level during conversion. A block diagram of the ADC is shown in Figure 19-1.
Internal reference voltages of nominally 1.1V or 2.56V are provided On-chip. The Internal refer-
ence voltage of 2.56V, can optionally be externally decoupled at the AREF (PA3) pin by a
capacitor, for better noise performance. Alternatively, VCC can be used as reference voltage for
single ended channels. There is also an option to use an external voltage reference and turn-off
the internal voltage reference. These options are selected using the REFS2:0 bits of the ADMUX
control register.
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Figure 19-1. Analog to Digital Converter Block Schematic
Prescaler
15 0
ADC Conversion
Complete IRQ
ADC10
MUX Decoder
Sample and Hold
Comparator
ADC Multiplexer
Output
ADC Multiplexer
Select (ADMUX)
ADC CTRL and Status
Register B (ADCSRB)
Internal 2.56/1.1V
Reference
Internal 1.8V
Reference
Temperature
Sensor
ADC CTR and Status
Register A (ADCSRA)
Conversion Logic
ADC Data Register
(ADCH/ ADCL)
10-bit DAC
Mux.
Gain
Amplifier
Pos.
Input
Mux.
Neg.
Input
Mux.
-
+
+
-
ADC[9..0]
ADPS1
ADPS2
REFS1
REFS2
GSEL
MUX5
CHANNEL SELECTION
GAIN SELECTION
REFS0
MUX4
MUX3
MUX2
MUX1
MUX0
ADLAR
ADEN
ADSC
ADATE
ADIF ADIF
ADIE
ADPS0
AGND
AREF
VCC
8-BIT DATA BUS
ADC9
ADC8
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0
Single Ended/
Differential Selection
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19.3 Operation
The ADC converts an analog input voltage to a 10-bit digital value through successive approxi-
mation. The minimum value represents GND and the maximum value represents the voltage on
VCC, the voltage on the AREF pin or an internal 1.1V / 2.56V voltage reference.
The voltage reference for the ADC may be selected by writing to the REFS2..0 bits in ADMUX.
The VCC supply, the AREF pin or an internal 1.1V / 2.56V voltage reference may be selected as
the ADC voltage reference. Optionally the internal 1.1V / 2.56V voltage reference may be decou-
pled by an external capacitor at the AREF pin to improve noise immunity.
The analog input channel and differential gain are selected by writing to the MUX5..0 bits in
ADMUX. Any of the 11 ADC input pins ADC10..0 can be selected as single ended inputs to the
ADC. The positive and negative inputs to the differential gain amplifier are described in Table
19-5.
If differential channels are selected, the differential gain stage amplifies the voltage difference
between the selected input pair by the selected gain factor, 1x, 8x, 20x or 32x, according to the
setting of the MUX5..0 bits in ADMUX and the GSEL bit in ADCSRB. This amplified value then
becomes the analog input to the ADC. If single ended channels are used, the gain amplifier is
bypassed altogether.
If the same ADC input pin is selected as both the positive and negative input to the differential
gain amplifier, the remaining offset in the gain stage and conversion circuitry can be measured
directly as the result of the conversion. This figure can be subtracted from subsequent conver-
sions with the same gain setting to reduce offset error to below 1 LSW.
The on-chip temperature sensor is selected by writing the code “111111” to the MUX5..0 bits in
ADMUX register when the ADC11 channel is used as an ADC input.
The ADC is enabled by setting the ADC Enable bit, ADEN in ADCSRA. Voltage reference and
input channel selections will not go into effect until ADEN is set. The ADC does not consume
power when ADEN is cleared, so it is recommended to switch off the ADC before entering power
saving sleep modes.
The ADC generates a 10-bit result which is presented in the ADC Data Registers, ADCH and
ADCL. By default, the result is presented right adjusted, but can optionally be presented left
adjusted by setting the ADLAR bit in ADMUX.
If the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read
ADCH. Otherwise, ADCL must be read first, then ADCH, to ensure that the content of the data
registers belongs to the same conversion. Once ADCL is read, ADC access to data registers is
blocked. This means that if ADCL has been read, and a conversion completes before ADCH is
read, neither register is updated and the result from the conversion is lost. When ADCH is read,
ADC access to the ADCH and ADCL Registers is re-enabled.
The ADC has its own interrupt which can be triggered when a conversion completes. When ADC
access to the data registers is prohibited between reading of ADCH and ADCL, the interrupt will
trigger even if the result is lost.
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19.4 Starting a Conversion
A single conversion is started by writing a logical one to the ADC Start Conversion bit, ADSC.
This bit stays high as long as the conversion is in progress and will be cleared by hardware
when the conversion is completed. If a different data channel is selected while a conversion is in
progress, the ADC will finish the current conversion before performing the channel change.
Alternatively, a conversion can be triggered automatically by various sources. Auto Triggering is
enabled by setting the ADC Auto Trigger Enable bit, ADATE in ADCSRA. The trigger source is
selected by setting the ADC Trigger Select bits, ADTS in ADCSRB (see description of the ADTS
bits for a list of the trigger sources). When a positive edge occurs on the selected trigger signal,
the ADC prescaler is reset and a conversion is started. This provides a method of starting con-
versions at fixed intervals. If the trigger signal still is set when the conversion completes, a new
conversion will not be started. If another positive edge occurs on the trigger signal during con-
version, the edge will be ignored. Note that an Interrupt Flag will be set even if the specific
interrupt is disabled or the Global Interrupt Enable bit in SREG is cleared. A conversion can thus
be triggered without causing an interrupt. However, the Interrupt Flag must be cleared in order to
trigger a new conversion at the next interrupt event.
Figure 19-2. ADC Auto Trigger Logic
Using the ADC Interrupt Flag as a trigger source makes the ADC start a new conversion as soon
as the ongoing conversion has finished. The ADC then operates in Free Running mode, con-
stantly sampling and updating the ADC Data Register. The first conversion must be started by
writing a logical one to the ADSC bit in ADCSRA. In this mode the ADC will perform successive
conversions independently of whether the ADC Interrupt Flag, ADIF is cleared or not.
If Auto Triggering is enabled, single conversions can be started by writing ADSC in ADCSRA to
one. ADSC can also be used to determine if a conversion is in progress. The ADSC bit will be
read as one during a conversion, independently of how the conversion was started.
Edge
Detector
Conversion
Logic
Prescaler
ADIF
ADSC
ADATE START CLK
ADC
ADTS[2:0]
.
.
.
.
SOURCE 1
SOURCE n
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19.5 Prescaling and Conversion Timing
Figure 19-3. ADC Prescaler
By default, the successive approximation circuitry requires an input clock frequency between 50
kHz and 200 kHz to get maximum resolution. If a lower resolution than 10 bits is needed, the
input clock frequency to the ADC can be higher than 200 kHz to get a higher sample rate.
The ADC module contains a prescaler, which generates an acceptable ADC clock frequency
from any CPU frequency above 100 kHz. The prescaling is set by the ADPS bits in ADCSRA.
The prescaler starts counting from the moment the ADC is switched on by setting the ADEN bit
in ADCSRA. The prescaler keeps running for as long as the ADEN bit is set, and is continuously
reset when ADEN is low.
When initiating a single ended conversion by setting the ADSC bit in ADCSRA, the conversion
starts at the following rising edge of the ADC clock cycle.
A normal conversion takes 13 ADC clock cycles. The first conversion after the ADC is switched
on (ADEN in ADCSRA is set) takes 25 ADC clock cycles in order to initialize the analog circuitry.
The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conver-
sion and 14.5 ADC clock cycles after the start of an first conversion. When a conversion is
complete, the result is written to the ADC Data Registers, and ADIF is set. In Single Conversion
mode, ADSC is cleared simultaneously. The software may then set ADSC again, and a new
conversion will be initiated on the first rising ADC clock edge.
When Auto Triggering is used, the prescaler is reset when the trigger event occurs. This assures
a fixed delay from the trigger event to the start of conversion. In this mode, the sample-and-hold
takes place two ADC clock cycles after the rising edge on the trigger source signal. Three addi-
tional CPU clock cycles are used for synchronization logic.
In Free Running mode, a new conversion will be started immediately after the conversion com-
pletes, while ADSC remains high. For a summary of conversion times, see Table 19-1.
7-Bit ADC Prescaler
ADC Clock Source
ADEN
START
CK
ADPS0
ADPS1
ADPS2
Reset
CK/2
CK/4
CK/8
CK/16
CK/32
CK/64
CK/128
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Figure 19-4. ADC Timing Diagram, First Conversion (Single Conversion Mode)
Figure 19-5. ADC Timing Diagram, Single Conversion
1 2 12 13 14 15 16 17 18 19 20 21 22 23 24 25 1 2 3
Cycle Number
First Conversion
Sign and MSB of Result
LSB of Result
Next
Conversion
MUX and REFS
Update
Conversion
Complete MUX and REFS
Update
ADC Clock
ADEN
ADSC
ADIF
ADCH
ADCL
Sample and Hold
12345678910111213 123
Cycle Number
One Conversion
Sign and MSB of Result
LSB of Result
Next Conversion
MUX and REFS
Update
Conversion
Complete MUX and REFS
Update
ADC Clock
ADSC
ADIF
ADCH
ADCL
Sample and Hold
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Figure 19-6. ADC Timing Diagram, Auto Triggered Conversion
Figure 19-7. ADC Timing Diagram, Free Running Conversion
12345678910111213 12
Cycle Number
One Conversion
Sign and MSB of Result
LSB of Result
Next Conversion
MUX and REFS
Update
Prescaler
Reset
Prescaler
Reset
Conversion
Complete
ADC Clock
Trigger
Source
ADIF
ADATE
ADCH
ADCL
Sample and Hold
Table 19-1. ADC Conversion Time
Condition
Sample & Hold
(Cycles from Start of Conversion) Total Conversion Time (Cycles)
First conversion 13.5 25
Normal conversions 1.5 13
Auto Triggered conversions 2 13.5
11 12 13 1 2 3 4
Cycle Number
One Conversion
Sign and MSB of Result
LSB of Result
Next Conversion
MUX and REFS
Update
Conversion
Complete
ADC Clock
ADSC
ADIF
ADCH
ADCL
Sample and Hold
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19.6 Changing Channel or Reference Selection
The MUX5:0 and REFS2:0 bits in the ADMUX Register are single buffered through a temporary
register to which the CPU has random access. This ensures that the channels and reference
selection only takes place at a safe point during the conversion. The channel and reference
selection is continuously updated until a conversion is started. Once the conversion starts, the
channel and reference selection is locked to ensure a sufficient sampling time for the ADC. Con-
tinuous updating resumes in the last ADC clock cycle before the conversion completes (ADIF in
ADCSRA is set).
Note that the conversion starts on the following rising ADC clock edge after ADSC is written. The
user is thus advised not to write new channel or reference selection values to ADMUX until one
ADC clock cycle after ADSC is written.
If Auto Triggering is used, the exact time of the triggering event can be indeterministic. Special
care must be taken when updating the ADMUX Register, in order to control which conversion
will be affected by the new settings.
If both ADATE and ADEN is written to one, an interrupt event can occur at any time. If the
ADMUX Register is changed in this period, the user cannot tell if the next conversion is based
on the old or the new settings. ADMUX can be safely updated in the following ways:
a. When ADATE or ADEN is cleared.
b. During conversion, minimum one ADC clock cycle after the trigger event.
c. After a conversion, before the Interrupt Flag used as trigger source is cleared.
When updating ADMUX in one of these conditions, the new settings will affect the next ADC
conversion.
19.6.1 ADC Input Channels
When changing channel selections, the user should observe the following guidelines to ensure
that the correct channel is selected:
In Single Conversion mode, always select the channel before starting the conversion. The chan-
nel selection may be changed one ADC clock cycle after writing one to ADSC. However, the
simplest method is to wait for the conversion to complete before changing the channel selection.
In Free Running mode, always select the channel before starting the first conversion. The chan-
nel selection may be changed one ADC clock cycle after writing one to ADSC. However, the
simplest method is to wait for the first conversion to complete, and then change the channel
selection. Since the next conversion has already started automatically, the next result will reflect
the previous channel selection. Subsequent conversions will reflect the new channel selection.
19.6.2 ADC Voltage Reference
The voltage reference for the ADC (VREF) indicates the conversion range for the ADC. Single
ended channels that exceed VREF will result in codes close to 0x3FF. VREF can be selected as
either VCC, or internal 1.1V / 2.56V voltage reference, or external AREF pin. The first ADC con-
version result after switching voltage reference source may be inaccurate, and the user is
advised to discard this result.
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19.7 ADC Noise Canceler
The ADC features a noise canceler that enables conversion during sleep mode to reduce noise
induced from the CPU core and other I/O peripherals. The noise canceler can be used with ADC
Noise Reduction and Idle mode. To make use of this feature, the following procedure should be
used:
a. Make sure that the ADC is enabled and is not busy converting. Single Conversion
mode must be selected and the ADC conversion complete interrupt must be enabled.
b. Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion
once the CPU has been halted.
c. If no other interrupts occur before the ADC conversion completes, the ADC interrupt
will wake up the CPU and execute the ADC Conversion Complete interrupt routine. If
another interrupt wakes up the CPU before the ADC conversion is complete, that
interrupt will be executed, and an ADC Conversion Complete interrupt request will be
generated when the ADC conversion completes. The CPU will remain in active mode
until a new sleep command is executed.
Note that the ADC will not be automatically turned off when entering other sleep modes than Idle
mode and ADC Noise Reduction mode. The user is advised to write zero to ADEN before enter-
ing such sleep modes to avoid excessive power consumption.
19.7.1 Analog Input Circuitry
The analog input circuitry for single ended channels is illustrated in Figure 19-8. An analog
source applied to ADCn is subjected to the pin capacitance and input leakage of that pin, regard-
less of whether that channel is selected as input for the ADC. When the channel is selected, the
source must drive the S/H capacitor through the series resistance (combined resistance in the
input path).
The ADC is optimized for analog signals with an output impedance of approximately 10 kΩ or
less. If such a source is used, the sampling time will be negligible. If a source with higher imped-
ance is used, the sampling time will depend on how long time the source needs to charge the
S/H capacitor, with can vary widely. The user is recommended to only use low impedent sources
with slowly varying signals, since this minimizes the required charge transfer to the S/H
capacitor.
Signal components higher than the Nyquist frequency (fADC/2) should not be present to avoid
distortion from unpredictable signal convolution. The user is advised to remove high frequency
components with a low-pass filter before applying the signals as inputs to the ADC.
Figure 19-8. Analog Input Circuitry
IIL
VCC/2
CS/H = 14pF
IIH
ADCn
1 to 100kΩ
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19.7.2 Analog Noise Canceling Techniques
Digital circuitry inside and outside the device generates EMI which might affect the accuracy of
analog measurements. If conversion accuracy is critical, the noise level can be reduced by
applying the following techniques:
a. Keep analog signal paths as short as possible. Make sure analog tracks run over the
analog ground plane, and keep them well away from high-speed switching digital
tracks.
b. Use the ADC noise canceler function to reduce induced noise from the CPU.
c. If any port pins are used as digital outputs, it is essential that these do not switch
while a conversion is in progress.
19.7.3 ADC Accuracy Definitions
An n-bit single-ended ADC converts a voltage linearly between GND and VREF in 2n steps
(LSBs). The lowest code is read as 0, and the highest code is read as 2n-1.
Several parameters describe the deviation from the ideal behavior:
• Offset: The deviation of the first transition (0x000 to 0x001) compared to the ideal transition (at
0.5 LSB). Ideal value: 0 LSB.
Figure 19-9. Offset Error
• Gain Error: After adjusting for offset, the Gain Error is found as the deviation of the last
transition (0x3FE to 0x3FF) compared to the ideal transition (at 1.5 LSB below maximum).
Ideal value: 0 LSB
Offset
Error
Output Code
Ideal ADC
Actual ADC
V
REF
Input Voltage
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Figure 19-10. Gain Error
• Integral Non-linearity (INL): After adjusting for offset and gain error, the INL is the maximum
deviation of an actual transition compared to an ideal transition for any code. Ideal value: 0
LSB.
Figure 19-11. Integral Non-linearity (INL)
• Differential Non-linearity (DNL): The maximum deviation of the actual code width (the interval
between two adjacent transitions) from the ideal code width (1 LSB). Ideal value: 0 LSB.
Output Code
Ideal ADC
Actual ADC
V
REF
Input Voltage
Gain
Error
Output Code
Ideal ADC
INL
Actual ADC
V
REF
Input Voltage
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Figure 19-12. Differential Non-linearity (DNL)
• Quantization Error: Due to the quantization of the input voltage into a finite number of codes, a
range of input voltages (1 LSB wide) will code to the same value. Always ± 0.5 LSB.
• Absolute Accuracy: The maximum deviation of an actual (unadjusted) transition compared to
an ideal transition for any code. This is the compound effect of offset, gain error, differential
error, non-linearity, and quantization error. Ideal value: ± 0.5 LSB.
19.8 ADC Conversion Result
After the conversion is complete (ADIF is high), the conversion result can be found in the ADC
Result Registers (ADCL, ADCH). The form of the conversion result depends on the type of the
conversion as there are three types of conversions: single ended conversion, unipolar differen-
tial conversion and bipolar differential conversion.
19.8.1 Single Ended Conversion
For single ended conversion, the result is
where VIN is the voltage on the selected input pin and VREF the selected voltage reference (see
Table 19-4 on page 158 and Table 19-5 on page 159). 0x000 represents analog ground, and
0x3FF represents the selected voltage reference minus one LSB. The result is presented in
one-sided form, from 0x3FF to 0x000.
19.8.2 Unipolar Differential Conversion
If differential channels and an unipolar input mode are used, the result is
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin,
and VREF the selected voltage reference (see Table 19-4 on page 158 and Table 19-5 on page
159). The voltage on the positive pin must always be larger than the voltage on the negative pin
or otherwise the voltage difference is saturated to zero. The result is presented in one-sided
form, from 0x000 (0d) to 0x3FF (+1023d). The GAIN is either 1x, 8x, 20x or 32x.
Output Code
0x3FF
0x000
0
1 LSB
DNL
V
REF
Input Voltage
ADC VIN 1024⋅
VREF
--------------------------=
ADC VPOS VNEG
–()1024⋅
VREF
--------------------------------------------------------GAIN⋅=
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19.8.3 Bipolar Differential Conversion
As default the ADC converter operates in the unipolar input mode, but the bipolar input mode
can be selected by writing the BIN bit in the ADCSRB to one. In the bipolar input mode two-sided
voltage differences are allowed and thus the voltage on the negative input pin can also be larger
than the voltage on the positive input pin. If differential channels and a bipolar input mode are
used, the result is
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin,
and VREF the selected voltage reference. The result is presented in two’s complement form, from
0x200 (-512d) through 0x000 (+0d) to 0x1FF (+511d). The GAIN is either 1x, 8x, 20x or 32x.
However, if the signal is not bipolar by nature (9 bits + sign as the 10th bit), this scheme loses
one bit of the converter dynamic range. Then, if the user wants to perform the conversion with
the maximum dynamic range, the user can perform a quick polarity check of the result and use
the unipolar differential conversion with selectable differential input pair. When the polarity check
is performed, it is sufficient to read the MSB of the result (ADC9 in ADCH). If the bit is one, the
result is negative, and if this bit is zero, the result is positive.
19.9 Temperature Measurement
The temperature measurement is based on an on-chip temperature sensor that is coupled to a
single ended ADC input. MUX[4..0] bits in ADMUX register enables the temperature sensor. The
internal 1.1V voltage reference must also be selected for the ADC voltage reference source in
the temperature sensor measurement. When the temperature sensor is enabled, the ADC con-
verter can be used in single conversion mode to measure the voltage over the temperature
sensor.
The measured voltage has a linear relationship to the temperature as described in Table 19-2.
The voltage sensitivity is approximately 1LSB/°C and the accuracy of the temperature measure-
ment is ±10°C using manufacturing calibration values (TS_GAIN, TS_OFFSET).
The values described in Table 19-2 are typical values. However, due to the process variation the
temperature sensor output varies from one chip to another.
ADC VPOS VNEG
–()512⋅
VREF
-----------------------------------------------------GAIN⋅=
Table 19-2. Temperature vs. Sensor Output Voltage (Typical Case): Example ADC Values
Temperature / °C -40°C +25 °C +125 °C
0x00F6 0x0144 0c01B8
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19.9.1 Manufacturing Calibration
Calibration values determined during test are available in the signature row.
The temperature in degrees Celsius can be calculated using the formula:
Where:
a. ADCH & ADCL are the ADC data registers,
b. is the temperature sensor gain
c. TS_OFFSET is the temperature sensor offset correction term
TS_GAIN is the unsigned fixed point 8-bit temperature sensor gain factor in 1/128th units stored
in the signature row.
TS_OFFSET is the signed twos complement temperature sensor offset reading stored in the sig-
nature row.
The table below summarizes the parameter signature row address vs product.
The following code example allows to read Signature Row data
.equ TS_GAIN = 0x0007
.equ TS_OFFSET = 0x0005
LDI R30,LOW(TS_GAIN)
LDI R31,HIGH (TS_GAIN)
RCALL Read_signature_row
MOV R17,R16 ; Save R16 result
LDI R30,LOW(TS_OFFSET)
LDI R31,HIGH (TS_OFFSET)
RCALL Read_signature_row
; R16 holds TS_OFFSET and R17 holds TS_GAIN
Read_signature_row:
IN R16,SPMCSR ; Wait for SPMEN ready
SBRC R16,SPMEN ; Exit loop here when SPMCSR is free
RJMP Read_signature_row
LDI R16,((1<<SIGRD)|(1<<SPMEN)) ; We need to set SIGRD and SPMEN
together
OUT SPMCSR,R16 ; and execute the LPM within 3 cycles
LPM R16,Z
RET
Table 19-3. Parameter Signature Row Address vs. Product
ATtiny261 ATtiny461 ATtiny861
TS_OFFSET 0x1F 0x05 0x05
TS_GAIN 0x1E 0x07 0x07
TADCH << 8 I ADCL[]273 25 TS_OFFSET–+–()128×
TS_GAIN
---------------------------------------------------------------------------------------------------------------------------------------------------------------- 25+=
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19.10 Register Description
19.10.1 ADMUX – ADC Multiplexer Selection Register
• Bit 7:6 – REFS1:REFS0: Voltage Reference Selection Bits
These bits and the REFS2 bit from the ADC Control and Status Register B (ADCSRB) select the
voltage reference for the ADC, as shown in Table 19-4. If these bits are changed during a
conversion, the change will not go in effect until this conversion is complete (ADIF in ADCSR is
set). Whenever these bits are changed, the next conversion will take 25 ADC clock cycles. If
active channels are used, using AVCC or an external AREF higher than (AVCC - 1V) is not
recommended, as this will affect ADC accuracy. The internal voltage reference options may not
be used if an external voltage is being applied to the AREF pin.
• Bit 5 – ADLAR: ADC Left Adjust Result
The ADLAR bit affects the presentation of the ADC conversion result in the ADC Data Register.
Write one to ADLAR to left adjust the result. Otherwise, the result is right adjusted. Changing the
ADLAR bit will affect the ADC Data Register immediately, regardless of any ongoing conver-
sions. For a complete description of this bit, see “ADCL and ADCH – The ADC Data Register” on
page 162.
• Bits 4:0 – MUX4:0: Analog Channel and Gain Selection Bits
These bits and the MUX5 bit from the ADC Control and Status Register B (ADCSRB) select
which combination of analog inputs are connected to the ADC. In case of differential input, gain
selection is also made with these bits. Selecting the same pin as both inputs to the differential
gain stage enables offset measurements. Selecting the single-ended channel ADC11 enables
the temperature sensor. Refer to Table 19-5 for details. If these bits are changed during a
conversion, the change will not go into effect until this conversion is complete (ADIF in ADCSRA
is set).
Bit 76543210
0x07 (0x27) REFS1 REFS0 ADLAR MUX4 MUX3 MUX2 MUX1 MUX0 ADMUX
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Table 19-4. Voltage Reference Selections for ADC
REFS2 REFS1 REFS0 Voltage Reference (VREF) Selection
X00V
CC used as Voltage Reference, disconnected from AREF.
X01
External Voltage Reference at AREF pin, Internal Voltage
Reference turned off.
0 1 0 Internal 1.1V Voltage Reference.
0 1 1 Reserved.
110
Internal 2.56V Voltage Reference without external bypass
capacitor, disconnected from AREF.
111
Internal 2.56V Voltage Reference with external bypass capacitor
at AREF pin.
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Table 19-5. Input Channel Selections
MUX5..0
Single Ended
Input
Positive
Differential Input
Negative
Differential Input Gain
000000 ADC0 (PA0)
NA NA NA
000001 ADC1 (PA1)
000010 ADC2 (PA2)
000011 ADC3 (PA4)
000100 ADC4 (PA5)
000101 ADC5 (PA6)
000110 ADC6 (PA7)
000111 ADC7 (PB4)
001000 ADC8 (PB5)
001001 ADC9 (PB6)
001010 ADC10 (PB7)
001011
NA
ADC0 (PA0) ADC1 (PA1) 20x
001100 ADC0 (PA0) ADC1 (PA1) 1x
001101 ADC1 (PA1) ADC1 (PA1) 20x
001110 ADC2 (PA2) ADC1 (PA1) 20x
001111 ADC2 (PA2) ADC1 (PA1) 1x
010000
N/A
ADC2 (PA2) ADC3 (PA4) 1x
010001 ADC3 (PA4) ADC3 (PA4) 20x
010010 ADC4 (PA5) ADC3 (PA4) 20x
010011 ADC4 (PA5) ADC3 (PA4) 1x
010100
NA
ADC4 (PA5) ADC5 (PA6) 20x
010101 ADC4 (PA5) ADC5 (PA6) 1x
010110 ADC5 (PA6) ADC5 (PA6) 20x
010111 ADC6 (PA7) ADC5 (PA6) 20x
011000 ADC6 (PA7) ADC5 (PA6) 1x
011001
NA
ADC8 (PB5) ADC9 (PB6) 20x
011010 ADC8 (PB5) ADC9 (PB6) 1x
011011 ADC9 (PB6) ADC9 (PB6) 20x
011100 ADC10 (PB7) ADC9 (PB6) 20x
011101 ADC10 (PB7) ADC9 (PB6) 1x
011110 1.1V N/A N/A N/A
011111 0V
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100000
N/A
ADC0(PA0) ADC1(PA1) 20x/32x
100001 ADC0(PA0) ADC1(PA1) 1x/8x
100010 ADC1(PA1 ADC0(PA0) 20x/32x
100011 ADC1(PA1) ADC0(PA0) 1x/8x
100100
N/A
ADC1(PA1) ADC2(PA2) 20x/32x
100101 ADC1(PA1) ADC2(PA2) 1x/8x
100110 ADC2(PA2 ADC1(PA1) 20x/32x
100111 ADC2(PA2) ADC1(PA1) 1x/8x
101000
N/A
ADC2(PA2) ADC0(PA0) 20x/32x
101001 ADC2(PA2) ADC0(PA0) 1x/8x
101010 ADC0(PA0) ADC2(PA2) 20x/32x
101011 ADC0(PA0) ADC2(PA2) 1x/8x
101100
N/A
ADC4(PA5) ADC5(PA6) 20x/32x
101101 ADC4(PA5) ADC5(PA6) 1x/8x
101110 ADC5(PA6) ADC4(PA5) 20x/32x
101111 ADC5(PA6) ADC4(PA5) 1x/8x
110000
N/A
ADC5(PA6) ADC6(PA7) 20x/32x
110001 ADC5(PA6) ADC6(PA7) 1x/8x
110010 ADC6(PA7) ADC5(PA6) 20x/32x
110011 ADC6(PA7) ADC5(PA6) 1x/8x
110100
N/A
ADC6(PA7) ADC4(PA5) 20x/32x
110101 ADC6(PA7) ADC4(PA5) 1x/8x
110110 ADC4(PA5) ADC6(PA7) 20x/32x
110111 ADC4(PA5) ADC6(PA7) 1x/8x
111000
N/A
ADC0(PA0) ADC0(PA0) 20x/32x
111001 ADC0(PA0) ADC0(PA0) 1x/8x
111010 ADC1(PA1) ADC1(PA1) 20x/32x
111011 ADC2(PA2) ADC2(PA2) 20x/32x
111100
N/A
ADC4(PA5) ADC4(PA5) 20x/32x
111101 ADC5(PA6) ADC5(PA6) 20x/32x
111110 ADC6(PA7) ADC6(PA7) 20x/32x
111111 ADC11 (1) N/A N/A N/A
1. For temperature sensor
Table 19-5. Input Channel Selections (Continued)
MUX5..0
Single Ended
Input
Positive
Differential Input
Negative
Differential Input Gain
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19.10.2 ADCSRA – ADC Control and Status Register A
• Bit 7 – ADEN: ADC Enable
Writing this bit to one enables the ADC. By writing it to zero, the ADC is turned off. Turning the
ADC off while a conversion is in progress, will terminate this conversion.
• Bit 6 – ADSC: ADC Start Conversion
In Single Conversion mode, write this bit to one to start each conversion. In Free Running mode,
write this bit to one to start the first conversion. The first conversion after ADSC has been written
after the ADC has been enabled, or if ADSC is written at the same time as the ADC is enabled,
will take 25 ADC clock cycles instead of the normal 13. This first conversion performs initializa-
tion of the ADC.
ADSC will read as one as long as a conversion is in progress. When the conversion is complete,
it returns to zero. Writing zero to this bit has no effect.
• Bit 5 – ADATE: ADC Auto Trigger Enable
When this bit is written to one, Auto Triggering of the ADC is enabled. The ADC will start a con-
version on a positive edge of the selected trigger signal. The trigger source is selected by setting
the ADC Trigger Select bits, ADTS in ADCSRB.
• Bit 4 – ADIF: ADC Interrupt Flag
This bit is set when an ADC conversion completes and the data registers are updated. The ADC
Conversion Complete Interrupt is executed if the ADIE bit and the I-bit in SREG are set. ADIF is
cleared by hardware when executing the corresponding interrupt handling vector. Alternatively,
ADIF is cleared by writing a logical one to the flag. Beware that if doing a Read-Modify-Write on
ADCSRA, a pending interrupt can be disabled. This also applies if the SBI and CBI instructions
are used.
• Bit 3 – ADIE: ADC Interrupt Enable
When this bit is written to one and the I-bit in SREG is set, the ADC Conversion Complete Inter-
rupt is activated.
• Bits 2:0 – ADPS2:0: ADC Prescaler Select Bits
These bits determine the division factor between the system clock frequency and the input clock
to the ADC.
Bit 76543210
0x06 (0x26) ADEN ADSC ADATE ADIF ADIE ADPS2 ADPS1 ADPS0 ADCSRA
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
162
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19.10.3 ADCL and ADCH – The ADC Data Register
19.10.3.1 ADLAR = 0
19.10.3.2 ADLAR = 1
When an ADC conversion is complete, the result is found in these two registers.
When ADCL is read, the ADC Data Register is not updated until ADCH is read. Consequently, if
the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read
ADCH. Otherwise, ADCL must be read first, then ADCH.
The ADLAR bit in ADMUX, and the MUXn bits in ADMUX affect the way the result is read from
the registers. If ADLAR is set, the result is left adjusted. If ADLAR is cleared (default), the result
is right adjusted.
• ADC9:0: ADC Conversion Result
These bits represent the result from the conversion, as detailed in “ADC Conversion Result” on
page 155.
Table 19-6. ADC Prescaler Selections
ADPS2 ADPS1 ADPS0 Division Factor
000 2
001 2
010 4
011 8
100 16
101 32
110 64
111 128
Bit 151413121110 9 8
0x05 (0x25) ––––––ADC9ADC8ADCH
0x04 (0x24) ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADC1 ADC0 ADCL
76543210
Read/Write RRRRRRRR
RRRRRRRR
Initial Value00000000
00000000
Bit 151413121110 9 8
0x05 (0x25) ADC9 ADC8 ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADCH
0x04 (0x24) ADC1 ADC0 ––––––ADCL
76543210
Read/Write RRRRRRRR
RRRRRRRR
Initial Value00000000
00000000
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19.10.4 ADCSRB – ADC Control and Status Register B
• Bit 7– BIN: Bipolar Input Mode
The gain stage is working in the unipolar mode as default, but the bipolar mode can be selected
by writing the BIN bit in the ADCSRB register. In the unipolar mode only one-sided conversions
are supported and the voltage on the positive input must always be larger than the voltage on
the negative input. Otherwise the result is saturated to the voltage reference. In the bipolar mode
two-sided conversions are supported and the result is represented in the two’s complement
form. In the unipolar mode the resolution is 10 bits and the bipolar mode the resolution is 9 bits +
1 sign bit.
• Bits 6 – GSEL: Gain Select
The Gain Select bit selects the 32x gain instead of the 20x gain and the 8x gain instead of the 1x
gain when the Gain Select bit is written to one.
• Bits 5 – Res: Reserved Bit
This bit is a reserved bit in the ATtiny261/461/861 and will always read as zero.
• Bits 4 – REFS2: Reference Selection Bit
These bit selects either the voltage reference of 1.1 V or 2.56 V for the ADC, as shown in Table
19-4. If active channels are used, using AVCC or an external AREF higher than (AVCC - 1V) is
not recommended, as this will affect ADC accuracy. The internal voltage reference options may
not be used if an external voltage is being applied to the AREF pin.
• Bits 3 – MUX5: Analog Channel and Gain Selection Bit 5
The MUX5 bit is the MSB of the Analog Channel and Gain Selection bits. Refer to Table 19-5 for
details. If this bit is changed during a conversion, the change will not go into effect until this
conversion is complete (ADIF in ADCSRA is set).
• Bits 2:0 – ADTS2:0: ADC Auto Trigger Source
If ADATE in ADCSRA is written to one, the value of these bits selects which source will trigger
an ADC conversion. If ADATE is cleared, the ADTS2:0 settings will have no effect. A conversion
will be triggered by the rising edge of the selected Interrupt Flag. Note that switching from a trig-
ger source that is cleared to a trigger source that is set, will generate a positive edge on the
trigger signal. If ADEN in ADCSRA is set, this will start a conversion. Switching to Free Running
mode (ADTS[2:0]=0) will not cause a trigger event, even if the ADC Interrupt Flag is set.
Bit 76543210
0x03 (0x23) BIN GSEL - REFS2 MUX5 ADTS2 ADTS1 ADTS0 ADCSRB
Read/Write R/W R/W R R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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19.10.5 DIDR0 – Digital Input Disable Register 0
• Bits 7:4,2:0 – ADC6D:ADC0D: ADC6:0 Digital Input Disable
When this bit is written logic one, the digital input buffer on the corresponding ADC pin is dis-
abled. The corresponding PIN register bit will always read as zero when this bit is set. When an
analog signal is applied to the ADC7:0 pin and the digital input from this pin is not needed, this
bit should be written logic one to reduce power consumption in the digital input buffer.
• Bit 3 – AREFD: AREF Digital Input Disable
When this bit is written logic one, the digital input buffer on the AREF pin is disabled. The corre-
sponding PIN register bit will always read as zero when this bit is set. When an analog signal is
applied to the AREF pin and the digital input from this pin is not needed, this bit should be written
logic one to reduce power consumption in the digital input buffer.
19.10.6 DIDR1 – Digital Input Disable Register 1
• Bits 7..4 – ADC10D..ADC7D: ADC10..7 Digital Input Disable
When this bit is written logic one, the digital input buffer on the corresponding ADC pin is dis-
abled. The corresponding PIN register bit will always read as zero when this bit is set. When an
analog signal is applied to the ADC10:7 pin and the digital input from this pin is not needed, this
bit should be written logic one to reduce power consumption in the digital input buffer.
Table 19-7. ADC Auto Trigger Source Selections
ADTS2 ADTS1 ADTS0 Trigger Source
0 0 0 Free Running mode
0 0 1 Analog Comparator
0 1 0 External Interrupt Request 0
0 1 1 Timer/Counter0 Compare Match A
1 0 0 Timer/Counter0 Overflow
1 0 1 Timer/Counter0 Compare Match B
1 1 0 Timer/Counter1 Overflow
1 1 1 Watchdog Interrupt Request
Bit 76543210
0x01 (0x21) ADC6D ADC5D ADC4D ADC3D AREFD ADC2D ADC1D ADC0D DIDR0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x02 (0x22) ADC10D ADC9D ADC8D ADC7D - DIDR1
Read/Write R/W R/W R/W R/W R R R R
Initial Value 0 0 0 0 0 0 0 0
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20. debugWIRE On-chip Debug System
20.1 Features •Complete Program Flow Control
•Emulates All On-chip Functions, Both Digital and Analog, except RESET Pin
•Real-time Operation
•Symbolic Debugging Support (Both at C and Assembler Source Level, or for Other HLLs)
•Unlimited Number of Program Break Points (Using Software Break Points)
•Non-intrusive Operation
•Electrical Characteristics Identical to Real Device
•Automatic Configuration System
•High-Speed Operation
•Programming of Non-volatile Memories
20.2 Overview
The debugWIRE On-chip debug system uses a One-wire, bi-directional interface to control the
program flow, execute AVR instructions in the CPU and to program the different non-volatile
memories.
20.3 Physical Interface
When the debugWIRE Enable (DWEN) Fuse is programmed and Lock bits are unprogrammed,
the debugWIRE system within the target device is activated. The RESET port pin is configured
as a wire-AND (open-drain) bi-directional I/O pin with pull-up enabled and becomes the commu-
nication gateway between target and emulator.
Figure 20-1. The debugWIRE Setup
Figure 20-1 shows the schematic of a target MCU, with debugWIRE enabled, and the emulator
connector. The system clock is not affected by debugWIRE and will always be the clock source
selected by the CKSEL Fuses.
When designing a system where debugWIRE will be used, the following observations must be
made for correct operation:
• Pull-Up resistor on the dW/(RESET) line must be in the range of 10k to 20 kΩ. However, the
pull-up resistor is optional.
• Connecting the RESET pin directly to VCC will not work.
• Capacitors inserted on the RESET pin must be disconnected when using debugWire.
• All external reset sources must be disconnected.
GND
dW (RESET)
VCC
dW
+1.8 to +5.5V
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20.4 Software Break Points
debugWIRE supports Program memory Break Points by the AVR Break instruction. Setting a
Break Point in AVR Studio® will insert a BREAK instruction in the Program memory. The instruc-
tion replaced by the BREAK instruction will be stored. When program execution is continued, the
stored instruction will be executed before continuing from the Program memory. A break can be
inserted manually by putting the BREAK instruction in the program.
The Flash must be re-programmed each time a Break Point is changed. This is automatically
handled by AVR Studio through the debugWIRE interface. The use of Break Points will therefore
reduce the Flash Data retention. Devices used for debugging purposes should not be shipped to
end customers.
20.5 Limitations of debugWIRE
The debugWIRE communication pin (dW) is physically located on the same pin as External
Reset (RESET). An External Reset source is therefore not supported when the debugWIRE is
enabled.
The debugWIRE system accurately emulates all I/O functions when running at full speed, i.e.,
when the program in the CPU is running. When the CPU is stopped, care must be taken while
accessing some of the I/O Registers via the debugger (AVR Studio).
A programmed DWEN Fuse enables some parts of the clock system to be running in all sleep
modes. This will increase the power consumption while in sleep. Thus, the DWEN Fuse should
be disabled when debugWire is not used.
20.6 Register Description
The following section describes the registers used with the debugWire.
20.6.1 DWDR – debugWire Data Register
The DWDR Register provides a communication channel from the running program in the MCU
to the debugger. This register is only accessible by the debugWIRE and can therefore not be
used as a general purpose register in the normal operations.
Bit 76543210
0x20 (0x40) DWDR[7:0] DWDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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21. Self-Programming the Flash
The device provides a Self-Programming mechanism for downloading and uploading program
code by the MCU itself. The Self-Programming can use any available data interface and associ-
ated protocol to read code and write (program) that code into the Program memory.
The Program memory is updated in a page by page fashion. Before programming a page with
the data stored in the temporary page buffer, the page must be erased. The temporary page buf-
fer is filled one word at a time using SPM and the buffer can be filled either before the Page
Erase command or between a Page Erase and a Page Write operation:
Alternative 1, fill the buffer before a Page Erase
• Fill temporary page buffer
• Perform a Page Erase
• Perform a Page Write
Alternative 2, fill the buffer after Page Erase
• Perform a Page Erase
• Fill temporary page buffer
• Perform a Page Write
If only a part of the page needs to be changed, the rest of the page must be stored (for example
in the temporary page buffer) before the erase, and then be re-written. When using alternative 1,
the Boot Loader provides an effective Read-Modify-Write feature which allows the user software
to first read the page, do the necessary changes, and then write back the modified data. If alter-
native 2 is used, it is not possible to read the old data while loading since the page is already
erased. The temporary page buffer can be accessed in a random sequence. It is essential that
the page address used in both the Page Erase and Page Write operation is addressing the same
page.
21.1 Performing Page Erase by SPM
To execute Page Erase, set up the address in the Z-pointer, write “00000011” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored.
The page address must be written to PCPAGE in the Z-register. Other bits in the Z-pointer will
be ignored during this operation.
• The CPU is halted during the Page Erase operation.
21.2 Filling the Temporary Buffer (Page Loading)
To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write
“00000001” to SPMCSR and execute SPM within four clock cycles after writing SPMCSR. The
content of PCWORD in the Z-register is used to address the data in the temporary buffer. The
temporary buffer will auto-erase after a Page Write operation or by writing the CTPB bit in
SPMCSR. It is also erased after a system reset. Note that it is not possible to write more than
one time to each address without erasing the temporary buffer.
If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded will be
lost.
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21.3 Performing a Page Write
To execute Page Write, set up the address in the Z-pointer, write “00000101” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored.
The page address must be written to PCPAGE. Other bits in the Z-pointer must be written to
zero during this operation.
• The CPU is halted during the Page Write operation.
21.4 Addressing the Flash During Self-Programming
The Z-pointer is used to address the SPM commands.
Since the Flash is organized in pages (see Table 22-7 on page 175), the Program Counter can
be treated as having two different sections. One section, consisting of the least significant bits, is
addressing the words within a page, while the most significant bits are addressing the pages.
This is shown in Figure 21-1. Note that the Page Erase and Page Write operations are
addressed independently. Therefore it is of major importance that the software addresses the
same page in both the Page Erase and Page Write operation.
The LPM instruction uses the Z-pointer to store the address. Since this instruction addresses the
Flash byte-by-byte, also the LSB (bit Z0) of the Z-pointer is used.
Figure 21-1. Addressing the Flash During SPM(1)
Note: 1. The different variables used in Figure 21-1 are listed in Table 22-7 on page 175.
Bit 1514131211109 8
ZH (R31) Z15 Z14 Z13 Z12 Z11 Z10 Z9 Z8
ZL (R30)Z7Z6Z5Z4Z3Z2Z1Z0
76543210
BIT
PAGEMSBPCMSB
ZPAGEMSBZPCMSB 0115
Z-register
Program
counter
Word address
within the page
Page address
within the flash
0
PCWORDPCPAGE
02
01
00
PAGEEND
PCWORD[PAGEMSB:0]
Page
Program Memory
Instructions Word
Page
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21.4.1 EEPROM Write Prevents Writing to SPMCSR
Note that an EEPROM write operation will block all software programming to Flash. Reading the
Fuses and Lock bits from software will also be prevented during the EEPROM write operation. It
is recommended that the user checks the status bit (EEPE) in the EECR Register and verifies
that the bit is cleared before writing to the SPMCSR Register.
21.4.2 Reading the Fuse and Lock Bits from Software
It is possible to read both the Fuse and Lock bits from software. To read the Lock bits, load the
Z-pointer with 0x0001 and set the RFLB and SPMEN bits in SPMCSR. When an LPM instruction
is executed within three CPU cycles after the RFLB and SPMEN bits are set in SPMCSR, the
value of the Lock bits will be loaded in the destination register. The RFLB and SPMEN bits will
auto-clear upon completion of reading the Lock bits or if no LPM instruction is executed within
three CPU cycles or no SPM instruction is executed within four CPU cycles. When RFLB and
SPMEN are cleared, LPM will work as described in the Instruction set Manual.
The algorithm for reading the Fuse Low byte is similar to the one described above for reading
the Lock bits. To read the Fuse Low byte, load the Z-pointer with 0x0000 and set the RFLB and
SPMEN bits in SPMCSR. When an LPM instruction is executed within three cycles after the
RFLB and SPMEN bits are set in the SPMCSR, the value of the Fuse Low byte (FLB) will be
loaded in the destination register as shown below. Refer to Table 22-5 on page 174 for a
detailed description and mapping of the Fuse Low byte.
Similarly, when reading the Fuse High byte, load 0x0003 in the Z-pointer. When an LPM instruc-
tion is executed within three cycles after the RFLB and SPMEN bits are set in the SPMCSR, the
value of the Fuse High byte (FHB) will be loaded in the destination register as shown below.
Refer to Table XXX on page XXX for detailed description and mapping of the Fuse High byte.
Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that are
unprogrammed, will be read as one.
21.4.3 Preventing Flash Corruption
During periods of low VCC, the Flash program can be corrupted because the supply voltage is
too low for the CPU and the Flash to operate properly. These issues are the same as for board
level systems using the Flash, and the same design solutions should be applied.
A Flash program corruption can be caused by two situations when the voltage is too low. First, a
regular write sequence to the Flash requires a minimum voltage to operate correctly. Secondly,
the CPU itself can execute instructions incorrectly, if the supply voltage for executing instructions
is too low.
Bit 76543210
Rd ––––––LB2LB1
Bit 76543210
Rd FLB7 FLB6 FLB5 FLB4 FLB3 FLB2 FLB1 FLB0
Bit 7654 3210
Rd FHB7 FHB6 FHB5 FHB4 FHB3 FHB2 FHB1 FHB0
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Flash corruption can easily be avoided by following these design recommendations (one is
sufficient):
1. Keep the AVR RESET active (low) during periods of insufficient power supply voltage.
This can be done by enabling the internal Brown-out Detector (BOD) if the operating volt-
age matches the detection level. If not, an external low VCC reset protection circuit can be
used. If a reset occurs while a write operation is in progress, the write operation will be
completed provided that the power supply voltage is sufficient.
2. Keep the AVR core in Power-down sleep mode during periods of low VCC. This will pre-
vent the CPU from attempting to decode and execute instructions, effectively protecting
the SPMCSR Register and thus the Flash from unintentional writes.
21.4.4 Programming Time for Flash when Using SPM
The calibrated RC Oscillator is used to time Flash accesses. Table 21-1 shows the typical pro-
gramming time for Flash accesses from the CPU.
Note: 1. Minimum and maximum programming time is per individual operation.
21.5 Register Description
21.5.1 SPMCSR – Store Program Memory Control and Status Register
The Store Program Memory Control and Status Register contains the control bits needed to con-
trol the Program memory operations.
• Bits 7:6 – Res: Reserved Bits
These bits are reserved bits in the ATtiny261/461/861 and always read as zero.
• Bit 5 – SIGRD: Signature Row Read
If this bit is written to one at the same time as SPMEN, the next LPM instruction within three
clock cycles will read a byte from the signature row into the destination register for details. An
SPM instruction within four cycles after SIGRD and SPMEN are set will have no effect.
• Bit 4 – CTPB: Clear Temporary Page Buffer
If the CTPB bit is written while filling the temporary page buffer, the temporary page buffer will be
cleared and the data will be lost.
• Bit 3 – RFLB: Read Fuse and Lock Bits
An LPM instruction within three cycles after RFLB and SPMEN are set in the SPMCSR Register,
will read either the Lock bits or the Fuse bits (depending on Z0 in the Z-pointer) into the destina-
tion register. See “EEPROM Write Prevents Writing to SPMCSR” on page 169 for details.
Table 21-1. SPM Programming Time(1)
Symbol Min Programming Time Max Programming Time
Flash write (Page Erase, Page Write, and
write Lock bits by SPM) 3.7 ms 4.5 ms
Bit 7 6 5 4 3 2 1 0
0x37 (0x57) –– SIGRD CTPB RFLB PGWRT PGERS SPMEN SPMCSR
Read/Write R R R R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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• Bit 2 – PGWRT: Page Write
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock
cycles executes Page Write, with the data stored in the temporary buffer. The page address is
taken from the high part of the Z-pointer. The data in R1 and R0 are ignored. The PGWRT bit
will auto-clear upon completion of a Page Write, or if no SPM instruction is executed within four
clock cycles. The CPU is halted during the entire Page Write operation.
• Bit 1 – PGERS: Page Erase
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock
cycles executes Page Erase. The page address is taken from the high part of the Z-pointer. The
data in R1 and R0 are ignored. The PGERS bit will auto-clear upon completion of a Page Erase,
or if no SPM instruction is executed within four clock cycles. The CPU is halted during the entire
Page Write operation.
• Bit 0 – SPMEN: Store Program Memory Enable
This bit enables the SPM instruction for the next four clock cycles. If written to one together with
either CTPB, RFLB, PGWRT, or PGERS, the following SPM instruction will have a special
meaning, see description above. If only SPMEN is written, the following SPM instruction will
store the value in R1:R0 in the temporary page buffer addressed by the Z-pointer. The LSB of
the Z-pointer is ignored. The SPMEN bit will auto-clear upon completion of an SPM instruction,
or if no SPM instruction is executed within four clock cycles. During Page Erase and Page Write,
the SPMEN bit remains high until the operation is completed.
Writing any other combination than “10001”, “01001”, “00101”, “00011” or “00001” in the lower
five bits will have no effect.
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22. Memory Programming
This section describes the different methods for Programming the ATtiny261/461/861 memories.
22.1 Program And Data Memory Lock Bits
The ATtiny261/461/861 provides two Lock bits which can be left unprogrammed (“1”) or can be
programmed (“0”) to obtain the additional security listed in Table 22-2. The Lock bits can only be
erased to “1” with the Chip Erase command. The ATtiny261/461/861 has no separate Boot
Loader section. The SPM instruction is enabled for the whole Flash, if the SELFPROGEN fuse is
programmed (“0”), otherwise it is disabled.
Note: 1. “1” means unprogrammed, “0” means programmed
Notes: 1. Program the Fuse bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
Table 22-1. Lock Bit Byte(1)
Lock Bit Byte Bit No Description Default Value
7 – 1 (unprogrammed)
6 – 1 (unprogrammed)
5 – 1 (unprogrammed)
4 – 1 (unprogrammed)
3 – 1 (unprogrammed)
2 – 1 (unprogrammed)
LB2 1 Lock bit 1 (unprogrammed)
LB1 0 Lock bit 1 (unprogrammed)
Table 22-2. Lock Bit Protection Modes(1)(2)
Memory Lock Bits Protection Type
LB Mode LB2 LB1
1 1 1 No memory lock features enabled.
210
Further programming of the Flash and EEPROM is disabled in
High-voltage and Serial Programming mode. The Fuse bits are
locked in both Serial and High-voltage Programming mode.(1)
300
Further programming and verification of the Flash and EEPROM
is disabled in High-voltage and Serial Programming mode. The
Fuse bits are locked in both Serial and High-voltage
Programming mode.(1)
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22.2 Fuse Bytes
The ATtiny261/461/861 has three Fuse bytes. Table 22-3, Table 22-4 and Table 22-5 describe
briefly the functionality of all the fuses and how they are mapped into the Fuse bytes. Note that
the fuses are read as logical zero, “0”, if they are programmed.
Notes: 1. See “Alternate Functions of Port B” on page 63 for description of RSTDISBL and DWEN
Fuses.
2. DWEN must be unprogrammed when Lock Bit security is required. See “Program And Data
Memory Lock Bits” on page 172.
3. The SPIEN Fuse is not accessible in SPI Programming mode.
4. See “WDTCR – Watchdog Timer Control Register” on page 46 for details.
5. See Table 23-4 on page 191 for BODLEVEL Fuse decoding.
6. When programming the RSTDISBL Fuse, High-voltage Serial programming has to be used to
change fuses to perform further programming.
Table 22-3. Fuse Extended Byte
Fuse High Byte Bit No Description Default Value
7 - 1 (unprogrammed)
6 - 1 (unprogrammed)
5 - 1 (unprogrammed)
4 - 1 (unprogrammed)
3 - 1 (unprogrammed)
2 - 1 (unprogrammed)
1 - 1 (unprogrammed)
SELFPRGEN 0 Self-Programming Enable 1 (unprogrammed)
Table 22-4. Fuse High Byte
Fuse High Byte Bit No Description Default Value
RSTDISBL(1) 7 External Reset disable 1 (unprogrammed)
DWEN(2) 6 DebugWIRE Enable 1 (unprogrammed)
SPIEN(3) 6Enable Serial Program and Data
Downloading
0 (programmed, SPI prog.
enabled)
WDTON(4) 4 Watchdog Timer always on 1 (unprogrammed)
EESAVE 3 EEPROM memory is preserved
through the Chip Erase
1 (unprogrammed, EEPROM
not preserved)
BODLEVEL2(5) 2 Brown-out Detector trigger level 1 (unprogrammed)
BODLEVEL1(5) 1 Brown-out Detector trigger level 1 (unprogrammed)
BODLEVEL0(5) 0 Brown-out Detector trigger level 1 (unprogrammed)
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Notes: 1. See “System Clock Prescaler” on page 32 for details.
2. The CKOUT Fuse allows the system clock to be output on PORTB5. See “Clock Output Buffer”
on page 30 for details.
3. The default value of SUT1..0 results in maximum start-up time for the default clock source.
See Table 7-7 on page 29 for details.
4. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8.0 MHz. See Table 7-6
on page 29 for details.
The status of the Fuse bits is not affected by Chip Erase. Note that the Fuse bits are locked if
Lock bit1 (LB1) is programmed. Program the Fuse bits before programming the Lock bits.
22.2.1 Latching of Fuses
The fuse values are latched when the device enters programming mode and changes of the
fuse values will have no effect until the part leaves Programming mode. This does not apply to
the EESAVE Fuse which will take effect once it is programmed. The fuses are also latched on
Power-up in Normal mode.
22.3 Signature Bytes
All Atmel microcontrollers have a three-byte signature code which identifies the device. This
code can be read in both serial and High-voltage Programming mode, also when the device is
locked. The three bytes reside in a separate address space. The ATtiny261/461/861signature
bytes are given in Table 22-6.
22.4 Calibration Byte
Signature area of the ATtiny261/461/861 has one byte of calibration data for the internal RC
Oscillator. This byte resides in the high byte of address 0x000. During reset, this byte is auto-
matically written into the OSCCAL Register to ensure correct frequency of the calibrated RC
Oscillator.
Table 22-5. Fuse Low Byte
Fuse Low Byte Bit No Description Default Value
CKDIV8(1) 7 Divide clock by 8 0 (programmed)
CKOUT(2) 6 Clock Output Enable 1 (unprogrammed)
SUT1 5 Select start-up time 1 (unprogrammed)(3)
SUT0 4 Select start-up time 0 (programmed)(3)
CKSEL3 3 Select Clock source 0 (programmed)(4)
CKSEL2 2 Select Clock source 0 (programmed)(4)
CKSEL1 1 Select Clock source 1 (unprogrammed)(4)
CKSEL0 0 Select Clock source 0 (programmed)(4)
Table 22-6. Device ID
Parts
Signature Bytes Address
0x000 0x001 0x002
ATtiny261 0x1E 0x91 0x0C
ATtiny461 0x1E 0x92 0x08
ATtiny861 0x1E 0x93 0x0D
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22.5 Reading the Signature Row from Software
To read the Signature Row from software, load the Z-pointer with the signature byte address
given in Table 22-6 on page 174 and set the SIGRD and SPMEN bits in SPMCSR. When an
LPM instruction is executed within three CPU cycles after the SIGRD and SPMEN bits are set in
SPMCSR, the signature byte value will be loaded in the destination register. The SIGRD and
SPMEN bits will auto-clear upon completion of reading the Signature Row Lock bits or if no LPM
instruction is executed within three CPU cycles. When SIGRD and SPMEN are cleared, LPM will
work as described in the Instruction set Manual.
Note: Before attempting to set SPMEN it is important to test this bit is cleared showing that the hardware
is ready for a new operation.
22.6 Page Size
22.7 Parallel Programming Parameters, Pin Mapping, and Commands
This section describes how to parallel program and verify Flash Program memory, EEPROM
Data memory, Memory Lock bits, and Fuse bits in the ATtiny261/461/861. Pulses are assumed
to be at least 250 ns unless otherwise noted.
22.7.1 Signal Names
In this section, some pins of the ATtiny261/461/861 are referenced by signal names describing
their functionality during parallel programming, see Figure 22-1 and Table 22-9. Pins not
described in the following table are referenced by pin names.
The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse.
The bit coding is shown in Table 22-11.
When pulsing WR or OE, the command loaded determines the action executed. The different
Commands are shown in Table 22-12.
Table 22-7. No. of Words in a Page and No. of Pages in the Flash
Device Flash Size Page Size PCWORD No. of Pages PCPAGE PCMSB
ATtiny261 1K words (2K bytes) 16 words PC[3:0] 64 PC[9:4] 9
ATtiny461 2K words (4K bytes) 32 words PC[4:0] 64 PC[10:5] 10
ATtiny861 4K words (8K bytes) 32 words PC[4:0] 128 PC[11:5] 11
Table 22-8. No. of Words in a Page and No. of Pages in the EEPROM
Device
EEPROM
Size Page Size PCWORD No. of Pages PCPAGE EEAMSB
ATtiny261 128 bytes 2 bytes EEA[1:0] 64 EEA[6:2] 6
ATtiny461 256 bytes 4 bytes EEA[1:0] 64 EEA[7:2] 7
ATtiny861 512 bytes 4 bytes EEA[1:0] 128 EEA[8:2] 8
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Figure 22-1. Parallel Programming
Table 22-9. Pin Name Mapping
Signal Name in
Programming Mode Pin Name I/O Function
WR PB0 I Write Pulse (Active low).
XA0 PB1 I XTAL Action Bit 0
XA1/BS2 PB2 I XTAL Action Bit 1. Byte Select 2 (“0” selects low byte, “1”
selects 2’nd high byte).
PAGEL/BS1 PB3 I Byte Select 1 (“0” selects low byte, “1” selects high byte).
Program Memory and EEPROM Data Page Load.
OE PB5 I Output Enable (Active low).
RDY/BSY PB6 O 0: Device is busy programming, 1: Device is ready for new
command.
DATA I/O PA7-PA0 I/O Bi-directional Data bus (Output when OE is low).
Table 22-10. Pin Values Used to Enter Programming Mode
Pin Symbol Value
PAGEL/BS1 Prog_enable[3] 0
XA1/BS2 Prog_enable[2] 0
XA0 Prog_enable[1] 0
WR Prog_enable[0] 0
Table 22-11. XA1 and XA0 Coding
XA1 XA0 Action when XTAL1 is Pulsed
0 0 Load Flash or EEPROM Address (High or low address byte determined by BS1).
0 1 Load Data (High or Low data byte for Flash determined by BS1).
1 0 Load Command
1 1 No Action, Idle
GND
PB0
PB1
PB2
PB3
XTAL1/ PB4
DAT
A
PB5
PB6
RESET
VCC
AVCC
PB7 to PB0
+5V
+5V
WR
OE
RDY/ BSY
XA1/ BS2
XA0
PAGEL/ BS1
+12V
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22.8 Parallel Programming
22.8.1 Enter Programming Mode
The following algorithm puts the device in parallel programming mode:
1. Apply 4.5 - 5.5V between VCC and GND.
2. Set RESET to “0” and toggle XTAL1 at least six times.
3. Set the Prog_enable pins listed in Table 22-10 on page 176 to “0000” and wait at least
100 ns.
4. Apply 11.5 - 12.5V to RESET. Any activity on Prog_enable pins within 100 ns after +12V
has been applied to RESET, will cause the device to fail entering programming mode.
5. Wait at least 50 µs before sending a new command.
22.8.2 Considerations for Efficient Programming
The loaded command and address are retained in the device during programming. For efficient
programming, the following should be considered.
• The command needs only be loaded once when writing or reading multiple memory locations.
• Skip writing the data value 0xFF, that is the contents of the entire EEPROM (unless the
EESAVE Fuse is programmed) and Flash after a Chip Erase.
• Address high byte needs only be loaded before programming or reading a new 256 word
window in Flash or 256 byte EEPROM. This consideration also applies to Signature bytes
reading.
22.8.3 Chip Erase
The Chip Erase will erase the Flash and EEPROM(1) memories plus Lock bits. The Lock bits are
not reset until the program memory has been completely erased. The Fuse bits are not
changed. A Chip Erase must be performed before the Flash and/or EEPROM are
reprogrammed.
Note: 1. The EEPRPOM memory is preserved during Chip Erase if the EESAVE Fuse is programmed.
Table 22-12. Command Byte Bit Coding
Command Byte Command Executed
1000 0000 Chip Erase
0100 0000 Write Fuse bits
0010 0000 Write Lock bits
0001 0000 Write Flash
0001 0001 Write EEPROM
0000 1000 Read Signature Bytes and Calibration byte
0000 0100 Read Fuse and Lock bits
0000 0010 Read Flash
0000 0011 Read EEPROM
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Load Command “Chip Erase”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “1000 0000”. This is the command for Chip Erase.
4. Give XTAL1 a positive pulse. This loads the command.
5. Give WR a negative pulse. This starts the Chip Erase. RDY/BSY goes low.
6. Wait until RDY/BSY goes high before loading a new command.
22.8.4 Programming the Flash
The Flash is organized in pages, see Table 22-7 on page 175. When programming the Flash,
the program data is latched into a page buffer. This allows one page of program data to be pro-
grammed simultaneously. The following procedure describes how to program the entire Flash
memory:
A. Load Command “Write Flash”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “0001 0000”. This is the command for Write Flash.
4. Give XTAL1 a positive pulse. This loads the command.
B. Load Address Low byte
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “0”. This selects low address.
3. Set DATA = Address low byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address low byte.
C. Load Data Low Byte
1. Set XA1, XA0 to “01”. This enables data loading.
2. Set DATA = Data low byte (0x00 - 0xFF).
3. Give XTAL1 a positive pulse. This loads the data byte.
D. Load Data High Byte
1. Set BS1 to “1”. This selects high data byte.
2. Set XA1, XA0 to “01”. This enables data loading.
3. Set DATA = Data high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the data byte.
1. E. Latch Data
2. Set BS1 to “1”. This selects high data byte.
3. Give PAGEL a positive pulse. This latches the data bytes. (See Figure 22-3 for signal
waveforms)
F. Repeat B through E until the entire buffer is filled or until all data within the page is loaded.
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While the lower bits in the address are mapped to words within the page, the higher bits address
the pages within the FLASH. This is illustrated in Figure 22-2 on page 179. Note that if less than
eight bits are required to address words in the page (pagesize < 256), the most significant bit(s)
in the address low byte are used to address the page when performing a Page Write.
G. Load Address High byte
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “1”. This selects high address.
3. Set DATA = Address high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address high byte.
H. Program Page
1. Give WR a negative pulse. This starts programming of the entire page of data. RDY/BSY
goes low.
2. Wait until RDY/BSY goes high (See Figure 22-3 for signal waveforms).
I. Repeat B through H until the entire Flash is programmed or until all data has been
programmed.
J. End Page Programming
1. 1. Set XA1, XA0 to “10”. This enables command loading.
2. Set DATA to “0000 0000”. This is the command for No Operation.
3. Give XTAL1 a positive pulse. This loads the command, and the internal write signals are
reset.
Figure 22-2. Addressing the Flash Which is Organized in Pages(1)
Note: 1. PCPAGE and PCWORD are listed in Table 22-7 on page 175.
PAGEMSBPCMSB
Program
counter
Word address
within Page
Page address
within the flash
PCWORDPCPAGE
02
01
00
PAGEEND
PCWORD [PAGEMSB:0]
Page
Program Memory
Instructions Word
Page
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Figure 22-3. Programming the Flash Waveforms(1)
Note: 1. “XX” is don’t care. The letters refer to the programming description above.
22.8.5 Programming the EEPROM
The EEPROM is organized in pages, see Table 22-8 on page 175. When programming the
EEPROM, the program data is latched into a page buffer. This allows one page of data to be
programmed simultaneously. The programming algorithm for the EEPROM data memory is as
follows (refer to “Programming the Flash” on page 178 for details on Command, Address and
Data loading):
1. A: Load Command “0001 0001”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. C: Load Data (0x00 - 0xFF).
5. E: Latch data (give PAGEL a positive pulse).
K: Repeat 3 through 5 until the entire buffer is filled.
L: Program EEPROM page
1. Set BS to “0”.
2. Give WR a negative pulse. This starts programming of the EEPROM page. RDY/BSY
goes low.
3. Wait until to RDY/BSY goes high before programming the next page (See Figure 22-4 for
signal waveforms).
XTAL1
RDY/ BSY
OE
RESET +12V
PAGEL/ BS1
XA0
XA1/ BS2
DATA
ABCDEBCD
F
EGH
0x10 XXXXXX ADDR. HIGHADDR. LOWADDR. LOW DATA HIGHDATA HIGH DATA LOWDATA LOW
WR
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Figure 22-4. Programming the EEPROM Waveforms
22.8.6 Reading the Flash
The algorithm for reading the Flash memory is as follows (refer to “Programming the Flash” on
page 178 for details on Command and Address loading):
1. A: Load Command “0000 0010”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The Flash word low byte can now be read at DATA.
5. Set BS to “1”. The Flash word high byte can now be read at DATA.
6. Set OE to “1”.
22.8.7 Reading the EEPROM
The algorithm for reading the EEPROM memory is as follows (refer to “Programming the Flash”
on page 178 for details on Command and Address loading):
1. A: Load Command “0000 0011”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The EEPROM Data byte can now be read at DATA.
5. Set OE to “1”.
22.8.8 Programming the Fuse Low Bits
The algorithm for programming the Fuse Low bits is as follows (refer to “Programming the Flash”
on page 178 for details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
XTAL
RDY/ BSY
OE
RESET +12V
PAGEL/ BS1
XA0
XA1/ BS2
DATA
WR
ABCEBC
K
EG
ADDR. HIGH ADDR. LOW0x11 DATA XX ADDR. LOW DATA XX
L
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22.8.9 Programming the Fuse High Bits
The algorithm for programming the Fuse High bits is as follows (refer to “Programming the
Flash” on page 178 for details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Set BS1 to “1” and BS2 to “0”. This selects high data byte.
4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. Set BS1 to “0”. This selects low data byte.
22.8.10 Programming the Extended Fuse Bits
The algorithm for programming the Extended Fuse bits is as follows (refer to “Programming the
Flash” on page 178 for details on Command and Data loading):
1. 1. A: Load Command “0100 0000”.
2. 2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. 3. Set BS1 to “0” and BS2 to “1”. This selects extended data byte.
4. 4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. 5. Set BS2 to “0”. This selects low data byte.
Figure 22-5. Programming the FUSES Waveforms
22.8.11 Programming the Lock Bits
The algorithm for programming the Lock bits is as follows (refer to “Programming the Flash” on
page 178 for details on Command and Data loading):
1. A: Load Command “0010 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs the Lock bit. If LB mode 3 is programmed
(LB1 and LB2 is programmed), it is not possible to program the Boot Lock bits by any
External Programming mode.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
The Lock bits can only be cleared by executing Chip Erase.
XTAL1
RDY/ BSY
OE
RESET +12V
PAGEL/ BS1
XA0
XA1/ BS2
DATA
WR
AC
0x40 DATA XX
AC
DATA DATAXX XX
AC
0x400x40
Write Fuse Low Byte Write Fuse High Byte Write Extended Fuse Byte
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22.8.12 Reading the Fuse and Lock Bits
The algorithm for reading the Fuse and Lock bits is as follows (refer to “Programming the Flash”
on page 178 for details on Command loading):
1. A: Load Command “0000 0100”.
2. Set OE to “0”, BS2 to “0” and BS1 to “0”. The status of the Fuse Low bits can now be
read at DATA (“0” means programmed).
3. Set OE to “0”, BS2 to “1” and BS1 to “1”. The status of the Fuse High bits can now be
read at DATA (“0” means programmed).
4. Set OE to “0”, BS2 to “1”, and BS1 to “0”. The status of the Extended Fuse bits can now
be read at DATA (“0” means programmed).
5. Set OE to “0”, BS2 to “0” and BS1 to “1”. The status of the Lock bits can now be read at
DATA (“0” means programmed).
6. Set OE to “1”.
Figure 22-6. Mapping Between BS1, BS2 and the Fuse and Lock Bits During Read
22.8.13 Reading the Signature Bytes
The algorithm for reading the Signature bytes is as follows (refer to “Programming the Flash” on
page 178 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte (0x00 - 0x02).
3. Set OE to “0”, and BS to “0”. The selected Signature byte can now be read at DATA.
4. Set OE to “1”.
22.8.14 Reading the Calibration Byte
The algorithm for reading the Calibration byte is as follows (refer to “Programming the Flash” on
page 178 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte, 0x00.
3. Set OE to “0”, and BS1 to “1”. The Calibration byte can now be read at DATA.
4. Set OE to “1”.
Fuse Low Byte
Extended Fuse Byte
BS2
BS1
DAT
A
BS2
Lock Bits
Fuse High Byte 1
0
1
0
1
0
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22.9 Serial Downloading
Both the Flash and EEPROM memory arrays can be programmed using the serial SPI bus while
RESET is pulled to GND. The serial interface consists of pins SCK, MOSI (input) and MISO (out-
put). After RESET is set low, the Programming Enable instruction needs to be executed first
before program/erase operations can be executed. NOTE, in Table 22-13 on page 184, the pin
mapping for SPI programming is listed. Not all parts use the SPI pins dedicated for the internal
SPI interface.
Figure 22-7. Serial Programming and Verify(1)
Notes: 1. If the device is clocked by the internal Oscillator, it is no need to connect a clock source to the
CLKI pin.
When programming the EEPROM, an auto-erase cycle is built into the self-timed programming
operation (in the Serial mode ONLY) and there is no need to first execute the Chip Erase
instruction. The Chip Erase operation turns the content of every memory location in both the
Program and EEPROM arrays into 0xFF.
Depending on CKSEL Fuses, a valid clock must be present. The minimum low and high periods
for the serial clock (SCK) input are defined as follows:
Low: > 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck >= 12 MHz
High: > 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck >= 12 MHz
Table 22-13. Pin Mapping Serial Programming
Symbol Pins I/O Description
MOSI PB0 I Serial Data in
MISO PB1 O Serial Data out
SCK PB2 I Serial Clock
GND
RESET/ PB7
VCC
MOSI
MISO
SCK
+1.8 to 5.5V
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22.9.1 Serial Programming Algorithm
When writing serial data to the ATtiny261/461/861, data is clocked on the rising edge of SCK.
When reading data from the ATtiny261/461/861, data is clocked on the falling edge of SCK. See
Figure 23-6 and Figure 23-7 for timing details.
To program and verify the ATtiny261/461/861 in the Serial Programming mode, the following
sequence is recommended (see four byte instruction formats in Table 22-15):
1. Power-up sequence:
Apply power between VCC and GND while RESET and SCK are set to “0”. In some sys-
tems, the programmer can not guarantee that SCK is held low during power-up. In this
case, RESET must be given a positive pulse of at least two CPU clock cycles duration
after SCK has been set to “0”.
2. Wait for at least 20 ms and enable serial programming by sending the Programming
Enable serial instruction to pin MOSI.
3. The serial programming instructions will not work if the communication is out of synchro-
nization. When in sync. the second byte (0x53), will echo back when issuing the third
byte of the Programming Enable instruction. Whether the echo is correct or not, all four
bytes of the instruction must be transmitted. If the 0x53 did not echo back, give RESET a
positive pulse and issue a new Programming Enable command.
4. The Flash is programmed one page at a time. The memory page is loaded one byte at a
time by supplying the 5 LSB of the address and data together with the Load Program
memory Page instruction. To ensure correct loading of the page, the data low byte must
be loaded before data high byte is applied for a given address. The Program memory
Page is stored by loading the Write Program memory Page instruction with the 6 MSB of
the address. If polling (RDY/BSY) is not used, the user must wait at least tWD_FLASH before
issuing the next page. (See Table 22-14.) Accessing the serial programming interface
before the Flash write operation completes can result in incorrect programming.
5. A: The EEPROM array is programmed one byte at a time by supplying the address and
data together with the appropriate Write instruction. An EEPROM memory location is first
automatically erased before new data is written. If polling (RDY/BSY) is not used, the
user must wait at least tWD_EEPROM before issuing the next byte. (See Table 22-14.) In a
chip erased device, no 0xFFs in the data file(s) need to be programmed.
B: The EEPROM array is programmed one page at a time. The Memory page is loaded
one byte at a time by supplying the 2 LSB of the address and data together with the Load
EEPROM Memory Page instruction. The EEPROM Memory Page is stored by loading
the Write EEPROM Memory Page Instruction with the 6 MSB of the address. When using
EEPROM page access only byte locations loaded with the Load EEPROM Memory Page
instruction is altered. The remaining locations remain unchanged. If polling (RDY/BSY) is
not used, the used must wait at least tWD_EEPROM before issuing the next page (See Table
22-8). In a chip erased device, no 0xFF in the data file(s) need to be programmed.
6. Any memory location can be verified by using the Read instruction which returns the con-
tent at the selected address at serial output MISO.
7. At the end of the programming session, RESET can be set high to commence normal
operation.
8. Power-off sequence (if needed):
Set RESET to “1”.
Tur n VCC power off.
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22.9.2 Serial Programming Instruction set
Table 22-15 on page 186 and Figure 22-8 on page 187 describes the Instruction set.
Table 22-14. Minimum Wait Delay Before Writing the Next Flash or EEPROM Location
Symbol Minimum Wait Delay
tWD_FLASH 4.5 ms
tWD_EEPROM 4.0 ms
tWD_ERASE 4.0 ms
tWD_FUSE 4.5 ms
Table 22-15. Serial Programming Instruction Set
Instruction/Operation
Instruction Format
Byte 1 Byte 2 Byte 3 Byte4
Programming Enable $AC $53 $00 $00
Chip Erase (Program Memory/EEPROM) $AC $80 $00 $00
Poll RDY/BSY $F0 $00 $00 data byte out
Load Instructions
Load Extended Address byte(1) $4D $00 Extended adr $00
Load Program Memory Page, High byte $48 adr MSB adr LSB high data byte in
Load Program Memory Page, Low byte $40 adr MSB adr LSB low data byte in
Load EEPROM Memory Page (page access) $C1 $00 0000 000aa data byte in
Read Instructions
Read Program Memory, High byte $28 adr MSB adr LSB high data byte out
Read Program Memory, Low byte $20 adr MSB adr LSB low data byte out
Read EEPROM Memory $A0 $00 00aa aaaa data byte out
Read Lock bits $58 $00 $00 data byte out
Read Signature Byte $30 $00 0000 000aa data byte out
Read Fuse bits $50 $00 $00 data byte out
Read Fuse High bits $58 $08 $00 data byte out
Read Extended Fuse Bits $50 $08 $00 data byte out
Read Calibration Byte $38 $00 $00 data byte out
Write Instructions(6)
Write Program Memory Page $4C adr MSB adr LSB $00
Write EEPROM Memory $C0 $00 00aa aaaa data byte in
Write EEPROM Memory Page (page access) $C2 $00 00aa aa00 $00
Write Lock bits $AC $E0 $00 data byte in
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Notes: 1. Not all instructions are applicable for all parts.
2. a = address
3. Bits are programmed ‘0’, unprogrammed ‘1’.
4. To ensure future compatibility, unused Fuses and Lock bits should be unprogrammed (‘1’).
5. Refer to the corresponding section for Fuse and Lock bits, Calibration and Signature bytes and Page size.
6. Instructions accessing program memory use a word address. This address may be random within the page range.
7. See http://www.atmel.com/avr for Application Notes regarding programming and programmers.
If the LSB in RDY/BSY data byte out is ‘1’, a programming operation is still pending. Wait until
this bit returns ‘0’ before the next instruction is carried out.
Within the same page, the low data byte must be loaded prior to the high data byte.
After data is loaded to the page buffer, program the EEPROM page, see Figure 22-8 on page
187.
Figure 22-8. Serial Programming Instruction Example
Write Fuse bits $AC $A0 $00 data byte in
Write Fuse High bits $AC $A8 $00 data byte in
Write Extended Fuse Bits $AC $A4 $00 data byte in
Table 22-15. Serial Programming Instruction Set (Continued)
Instruction/Operation
Instruction Format
Byte 1 Byte 2 Byte 3 Byte4
Addr MSB
Bit 15 B Bit 15 00B
Load Program Memory Page (High/Low Byte)/
Load EEPROM Memory Page (Page access)
Write Program Memory Page/
Write EEPROM Memory Page
Byte 1 Byte 2 Byte 3 Byte 4
Page 0
Page 1
Page 2
Page N-1
Byte 1 Byte 2 Byte 3 Byte 4
Addr LSB
Page Offset
Page Number
Addr MSB Addr LSB
Page Buffer
Serial Programming Instruction
Program Memory/
EEPROM Memory
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23. Electrical Characteristics
23.1 Absolute Maximum Ratings*
Notes: 1. Maximum current per port = ±30mA
23.2 DC Characteristics
Operating Temperature..................................–55°C to +125°C *NOTICE: Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent dam-
age to the device. This is a stress rating only and
functional operation of the device at these or
other conditions beyond those indicated in the
operational sections of this specification is not
implied. Exposure to absolute maximum rating
conditions for extended periods may affect device
reliability.
Storage Temperature .....................................–65°C to +150°C
Voltage on any Pin except RESET
with respect to Ground ...............................–0.5V to VCC+0.5V
Voltage on RESET with respect to Ground.....–0.5V to +13.0V
Maximum Operating Voltage ............................................ 6.0V
DC Current per I/O Pin ................................................ 40.0mA
DC Current VCC and GND Pins................................. 200.0mA
Injection Current at VCC=0V .................................... ±5.0mA(1)
Injection Current at VCC=5V ....................................... ±1.0mA
TA = –40°C to +125°C, VCC = 2.7V to 5.5V (unless otherwise noted)(1)
Symbol Parameter Condition Min. Typ. Max. Units
VIL Input Low-voltage Except XTAL1 and RESET pin –0.5 0.2VCC V
VIH Input High-voltage Except XTAL1 and RESET pin 0.7VCC(3) VCC +0.5 V
VIL1 Input Low-voltage XTAL1 pin, External
Clock Selected –0.5 0.1VCC V
VIH1 Input High-voltage XTAL1 pin, External
Clock Selected 0.8VCC(3) VCC +0.5 V
VIL2 Input Low-voltage RESET pin –0.5 0.2VCC V
VIH2 Input High-voltage RESET pin 0.9VCC(3) VCC +0.5 V
VIL3 Input Low-voltage RESET pin as I/O –0.5 0.2VCC V
VIH3 Input High-voltage RESET pin as I/O 0.7VCC(3) VCC +0.5 V
VOL Output Low Voltage(4)
(Except Reset pin)
IOL = 10mA, VCC = 5V
IOL = 5mA, VCC = 3V
0.6
0.5
V
V
VOH Output High-voltage(5)
(Except Reset pin)
IOH = –10mA, VCC = 5V
IOH = –5mA, VCC = 3V
4.3
2.5
V
V
IIL Input Leakage
Current I/O Pin
Vcc = 5.5V, pin low
(absolute value) 250 nA
IIH Input Leakage
Current I/O Pin
Vcc = 5.5V, pin high
(absolute value) 250 nA
RRST Reset Pull-up Resistor 30 60 kΩ
RPU I/O Pin Pull-up Resistor 20 50 kΩ
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Notes: 1. All DC Characteristics contained in this data sheet are based on simulation and characterization of ATtiny261/461/861 AVR
microcontrollers manufactured in a typical process technology. These values are preliminary values representing design tar-
gets, and will be updated after characterization of actual Automotive silicon.
2. “Max” means the highest value where the pin is guaranteed to be read as low.
3. “Min” means the lowest value where the pin is guaranteed to be read as high.
4. Although each I/O port can sink more than the test conditions (10mA at VCC = 5V, 5mA at VCC = 3V) under steady state con-
ditions (non-transient), the following must be observed:
1] The sum of all IOL, for all ports, should not exceed 60mA.
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater
than the listed test condition.
5. Although each I/O port can source more than the test conditions (10mA at VCC = 5V, 5mA at VCC = 3V) under steady state
conditions (non-transient), the following must be observed:
1] The sum of all IOH, for all ports, should not exceed 60mA.
If IOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current
greater than the listed test condition.
6. Values using methods described in “Minimizing Power Consumption” on page 36. Power Reduction is enabled
(PRR = 0xFF) and there is no I/O drive.
7. BOD Disabled.
ICC
Power Supply Current
Active 4MHz, VCC = 3V(6) ATD On 1.45 2 mA
Active 8MHz, VCC = 5V(6) ATD On 3.96 6 mA
Active 16MHz, VCC = 5V(6) ATD On 7.16 10 mA
Idle 4MHz, VCC = 3V(6) 0.25 0.4 mA
Idle 8MHz, VCC = 5V(6) 0.96 1.2 mA
Idle 16MHz, VCC = 5V(6) 1.91 2.5 mA
Power-down mode
WDT enabled, VCC = 3V(7) 450µA
WDT disabled, VCC = 3V(7) 0.12 30 µA
WDT enabled, VCC = 5V(7) 675µA
WDT disabled, VCC = 5V(7) 0.13 45 µA
VACIO Analog Comparator
Input Offset Voltage VCC = 5V, 0.1VCC <Vin<V
CC – 100mV 10 40 mV
IACLK Analog Comparator
Input Leakage Current VCC = 5V, Vin = VCC/2 –50 50 nA
TA = –40°C to +125°C, VCC = 2.7V to 5.5V (unless otherwise noted)(1) (Continued)
Symbol Parameter Condition Min. Typ. Max. Units
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23.3 Speed Grades
Figure 23-1. Maximum Frequency vs. VCC
23.4 Clock Characteristics
23.4.1 Calibrated Internal RC Oscillator Accuracy
Notes: 1. Voltage range for ATtiny261/461/861.
23.4.2 External Clock Drive Waveforms
Figure 23-2. External Clock Drive Waveforms
Safe Operating Area
2.7V
8MHz
16MHz
5.5V4.5V
Table 23-1. Calibration Accuracy of Internal RC Oscillator
Frequency VCC Temperature Calibration Accuracy
Factory
Calibration 8.0 MHz 3V 25°C ±2%
2.7V to 5.5V(1) –40°C to +125°C ±17%
tCHCX
VIH1
VIL1
tCHCX
tCLCH tCHCL
tCLCX
tCLCL
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23.4.3 External Clock Drive
23.5 System and Reset Characteristics
Notes: 1. Values are guidelines only.
Table 23-2. External Clock Drive
Symbol Parameter
VCC = 2.7 - 5.5V VCC = 4.5 - 5.5V
UnitsMin. Max. Min. Max.
1/tCLCL Clock Frequency 0 8 0 16 MHz
tCLCL Clock Period 125 62.5 ns
tCHCX High Time 40 20 ns
tCLCX Low Time 40 20 ns
tCLCH Rise Time 1.6 0.5 µs
tCHCL Fall Time 1.6 0.5 µs
ΔtCLCL Change in period from one clock cycle to the next 2 2 %
Table 23-3. Reset, Brown-out and Internal Voltage Characteristics(1)
Symbol Parameter Condition Min Typ Max Units
tRST Minimum pulse width on
RESET Pin VCC = 3V 2.5 µs
VHYST Brown-out Detector Hysteresis 50 mV
tBOD Min Pulse Width on Brown-out
Reset 2µs
VBG Bandgap reference voltage VCC = 3.0V,
TA=25°C 1.0 1.1 1.2 V
tBG Bandgap reference start-up
time
VCC = 2.7V,
TA=25°C 40 70 µs
IBG Bandgap reference current
consumption
VCC = 2.7V,
TA=25°C 15 µA
Table 23-4. BODLEVEL Fuse Coding(1)
BODLEVEL [2..0] Fuses Min VBOT Typ VBOT Max VBOT Units
111 BOD Disabled
110 1.68 1.8 1.92
V101 2.5 2.7 2.9
100 4.0 4.3 4.6
011
Reserved
010
001
000
Note: 1. VBOT may be below nominal minimum operating voltage for some devices. For devices where
this is the case, the device is tested down to VCC = VBOT during the production test. This guar-
antees that a Brown-out Reset will occur before VCC drops to a voltage where correct
operation of the microcontroller is no longer guaranteed.
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23.6 ADC Characteristics
Table 23-5. ADC Characteristics, Single Ended Channels, -40°C +125°C
Symbol Parameter Condition Min Typ Max Units
Resolution Single Ended Conversion 10 Bits
TUE Absolute accuracy VCC = 4V, VREF = 4V,
ADC clock = 200 kHz 2.0 4.0 LSB
INL Integral Non-linearity VCC = 4V,VREF = 4V,
ADC clock = 200 kHz 0.6 1.8 LSB
DNL Differential Non-linearity (DNL) VCC = 4V, VREF = 4V,
ADC clock = 200 kHz 0.2 0.6 LSB
Gain Error VCC = 4V, VREF = 4V,
ADC clock = 200 kHz -5.0 -2.0 3.0 LSB
Offset Error VCC = 4V, VREF = 4V,
ADC clock = 200 kHz -3.5 1.2 3.5 LSB
VREF External Reference Voltage 2.56 AVCC V
Clock Frequency 50 200 kHz
AVCC Analog Supply Frequency VCC - 0.3 VCC + 0.3 V
VINT Internal Voltage Reference 1.0 1.1 1.2 V
RAIN Analog Input Resistance 100 MΩ
RRef Reference Input Resistance 21 30 39 kΩ
Temperature Sensor Accuracy
After Firmware Calibration
Internal VREF
VCC = 3V
±10 °C
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Table 23-6. ADC Characteristics, Differential Channels, -40°C +125°C
Symbol Parameter Condition Min Typ Max Units
Resolution
Differential conversion,
gain = 1x or 8x 8
Bits
Differential conversion,
gain = 20x or 32x 8
TUE Absolute accuracy
Gain = 1x / 8x, BIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
1.7 4.0
LSB
Gain = 20x / 32x, BIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
2.0 5.0
Gain = 1x / 8x, UNIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
2.3 5.0
Gain = 20x / 32x, UNIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
3.0 6.0
INL Integral Non-linearity
Gain = 1x / 8x, BIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
0.3 1.5
LSB
Gain = 20x / 32x, BIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
0.7 3.0
Gain = 1x / 8x, UNIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
1.0 3.0
Gain = 20x / 32x, UNIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
2.0 6.0
DNL Differential Non-linearity
Gain = 1x / 8x, BIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
0.3 1.0
LSB
Gain = 20x / 32x, BIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
0.4 1.2
Gain = 1x / 8x, UNIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
0.4 1.0
Gain = 20x / 32x, UNIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
0.8 2.5
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Gain error
Gain = 1x / 8x, BIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
-4.0 2.0 4.0
LSB
Gain = 20x / 32x, BIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
-4.0 1.4 4.0
Gain = 1x / 8x, UNIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
-5.0 -2.6 5.0
Gain = 20x / 32x, UNIPOLAR,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
-5.0 -0.8 5.0
Offset error
Gain = 1x,
VCC = 5V, VREF = 4V,
ADC clock = 200 kHz
-3.0 0.6 3.0 LSB
VREF External Reference voltage 2.56 AVCC-0.5 V
Table 23-6. ADC Characteristics, Differential Channels, -40°C +125°C (Continued)
Symbol Parameter Condition Min Typ Max Units
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23.7 Parallel Programming Characteristics
Figure 23-3. Parallel Programming Timing, Including some General Timing Requirements
Figure 23-4. Parallel Programming Timing, Loading Sequence with Timing Requirements(1)
Note: 1. The timing requirements shown in Figure 23-3 (i.e., tDVXH, tXHXL, and tXLDX) also apply to load-
ing operation.
XTAL1
WR
RDY/ BSY
Data and Control
(DATA, XA0,
XA1/ BS2,
PAGEL/BS1)
tXHXL
tXLWL
tDVXH
tBVPH tPLBX tBVWL tWLBX
tPLWL
tWLWH
tWLRL
tWLRH
tXLDX
XTAL1
PAGEL/BS1
DATA
XA0
XA1/BS2
tXLXH
Load Address
(Low Byte)
Load Data
(Low Byte)
Load Data
(High Byte)
Load Address
(Low Byte)
ADDR0 (Low Byte) ADDR1 (Low Byte)DATA (Low Byte) DATA (High Byte)
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Figure 23-5. Parallel Programming Timing, Reading Sequence (within the Same Page) with
Timing Requirements(1)
Note: 1. The timing requirements shown in Figure 23-3 (i.e., tDVXH, tXHXL, and tXLDX) also apply to read-
ing operation.
Table 23-7. Parallel Programming Characteristics, VCC = 5V ± 10%
Symbol Parameter Min Typ Max Units
VPP Programming Enable Voltage 11.5 12.5 V
IPP Programming Enable Current 250 µA
tDVXH Data and Control Valid before XTAL1 High 67 ns
tXLXH XTAL1 Low to XTAL1 High 200 ns
tXHXL XTAL1 Pulse Width High 150 ns
tXLDX Data and Control Hold after XTAL1 Low 67 ns
tXLWL XTAL1 Low to WR Low 0 ns
tBVPH BS1 Valid before PAGEL High 67 ns
tPHPL PAGEL Pulse Width High 150 ns
tPLBX BS1 Hold after PAGEL Low 67 ns
tWLBX BS2/1 Hold after WR Low 67 ns
tPLWL PAGEL Low to WR Low 67 ns
tBVWL BS1 Valid to WR Low 67 ns
tWLWH WR Pulse Width Low 150 ns
tWLRL WR Low to RDY/BSY Low 0 1 µs
tWLRH WR Low to RDY/BSY High(1) 3.7 4.5 ms
tWLRH_CE WR Low to RDY/BSY High for Chip Erase(2) 7.5 9 ms
tXLOL XTAL1 Low to OE Low 0 ns
tBVDV BS1 Valid to DATA valid 0 250 ns
tOLDV OE Low to DATA Valid 250 ns
tOHDZ OE High to DATA Tri-stated 250 ns
Notes: 1. tWLRH is valid for the Write Flash, Write EEPROM, Write Fuse bits and Write Lock bits
commands.
2. tWLRH_CE is valid for the Chip Erase command.
XTAL1
PAGEL/BS1
DATA
OE
XA0
XA1/BS2
tXLOL
tOLDV
tOHDZ
tBVDV
Load Address
(Low Byte)
Load Data
(Low Byte)
Read Data
(High Byte)
Load Address
(Low Byte)
ADDR0 (Low Byte) ADDR1 (Low Byte)DATA (Low Byte) DATA (High Byte)
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23.8 Serial Programming Characteristics
Figure 23-6. Serial Programming Waveforms
Figure 23-7. Serial Programming Timing
Note: 1. 2 tCLCL for fck < 12 MHz, 3 tCLCL for fck >= 12 MHz
Table 23-8. Serial Programming Characteristics, TA = -40°C to 125°C, VCC = 2.7 - 5.5V
(Unless Otherwise Noted)
Symbol Parameter Min Typ Max Units
1/tCLCL Oscillator Frequency (ATtiny261/461/861V) 0 4 MHz
tCLCL Oscillator Period (ATtiny261/461/861V) 250 ns
1/tCLCL Oscillator Frequency (ATtiny261/461/861L, VCC =
2.7 - 5.5V) 010MHz
tCLCL Oscillator Period (ATtiny261/461/861L, VCC = 2.7 -
5.5V) 100 ns
1/tCLCL Oscillator Frequency (ATtiny261/461/861, VCC = 4.5V
- 5.5V) 016MHz
tCLCL Oscillator Period (ATtiny261/461/861, VCC = 4.5V -
5.5V) 50 ns
tSHSL SCK Pulse Width High 2 tCLCL* ns
tSLSH SCK Pulse Width Low 2 tCLCL*ns
tOVSH MOSI Setup to SCK High tCLCL ns
tSHOX MOSI Hold after SCK High 2 tCLCL ns
tSLIV SCK Low to MISO Valid TBD TBD TBD ns
MSB
SERIAL DATA INPUT
(MOSI)
SERIAL DATA OUTPUT
(MISO) MSB
LSB
LSB
SERIAL CLOCK INPUT
(SCK)
SAMPLE
MOSI
SCK
MISO
tOVSH tSHOX
tSHSL
tSLSH
tSLIV
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24. Typical Characteristics
The data contained in this section is largely based on simulations and characterization of similar
devices in the same process and design methods. These values are preliminary values representing
design targets, and will be updated after characterization of actual Automotive silicon.
Thus, the data should be treated as indications of how the part will behave.
The following charts show typical behavior. These figures are not tested during manufacturing.
All current consumption measurements are performed with all I/O pins configured as inputs and
with internal pull-ups enabled. A sine wave generator with rail-to-rail output is used as clock
source.
The power consumption in Power-down mode is independent of clock selection.
The current consumption is a function of several factors such as: operating voltage, operating
frequency, loading of I/O pins, switching rate of I/O pins, code executed and ambient tempera-
ture. The dominating factors are operating voltage and frequency.
The current drawn from capacitive loaded pins may be estimated (for one pin) as CL*VCC*f where
CL = load capacitance, VCC = operating voltage and f = average switching frequency of I/O pin.
The parts are characterized at frequencies higher than test limits. Parts are not guaranteed to
function properly at frequencies higher than the ordering code indicates.
The difference between current consumption in Power-down mode with Watchdog Timer
enabled and Power-down mode with Watchdog Timer disabled represents the differential cur-
rent drawn by the Watchdog Timer.
Unless otherwise specified the data contained in this chapter are for -40°C to +85°C.
24.1 Active Supply Current
Figure 24-1. Active Supply Current vs. Low Frequency (0.1 - 1.0 MHz)
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Figure 24-2. Active Supply Current vs. Frequency (1 - 16 MHz)
24.2 Idle Supply Current
Figure 24-3. Idle Supply Current vs. Frequency (1 - 16 MHz)
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24.3 Supply Current of I/O modules
The tables and formulas below can be used to calculate the additional current consumption for
the different I/O modules in Active and Idle mode. The enabling or disabling of the I/O modules
are controlled by the Power Reduction Register. See “PRR – Power Reduction Register” on
page 38 for details.
It is possible to calculate the typical current consumption based on the numbers from Table 24-1
for other VCC and frequency settings than listed in Table 24-2.
24.3.1 Example
Calculate the expected current consumption in idle mode with TIMER0, ADC, and USI enabled
at VCC = 2.0V and F = 1MHz. From Table 24-2, third column, we see that we need to add 10%
for the TIMER0, 27.3% for the ADC, and 6.5% for the USI module. Reading from Figure 24-3 on
page 199, we find that the idle current consumption is ~0,085 mA at VCC = 2.0V and F=1MHz.
The total current consumption in idle mode with TIMER0, ADC, and USI enabled, gives:
Table 24-1. Additional Current Consumption for the different I/O modules (absolute values)
PRR bit Typical numbers
VCC = 2V, F = 1MHz VCC = 3V, F = 4MHz VCC = 5V, F = 8MHz
PRTIM1 65 uA 423 uA 1787 uA
PRTIM0 7 uA 39 uA 165 uA
PRUSI 5 uA 25 uA 457 uA
PRADC 18 uA 111 uA 102 uA
Table 24-2. Additional Current Consumption (percentage) in Active and Idle mode
PRR bit
Additional Current consumption
compared to Active with external
clock (see Figure 24-1 on page 198
and Figure 24-2 on page 199)
Additional Current consumption
compared to Idle with external clock
PRTIM1 26.9% 103.7%
PRTIM0 2.6% 10.0%
PRUSI 1.7% 6.5%
PRADC 7.1% 27.3%
ICCtotal 0,085mA 1 0,10 0,273 0,065++ +()•0,122mA≈≈
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24.4 Power-down Supply Current
Figure 24-4. Power-down Supply Current vs. VCC (Watchdog Timer Disabled)
Figure 24-5. Power-down Supply Current vs. VCC (Watchdog Timer Enabled)
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24.5 Pin Pull-up
Figure 24-6. I/O Pin pull-up Resistor Current vs. Input Voltage (VCC = 5V)
Figure 24-7. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 5V)
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24.6 Pin Driver Strength
Figure 24-8. I/O Pin Output Voltage vs. Sink Current (VCC = 3V)
Figure 24-9. I/O Pin Output Voltage vs. Sink Current (VCC = 5V)
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Figure 24-10. I/O Pin Output Voltage vs. Source Current (VCC = 3V)
Figure 24-11. I/O Pin Output Voltage vs. Source Current (VCC = 5V)
24.7 Pin Threshold and Hysteresis
Figure 24-12. I/O Pin Input Threshold Voltage vs. VCC (VIH, I/O Pin Read as ‘1’)
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Figure 24-13. I/O Pin Input Threshold Voltage vs. VCC (VIL, I/O Pin Read as ‘0’)
Figure 24-14. Reset Input Threshold Voltage vs. VCC (VIH, Reset Read as ‘1’)
Figure 24-15. Reset Input Threshold Voltage vs. VCC (VIL, Reset Read as ‘0’)
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24.8 BOD Threshold and Analog Comparator Offset
Figure 24-16. BOD Threshold vs. Temperature (BOD Level is 4.3V)
Figure 24-17. BOD Threshold vs. Temperature (BOD Level is 2.7V)
Figure 24-18. BOD Threshold vs. Temperature (BOD Level is 1.8V)
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24.9 Internal Oscillator Speed
Figure 24-19. Watchdog Oscillator Frequency vs. Temperature
Figure 24-20. Calibrated 8.0 MHz RC Oscillator Frequency vs. Temperature
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25. Register Summary
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
0x3F (0x5F) SREG I T H S V N Z C page 11
0x3E (0x5E) SPH – – – – – SP10 SP9 SP8 page 13
0x3D (0x5D) SPL SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 page 13
0x3C (0x5C) Reserved –
0x3B (0x5B) GIMSK INT1 INT0 PCIE1 PCIE0 – – – – page 53
0x3A (0x5A) GIFR INTF1 INTF0 PCIF – – – – – page 53
0x39 (0x59) TIMSK OCIE1D OCIE1A OCIE1B OCIE0A OCIE0B TOIE1 TOIE0 TICIE0 page 87, page 125
0x38 (0x58) TIFR OCF1D OCF1A OCF1B OCF0A OCF0B TOV1 TOV0 ICF0 page 88, page 126
0x37 (0x57) SPMCSR –– SIGRD CTPB RFLB PGWRT PGERS SPMEN page 170
0x36 (0x56) PRR PRTIM1 PRTIM0 PRUSI PRADC page 36
0x35 (0x55) MCUCR –PUDSESM1SM0 –ISC01ISC00page 38, page 69, page 52
0x34 (0x54) MCUSR – – – – WDRF BORF EXTRF PORF page 46,
0x33 (0x53) TCCR0B – – – TSM PSR0 CS02 CS01 CS00 page 71
0x32 (0x52) TCNT0L Timer/Counter0 Counter Register Low Byte page 86
0x31 (0x51) OSCCAL Oscillator Calibration Register page 32
0x30 (0x50) TCCR1A COM1A1 COM1A0 COM1B1 COM1B0 FOC1A FOC1B PWM1A PWM1B page 115
0x2F (0x4F) TCCR1B PWM1X PSR1 DTPS11 DTPS10 CS13 CS12 CS11 CS10 page 170
0x2E (0x4E) TCNT1 Timer/Counter1 Counter Register page 123
0x2D (0x4D) OCR1A Timer/Counter1 Output Compare Register A page 124
0x2C (0x4C) OCR1B Timer/Counter1 Output Compare Register B page 124
0x2B (0x4B) OCR1C Timer/Counter1 Output Compare Register C page 124
0x2A (0x4A) OCR1D Timer/Counter1 Output Compare Register D page 125
0x29 (0x49) PLLCSR LSM PCKE PLLE PLOCK page 90
0x28 (0x48) CLKPR CLKPCE CLKPS3 CLKPS2 CLKPS1 CLKPS0 page 33
0x27 (0x47) TCCR1C COM1A1S COM1A0S COM1B1S COM1B0S COM1D1 COM1D0 FOC1D PWM1D page 119
0x26 (0x46) TCCR1D FPIE1 FPEN1 FPNC1 FPES1 FPAC1 FPF1 WGM11 WGM10 page 121
0x25 (0x45) TC1H TC19 TC18 page 123
0x24 (0x44) DT1 DT1H3 DT1H2 DT1H1 DT1H0 DT1L3 DT1L2 DT1L1 DT1L0 page 127
0x23 (0x43) PCMSK0 PCINT7 PCINT6 PCINT5 PCINT4 PCINT3 PCINT2 PCINT1 PCINT0 page 54
0x22 (0x42) PCMSK1 PCINT15 PCINT14 PCINT13 PCINT12 PCINT11 PCINT10 PCINT9 PCINT8 page 54
0x21 (0x41) WDTCR WDIF WDIE WDP3 WDCE WDE WDP2 WDP1 WDP0 page 46
0x20 (0x40) DWDR DWDR[7:0] page 36
0x1F (0x3F) EEARH EEAR8 page 22
0x1E (0x3E) EEARL EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 page 22
0x1D (0x3D) EEDR EEPROM Data Register page 23
0x1C (0x3C) EECR –– EEPM1 EEPM0 EERIE EEMPE EEPE EERE page 23
0x1B (0x3B) PORTA PORTA7 PORTA6 PORTA5 PORTA4 PORTA3 PORTA2 PORTA1 PORTA0 page 69
0x1A (0x3A) DDRA DDA7 DDA6 DDA5 DDA4 DDA3 DDA2 DDA1 DDA0 page 69
0x19 (0x39) PINA PINA7 PINA6 PINA5 PINA4 PINA3 PINA2 PINA1 PINA0 page 69
0x18 (0x38) PORTB PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 page 69
0x17 (0x37) DDRB DDB7 DDB6 DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 page 69
0x16 (0x36) PINB PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 page 69
0x15 (0x35) TCCR0A TCW0 ICEN0 ICNC0 ICES0 ACIC0 CTC0 page 85
0x14 (0x34) TCNT0H Timer/Counter0 Counter Register High Byte page 86
0x13 (0x33) OCR0A Timer/Counter0 Output Compare Register A page 86
0x12 (0x32) OCR0B Timer/Counter0 Output Compare Register B page 86
0x11 (0x31) USIPP USIPOS page 139
0x10 (0x30) USIBR USI Buffer Register page 136
0x0F (0x2F) USIDR USI Data Register page 135
0x0E (0x2E) USISR USISIF USIOIF USIPF USIDC USICNT3 USICNT2 USICNT1 USICNT0 page 136
0x0D (0x2D) USICR USISIE USIOIE USIWM1 USIWM0 USICS1 USICS0 USICLK USITC page 137
0x0C (0x2C) GPIOR2 General Purpose I/O Register 2 page 24
0x0B (0x2B) GPIOR1 General Purpose I/O Register 1 page 24
0x0A (0x2A) GPIOR0 General Purpose I/O Register 0 page 24
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses
should never be written.
2. I/O Registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the Status Flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and SBI
instructions will only operation the specified bit, and can therefore be used on registers containing such Status Flags. The
CBI and SBI instructions work with registers 0x00 to 0x1F only.
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0x09 (0x29) ACSRB HSEL HLEV ACM2 ACM1 ACM0 page 143
0x08 (0x28) ACSRA ACD ACBG ACO ACI ACIE ACME ACIS1 ACIS0 page 140
0x07 (0x27) ADMUX REFS1 REFS0 ADLAR MUX4 MUX3 MUX2 MUX1 MUX0 page 158
0x06 (0x26) ADCSRA ADEN ADSC ADATE ADIF ADIE ADPS2 ADPS1 ADPS0 page 161
0x05 (0x25) ADCH ADC Data Register High Byte page 162
0x04 (0x24) ADCL ADC Data Register Low Byte page 162
0x03 (0x23) ADCSRB BIN GSEL REFS2MUX5ADTS2ADTS1ADTS0 page 163
0x02 (0x22) DIDR1 ADC10D ADC9D ADC8D ADC7D page 164
0x01 (0x21) DIDR0 ADC6D ADC5D ADC4D ADC3D AREFD ADC2D ADC1D ADC0D page 164
0x00 (0x20) TCCR1E –- OC1OE5 OC1OE4 OC1OE3 OC1OE2 OC1OE1 OC1OE0 page 122
25. Register Summary (Continued)
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses
should never be written.
2. I/O Registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the Status Flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and SBI
instructions will only operation the specified bit, and can therefore be used on registers containing such Status Flags. The
CBI and SBI instructions work with registers 0x00 to 0x1F only.
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26. Instruction Set Summary
Mnemonics Operands Description Operation Flags #Clocks
ARITHMETIC AND LOGIC INSTRUCTIONS
ADD Rd, Rr Add two Registers Rd ← Rd + Rr Z,C,N,V,H 1
ADC Rd, Rr Add with Carry two Registers Rd ← Rd + Rr + C Z,C,N,V,H 1
ADIW Rdl,K Add Immediate to Word Rdh:Rdl ← Rdh:Rdl + K Z,C,N,V,S 2
SUB Rd, Rr Subtract two Registers Rd ← Rd - Rr Z,C,N,V,H 1
SUBI Rd, K Subtract Constant from Register Rd ← Rd - K Z,C,N,V,H 1
SBC Rd, Rr Subtract with Carry two Registers Rd ← Rd - Rr - C Z,C,N,V,H 1
SBCI Rd, K Subtract with Carry Constant from Reg. Rd ← Rd - K - C Z,C,N,V,H 1
SBIW Rdl,K Subtract Immediate from Word Rdh:Rdl ← Rdh:Rdl - K Z,C,N,V,S 2
AND Rd, Rr Logical AND Registers Rd ← Rd • Rr Z,N,V 1
ANDI Rd, K Logical AND Register and Constant Rd ← Rd • K Z,N,V 1
OR Rd, Rr Logical OR Registers Rd ← Rd v Rr Z,N,V 1
ORI Rd, K Logical OR Register and Constant Rd ← Rd v K Z,N,V 1
EOR Rd, Rr Exclusive OR Registers Rd ← Rd ⊕ Rr Z,N,V 1
COM Rd One’s Complement Rd ← 0xFF − Rd Z,C,N,V 1
NEG Rd Two’s Complement Rd ← 0x00 − Rd Z,C,N,V,H 1
SBR Rd,K Set Bit(s) in Register Rd ← Rd v K Z,N,V 1
CBR Rd,K Clear Bit(s) in Register Rd ← Rd • (0xFF - K) Z,N,V 1
INC Rd Increment Rd ← Rd + 1 Z,N,V 1
DEC Rd Decrement Rd ← Rd − 1 Z,N,V 1
TST Rd Test for Zero or Minus Rd ← Rd • Rd Z,N,V 1
CLR Rd Clear Register Rd ← Rd ⊕ Rd Z,N,V 1
SER Rd Set Register Rd ← 0xFF None 1
BRANCH INSTRUCTIONS
RJMP k Relative Jump PC ← PC + k + 1 None 2
IJMP Indirect Jump to (Z) PC ← Z None 2
RCALL k Relative Subroutine Call PC ← PC + k + 1 None 3
ICALL Indirect Call to (Z) PC ← ZNone3
RET Subroutine Return PC ← STACK None 4
RETI Interrupt Return PC ← STACK I 4
CPSE Rd,Rr Compare, Skip if Equal if (Rd = Rr) PC ← PC + 2 or 3 None 1/2/3
CP Rd,Rr Compare Rd − Rr Z, N,V,C,H 1
CPC Rd,Rr Compare with Carry Rd − Rr − CZ, N,V,C,H1
CPI Rd,K Compare Register with Immediate Rd − KZ, N,V,C,H1
SBRC Rr, b Skip if Bit in Register Cleared if (Rr(b)=0) PC ← PC + 2 or 3 None 1/2/3
SBRS Rr, b Skip if Bit in Register is Set if (Rr(b)=1) PC ← PC + 2 or 3 None 1/2/3
SBIC P, b Skip if Bit in I/O Register Cleared if (P(b)=0) PC ← PC + 2 or 3 None 1/2/3
SBIS P, b Skip if Bit in I/O Register is Set if (P(b)=1) PC ← PC + 2 or 3 None 1/2/3
BRBS s, k Branch if Status Flag Set if (SREG(s) = 1) then PC←PC+k + 1 None 1/2
BRBC s, k Branch if Status Flag Cleared if (SREG(s) = 0) then PC←PC+k + 1 None 1/2
BREQ k Branch if Equal if (Z = 1) then PC ← PC + k + 1 None 1/2
BRNE k Branch if Not Equal if (Z = 0) then PC ← PC + k + 1 None 1/2
BRCS k Branch if Carry Set if (C = 1) then PC ← PC + k + 1 None 1/2
BRCC k Branch if Carry Cleared if (C = 0) then PC ← PC + k + 1 None 1/2
BRSH k Branch if Same or Higher if (C = 0) then PC ← PC + k + 1 None 1/2
BRLO k Branch if Lower if (C = 1) then PC ← PC + k + 1 None 1/2
BRMI k Branch if Minus if (N = 1) then PC ← PC + k + 1 None 1/2
BRPL k Branch if Plus if (N = 0) then PC ← PC + k + 1 None 1/2
BRGE k Branch if Greater or Equal, Signed if (N ⊕ V= 0) then PC ← PC + k + 1 None 1/2
BRLT k Branch if Less Than Zero, Signed if (N ⊕ V= 1) then PC ← PC + k + 1 None 1/2
BRHS k Branch if Half Carry Flag Set if (H = 1) then PC ← PC + k + 1 None 1/2
BRHC k Branch if Half Carry Flag Cleared if (H = 0) then PC ← PC + k + 1 None 1/2
BRTS k Branch if T Flag Set if (T = 1) then PC ← PC + k + 1 None 1/2
BRTC k Branch if T Flag Cleared if (T = 0) then PC ← PC + k + 1 None 1/2
BRVS k Branch if Overflow Flag is Set if (V = 1) then PC ← PC + k + 1 None 1/2
BRVC k Branch if Overflow Flag is Cleared if (V = 0) then PC ← PC + k + 1 None 1/2
BRIE k Branch if Interrupt Enabled if ( I = 1) then PC ← PC + k + 1 None 1/2
BRID k Branch if Interrupt Disabled if ( I = 0) then PC ← PC + k + 1 None 1/2
BIT AND BIT-TEST INSTRUCTIONS
SBI P,b Set Bit in I/O Register I/O(P,b) ← 1None2
CBI P,b Clear Bit in I/O Register I/O(P,b) ← 0None2
LSL Rd Logical Shift Left Rd(n+1) ← Rd(n), Rd(0) ← 0 Z,C,N,V 1
LSR Rd Logical Shift Right Rd(n) ← Rd(n+1), Rd(7) ← 0 Z,C,N,V 1
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ROL Rd Rotate Left Through Carry Rd(0)←C,Rd(n+1)← Rd(n),C←Rd(7) Z,C,N,V 1
ROR Rd Rotate Right Through Carry Rd(7)←C,Rd(n)← Rd(n+1),C←Rd(0) Z,C,N,V 1
ASR Rd Arithmetic Shift Right Rd(n) ← Rd(n+1), n=0..6 Z,C,N,V 1
SWAP Rd Swap Nibbles Rd(3..0)←Rd(7..4),Rd(7..4)←Rd(3..0) None 1
BSET s Flag Set SREG(s) ← 1 SREG(s) 1
BCLR s Flag Clear SREG(s) ← 0 SREG(s) 1
BST Rr, b Bit Store from Register to T T ← Rr(b) T 1
BLD Rd, b Bit load from T to Register Rd(b) ← TNone1
SEC Set Carry C ← 1C1
CLC Clear Carry C ← 0 C 1
SEN Set Negative Flag N ← 1N1
CLN Clear Negative Flag N ← 0 N 1
SEZ Set Zero Flag Z ← 1Z1
CLZ Clear Zero Flag Z ← 0 Z 1
SEI Global Interrupt Enable I ← 1I1
CLI Global Interrupt Disable I ← 0 I 1
SES Set Signed Test Flag S ← 1S1
CLS Clear Signed Test Flag S ← 0 S 1
SEV Set Twos Complement Overflow. V ← 1V1
CLV Clear Twos Complement Overflow V ← 0 V 1
SET Set T in SREG T ← 1T1
CLT Clear T in SREG T ← 0 T 1
SEH Set Half Carry Flag in SREG H ← 1H1
CLH Clear Half Carry Flag in SREG H ← 0 H 1
DATA TRANSFER INSTRUCTIONS
MOV Rd, Rr Move Between Registers Rd ← Rr None 1
MOVW Rd, Rr Copy Register Word Rd+1:Rd ← Rr+1:Rr None 1
LDI Rd, K Load Immediate Rd ← KNone1
LD Rd, X Load Indirect Rd ← (X) None 2
LD Rd, X+ Load Indirect and Post-Inc. Rd ← (X), X ← X + 1 None 2
LD Rd, - X Load Indirect and Pre-Dec. X ← X - 1, Rd ← (X) None 2
LD Rd, Y Load Indirect Rd ← (Y) None 2
LD Rd, Y+ Load Indirect and Post-Inc. Rd ← (Y), Y ← Y + 1 None 2
LD Rd, - Y Load Indirect and Pre-Dec. Y ← Y - 1, Rd ← (Y) None 2
LDD Rd,Y+q Load Indirect with Displacement Rd ← (Y + q) None 2
LD Rd, Z Load Indirect Rd ← (Z) None 2
LD Rd, Z+ Load Indirect and Post-Inc. Rd ← (Z), Z ← Z+1 None 2
LD Rd, -Z Load Indirect and Pre-Dec. Z ← Z - 1, Rd ← (Z) None 2
LDD Rd, Z+q Load Indirect with Displacement Rd ← (Z + q) None 2
LDS Rd, k Load Direct from SRAM Rd ← (k) None 2
ST X, Rr Store Indirect (X) ← Rr None 2
ST X+, Rr Store Indirect and Post-Inc. (X) ← Rr, X ← X + 1 None 2
ST - X, Rr Store Indirect and Pre-Dec. X ← X - 1, (X) ← Rr None 2
ST Y, Rr Store Indirect (Y) ← Rr None 2
ST Y+, Rr Store Indirect and Post-Inc. (Y) ← Rr, Y ← Y + 1 None 2
ST - Y, Rr Store Indirect and Pre-Dec. Y ← Y - 1, (Y) ← Rr None 2
STD Y+q,Rr Store Indirect with Displacement (Y + q) ← Rr None 2
ST Z, Rr Store Indirect (Z) ← Rr None 2
ST Z+, Rr Store Indirect and Post-Inc. (Z) ← Rr, Z ← Z + 1 None 2
ST -Z, Rr Store Indirect and Pre-Dec. Z ← Z - 1, (Z) ← Rr None 2
STD Z+q,Rr Store Indirect with Displacement (Z + q) ← Rr None 2
STS k, Rr Store Direct to SRAM (k) ← Rr None 2
LPM Load Program Memory R0 ← (Z) None 3
LPM Rd, Z Load Program Memory Rd ← (Z) None 3
LPM Rd, Z+ Load Program Memory and Post-Inc Rd ← (Z), Z ← Z+1 None 3
SPM Store Program Memory (z) ← R1:R0 None
IN Rd, P In Port Rd ← PNone1
OUT P, Rr Out Port P ← Rr None 1
PUSH Rr Push Register on Stack STACK ← Rr None 2
POP Rd Pop Register from Stack Rd ← STACK None 2
MCU CONTROL INSTRUCTIONS
NOP No Operation None 1
SLEEP Sleep (see specific descr. for Sleep function) None 1
WDR Watchdog Reset (see specific descr. for WDR/Timer) None 1
BREAK Break For On-chip Debug Only None N/A
26. Instruction Set Summary (Continued)
Mnemonics Operands Description Operation Flags #Clocks
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27. Ordering Information
Notes: 1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging, complies to the European Directive for Restriction of Hazardous Substances (RoHS directive).
Also Halide free and fully Green.
3. For Speed vs. VCC, see Figure 23.3 on page 190.
Table 27-1. Available Product Offering
Ordering Code(2) Speed (MHz)(3) Power Supply (V) Package(1) Operation Range
ATtiny261-15SZ 16 2.7 - 5.5 TG Automotive (-40° to +125°C)
ATtiny261-15MZ 16 2.7 - 5.5 PN Automotive (-40° to +125°C)
ATtiny261-15XZ 16 2.7 - 5.5 6G Automotive (-40° to +125°C)
ATtiny261-15MAZ 16 2.7 - 5.5 PC Automotive (-40° to +125°C)
ATtiny461-15SZ 16 2.7 - 5.5 TG Automotive (-40° to +125°C)
ATtiny461-15MZ 16 2.7 - 5.5 PN Automotive (-40° to +125°C)
ATtiny461-15XZ 16 2.7 - 5.5 6G Automotive (-40° to +125°C)
ATtiny461-15MAZ 16 2.7 - 5.5 PC Automotive (-40° to +125°C)
ATtiny861-15SZ 16 2.7 - 5.5 TG Automotive (-40° to +125°C)
ATtiny861-15MZ 16 2.7 - 5.5 PN Automotive (-40° to +125°C)
ATtiny861-15XZ 16 2.7 - 5.5 6G Automotive (-40° to +125°C)
ATtiny861-15MAZ 16 2.7 - 5.5 PC Automotive (-40° to +125°C)
Package Type
PN 32-pad, 5.0x5.0 mm Body, Lead Pitch 0.50 mm, Quad Flat No Lead Package (QFN)
TG 20-lead, 0.300" Wide Body Lead, Plastic Gull Wing Small Outline Package (SOIC)
6G
20-lead, 4.4x6.5 mm Body, 0.65 mm Pitch, Lead Length: 0.6 mm
Thin Shrink Small Outline Package (TSSOP)
PC 20-lead, 4.0x4.0 mm Body, 0.50 mm Pitch, Quad Flat No Lead Package (QFN)
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28. Packaging Information
Figure 28-1. PN
Package Drawing Contact:
packagedrawings@atmel.com
GPC DRAWING NO.
REV. TITLE
PNZMF I
01/31/12
PN, 32 Leads - 0.50mm Pitch, 5x5mm
Very Thin Quad Flat no Lead Package (VQFN) Sawn
D
E
D2
E2
1
b
PIN1 ID
e
See Options
A, B
Option A
Pin 1# Chamfer
(C 0.30)
Pin 1# Notch
(C 0.20 R)
Option B
L
Drawings not scaled
N
1.Notes:
2.
This drawing is for general information only. Refer to JEDEC Drawing MO-220, Variation VHHD-2, for proper dimensions, tolerances, datums, etc.
Dimensions b applies to metallized terminal and is measured between 0.15mm and 0.30mm from the terminal tip.
If the terminal has the optical radius on the other end of the terminal, the dimensions should not be measured in that radius area.
A
A3
A1
0.080 C
C
1
0.30
Dia. Typ. Laser Marking
Seating Plane
COMMON DIMENSIONS
(Unit of Measure = mm)
MIN NOM NOTEMAXSymbol
0.050.00
0.80 0.85
A1
0.500.30 0.40L
32
0.50 BSC
n
e
0.30 20.18 0.25b
3.203.00 3.10D2/E2
5.00 BSCD/E
0.20 REFA3
0.90A
Top View Side View
Bottom View
214
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Figure 28-2. TG
Package Drawing Contact:
packagedrawings@atmel.com
GPC DRAWING NO.
REV. TITLE
TG N
09/10/07
TG, 20 Lead, 0.300” Body Width
Plastic Gull Wing Small outline Package (SOIC)
MM
A 2.65 .0932.35 .104
A1 0.300.10 .004 .012
B0.490.35 .014 .019
C0.320.23 .009 .013
D 13.0012.60 .496 .512
E7.607.40 .291 .299
L
N20
Q0° 8°
20
1.270.40
0.750.25
.016 .050
e BSC1.27 .050
.394 .419
.010 .029
BSC
INCH
SEATING PLANE
h x 45°
0.25 (0.010)
0.25 (0.010)
0.356mm (0.014)MIN
0.10 (0.004) C
A
AA1
D
D
eC
M
MDBAS
MB
INDEX
AREA
H
E
N
C
Q
1
B
B
H
h
10.00 10.65
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Figure 28-3. 6G
Package Drawing Contact:
packagedrawings@atmel.com
GPC DRAWING NO.
REV. TITLE
6G A
20/12/07
6G, 20 Leads - 4.4x6.5mm Body - 0.65mm Pitch - Lead length: 0.6mm
THIN SHRINK SMALL OUTLINE
INDEX
AREA
N
0.10 ( . 004 )
0.25 ( . 010 )
H
C
C
L
A
A
MM
A 1.10 .043
A1 0.150.05 .002 .006
b0.300.19 .007 .012
C0.200.09 .003 .008
D6.606.40 .252 .260
E4.504.30 .169 .177
L
N20
Q 0° ~8° 0° ~8°
20
0.700.50 .020 .028
e BSC0.65 .026 BSC
INCH
SEATING PLANE
Q
A1
0MD D
D
e
D
C
A - B
E
B
H BSC6.40 .252 BSC
216
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Figure 28-4. PC
Package Drawing Contact:
packagedrawings@atmel.com
GPC DRAWING NO.
REV. TITLE
PC I
06/25/09
PC, 20-Lead - 4.0x4.0mm Body, 0.50mm Pitch
Quad Flat No Lead Package (QFN)
Top View
Bottom View
Side View
D
E
1.00 REF
See Option A, B, C
1
NNN
11
Option A
Pin 1# Chamfer
(C 0.30)
Pin 1# Notch
(0.20 R)
Pin 1#
Triangle
Option B Option C
0.15 (4x)
0.08 C
0.10 C C
J
A
b
E2
D2
e
L
1
N
SEATING PLANE
DRAWINGS NOT SCALED
Compliant JEDEC Standard MO-220 Variation WGGD-5
COMMON DIMENSIONS IN MM
SYMBOL MIN. NOM. MAX.
A 0.70 0.75 0.80
D/E 3.90 4.00 4.10
L 0.35 0.45 0.55
b 0,20 0.25 0.30
D2/E2 2.50 2.60
N20
e 0.50 BSC
2.70
J 0.00 0.05
NOTES
PIN #1 Identifier
Laser Marking
1.00 REF
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29. Errata
29.1 Errata ATtiny261
The revision letter in this section refers to the revision of the ATtiny261 device.
29.1.1 Rev A
Trigger reference levels of the Analog Comparator.
29.2 Errata ATtiny461
The revision letter in this section refers to the revision of the ATtiny461 device.
29.2.1 Rev B
Trigger reference levels of the Analog Comparator.
29.3 Errata ATtiny861
The revision letter in this section refers to the revision of the ATtiny861 device.
29.3.1 Rev B
Trigger reference levels of the Analog Comparator.
29.4 Errata Description
29.4.1 Trigger Reference Levels of the Analog Comparator
The Analog Comparator should not used with trigger reference levels of less than 300mV with
respect to GND.
Problem Fix/Workaround
No workaround.
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30. Revision History
30.1 7753F-AVR-01/11
• Trigger reference levels of the Analog Comparator errata added
30.2 7753E-AVR-06/10
• Ordering Information updated
• DC Characteristics table updated
30.3 7753D-AVR-11/09
• Ordering Information updated
• QFN pinout added
• Internal RC Oscillator Accuracy updated
30.4 7753C-AVR-07/09
• QFN package added
• ADC characteristics updated
• Temps sensor updated
• Typical characteristics updated
30.5 7753B-AVR-08/08
• Added 6G product offering to Ordering Information.
30.6 7753A-AVR-11/07
• First datasheet draft - initial automotive version. Started from industrial datasheet
doc2588 rev.B - 01/07
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31. Table of Contents
Features ..................................................................................................... 1
1 Pin Configurations ................................................................................... 2
1.1 Disclaimer ..........................................................................................................3
1.2 Automotive Quality Grade .................................................................................3
2 Overview ................................................................................................... 4
2.1 Block Diagram ...................................................................................................4
2.2 Pin Descriptions .................................................................................................5
3 Resources ................................................................................................. 7
4 About Code Examples ............................................................................. 8
5 AVR CPU Core .......................................................................................... 9
5.1 Overview ............................................................................................................9
5.2 ALU – Arithmetic Logic Unit .............................................................................10
5.3 Status Register ................................................................................................11
5.4 General Purpose Register File ........................................................................12
5.5 Stack Pointer ...................................................................................................13
5.6 Instruction Execution Timing ...........................................................................14
5.7 Reset and Interrupt Handling ...........................................................................15
6 AVR Memories ........................................................................................ 17
6.1 In-System Re-programmable Flash Program Memory ....................................17
6.2 SRAM Data Memory ........................................................................................17
6.3 EEPROM Data Memory ..................................................................................18
6.4 I/O Memory ......................................................................................................22
6.5 Register Description ........................................................................................22
7 System Clock and Clock Options ......................................................... 25
7.1 Clock Systems and their Distribution ...............................................................25
7.2 Clock Sources .................................................................................................27
7.3 Default Clock Source .......................................................................................27
7.4 External Clock .................................................................................................27
7.5 High Frequency PLL Clock - PLLCLK .............................................................28
7.6 Calibrated Internal RC Oscillator .....................................................................29
7.7 128 kHz Internal Oscillator ..............................................................................30
7.8 Low-frequency Crystal Oscillator .....................................................................30
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7.9 Crystal Oscillator .............................................................................................30
7.10 Clock Output Buffer .........................................................................................32
7.11 System Clock Prescaler ..................................................................................32
7.12 Register Description ........................................................................................32
8 Power Management and Sleep Modes ................................................. 35
8.1 Sleep Modes ....................................................................................................35
8.2 Idle Mode .........................................................................................................35
8.3 ADC Noise Reduction Mode ............................................................................36
8.4 Power-down Mode ...........................................................................................36
8.5 Standby Mode .................................................................................................36
8.6 Power Reduction Register ...............................................................................36
8.7 Minimizing Power Consumption ......................................................................36
8.8 Register Description ........................................................................................38
9 System Control and Reset .................................................................... 40
9.1 Internal Voltage Reference ..............................................................................44
9.2 Watchdog Timer ..............................................................................................44
9.3 Timed Sequences for Changing the Configuration of the Watchdog Timer ....45
9.4 Register Description ........................................................................................45
10 Interrupts ................................................................................................ 50
10.1 Interrupt Vectors in ATtiny261/461/861 ...........................................................50
11 External Interrupts ................................................................................. 52
11.1 Register Description ........................................................................................52
12 I/O Ports .................................................................................................. 55
12.1 Overview ..........................................................................................................55
12.2 Ports as General Digital I/O .............................................................................56
12.3 Alternate Port Functions ..................................................................................60
12.4 Register Description ........................................................................................69
13 Timer/Counter0 Prescaler ..................................................................... 70
13.1 Register Description ........................................................................................71
14 Timer/Counter0 ...................................................................................... 73
14.1 Features ..........................................................................................................73
14.2 Overview ..........................................................................................................73
14.3 Timer/Counter Clock Sources .........................................................................74
14.4 Counter Unit ....................................................................................................74
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14.5 Modes of Operation .........................................................................................75
14.6 Input Capture Unit ...........................................................................................77
14.7 Output Compare Unit .......................................................................................78
14.8 Timer/Counter Timing Diagrams .....................................................................79
14.9 Accessing Registers in 16-bit Mode ................................................................81
14.10 Register Description ........................................................................................85
15 Timer/Counter1 Prescaler ..................................................................... 89
15.1 Register Description ........................................................................................90
16 Timer/Counter1 ...................................................................................... 92
16.1 Features ..........................................................................................................92
16.2 Overview ..........................................................................................................92
16.3 Counter Unit ....................................................................................................96
16.4 Output Compare Unit .......................................................................................97
16.5 Dead Time Generator ......................................................................................99
16.6 Compare Match Output Unit ..........................................................................100
16.7 Modes of Operation .......................................................................................102
16.8 Timer/Counter Timing Diagrams ...................................................................109
16.9 Fault Protection Unit ......................................................................................111
16.10 Accessing 10-Bit Registers ............................................................................112
16.11 Register Description ......................................................................................115
17 USI – Universal Serial Interface .......................................................... 128
17.1 Features ........................................................................................................128
17.2 Overview ........................................................................................................128
17.3 Functional Descriptions .................................................................................129
17.4 Alternative USI Usage ...................................................................................135
17.5 Register Descriptions ....................................................................................135
18 AC – Analog Comparator .................................................................... 140
18.1 Register Description ......................................................................................140
18.2 Analog Comparator Multiplexed Input ...........................................................142
19 ADC – Analog to Digital Converter ..................................................... 144
19.1 Features ........................................................................................................144
19.2 Overview ........................................................................................................144
19.3 Operation .......................................................................................................146
19.4 Starting a Conversion ....................................................................................147
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19.5 Prescaling and Conversion Timing ................................................................148
19.6 Changing Channel or Reference Selection ...................................................151
19.7 ADC Noise Canceler .....................................................................................152
19.8 ADC Conversion Result .................................................................................153
19.9 Temperature Measurement ...........................................................................156
19.10 Register Description ......................................................................................158
20 debugWIRE On-chip Debug System .................................................. 165
20.1 Features ........................................................................................................165
20.2 Overview ........................................................................................................165
20.3 Physical Interface ..........................................................................................165
20.4 Software Break Points ...................................................................................166
20.5 Limitations of debugWIRE .............................................................................166
20.6 Register Description ......................................................................................166
21 Self-Programming the Flash ............................................................... 167
21.1 Performing Page Erase by SPM ....................................................................167
21.2 Filling the Temporary Buffer (Page Loading) .................................................167
21.3 Performing a Page Write ...............................................................................168
21.4 Addressing the Flash During Self-Programming ...........................................168
21.5 Register Description ......................................................................................170
22 Memory Programming ......................................................................... 172
22.1 Program And Data Memory Lock Bits ...........................................................172
22.2 Fuse Bytes .....................................................................................................173
22.3 Signature Bytes .............................................................................................174
22.4 Calibration Byte .............................................................................................174
22.5 Reading the Signature Row from Software ...................................................175
22.6 Page Size ......................................................................................................175
22.7 Parallel Programming Parameters, Pin Mapping, and Commands ...............175
22.8 Parallel Programming ....................................................................................177
22.9 Serial Downloading ........................................................................................184
23 Electrical Characteristics .................................................................... 188
23.1 Absolute Maximum Ratings* .........................................................................188
23.2 DC Characteristics .........................................................................................188
23.3 Speed Grades ...............................................................................................190
23.4 Clock Characteristics .....................................................................................190
23.5 System and Reset Characteristics ................................................................191
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23.6 ADC Characteristics ......................................................................................192
23.7 Parallel Programming Characteristics ...........................................................195
23.8 Serial Programming Characteristics ..............................................................197
24 Typical Characteristics ........................................................................ 198
24.1 Active Supply Current ....................................................................................198
24.2 Idle Supply Current ........................................................................................199
24.3 Supply Current of I/O modules ......................................................................200
24.4 Power-down Supply Current ..........................................................................201
24.5 Pin Pull-up .....................................................................................................202
24.6 Pin Driver Strength ........................................................................................203
24.7 Pin Threshold and Hysteresis ........................................................................204
24.8 BOD Threshold and Analog Comparator Offset ............................................206
24.9 Internal Oscillator Speed ...............................................................................207
25 Register Summary ............................................................................... 208
26 Instruction Set Summary .................................................................... 210
27 Ordering Information ........................................................................... 212
28 Packaging Information ........................................................................ 213
29 Errata ..................................................................................................... 217
29.1 Errata ATtiny261 ............................................................................................217
29.2 Errata ATtiny461 ............................................................................................217
29.3 Errata ATtiny861 ............................................................................................217
29.4 Errata Description ..........................................................................................217
30 Revision History ................................................................................... 218
30.1 7753D-AVR-11/09 .........................................................................................218
30.2 7753C-AVR-07/09 .........................................................................................218
30.3 7753B-AVR-08/08 .........................................................................................218
30.4 7753A-AVR-11/07 .........................................................................................218
31 Table of Contents ................................................................................. 219
7753F–AVR–01/11
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