1
XR20M1170
I2C/SPI UART WITH 64-BYTE FIFO
JUNE 2019 REV. 1.1.2
GENERAL DESCRIPTION
The XR20M11701 is a high performance universal
asynchronous receiver and transmitter (UART) with
64 byte TX and RX FIFOs and a selectable I2C/SPI
slave interface. The XR20M1170 operates from 1.62
to 3.63 volts. The enhanced features in the
XR20M1170 include a programmable fractional baud
rate generator, an 8X and 4X sampling rate that
allows for a maximum baud rate of 16Mbps at 3.3V.
The standard features include 16 selectable TX and
RX FIFO trigger levels, automatic hardware (RTS/
CTS) and software (Xon/Xoff) flow control, and a
complete modem interface. Onboard registers
provide the user with operational status and data
error flags. An internal loopback capability allows
system diagnostics. The XR20M1170 is available in
the 24-pin QFN, 16-pin QFN, 24-pin TSSOP and 16-
pin TSSOP packages.
NOTE: 1 Covered by U.S. Patent #5,649,122
APPLICATIONS
Portable appliances
Battery-operated devices
Cellular data devices
Factory automation and process controls
FEATURES
1.62 to 3.6 Volt operation
Selectable I2C/SPI interface
SPI clock frequency up to
18MHz at 3.3V
16MHz at 2.5V
8MHz at 1.8V
Full-featured UART
Data rate of up to 16Mbps at 3.3V
Data rate of up to 12.5Mbps at 2.5V
Data rate of up to 8Mbps at 1.8V
Fractional baud rate generator
Transmit and receive FIFOs of 64 bytes
16 selectable TX and RX FIFO trigger levels
Automatic hardware (RTS/CTS) flow control
Automatic software (Xon/Xoff) flow control
Halt and resume transmission control
Automatic RS-485 half-duplex direction control
output via RTS#
Wireless Infrared (IrDA 1.0 and 1.1) encoder/
decoder
Automatic sleep mode (< 15uA at 3.3V)
General purpose I/Os
Full modem interface
Crystal oscillator (up to 24MHz) or external clock
(up to 64MHz) input
24-QFN, 16-QFN, 24-TSSOP, 16-TSSOP
packages
FIGURE 1. XR20M1170 BLOCK DIAGRAM
I2C/SPI
Interface
I2C/SPI#
SO
A1/SI
A0/CS#
SCL
SDA
IRQ#
Crystal Osc/Buffer
BRG
UART
Regs
XTAL2
XTAL1
64 Byte
TX FIFO
GPIOs
TX
RX
CTS#
RTS#
GPIO[7:0]
1.62V – 3.63VVCC
64 Byte
RX FIFO
XR20M1170
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
FIGURE 2. PIN OUT ASSIGNMENT
24-Pin
TSSOP
3
5
4
7
6
8
9
10
11
12
1
2
13
14
15
16
17
18
19
20
21
22
23
24VCC
A0/CS#
A1/SI
SO
GPIO0
GPIO1
I2C/SPI#
RX
TX
GPIO2
XTAL1
XTAL2
GPIO7/RI#
GPIO6/CD#
CTS#
RESET#
GPIO4/DSR#
GPIO5/DTR#
RTS#
IRQ#
SCL
SDA
GND
GPIO3
16-Pin
TSSOP
3
5
4
7
6
8
1
2
A0/CS#
A1/SI
SO
I2C/SPI#
RX
TX
XTAL1
XTAL2 9
10
11
12
13
14
15
16 VCC
CTS#
RESET#
RTS#
IRQ#
SCL
SDA
GND
24-Pin QFN
123456
GPIO1
I2C/SPI#
RX
TX
GPIO0
SO
11
12
7
10
8
9XTAL2
GPIO3
GND
SDA
XTAL1
GPIO2
18 17 16 15 14 13
20
19
24
21
23
22VCC
GPIO7/RI#
GPIO6/CD#
CTS#
A0/CS#
A1/SI
GPIO5/DTR#
RTS#
IRQ#
SCL
GPIO4/DSR#
RESET#
16-Pin
QFN
1234
RX
TX
I2C/SPI#
SO
5
8
6
7GND
SDA
XTAL2
XTAL1
12 11 10 9
16
13
15
14
VCC
CTS#
A0/CS#
A1/SI
IRQ#
SCL
RTS#
RESET#
XR20M1170
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
NOTES:
1. Refer to www.maxlinear.com/XR20M1170 for most up-to-date Ordering Information
2. Visit www.maxlinear.com for additional information on Environmental Rating.
PIN DESCRIPTIONS
ORDERING INFORMATION(1)
PART NUMBER OPERATING TEMPERATURE RANGE LEAD-FREE PACKAGE PACKAGING METHOD
XR20M1170IL24-F
-40°C to +85°C Yes(2)
24-pin QFN Tray
XR20M1170IL24TR-F Tape and Reel
XR20M1170IL16-F 16-pin QFN Tray
XR20M1170IL16TR-F Tape and Reel
XR20M1170IG24-F 24-Lead TSSOP Tube
XR20M1170IG16-F 16-Lead TSSOP Tube
XR20M1170IG16TR-F Tape and Reel
XR20M1170L24-0A-EB 24-pin QFN XR20M1170 Evaluation Board, RS-232 and RS-485 capable
XR20M1170L24-0B-EB 24-pin QFN XR20M1170 Evaluation Board, RS-232 only
XR20M1170L16-0A-EB 16-pin QFN XR20M1170 Evaluation Board, RS-232 and RS-485 capable
XR20M1170L16-0B-EB 16-pin QFN XR20M1170 Evaluation Board, RS-232 only
XR20M1170G24-0A-EB 24-pin TSSOP XR20M1170 Evaluation Board, RS-232 and RS-485 capable
XR20M1170G24-0B-EB 24-pin TSSOP XR20M1170 Evaluation Board, RS-232 only
XR20M1170G16-0A-EB 16-pin TSSOP XR20M1170 Evaluation Board, RS-232 and RS-485 capable
XR20M1170G16-0B-EB 16-pin TSSOP XR20M1170 Evaluation Board, RS-232 only
Pin Description
NAME 24-QFN
PIN #
16-QFN
PIN #
24-TSSOP
PIN#
16-TSSOP
PIN # TYPE DESCRIPTION
I2C (SPI) INTERFACE
GPIO0 2 - 5 - I/O General purpose I/O pin.
GPIO1 3 - 6 - I/O General purpose I/O pin.
I2C/SPI# 4 2 7 4 I/O I2C-bus or SPI interface select. I2C-bus interface
is selected if this pin is HIGH. SPI interface is
selected if this pin is LOW.
RX 5 3 8 5 I UART receive data or infrared receive data. UART
receive data input must idle HIGH. Infrared receive
data input must idle LOW. If this pin is not used, tie
it to VCC or pull it high via a 100kΩ resistor.
TX 6 4 9 6 O UART transmit data or infrared encoder data. In
the standard UART transmit data mode, the TX
signal will be HIGH during reset or idle (no data). In
the Infrared Mode, the inactive state (no data) for
the infrared encoder/decoder interface is LOW. If
this pin is not used, it should be left unconnected.
GPIO2 7 - 10 - I/O General purpose I/O pin.
XTAL1 8 5 11 7 I Crystal or external clock input.
XR20M1170
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
XTAL2 9 6 12 8 O Crystal or buffered clock output.
GPIO3 10 - 13 - I/O General purpose I/O pin.
GND 11 7 14 9 Pwr Power supply common, ground.
SDA 12 8 15 10 O I2C-bus data input/output (open-drain). If SPI
configuration is selected, then this pin is undefined
and must be connected to VCC.
SCL 13 9 16 11 I I2C-bus or SPI serial input clock.
When the I2C-bus interface is selected, the serial
clock idles HIGH. When the SPI interface is
selected, the serial clock idles LOW.
IRQ# 14 10 17 12 OD Interrupt output (open-drain, active LOW).
RTS# 15 11 18 13 O UART Request-To-Send. This output can be used
for auto RTS hardware flow control, auto RS-485
half-duplex direction control or as a general
purpose output.
GPIO5
DTR#
16 - 19 - I/O General purpose I/O pin or DTR# output.
GPIO4
DSR#
17 - 20 - I/O General purpose I/O pin or DSR# input.
RESET# 18 12 21 14 I Reset (active LOW) - A longer than 40ns LOW
pulse on this pin will reset the internal registers and
all outputs. The UART transmitter output will be
idle and the receiver input will be ignored.
CTS# 19 13 22 15 I UART Clear-To-Send. This input can be used for
auto CTS hardware flow control or as a general
purpose input.
GPIO6
CD#
20 - 23 - I/O General purpose I/O pin or CD# input.
GPIO7
RI#
21 - 24 - I/O General purpose I/O pin or RI# input.
VCC 22 14 1 16 Pwr 1.62V to 3.6V power supply.
A0
CS#
23 15 2 1 I I2C-bus device address select A0 or SPI chip
select. If I2C-bus configuration is selected, this pin
along with the A1 pin allows user to change the
device’s base address. If SPI configuration is
selected, this pin is the SPI chip select pin
(Schmitt-trigger, active LOW).
A1
SI
24 16 3 2 I I2C-bus device address select A1 or SPI data input
pin. If I2C-bus configuration is selected, this pin
along with the A0 pin allows user to change the
device’s base address. If SPI configuration is
selected, this pin is the SPI data input pin.
Pin Description
NAME 24-QFN
PIN #
16-QFN
PIN #
24-TSSOP
PIN#
16-TSSOP
PIN # TYPE DESCRIPTION
XR20M1170
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
Pin type: I = Input, O = Output, I/O = Input/output, OD = Output Open Drain.
SO 1 1 4 3 O SPI data output pin. If SPI configuration is
selected then this pin is a three-stateable output
pin. If I2C-bus configuration is selected, this pin is
undefined and must be left unconnected.
- PAD PAD - - Pwr The center pad on the backside of the QFN
packages is metallic and is not electrically
connected to anything inside the device. It must be
soldered on to the PCB and may be optionally
connected to GND on the PCB. The thermal pad
size on the PCB should be the approximate size of
this center pad and should be solder mask defined.
The solder mask opening should be at least
0.0025" inwards from the edge of the PCB thermal
pad.
NC - - - - - No connection.
Pin Description
NAME 24-QFN
PIN #
16-QFN
PIN #
24-TSSOP
PIN#
16-TSSOP
PIN # TYPE DESCRIPTION
XR20M1170
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
1.0 PRODUCT DESCRIPTION
The XR20M1170 integrates a selectable I2C/SPI bus interface with an enhanced Universal Asynchronous
Receiver and Transmitter (UART). The configuration registers set is 16550 UART compatible for control, status
and data transfer. Additionally, the XR20M1170 has 64-bytes of transmit and receive FIFOs, automatic RTS/
CTS hardware flow control, automatic Xon/Xoff and special character software flow control, programmable
transmit and receive FIFO trigger levels, infrared encoder and decoder (IrDA 1.0 and 1.1), programmable
fractional baud rate generator with a prescaler of divide by 1 or 4, and data rate up to 16 Mbps with 4X
sampling clock rate. The XR20M1170 is a 1.62V to 3.63V device. The XR20M1170 is fabricated with an
advanced CMOS process.
Enhanced Features
The XR20M1170 UART provides a solution that supports 64 bytes of transmit and receive FIFO memory,
instead of 16 bytes in the industry standard 16C550. The XR20M1170 is designed to work with low supply
voltage and high performance data communication systems that require fast data processing time. Increased
performance is realized in the XR20M1170 by the larger transmit and receive FIFOs, FIFO trigger level control
and automatic flow control mechanism. This allows the external processor to handle more networking tasks
within a given time. For example, the 16C550 with a 16 byte FIFO, unloads 16 bytes of receive data in 1.53ms
(This example uses a character length of 11 bits, including start/stop bits at 115.2kbps). This means the
external CPU will have to service the receive FIFO at 1.53ms intervals. However with the 64 byte FIFO in the
XR20M1170, the data buffer will not require unloading/loading for 6.1ms. This increases the service interval
giving the external CPU additional time for other applications and reducing the overall UART interrupt servicing
time. In addition, the programmable FIFO level trigger interrupt and automatic hardware/software flow control
is uniquely provided for maximum data throughput performance especially when operating in a multi-channel
system. The combination of the above greatly reduces the CPU’s bandwidth requirement, increases
performance, and reduces power consumption.
The XR20M1170 supports a half-duplex output direction control signaling pin, RTS#, to enable and disable the
external RS-485 transceiver operation. It automatically switches the logic state of the output pin to the receive
state after the last stop-bit of the last character has been shifted out of the transmitter. After receiving, the logic
state of the output pin switches back to the transmit state when a data byte is loaded in the transmitter. The
auto RS-485 direction control pin is not activated after reset. To activate the direction control function, the user
has to set EFCR bit-4 to “1”. This pin is HIGH for receive state and LOW for transmit state. The polarity of the
RTS# pin can be inverted via EFCR bit-5.
Data Rate
The XR20M1170 is capable of operation up to 16Mbps at 3.3V with 4X internal sampling clock rate, 8Mbps at
3.3V with 8X sampling clock rate, and 4Mbps at 3.3V with 16X internal sampling clock rate. The device can
operate with an external 24MHz crystal on pins XTAL1 and XTAL2, or external clock source of up to 64MHz on
XTAL1 pin. With a typical crystal of 14.7456MHz and through a software option, the user can set the prescaler
bit for data rates of up to 3.68Mbps.
The rich feature set of the XR20M1170 is available through the internal registers. Automatic hardware/software
flow control, programmable transmit and receive FIFO trigger levels, programmable TX and RX baud rates,
infrared encoder/decoder interface, modem interface controls, and a sleep mode are all standard features.
Following a power on reset or an external reset, the XR20M1170 is software compatible with previous
generation of 16C450, 16C550 and 16C2550 UARTs.
XR20M1170
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
2.0 FUNCTIONAL DESCRIPTIONS
2.1 CPU Interface
The XR20M1170 can operate with either an I2C-bus interface or an SPI interface. The CPU interface is
selected via the I2C/SPI# input pin.
2.1.1 I2C-bus Interface
The I2C-bus interface is compliant with the Standard-Mode and Fast-Mode I2C-bus specifications. The I2C-
bus interface consists of two lines: serial data (SDA) and serial clock (SCL). In the Standard-Mode, the serial
clock and serial data can go up to 100 kbps, and in the Fast-Mode the serial clock and serial data can go up to
400 kbps. The first byte sent by an I2C-bus master contains a start bit (SDA transition from HIGH to LOW
when SCL is HIGH), 7-bit slave address and whether it is a read or write transaction. The next byte is the sub-
address that contains the address of the register to access. The XR20M1170 responds to each write with an
acknowledge (SDA driven LOW by XR20M1170 for one clock cycle when SCL is HIGH). If the TX FIFO is full,
the XR20M1170 will respond with a negative acknowledge (SDA driven HIGH by XR20M1170 for one clock
cycle when SCL is HIGH) when the CPU tries to write to the TX FIFO. The last byte sent by an I2C-bus master
contains a stop bit (SDA transition from LOW to HIGH when SCL is HIGH). See Figures 3-5 below. For
complete details, see the I2C-bus specifications.
FIGURE 3. I2C START AND STOP CONDITIONS
FIGURE 4. MASTER WRITES TO SLAVE (XR20M1170)
FIGURE 5. MASTER READS FROM SLAVE (XR20M1170)
SDA
SCL
S P
START condition STOP condition
SWAAAP
SLAVE
ADDRESS
REGISTER
ADDRESS nDATA
White block: host to UART
Grey block: UART to host
SWAAR
SLAVE
ADDRESS
REGISTER
ADDRESS
White block: host to UART
Grey block: UART to host
AS SLAVE
ADDRESS nDATA ANAPLAST DATA
XR20M1170
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
FIGURE 6. I2C DATA FORMATS
XR20M1170
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
2.1.1.1 I2C-bus Addressing
There could be many devices on the I2C-bus. To distinguish itself from the other devices on the I2C-bus, there
are eight possible slave addresses that can be selected for the XR20M1170 using the A1 and A0 address
lines. Table 1 below shows the different addresses that can be selected. Note that there are two different
ways to select each I2C address.
An I2C sub-address is sent by the I2C master following the slave address. The sub-address contains the
UART register address being accessed. A read or write transaction is determined by bit-0 of the slave
address. If bit-0 is’0’, then it is a write transaction. If bit-0 is ’1’, then it is a read transaction. If bit-0 is a logic
1, then it is a read transaction. Table 2 below lists the functions of the bits in the I2C sub-address.
After the last read or write transaction, the I2C-bus master will set the SCL signal back to its idle state (HIGH).
TABLE 1: XR20M1170 I2C ADDRESS MAP
A1 A0 I2C ADDRESS
VCC VCC 0x60 (0110 000X)
VCC GND 0x62 (0110 001X)
VCC SCL 0x64 (0110 010X)
VCC SDA 0x66 (0110 011X)
GND VCC 0x68 (0110 100X)
GND GND 0x6A (0110 101X)
GND SCL 0x6C (0110 110X)
GND SDA 0x6E (0110 111X)
SCL VCC 0x60 (0110 000X)
SCL GND 0x62 (0110 001X)
SCL SCL 0x64 (0110 010X)
SCL SDA 0x66 (0110 011X)
SDA VCC 0x68 (0110 100X)
SDA GND 0x6A (0110 101X)
SDA SCL 0x6C (0110 110X)
SDA SDA 0x6E (0110 111X)
TABLE 2: I2C SUB-ADDRESS (REGISTER ADDRESS)
BIT FUNCTION
7 Reserved
6:3 UART internal Register Address A3:A0
2:1 UART channel select
’00’ = UART Channel A, other values are reserved.
0 Reserved
XR20M1170
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
2.1.2 SPI Bus Interface
The SPI interface consists of four lines: serial clock (SCL), chip select (CS#), slave output (SO), and slave
input (SI). The serial clock, slave output, and slave input can be as fast as 18MHz at 3.3V. To access the
device in the SPI mode, the CS# signal for the XR20M1170 is asserted by the SPI master, then the SPI master
starts toggling the SCL signal with the appropriate transaction information. The first bit sent by the SPI master
includes whether it is a read or write transaction and the UART register being accessed. See Table 3 below.
The 64 byte TX FIFO can be loaded with data or 64 byte RX FIFO data can be unloaded in one SPI write or
read sequence.
TABLE 3: SPI FIRST BYTE FORMAT
BIT FUNCTION
7 Read/Write#
Logic 1 = Read
Logic 0 = Write
6:3 UART internal Register Address A3:A0
2:1 UART channel select
’00’ = UART Channel A, other values are reserved.
0 Reserved
FIGURE 7. SPI WRITE
FIGURE 8. SPI READ
FIGURE 9. SPI FIFO WRITE
R/W A3 A2 A1 A0 0 0 X D7 D6 D5 D4 D3 D2 D1 D0
SCLK
SI
R/WA3A2A1A0 0 0 X
D7 D6 D5 D4 D3 D2 D1 D0
SCLK
SI
SO
R/W A3 A2 A1 A0 0 0 X D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0
SCLK
SO
last bit
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
After the last read or write transaction, the SPI master will set the SCL signal back to its idle state (LOW).
2.2 Device Reset
The RESET# input resets the internal registers and the serial interface outputs in the UART to its default state
(see Table 16). An active low pulse of longer than 40ns duration will be required to activate the reset function in
the device.
2.3 Internal Registers
The XR20M1170 has a set of enhanced registers for control, monitoring and data loading and unloading. The
configuration register set is compatible to the industry standard ST16C550. These registers function as data
holding registers (THR/RHR), interrupt status and control registers (ISR/IER), a FIFO control register (FCR),
receive line status and control registers (LSR/LCR), modem status and control registers (MSR/MCR),
programmable data rate (clock) divisor registers (DLL/DLM/DLD), and a user accessible scratchpad register
(SPR).
Beyond the general 16C550 features and capabilities, the XR20M1170 offers enhanced feature registers
(EFR, Xon/Xoff 1, Xon/Xoff 2, TCR, TLR, TXLVL, RXLVL, IODir, IOState, IOIntEna, IOControl, EFCR and DLD)
that provide automatic RTS and CTS hardware flow control, Xon/Xoff software flow control, automatic RS-485
half-duplex direction output enable or disable, TX and RX FIFO level counters, and programmable FIFO trigger
level control. For complete details, see “Section 3.0, UART Internal Registers” on page 24.
2.4 IRQ# Output
The IRQ# interrupt output changes according to the operating mode and enhanced features setup. Table 4
and 5 summarize the operating behavior for the transmitter and receiver. Also see Figures 21 through 35.
FIGURE 10. SPI FIFO READ
TABLE 4: IRQ# PIN OPERATION FOR TRANSMITTER
Auto RS485
Mode
FCR BIT-0 = 0
(FIFO DISABLED)FCR BIT-0 = 1 (FIFO ENABLED)
IRQ# Pin NO HIGH = a byte in THR
LOW = THR empty
HIGH = FIFO above trigger level
LOW = FIFO below trigger level or FIFO empty
IRQ# Pin YES HIGH = a byte in THR
LOW = transmitter empty
HIGH = FIFO above trigger level
LOW = FIFO below trigger level or transmitter empty
TABLE 5: IRQ# PIN OPERATION FOR RECEIVER
FCR BIT-0 = 0
(FIFO DISABLED)
FCR BIT-0 = 1
(FIFO ENABLED)
IRQ# Pin HIGH = no data
LOW = 1 byte
HIGH = FIFO below trigger level
LOW = FIFO above trigger level
SCLK
D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0
last bit
R/WA3A2A1A0 0 0 X
XR20M1170
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
2.5 Crystal Oscillator or External Clock Input
The XR20M1170 includes an on-chip oscillator (XTAL1 and XTAL2) to produce a clock for both UART sections
in the device. The crystal oscillator provides a system clock to the Baud Rate Generators (BRG) section found
in each of the UARTs. XTAL1 is the input to the oscillator or external clock buffer input with XTAL2 pin being the
output. Please note that the input XTAL1 is not 5V tolerant and so the maximum at the pin should be VCC. For
programming details, see ““Section 2.6, Programmable Baud Rate Generator with Fractional Divisor” on
page 12.”
The on-chip oscillator is designed to use an industry standard microprocessor crystal (parallel resonant,
fundamental frequency with 10-22pF capacitance load, ESR of 20-120Ω and 100 ppm frequency tolerance)
connected externally between the XTAL1 and XTAL2 pins (see Figure 11). The programmable baud rate
generator is capable of operating with a crystal oscillator frequency of up to 24MHz. However, with an external
clock input on XTAL1 pin, it can extend its operation up to 64MHz (16 Mbps serial data rate) at 3.3V with an 4X
sampling rate. For further reading on the oscillator circuit please see the Application Note DAN108 on the
MaxLinear web site at http://www.maxlinear.com.
2.6 Programmable Baud Rate Generator with Fractional Divisor
Each UART has its own Baud Rate Generator (BRG) with a prescaler for the transmitter and receiver. The
prescaler is controlled by a software bit in the MCR register. The MCR register bit-7 sets the prescaler to divide
the input crystal or external clock by 1 or 4. The output of the prescaler clocks to the BRG. The BRG further
divides this clock by a programmable divisor between 1 and (216 - 0.0625) in increments of 0.0625 (1/16) to
obtain a 16X, 8X or 4X sampling clock of the serial data rate. The sampling clock is used by the transmitter for
data bit shifting and receiver for data sampling. The BRG divisor (DLL, DLM and DLD registers) defaults to the
value of ’1’ (DLL = 0x01, DLM = 0x00 and DLD = 0x00) upon power-up. Therefore, the BRG must be
programmed during initialization to the operating data rate. The DLL and DLM registers provide the integer part
of the divisor and the DLD register provides the fractional part of the divisor. The four lower bits of the DLD are
used to select a value from 0 (for setting 0000) to 0.9375 or 15/16 (for setting 1111). Programming the Baud
Rate Generator Registers DLL, DLM and DLD provides the capability for selecting the operating data rate.
Table 6 shows the standard data rates available with a 24MHz crystal or external clock at 16X clock rate. If the
pre-scaler is used (MCR bit-7 = 1), the output data rate will be 4 times less than that shown in Table 6. At a 8X
sampling rate these data rates would double, and at a 4X sampling rate these data rates would quadruple.
Also, when using a 8X sampling mode, the bit time will have a jitter of ± 1/16 whenever the DLD is non-zero
FIGURE 11. TYPICAL OSCILLATOR CONNECTIONS
10-22 pF
XTAL1 XTAL2
10-22 pF
500K – 1Mё
0 – 120 ё
Optional
R1
Y1
C1 C2
1.8432 MHz to
24 MHz
R2
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
and is an odd number. When using a 4X sampling mode, the bit time will have a jitter of ±1/8 whenever DLD is
non-zero, odd and not a multiple of 4. When using a non-standard data rate crystal or external clock, the
divisor value can be calculated with the following equation(s):
The closest divisor that is obtainable in the XR20M1170 can be calculated using the following formula:
In the formulas above, please note that:
TRUNC (N) = Integer Part of N. For example, TRUNC (5.6) = 5.
ROUND (N) = N rounded towards the closest integer. For example, ROUND (7.3) = 7 and ROUND (9.9) = 10.
A >> B indicates right shifting the value ’A’ by ’B’ number of bits. For example, 0x78A3 >> 8 = 0x0078.
Required Divisor (decimal)=(XTAL1 clock frequency / prescaler) /(serial data rate x 16), with 16X mode, DLD[5:4]=’00’
Required Divisor (decimal)= (XTAL1 clock frequency / prescaler / (serial data rate x 8), with 8X mode, DLD[5:4] = ’01’
Required Divisor (decimal)= (XTAL1 clock frequency / prescaler / (serial data rate x 4), with 4X mode, DLD[5:4] = ’10’
ROUND( (Required Divisor - TRUNC(Required Divisor) )*16)/16 + TRUNC(Required Divisor), where
DLM = TRUNC(Required Divisor) >> 8
DLL = TRUNC(Required Divisor) & 0xFF
DLD = ROUND( (Required Divisor-TRUNC(Required Divisor) )*16)
FIGURE 12. BAUD RATE GENERATOR
XTAL1
XTAL2
Crystal
Osc/
Buffer
MCR Bit-7=0
(default)
MCR Bit-7=1
DLL, DLM and DLD
Registers
Prescaler
Divide by 1
Prescaler
Divide by 4
16X or 8X or 4X
Sampling
Rate Clock
to Transmitter
and Receiver
Fractional Baud
Rate Generator
Logic
XR20M1170
14
I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
2.7 Transmitter
The transmitter section comprises of an 8-bit Transmit Shift Register (TSR) and 64 bytes of FIFO which
includes a byte-wide Transmit Holding Register (THR). TSR shifts out every data bit with the 16X/8X/4X
internal clock. A bit time is 16 (8 if 8X or 4 if 4X) clock periods (see DLD[5:4]). The transmitter sends the start-
bit followed by the number of data bits, inserts the proper parity-bit if enabled, and adds the stop-bit(s). The
status of the FIFO and TSR are reported in the Line Status Register (LSR[6:5]).
TABLE 6: TYPICAL DATA RATES WITH A 24MHZ CRYSTAL OR EXTERNAL CLOCK AT 16X SAMPLING
Required
Output Data
Rate
DIVISOR FOR
16x Clock
(Decimal)
DIVISOR
OBTAINABLE IN
XR20M1170
DLM PROGRAM
VALUE (HEX)
DLL PROGRAM
VALUE (HEX)
DLD PROGRAM
VALUE (HEX)
DATA ERROR
RATE (%)
400 3750 3750 E A6 0 0
2400 625 625 2 71 0 0
4800 312.5 312 8/16 1 38 8 0
9600 156.25 156 4/16 0 9C 4 0
10000 150 150 0 96 0 0
19200 78.125 78 2/16 0 4E 2 0
25000 60 60 0 3C 0 0
28800 52.0833 52 1/16 0 34 1 0.04
38400 39.0625 39 1/16 0 27 1 0
50000 30 30 0 1E 0 0
57600 26.0417 26 1/16 0 1A 1 0.08
75000 20 20 0 14 0 0
100000 15 15 0 F 0 0
115200 13.0208 13 0 D 0 0.16
153600 9.7656 9 12/16 0 9 C 0.16
200000 7.5 7 8/16 0 7 8 0
225000 6.6667 6 11/16 0 6 B 0.31
230400 6.5104 6 8/16 0 6 8 0.16
250000 6 6 0 6 0 0
300000 5 5 0 5 0 0
400000 3.75 3 12/16 0 3 C 0
460800 3.2552 3 4/16 0 3 4 0.16
500000 3 3 0 3 0 0
750000 2 2 0 2 0 0
921600 1.6276 1 10/16 0 1 A 0.16
1000000 1.5 1 8/16 0 1 8 0
XR20M1170
15
REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
2.7.1 Transmit Holding Register (THR) - Write Only
The transmit holding register is an 8-bit register providing a data interface to the host processor. The host
writes the transmit data byte to the THR to be converted into a serial data stream including start-bit, data bits,
parity-bit and stop-bit(s). The least-significant-bit (bit-0) becomes first data bit to go out. The THR is the input
register to the transmit FIFO of 64 bytes when FIFO operation is enabled by FCR bit-0. Every time a write
operation is made to the THR, the FIFO data pointer is automatically bumped to the next sequential data
location.
2.7.2 Transmitter Operation in non-FIFO Mode
The host loads transmit data to THR one character at a time. The THR empty flag (LSR bit-5) is set when the
data byte is transferred to TSR. THR flag can generate a transmit empty interrupt (ISR bit-1) when it is enabled
by IER bit-1. The TSR flag (LSR bit-6) is set when TSR becomes completely empty.
2.7.3 Transmitter Operation in FIFO Mode
The host may fill the transmit FIFO with up to 64 bytes of transmit data. The THR empty flag (LSR bit-5) is set
whenever the FIFO is empty. The THR empty flag can generate a transmit empty interrupt (ISR bit-1) when the
amount of data in the FIFO falls below its programmed trigger level. The transmit empty interrupt is enabled by
IER bit-1. The TSR flag (LSR bit-6) is set when TSR/FIFO becomes empty.
FIGURE 13. TRANSMITTER OPERATION IN NON-FIFO MODE
FIGURE 14. TRANSMITTER OPERATION IN FIFO AND FLOW CONTROL MODE
Transmit
Holding
Register
(THR)
Transmit Shift Register (TSR)
Data
Byte
L
S
B
M
S
B
THR Interrupt (ISR bit-1)
Enabled by IER bit-1
TXNOFIFO1
16X or 8X or 4X
Clock
( DLD[5:4] )
Transmit Data Shift Register
(TSR)
Transmit
Data Byte THR Interrupt (ISR bit-1) falls
below the programmed Trigger
Level and then when becomes
empty. FIFO is Enabled by FCR
bit-0=1
Transmit
FIFO
16X or 8X or 4X Clock
( DLD[5:4] )
Auto CTS Flow Control (CTS# pin)
Auto Software Flow Control
Flow Control Characters
(Xoff1/2 and Xon1/2 Reg.)
TXFIFO1
XR20M1170
16
I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
2.8 Receiver
The receiver section contains an 8-bit Receive Shift Register (RSR) and 64 bytes of FIFO which includes a
byte-wide Receive Holding Register (RHR). The RSR uses the 16X/8X/4X clock (DLD [5:4]) for timing. It
verifies and validates every bit on the incoming character in the middle of each data bit. On the falling edge of
a start or false start bit, an internal receiver counter starts counting at the 16X/8X/4X clock rate. After 8 clocks
(or 4 if 8X or 2 if 4X) the start bit period should be at the center of the start bit. At this time the start bit is
sampled and if it is still a logic 0, it is validated. Evaluating the start bit in this manner prevents the receiver from
assembling a false character. The rest of the data bits and stop bits are sampled and validated in this same
manner to prevent false framing. If there were any error(s), they are reported in the LSR register bits 2-4. Upon
unloading the receive data byte from RHR, the receive FIFO pointer is bumped and the error tags are
immediately updated to reflect the status of the data byte in RHR register. RHR can generate a receive data
ready interrupt upon receiving a character or delay until it reaches the FIFO trigger level. Furthermore, data
delivery to the host is guaranteed by a receive data ready time-out interrupt when data is not received for 4
word lengths as defined by LCR[1:0] plus 12 bits time. This is equivalent to 3.7-4.6 character times. The RHR
interrupt is enabled by IER bit-0.
2.8.1 Receive Holding Register (RHR) - Read-Only
The Receive Holding Register is an 8-bit register that holds a receive data byte from the Receive Shift
Register. It provides the receive data interface to the host processor. The RHR register is part of the receive
FIFO of 64 bytes by 11-bits wide, the 3 extra bits are for the 3 error tags to be reported in LSR register. When
the FIFO is enabled by FCR bit-0, the RHR contains the first data character received by the FIFO. After the
RHR is read, the next character byte is loaded into the RHR and the errors associated with the current data
byte are immediately updated in the LSR bits 2-4.
FIGURE 15. RECEIVER OPERATION IN NON-FIFO MODE
Receive Data Shift
Register (RSR)
Receive
Data Byte
and Errors RHR Interrupt (ISR bit-2)
Receive Data
Holding Register
(RHR)
RXFIFO1
16X or 8X or 4X Clock
( DLD[5:4] )
Receive Data Characters
Data Bit
Validation
Error
Tags in
LSR bits
4:2
XR20M1170
17
REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
2.9 Auto RTS (Hardware) Flow Control
Automatic RTS hardware flow control is used to prevent data overrun to the local receiver FIFO. The RTS#
output is used to request remote unit to suspend/resume data transmission. The auto RTS flow control
features is enabled to fit specific application requirement (see Figure 17):
Enable auto RTS flow control using EFR bit-6.
The auto RTS function must be started by asserting RTS# output pin (MCR bit-1 to logic 1 after it is enabled).
If using the Auto RTS interrupt:
Enable RTS interrupt through IER bit-6 (after setting EFR bit-4). The UART issues an interrupt when the
RTS# pin makes a transition from low to high: ISR bit-5 will be set to logic 1.
2.10 Auto RTS Halt and Resume
The RTS# pin will not be forced HIGH (RTS off) until the receive FIFO reaches the Halt Level (TCR[3:0]). The
RTS# pin will return LOW after the RX FIFO is unloaded to the Resume Level (TCR[7:4]). Under these
conditions, the XR20M1170 will continue to accept data if the remote UART continues to transmit data. It is the
responsibility of the user to ensure that the Halt Level is greater than the Resume Level. If interrupts are used,
it is recommended that Halt Level > RX Trigger Level > Resume Level. The auto RTS function is initiated
when the RTS# output pin is asserted LOW (RTS On).
2.11 Auto CTS Flow Control
Automatic CTS flow control is used to prevent data overrun to the remote receiver FIFO. The CTS# input is
monitored to suspend or restart the local transmitter. The auto CTS flow control feature is selected to fit specific
application requirement (see Figure 17):
Enable auto CTS flow control using EFR bit-7.
If using the Auto CTS interrupt:
Enable CTS interrupt through IER bit-7 (after setting EFR bit-4). The UART issues an interrupt when the
CTS# pin is de-asserted (HIGH): ISR bit-5 will be set to 1, and UART will suspend transmission as soon as
FIGURE 16. RECEIVER OPERATION IN FIFO AND AUTO RTS FLOW CONTROL MODE
Receive Data Shift
Register (RSR)
RXFIFO1
16X or 8X or 4X Clock
( DLD[5:4] )
Error Tags
(64-sets)
Error Tags in
LSR bits 4:2
Receive Data Characters
FIFO
Trigger=16
Example
: - RX FIFO trigger level selected at 16 bytes
(See Note Below)
Data fills to
Halt Level
Data falls to
Resume Level
Data Bit
Validation
Receive
Data FIFO
Receive
Data
Receive Data
Byte and Errors
RHR Interrupt (ISR bit-2) programmed for
desired FIFO trigger level.
FIFO is Enabled by FCR bit-0=1
RTS# de-asserts when data fills to the Halt Level
to suspend remote transmitter.
Enable by EFR bit-6=1, MCR bit-1.
RTS# re-asserts when data falls to the Resume
Level to restart remote transmitter.
Enable by EFR bit-6=1, MCR bit-1.
64 bytes by 11-bit wide
FIFO
XR20M1170
18
I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
the stop bit of the character in process is shifted out. Transmission is resumed after the CTS# input is re-
asserted (LOW), indicating more data may be sent.
FIGURE 17. AUTO RTS AND CTS FLOW CONTROL OPERATION
The local UART (UARTA) starts data transfer by asserting RTSA# (1). RTSA# is normally connected to CTSB# (2) of
remote UART (UARTB). CTSB# allows its transmitter to send data (3). TXB data arrives and fills UARTA receive FIFO
(4). When RXA data fills up to its receive FIFO trigger level, UARTA activates its RXA data ready interrupt (5) and
continues to receive and put data into its FIFO. If interrupt service latency is long and data is not being unloaded, UARTA
monitors its receive data fill level to match the upper threshold of RTS delay and de-assert RTSA# (6). CTSB# follows
(7) and request UARTB transmitter to suspend data transfer. UARTB stops or finishes sending the data bits in its
transmit shift register (8). When receive FIFO data in UARTA is unloaded to match the lower threshold of RTS delay (9),
UARTA re-asserts RTSA# (10), CTSB# recognizes the change (11) and restarts its transmitter and data flow again until
next receive FIFO trigger (12). This same event applies to the reverse direction when UARTA sends data to UARTB
with RTSB# and CTSA# controlling the data flow.
RTSA# CTSB#
RXA TXB Transmitter
Receiver FIFO
Trigger Reached
Auto RTS
Trigger Level
Auto CTS
Monitor
RTSA#
TXB
RXA FIFO
CTSB#
Remote UART
UARTB
Local UART
UARTA
ON OFF ON
Suspend Restart
RTS High
Threshold
Data Starts
ON OFF ON
Assert RTS# to Begin
Transmission
1
2
3
4
5
6
7
Receive
Data RTS Low
Threshold
9
10
11
Receiver FIFO
Trigger Reached
Auto RTS
Trigger Level
Transmitter
Auto CTS
Monitor
RTSB#CTSA#
RXBTXA
INTA
(RXA FIFO
Interrupt)
RX FIFO
Trigger Level
RX FIFO
Trigger Level
8
12
RTSCTS1
XR20M1170
19
REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
2.12 Auto Xon/Xoff (Software) Flow Control
When software flow control is enabled (See Table 15), the XR20M1170 compares one or two sequential
receive data characters with the programmed Xon or Xoff-1,2 character value(s). If receive character(s) (RX)
match the programmed values, the XR20M1170 will halt transmission (TX) as soon as the current character
has completed transmission. When a match occurs, the Xoff (if enabled via IER bit-5) flag will be set and the
interrupt output pin will be activated. Following a suspension due to a match of the Xoff character, the
XR20M1170 will monitor the receive data stream for a match to the Xon-1,2 character. If a match is found, the
XR20M1170 will resume operation and clear the flags (ISR bit-4).
Upon power-up, the contents of the Xon/Xoff 8-bit flow control registers to 0x00. The user can write any Xon/
Xoff value desired for software flow control. These registers are not reset by a hardware or software reset.
Different conditions can be set to detect Xon/Xoff characters (See Table 15) and suspend/resume
transmissions. When double 8-bit Xon/Xoff characters are selected, the XR20M1170 compares two
consecutive receive characters with two software flow control 8-bit values (Xon1, Xon2, Xoff1, Xoff2) and
controls TX transmissions accordingly. Under the above described flow control mechanisms, flow control
characters are not placed (stacked) in the user accessible RX data buffer or FIFO.
In the event that the receive buffer is overfilling and flow control needs to be executed, the XR20M1170
automatically sends the Xoff-1,2 via the serial TX output to the remote modem when the RX FIFO reaches the
Halt Level (TCR[3:0]). To clear this condition, the XR20M1170 will transmit the programmed Xon-1,2
characters as soon as RX FIFO falls down to the Resume Level.
2.13 Special Character Detect
A special character detect feature is provided to detect an 8-bit character when bit-5 is set in the Enhanced
Feature Register (EFR). When this character (Xoff2) is detected, it will be placed in the FIFO along with normal
incoming RX data.
The XR20M1170 compares each incoming receive character with Xoff-2 data. If a match exists, the received
data will be transferred to FIFO and ISR bit-4 will be set to indicate detection of special character. Although the
Internal Register Table shows Xon, Xoff Registers with eight bits of character information, the actual number of
bits is dependent on the programmed word length. Line Control Register (LCR) bits 0-1 defines the number of
character bits, i.e., either 5 bits, 6 bits, 7 bits, or 8 bits. The word length selected by LCR bits 0-1 also
determines the number of bits that will be used for the special character comparison.
2.14 Auto RS485 Half-duplex Control
The auto RS485 half-duplex direction control changes the behavior of the transmitter when enabled by EFCR
bit-4. It also changes the behavior of the transmit empty interrupt (see Table 4). When idle, the auto RS-485
half-duplex direction control signal (RTS#) is HIGH for receive mode. When data is loaded into the THR for
transmission, the RTS# output is automatically asserted LOW prior to sending the data. After the last stop bit of
the last character that has been transmitted, the RTS# signal is automatically de-asserted. This helps in turning
around the transceiver to receive the remote station’s response. When the host is ready to transmit the next
polling data packet, it only has to load data bytes to the transmit FIFO. The transmitter automatically re-asserts
RTS# (LOW) output prior to sending the data. The polarity of the RTS# output pin can be inverted by setting
EFCR[5] = 1.
2.14.1 Normal Multidrop Mode
Normal multidrop mode is enabled when EFCR bit-0 = 1 and EFR bit-5 = 0 (Special Character Detect
disabled). The receiver is set to Force Parity 0 (LCR[5:3] = ’111’) in order to detect address bytes.
With the receiver initially disabled, it ignores all the data bytes (parity bit = 0) until an address byte is received
(parity bit = 1). This address byte will cause the UART to set the parity error. The UART will generate an LSR
interrupt and place the address byte in the RX FIFO. The software then examines the byte and enables the
receiver if the address matches its slave address, otherwise, it does not enable the receiver.
If the receiver has been enabled, the receiver will receive the subsequent data. If an address byte is received,
it will generate an LSR interrupt. The software again examines the byte and if the address matches its slave
XR20M1170
20
I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
address, it does not have to anything. If the address does not match its slave address, then the receiver
should be disabled.
2.14.2 Auto Address Detection
Auto address detection mode is enabled when EFCR bit-0 = 1 and EFR bit-5 = 1. The desired slave address
will need to be written into the XOFF2 register. The receiver will try to detect an address byte that matches the
programmed character in the XOFF2 register. If the received byte is a data byte or an address byte that does
not match the programmed character in the XOFF2 register, the receiver will discard this data. Upon receiving
an address byte that matches the XOFF2 character, the receiver will be automatically enabled if not already
enabled, and the address character is pushed into the RX FIFO along with the parity bit (in place of the parity
error bit). The receiver also generates an LSR interrupt. The receiver will then receive the subsequent data. If
another address byte is received and this address does not match the programmed XOFF2 character, then the
receiver will automatically be disabled and the address byte is ignored. If the address byte matches XOFF2,
the receiver will put this byte in the RX FIFO along with the parity bit in the parity error bit.
XR20M1170
21
REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
2.15 Infrared Mode
The XR20M1170 UART includes the infrared encoder and decoder compatible to the IrDA (Infrared Data
Association) version 1.0 and 1.1. The IrDA 1.0 standard that stipulates the infrared encoder sends out a 3/16 of
a bit wide HIGH-pulse for each “0” bit in the transmit data stream with a data rate up to 115.2kbps. For the IrDA
1.1 standard, the infrared encoder sends out a 1/4 of a bit time wide HIGH-pulse for each "0" bit in the transmit
data stream with a data rate up to 1.152Mbps. This signal encoding reduces the on-time of the infrared LED,
hence reduces the power consumption. See Figure 18 below.
The infrared encoder and decoder are enabled by setting MCR register bit-6 to a ‘1’. With this bit enabled, the
infrared encoder and decoder is compatible to the IrDA 1.0 standard. For the infrared encoder and decoder to
be compatible to the IrDA 1.1 standard, EFCR bit-7 will also need to be set to a ’1’. When the infrared feature
is enabled, the transmit data output TX idles LOW. Likewise, the RX input also idles LOW, see Figure 18.
The wireless infrared decoder receives the input pulse from the infrared sensing diode on the RX pin. Each
time it senses a light pulse, it returns a logic 1 to the data bit stream.
After power-up, the infrared mode can be controlled via MCR bit-6.
FIGURE 18. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING
Character
Data Bits
Start
Stop
0000 0
11 111
TX Data
Transmit
IR Pulse
(TX Pin)
Bit Time 1/2 Bit Time
3/16 or 1/4
Bit Time IrEncoder-1
Character
Data Bits
Start
Stop
0000 0
11 111
Bit Time
1/16 Clock Delay
IRdecoder-1
RX Data
Receive
IR Pulse
(RX pin)
XR20M1170
22
I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
2.16 Sleep Mode with Auto Wake-Up
The XR20M1170 supports low voltage system designs, hence a sleep mode is included to reduce its power
consumption when the chip is not actively used.
All of these conditions must be satisfied for the XR20M1170 to enter sleep mode:
No interrupts pending for the XR20M1170 (ISR bit-0 = 1)
Sleep mode of both channels are enabled (IER bit-4 = 1)
Modem inputs are not toggling (MSR bits 0-3 = 0)
RX input pin is idling HIGH
The XR20M1170 stops its crystal oscillator to conserve power in the sleep mode. The user can check the
XTAL2 pin for no clock output as an indication that the device has entered the sleep mode.
The XR20M1170 resumes normal operation by any of the following:
A receive data start bit transition (HIGH to LOW)
A data byte is loaded to the transmitter, THR or FIFO
A change of logic state on any of the modem or general purpose serial inputs: CTS#, DSR#, CD#, RI#
If the XR20M1170 is awakened by any one of the above conditions, it will return to the sleep mode
automatically after all interrupting conditions have been serviced and cleared. If the XR20M1170 is awakened
by the modem inputs, a read to the MSR is required to reset the modem inputs. In any case, the sleep mode
will not be entered while an interrupt is pending. The XR20M1170 will stay in the sleep mode of operation until
it is disabled by setting IER bit-4 to a logic 0.
If the serial clock, serial data, and modem input lines remain steady when the XR20M1170 is in sleep mode,
the maximum current will be in the microamp range as specified in the DC Electrical Characteristics on
page 42.
A word of caution: owing to the starting up delay of the crystal oscillator after waking up from sleep mode, the
first few receive characters may be lost. The number of characters lost during the restart also depends on your
operating data rate. More characters are lost when operating at higher data rate. Also, it is important to keep
RX input idling HIGH or “marking” condition during sleep mode to avoid receiving a “break” condition upon the
restart. This may occur when the external interface transceivers (RS-232, RS-485, or another type) are also
put to sleep mode and cannot maintain the “marking” condition. To avoid this, the designer can use a 47kΩ to
100kΩ pull-up resistor on the RX input pin.
XR20M1170
23
REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
2.17 Internal Loopback
The XR20M1170 UART provides an internal loopback capability for system diagnostic purposes. The internal
loopback mode is enabled by setting MCR register bit-4 to logic 1. All regular UART functions operate normally.
Figure 19 shows how the modem port signals are re-configured. Transmit data from the transmit shift register
output is internally routed to the receive shift register input allowing the system to receive the same data that it
was sending. The TX, RTS# and DTR# pins are held while the CTS#, DSR# CD# and RI# inputs are ignored.
Caution: the RX input pin must be held HIGH during loopback test, else upon exiting the loopback test the
UART may detect and report a false “break” signal. Also, Auto RTS/CTS flow control is not supported during
internal loopback.
FIGURE 19. INTERNAL LOOP BACK
TX
RX
Modem / General Purpose Control Logic
Internal Data Bus Lines and Control Signals
RTS#
MCR bit-4=1
VCC
VCC
Transmit Shift Register
(THR/FIFO)
Receive Shift Register
(RHR/FIFO)
CTS#
DTR#
DSR#
RI#
CD#
OP1#
RTS#
CTS#
DTR#
DSR#
RI#
CD#
VCC
OP2#
XR20M1170
24
I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
3.0 UART INTERNAL REGISTERS
The complete register set is shown below in Table 7 and Table 8.
TABLE 7: UART INTERNAL REGISTER ADDRESSES
ADDRESS REGISTER READ/WRITE COMMENTS
16C550 COMPATIBLE REGISTERS
0X00 RHR - Receive Holding Register
THR - Transmit Holding Register
Read-only
Write-only LCR[7] = 0
0X00 DLL - Divisor LSB Read/Write
LCR[7] = 1, LCR 0xBF
0X01 DLM - Divisor MSB Read/Write
0X02 DLD - Divisor Fractional Read/Write LCR[7] = 1, LCR 0xBF,
EFR[4] = 1
0X01 IER - Interrupt Enable Register Read/Write
LCR[7] = 0
0X02 ISR - Interrupt Status Register
FCR - FIFO Control Register
Read-only
Write-only
0X03 LCR - Line Control Register Read/Write
0X04 MCR - Modem Control Register Read/Write
LCR 0xBF
0X05 LSR - Line Status Register Read-only
0X06 MSR - Modem Status Register Read-only See Table 12
0X07 SPR - Scratch Pad Register Read/Write See Table 13
0X06 TCR - Transmission Control Register Read/Write See Table 12
0X07 TLR - Trigger Level Register Read/Write See Table 13
0X08 TXLVL - Transmit FIFO Level Read-only
LCR[7] = 0
0x09 RXLVL - Receive FIFO Level Read-only
0x0A IODir - GPIO Direction Control Register Read/Write
0x0B IOState - GPIO State Register Read/Write
0x0C IOIntEna - GPIO Interrupt Enable Register Read/Write
0x0D Reserved -
0x0E IOControl - GPIO Control Register Read/Write
0x0F EFCR - Extra Features Control Register Read/Write
0x02 EFR - Enhanced Function Register Read/Write
LCR = 0xBF
0x04 Xon-1 - Xon Character 1 Read/Write
0x05 Xon-2 - Xon Character 2 Read/Write
0x06 Xoff-1 - Xoff Character 1 Read/Write
0x07 Xoff-2 - Xoff Character 2 Read/Write
XR20M1170
25
REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
.
TABLE 8: INTERNAL REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED WHEN EFR BIT-4=1
ADDR REG
NAME
READ/
WRITE BIT-7 BIT-6 BIT-5 BIT-4 BIT-3 BIT-2 BIT-1 BIT-0 COMMENT
16C550 Compatible Registers
0x00 RHR RD Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
LCR[7]=0
0x00 THR WR Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
0x01 IER RD/WR 0/ 0/ 0/ 0/ Modem
Stat. Int.
Enable
RX Line
Stat. Int.
Enable
TX
Empty
Int
Enable
RX Data
Int.
Enable
CTS Int.
Enable
RTS Int.
Enable
Xoff Int.
Enable
Sleep
Mode
Enable
0x02 ISR RD FIFOs
Enabled
FIFOs
Enabled
0/ 0/ INT
Source
Bit-3
INT
Source
Bit-2
INT
Source
Bit-1
INT
Source
Bit-0
INT
Source
Bit-5
INT
Source
Bit-4
0x02 FCR WR RX FIFO
Trigger
RX FIFO
Trigger
0/ 0/ 0 TX FIFO
Reset
RX FIFO
Reset
FIFOs
Enable
TX FIFO
Trigger
TX FIFO
Trigger
0x03 LCR RD/WR Divisor
Enable
Set TX
Break
Set
Parity
Even
Parity
Parity
Enable
Stop Bits Word
Length
Bit-1
Word
Length
Bit-0
0x04 MCR RD/WR 0/ 0/ 0/ Internal
Lopback
Enable
OP2#
(Internal)
OP1#
(Internal)/
RTS#
Output
Control
DTR#
Output
Control
LCR0xBF
Clock
Pres-
caler
Select
IR Mode XonAny Enable
TCR and
TLR
0x05 LSR RD RX FIFO
Global
Error
THR &
TSR
Empty
THR
Empty
RX
Break
RX
Framing
Error
RX
Parity
Error
RX
Overrun
Error
RX Data
Ready
0x06 MSR RD CD#
Input
RI# Input DSR#
Input
CTS#
Input
Delta
CD#
Delta RI# Delta
DSR#
Delta
CTS# See Table 12
0x07 SPR RD/WR Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0 See Table 13
0x06 TCR RD/WR Resume
Bit-3
Resume
Bit-2
Resume
Bit-1
Resume
Bit-0
Halt
Bit-3
Halt
Bit-2
Halt
Bit-1
Halt
Bit-0 See Table 12
0x07 TLR RD/WR RX Trig
Bit-3
RX Trig
Bit-2
RX Trig
Bit-1
RX Trig
Bit-0
TX Trig
Bit-3
TX Trig
Bit-2
TX Trig
Bit-1
TX Trig
Bit-0 See Table 13
0x08 TXLVL RD/WR 0 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
0x09 RXLVL RD/WR 0 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
0x0A IODir RD/WR Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
XR20M1170
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
4.0 INTERNAL REGISTER DESCRIPTIONS
4.1 Receive Holding Register (RHR) - Read- Only
See “Section 2.8, Receiver” on page 16.
4.2 Transmit Holding Register (THR) - Write-Only
See “Section 2.7, Transmitter” on page 14.
4.3 Interrupt Enable Register (IER) - Read/Write
The Interrupt Enable Register (IER) masks the interrupts from receive data ready, transmit empty, line status
and modem status registers. These interrupts are reported in the Interrupt Status Register (ISR).
4.3.1 IER versus Receive FIFO Interrupt Mode Operation
When the receive FIFO (FCR BIT-0 = 1) and receive interrupts (IER BIT-0 = 1) are enabled, the RHR interrupts
(see ISR bits 2 and 3) status will reflect the following:
0x0B IOState RD/WR Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
0x0C IOIntEna RD/WR Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
0x0D reserved - 0 0 0 0 0 0 0 0
0x0E IOControl RD/WR 0 0 0 0 UART
SW
Reset
0 GPIO or
Modem
IO
IOLatch
0x0F EFCR RD/WR Fast IR
Mode
0 Auto
RS485
Invert
Auto
RS485
Enable
0 TX
Disable
RX
Disable
9-Bit
Mode
Baud Rate Generator Divisor
0x00 DLL RD/WR Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0 LCR[7]=1
LCR0xBF
0x01 DLM RD/WR Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
0x02 DLD RD/WR Bit-7 Bit-6 4X Mode 8X Mode Frac-
tional
Divisor
Bit-3
Frac-
tional
Divisor
Bit-2
Frac-
tional
Divisor
Bit-1
Frac-
tional
Divisor
Bit-0
LCR[7]=1
LCR0xBF
EFR[4]=1
Enhanced Registers
0x02 EFR RD/WR Auto
CTS
Enable
Auto RTS
Enable
Special
Char
Select
Enable
IER [7:4],
ISR [5:4],
FCR[5:4],
MCR[7:5],
DLD
Soft-
ware
Flow
Cntl
Bit-3
Software
Flow Cntl
Bit-2
Soft-
ware
Flow
Cntl
Bit-1
Soft-
ware
Flow
Cntl
Bit-0
LCR=0XBF
0x04 XON1 RD/WR Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
0x05 XON2 RD/WR Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
0x06 XOFF1 RD/WR Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
0x07 XOFF2 RD/WR Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
TABLE 8: INTERNAL REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED WHEN EFR BIT-4=1
ADDR REG
NAME
READ/
WRITE BIT-7 BIT-6 BIT-5 BIT-4 BIT-3 BIT-2 BIT-1 BIT-0 COMMENT
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
A. The receive data available interrupts are issued to the host when the FIFO has reached the programmed
trigger level. It will be cleared when the FIFO drops below the programmed trigger level.
B. FIFO level will be reflected in the ISR register when the FIFO trigger level is reached. Both the ISR register
status bit and the interrupt will be cleared when the FIFO drops below the trigger level.
C. The receive data ready bit (LSR BIT-0) is set as soon as a character is transferred from the shift register to
the receive FIFO. It is reset when the FIFO is empty.
4.3.2 IER versus Receive/Transmit FIFO Polled Mode Operation
When FCR BIT-0 equals a logic 1 for FIFO enable; resetting IER bits 0-3 enables the XR20M1170 in the FIFO
polled mode of operation. Since the receiver and transmitter have separate bits in the LSR either or both can
be used in the polled mode by selecting respective transmit or receive control bit(s).
A. LSR BIT-0 indicates there is data in RHR or RX FIFO.
B. LSR BIT-1 indicates an overrun error has occurred and that data in the FIFO may not be valid.
C. LSR BIT 2-4 provides the type of receive data errors encountered for the data byte in RHR, if any.
D. LSR BIT-5 indicates THR is empty.
E. LSR BIT-6 indicates when both the transmit FIFO and TSR are empty.
F. LSR BIT-7 indicates a data error in at least one character in the RX FIFO.
IER[0]: RHR Interrupt Enable
The receive data ready interrupt will be issued when RHR has a data character in the non-FIFO mode or when
the receive FIFO has reached the programmed trigger level in the FIFO mode.
Logic 0 = Disable the receive data ready interrupt (default).
Logic 1 = Enable the receiver data ready interrupt.
IER[1]: THR Interrupt Enable
This bit enables the Transmit Ready interrupt which is issued whenever the THR becomes empty in the non-
FIFO mode or when spaces in the FIFO is above the programmed trigger level in the FIFO mode. If the THR is
empty when this bit is enabled, an interrupt will be generated.
Logic 0 = Disable Transmit Ready interrupt (default).
Logic 1 = Enable Transmit Ready interrupt.
IER[2]: Receive Line Status Interrupt Enable
If any of the LSR register bits 1, 2, 3, 4 or 7 is a logic 1, it will generate an interrupt to inform the host controller
about the error status of the current data byte in FIFO. LSR bit-1 generates an interrupt immediately when the
character has been received. LSR bit-7 is set if any character in the RX FIFO has a parity or framing error, or is
a break character. LSR[4:2] always show the error status for the received character available for reading from
the RX FIFO. If IER[2] = 1, an LSR interrupt will be generated as long as LSR[7] = 1, ie. the RX FIFO contains
at lease one character with an error.
Logic 0 = Disable the receiver line status interrupt (default).
Logic 1 = Enable the receiver line status interrupt.
IER[3]: Modem Status Interrupt Enable
Logic 0 = Disable the modem status register interrupt (default).
Logic 1 = Enable the modem status register interrupt.
IER[4]: Sleep Mode Enable (requires EFR bit-4 = 1)
Logic 0 = Disable Sleep Mode (default).
Logic 1 = Enable Sleep Mode. See Sleep Mode section for further details.
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
IER[5]: Xoff Interrupt Enable (requires EFR bit-4=1)
Logic 0 = Disable the software flow control, receive Xoff interrupt (default).
Logic 1 = Enable the receive Xoff interrupt. See Software Flow Control section for details.
IER[6]: RTS# Output Interrupt Enable (requires EFR bit-4=1)
Logic 0 = Disable the RTS# interrupt (default).
Logic 1 = Enable the RTS# interrupt. The UART issues an interrupt when the RTS# pin makes a transition
from low to high.
IER[7]: CTS# Input Interrupt Enable (requires EFR bit-4=1)
Logic 0 = Disable the CTS# interrupt (default).
Logic 1 = Enable the CTS# interrupt. The UART issues an interrupt when CTS# pin makes a transition from
low to high.
4.4 Interrupt Status Register (ISR) - Read-Only
The UART provides multiple levels of prioritized interrupts to minimize external software interaction. The
Interrupt Status Register (ISR) provides the user with six interrupt status bits. Performing a read cycle on the
ISR will give the user the current highest pending interrupt level to be serviced, others are queued up to be
serviced next. No other interrupts are acknowledged until the pending interrupt is serviced. The Interrupt
Source Table, Table 9, shows the data values (bit 0-5) for the interrupt priority levels and the interrupt sources
associated with each of these interrupt levels.
4.4.1 Interrupt Generation:
LSR is by any of the LSR bits 1, 2, 3, 4 and 7.
RXRDY is by RX trigger level.
RXRDY Time-out is by a 4-char plus 12 bits delay timer.
TXRDY is by TX trigger level or TX FIFO empty (or transmitter empty in auto RS-485 control).
MSR is by any of the MSR bits 0, 1, 2 and 3.
GPIO is when any of the GPIO inputs toggle.
Receive Xoff/Special character is by detection of a Xoff or special character.
CTS# is when its transmitter toggles the input pin (from LOW to HIGH) during auto CTS flow control.
RTS# is when its receiver toggles the output pin (from LOW to HIGH) during auto RTS flow control.
4.4.2 Interrupt Clearing:
LSR interrupt is cleared by reading all characters with errors out of the RX FIFO.
RXRDY interrupt is cleared by reading data until FIFO falls below the trigger level.
RXRDY Time-out interrupt is cleared by reading RHR.
TXRDY interrupt is cleared by a read to the ISR register or writing to THR.
MSR interrupt is cleared by a read to the MSR register.
GPIO interrupt is cleared by reading the IOState register.
Xoff interrupt is cleared when Xon character(s) is received.
Special character interrupt is cleared by a read to ISR.
RTS# and CTS# flow control interrupts are cleared by a read to the MSR register.
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
]
ISR[0]: Interrupt Status
Logic 0 = An interrupt is pending and the ISR contents may be used as a pointer to the appropriate interrupt
service routine.
Logic 1 = No interrupt pending (default condition).
ISR[3:1]: Interrupt Status
These bits indicate the source for a pending interrupt at interrupt priority levels (See Interrupt Source Table 9).
ISR[4]: Xoff/Xon or Special Character Interrupt Status
This bit is set when EFR[4] = 1 and IER[5] = 1. ISR bit-4 indicates that the receiver detected a data match of
the Xoff character(s). If this is an Xoff interrupt, it is cleared when XON is received. If it is a special character
interrupt, it is cleared by reading ISR.
ISR[5]: RTS#/CTS# Interrupt Status
This bit is enabled when EFR[4] = 1. ISR bit-5 indicates that the CTS# or RTS# has been de-asserted.
ISR[7:6]: FIFO Enable Status
These bits are set to a logic 0 when the FIFOs are disabled. They are set to a logic 1 when the FIFOs are
enabled.
4.5 FIFO Control Register (FCR) - Write-Only
This register is used to enable the FIFOs, clear the FIFOs and set the transmit/receive FIFO trigger levels. The
FIFO mode is defined as follows:
FCR[0]: TX and RX FIFO Enable
Logic 0 = Disable the transmit and receive FIFO (default).
Logic 1 = Enable the transmit and receive FIFOs. This bit must be set to logic 1 when other FCR bits are
written or they will not be programmed.
TABLE 9: INTERRUPT SOURCE AND PRIORITY LEVEL
PRIORITY ISR REGISTER STATUS BITS SOURCE OF INTERRUPT
LEVEL BIT-5 BIT-4 BIT-3 BIT-2 BIT-1 BIT-0
1 0 0 0 1 1 0 LSR (Receiver Line Status Register)
2 0 0 1 1 0 0 RXRDY (Receive Data Time-out)
3 0 0 0 1 0 0 RXRDY (Received Data Ready)
4 0 0 0 0 1 0 TXRDY (Transmit Ready)
5 0 0 0 0 0 0 MSR (Modem Status Register)
6 1 1 0 0 0 0 GPIO (General Purpose Inputs)
7 0 1 0 0 0 0 RXRDY (Received Xoff or Special character)
8 1 0 0 0 0 0 CTS#, RTS# change of state
- 0 0 0 0 0 1 None (default)
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
FCR[1]: RX FIFO Reset
This bit is only active when FCR bit-0 is a ‘1’ and requires at least 3 XTAL clocks to reset.
Logic 0 = No receive FIFO reset (default)
Logic 1 = Reset the receive FIFO pointers and FIFO level counter logic (the receive shift register is not
cleared or altered). This bit will return to a logic 0 after resetting the FIFO.
FCR[2]: TX FIFO Reset
This bit is only active when FCR bit-0 is a ‘1’ and requires at least 3 XTAL clocks to reset.
Logic 0 = No transmit FIFO reset (default).
Logic 1 = Reset the transmit FIFO pointers and FIFO level counter logic (the transmit shift register is not
cleared or altered). This bit will return to a logic 0 after resetting the FIFO.
FCR[3]: Reserved
This is a legacy register bit that does not have any functionality in the XR20M1170.
FCR[5:4]: Transmit FIFO Trigger Select (requires EFR bit-4=1)
(logic 0 = default, TX trigger level = 1)
These 2 bits set the trigger level for the transmit FIFO. The UART will issue a transmit interrupt when the
number of spaces in the FIFO is above the selected trigger level, or when it gets empty in case that the FIFO
did not get filled over the trigger level on last re-load. Table 10 shows the selections. The UART will issue a
transmit interrupt when the number of available spaces in the FIFO is less than the transmit trigger level.
Table 10 shows the selections.
FCR[7:6]: Receive FIFO Trigger Select
(logic 0 = default, RX trigger level =1)
These 2 bits are used to set the trigger level for the receive FIFO. The UART will issue a receive interrupt when
the number of the characters in the FIFO is greater than the receive trigger level or when a receive data
timeout occurs (see “Section 2.8, Receiver” on page 16).
TABLE 10: TRANSMIT AND RECEIVE FIFO TRIGGER LEVEL SELECTION
FCR
BIT-7
FCR
BIT-6
FCR
BIT-5
FCR
BIT-4
RECEIVE
TRIGGER LEVEL
(CHARACTERS)
TRANSMIT
TRIGGER LEVEL
(SPACES)
0
0
1
1
0
1
0
1
0
0
1
1
0
1
0
1
8
16
56
60
8
16
32
56
XR20M1170
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
4.6 Line Control Register (LCR) - Read/Write
The Line Control Register is used to specify the asynchronous data communication format. The word or
character length, the number of stop bits, and the parity are selected by writing the appropriate bits in this
register.
LCR[1:0]: TX and RX Word Length Select
These two bits specify the word length to be transmitted or received.
LCR[2]: TX and RX Stop-bit Length Select
The length of stop bit is specified by this bit in conjunction with the programmed word length.
LCR[3]: TX and RX Parity Select
Parity or no parity can be selected via this bit. The parity bit is a simple way used in communications for data
integrity check. See Table 11 for parity selection summary below.
Logic 0 = No parity.
Logic 1 = A parity bit is generated during the transmission while the receiver checks for parity error of the
data character received (default).
LCR[4]: TX and RX Parity Select
If the parity bit is enabled with LCR bit-3 set to a logic 1, LCR bit-4 selects the even or odd parity format.
Logic 0 = ODD Parity is generated by forcing an odd number of logic 1’s in the transmitted character. The
receiver must be programmed to check the same format.
Logic 1 = EVEN Parity is generated by forcing an even number of logic 1’s in the transmitted character. The
receiver must be programmed to check the same format (default).
BIT-1 BIT-0 WORD LENGTH
0 0 5
0 1 6 (default)
1 0 7
1 1 8
BIT-2 WORD
LENGTH
STOP BIT LENGTH
(BIT TIME(S))
0 5,6,7,8 1
1 5 1-1/2
1 6,7,8 2 (default)
XR20M1170
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
LCR[5]: TX and RX Parity Select
If the parity bit is enabled, LCR bit-5 selects the forced parity format.
LCR bit-5 = logic 0, parity is not forced (default).
LCR bit-5 = logic 1 and LCR bit-4 = logic 0, parity bit is forced to a logical 1 for the transmit and receive data.
LCR bit-5 = logic 1 and LCR bit-4 = logic 1, parity bit is forced to a logical 0 for the transmit and receive data.
LCR[6]: Transmit Break Enable
When enabled, the break control bit causes a break condition to be transmitted (the TX output is forced to a
“space", LOW state). This condition remains, until disabled by setting LCR bit-6 to a logic 0.
Logic 0 = No TX break condition (default).
Logic 1 = Forces the transmitter output (TX) to a “space”, LOW, for alerting the remote receiver of a line
break condition.
LCR[7]: Baud Rate Divisors Enable
Baud rate generator divisor (DLL, DLM and DLD) enable.
Logic 0 = Data registers are selected (default).
Logic 1 = Divisor latch registers are selected.
4.7 Modem Control Register (MCR) or General Purpose Outputs Control - Read/Write
The MCR register is used for controlling the serial/modem interface signals or general purpose inputs/outputs.
MCR[0]: DTR# Output
The DTR# pin is a modem control output. If the modem interface is not used, this output may be used as a
general purpose output.
Logic 0 = Force DTR# output HIGH (default).
Logic 1 = Force DTR# output LOW.
MCR[1]: RTS# Output
The RTS# pin is a modem control output and may be used for automatic hardware flow control by enabled by
EFR bit-6. The RTS# pin can also be used for auto RS485 half-duplex direction control enabled by FCTR bit-3.
If the modem interface is not used, this output may be used as a general purpose output.
Logic 0 = Force RTS# HIGH (default).
Logic 1 = Force RTS# LOW.
TABLE 11: PARITY SELECTION
LCR BIT-5 LCR BIT-4 LCR BIT-3 PARITY SELECTION
X X 0 No parity
0 0 1 Odd parity
0 1 1 Even parity
1 0 1 Force parity to mark, “1”
1 1 1 Forced parity to space, “0”
XR20M1170
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
MCR[2]: OP1# / TCR and TLR Enable
OP1# is not available as an output pin on the XR20M1170. But it is available for use during Internal Loopback
Mode (MCR[4] = 1). In the Internal Loopback Mode, this bit is used to write the state of the modem RI#
interface signal.
This bit is also used to select between the MSR and TCR registers at address offset 0x6 and the SPR and TLR
registers at address offset 0x7. Table 12 and Table 13 below shows how these registers are accessed.
MCR[3]: OP2#
OP2# is not available as an output on the XR20M1170 but can be controlled in internal loopback mode.
Logic 0 = OP2# set HIGH (default).
Logic 1 = OP2# set LOW.
MCR[4]: Internal Loopback Enable
Logic 0 = Disable loopback mode (default).
Logic 1 = Enable local loopback mode, see loopback section and Figure 19.
MCR[5]: Xon-Any Enable (requires EFR bit-4 = 1 to write to this bit)
Logic 0 = Disable Xon-Any function (default).
Logic 1 = Enable Xon-Any function. In this mode, any RX character received will resume transmit operation.
The RX character will be loaded into the RX FIFO, unless the RX character is an Xon or Xoff character and
the XR20M1170 is programmed to use the Xon/Xoff flow control.
MCR[6]: IR Mode Enable (requires EFR bit-4 = 1 to write to this bit)
This bit enables the infrared mode and/or controls the infrared mode after power-up. See “Section 2.15,
Infrared Mode” on page 21 for complete details.
Logic 0 = Reserved (default).
Logic 1 = Enable IR Mode.
TABLE 12: REGISTER AT ADDRESS OFFSET 0X6
EFR[4] MCR[2] Register at Address Offset 0x6
0 X Modem Status Register (MSR)
1 0 Modem Status Register (MSR)
1 1 Trigger Control Register (TCR)
TABLE 13: REGISTER AT ADDRESS OFFSET 0X7
EFR[4] MCR[2] Register at Address Offset 0x7
0 X Scratchpad Register (SPR)
1 0 Scratchpad Register (SPR)
1 1 Trigger Level Register (TLR)
XR20M1170
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
MCR[7]: Clock Prescaler Select (requires EFR bit-4 = 1 to write to this bit)
Logic 0 = divide by one. The input clock from the crystal or external clock is fed directly to the Programmable
Baud Rate Generator without further modification, i.e., divide by one (default).
Logic 1 = divide by four. The prescaler divides the input clock from the crystal or external clock by four and
feeds it to the Programmable Baud Rate Generator, hence, data rates become one-forth.
4.8 Line Status Register (LSR) - Read Only
This register provides the status of data transfers between the UART and the host.
LSR[0]: Receive Data Ready Indicator
Logic 0 = No data in receive holding register or FIFO (default).
Logic 1 = Data has been received and is saved in the receive holding register or FIFO.
LSR[1]: Receiver Overrun Error Flag
Logic 0 = No overrun error (default).
Logic 1 = Overrun error. A data overrun error condition occurred in the Receive Shift Register. This happens
when additional data arrives while the FIFO is full. In this case the previous data in the Receive Shift Register
is overwritten. Note that under this condition the data byte in the Receive Shift Register is not transferred into
the FIFO, therefore the data in the FIFO is not corrupted by the error.
LSR[2]: Receive Data Parity Error Tag
Logic 0 = No parity error (default).
Logic 1 = Parity error. The receive character in RHR does not have correct parity information and is suspect.
This error is associated with the character available for reading in RHR.
LSR[3]: Receive Data Framing Error Tag
Logic 0 = No framing error (default).
Logic 1 = Framing error. The receive character did not have a valid stop bit(s). This error is associated with
the character available for reading in RHR.
LSR[4]: Receive Break Error Tag
Logic 0 = No break condition (default).
Logic 1 = The receiver received a break signal (RX was LOW for at least one character frame time). In the
FIFO mode, only one break character is loaded into the FIFO.
LSR[5]: Transmit Holding Register Empty Flag
This bit is the Transmit Holding Register empty indicator. The THR bit is set to a logic 1 when the last data byte
is transferred from the Transmit Holding Register to the Transmit Shift Register. The bit is reset to logic 0
concurrently with the data loading to the Transmit Holding Register by the host. In the FIFO mode, this bit is set
when the transmit FIFO is empty, it is cleared when the transmit FIFO contains at least 1 byte.
LSR[6]: THR and TSR Empty Flag
This bit is set to a logic 1 whenever the transmitter goes idle. It is set to logic 0 whenever either the THR or
TSR contains a data character. In the FIFO mode, this bit is set to a logic 1 whenever the transmit FIFO and
Transmit Shift Register are both empty.
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
LSR[7]: Receive FIFO Data Error Flag
Logic 0 = No FIFO error (default).
Logic 1 = A global indicator for the sum of all error bits in the RX FIFO. At least one parity error, framing error
or break indication is in the FIFO data. This bit clears when there is no more error(s) in any of the bytes in the
RX FIFO.
4.9 Modem Status Register (MSR) - Read Only
This register provides the current state of the modem interface input signals. Lower four bits of this register are
used to indicate the changed information. These bits are set to a logic 1 whenever a signal from the modem
changes state. These bits may be used for general purpose inputs when they are not used with modem
signals.
MSR[0]: Delta CTS# Input Flag
Logic 0 = No change on CTS# input (default).
Logic 1 = The CTS# input has changed state since the last time it was monitored. A modem status interrupt
will be generated if the MSR interrupt is enabled (IER bit-3).
MSR[1]: Delta DSR# Input Flag
Logic 0 = No change on DSR# input (default).
Logic 1 = The DSR# input has changed state since the last time it was monitored. A modem status interrupt
will be generated if the MSR interrupt is enabled (IER bit-3).
MSR[2]: Delta RI# Input Flag
Logic 0 = No change on RI# input (default).
Logic 1 = The RI# input has changed from a LOW to HIGH, ending of the ringing signal. A modem status
interrupt will be generated if the MSR interrupt is enabled (IER bit-3).
MSR[3]: Delta CD# Input Flag
Logic 0 = No change on CD# input (default).
Logic 1 = Indicates that the CD# input has changed state since the last time it was monitored. A modem
status interrupt will be generated if the MSR interrupt is enabled (IER bit-3).
MSR[4]: CTS Input Status
CTS# pin may function as automatic hardware flow control signal input if it is enabled and selected by Auto
CTS (EFR bit-7). Auto CTS flow control allows starting and stopping of local data transmissions based on the
modem CTS# signal. A HIGH on the CTS# pin will stop the UART transmitter as soon as the current character
has finished transmission, and a LOW will resume data transmission. Normally MSR bit-4 bit is the
complement of the CTS# input. However in the loopback mode, this bit is equivalent to the RTS# bit in the
MCR register. The CTS# input may be used as a general purpose input when the modem interface is not used.
MSR[5]: DSR Input Status
Normally this bit is the complement of the DSR# input. In the loopback mode, this bit is equivalent to the DTR#
bit in the MCR register. The DSR# input may be used as a general purpose input when the modem interface is
not used.
MSR[6]: RI Input Status
Normally this bit is the complement of the RI# input. In the loopback mode this bit is equivalent to bit-2 in the
MCR register. The RI# input may be used as a general purpose input when the modem interface is not used.
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
MSR[7]: CD Input Status
Normally this bit is the complement of the CD# input. In the loopback mode, this bit is equivalent to bit-3 in the
MCR register. The CD# input may be used as a general purpose input when the modem interface is not used.
4.10 Scratch Pad Register (SPR) - Read/Write
This is a 8-bit general purpose register for the user to store temporary data. The content of this register is
preserved during sleep mode but becomes 0xFF (default) after a power off-on cycle. There are also two other
registers (TLR and FIFO Rdy) that share the same address location as the Scratch Pad Register. See
Table 13.
4.11 Transmission Control Register (TCR) - Read/Write (requires EFR bit-4 = 1)
This register replaces MSR and is accessible only when MCR[2] = 1. This 8-bit register is used to store the RX
FIFO threshold levels to halt/resume transmission during hardware or software flow control.
TCR[3:0]: RX FIFO Halt Level
A value of 0-60 (decimal value of TCR[3:0] multiplied by 4) can be selected as the Halt Level. When the RX
FIFO is greater than or equal to this value, the RTS# output will be de-asserted if Auto RTS flow control is used
or the XOFF character(s) will be transmitted if Auto XON/XOFF flow control is used. It is recommended that
this value is greater than the RX Trigger Level.
TCR[7:4]: RX FIFO Resume Level
A value of 0-60 (decimal value of TCR[7:4] multiplied by 4) can be selected as the Resume Level. When the
RX FIFO is less than or equal to this value, the RTS# output will be re-asserted if Auto RTS flow control is used
or the XON character(s) will be transmitted if Auto XON/XOFF flow control is used. It is recommended that this
value is less than the RX Trigger Level.
4.12 Trigger Level Register (TLR) - Read/Write (requires EFR bit-4 = 1)
This register replaces SPR and is accessible under the conditions listed in Table 13. This 8-bit register is used
to store the RX and TX FIFO trigger levels used for interrupts.
TLR[3:0]: TX FIFO Trigger Level
A value of 4-60 (decimal value of TCR[3:0] multiplied by 4) can be selected as the TX FIFO Trigger Level.
When the number of available spaces in the TX FIFO is greater than or equal to this value, a Transmit Ready
interrupt is generated. For any non-zero value, TCR[3:0] will be used as the TX FIFO Trigger Level. If
TCR[3:0] = 0x0, then the TX FIFO Trigger Level is the value selected by FCR[5:4]. See Table 10.
TLR[7:4]: RX FIFO Trigger Level
A value of 4-60 (decimal value of TCR[7:4] multiplied by 4) can be selected as the RX FIFO trigger level.
When the number of characters received in the RX FIFO is greater than or equal to this value, a Receive Data
Ready interrupt is generated (a Receive Data Timeout interrupt is independent of the RX FIFO Trigger Level
and can be generated any time there is at least 1 byte in the RX FIFO and the RX input has been idle for the
timeout period described in “Section 2.8, Receiver” on page 16). For any non-zero value, TCR[7:4] will be
used as the RX FIFO trigger level. If TCR[7:4] = 0x0, then the RX FIFO trigger level is the value selected by
FCR[7:6]. See Table 10.
4.13 Transmit FIFO Level Register (TXLVL) - Read-only
This register reports the number of spaces available in the TX FIFO. If the TX FIFO is empty, the TXLVL
Register will report that there are 64 spaces available. If the TX FIFO is full, the TXLVL Register will report that
there are 0 spaces available.
4.14 Receive FIFO Level Register (RXLVL) - Read-only
This register reports the number of characters available in the RX FIFO. If the RX FIFO is empty, the RXLVL
Register will report that there are 0 characters available. If the RX FIFO is full, the RXLVL Register will report
that there are 64 characters available.
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
4.15 GPIO Direction Register (IODir) - Read/Write
This register is used to program the direction of the GPIO pins. Bit-7 to bit-0 controls GPIO7 to GPIO0.
Logic 0 = set GPIO pin as input
Logic 1 = set GPIO pin as output
4.16 GPIO State Register (IOState) = Read/Write
This register reports the state of all GPIO pins during a read and writes to any GPIO that is an output.
Logic 0 = set output pin LOW
Logic 1 = set output pin HIGH
4.17 GPIO Interrupt Enable Register (IOIntEna) - Read/Write
This register enables the interrupt for the GPIO pins. The interrupts for GPIO[7:4] are only enabled if
IOControl[1] = 0. If IOControl[0] = 1 (GPIO pins are selected as modem IOs) , then IOIntEna[7:4] will have no
effect on GPIO[7:4].
Logic 0 = a change in the input pin will not generate an interrupt
Logic 1 = a change in the input will generate an interrupt
4.18 GPIO Control Register (IOControl) - Read/Write
IOControl[7:4]: Reserved
IOControl[3]: UART Software Reset
Writing a logic 1 to this bit will reset the device. Once the device is reset, this bit will automatically be set to a
logic 0.
IOControl[2]: Reserved
IOControl[1]: GPIO[7:4] or Modem IO Select
This bit controls whether GPIO[7:4] behave as GPIO pins or as modem IO pins (RI#, CD#, DTR#, DSR#)
Logic 0 = GPIO[7:4] behave as GPIO pins
Logic 1 = GPIO[7:4] behave as RI#, CD#, DTR#, DSR#
IOControl[0]: IO Latch
This bit enable/disable GPIO inputs latching.
Logic 0 = GPIO input values are not latched. A change in any GPIO input generates an interrupt. A read of
the IOState register clears the interrupt. If the input goes back to its initial logic state before the input register
is read, then the interrupt is cleared.
Logic 1 = GPIO input values are latched. A change in the GPIO input generates an interrupt and the input
logic value is loaded in the bit of the corresponding input state register (IOState). A read of the IOState
Register clears the interrupt. If the input pin goes back to its initial logic state before the interrupt register is
read, then the interrupt is not cleared and the corresponding bit of the IOState Register keeps the logic value
that generated the interrupt.
4.19 Extra Features Control Register (EFCR) - Read/Write
EFCR[7]: IrDA mode
This bit selects between the slow and fast IrDA modes. See “Section 2.15, Infrared Mode” on page 21 for
complete details.
Logic 0 = IrDA version 1.0, 3/16 pulse ratio, data rate up to 115.2kbps
Logic 1 = IrDA version 1.1, 1/4 pulse ratio, data rate up to 1.152Mbps
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
EFCR[6]: Reserved
EFCR[5]: Auto RS-485 Polarity Inversion
This bit changes the polarity of the auto RS-485 half-duplex direction control output (RTS#). This bit will only
affect the behavior of the RTS# output if EFCR[4] = 1. See “Section 2.14, Auto RS485 Half-duplex Control” on
page 19 for complete details.
Logic 0 = RTS# output is LOW when transmitting and HIGH when receiving.
Logic 1 = RTS# output is HIGH when transmitting and LOW when receiving.
EFCR[4]: Auto RS-485 Enable
This bit enables the RTS# output as the auto RS-485 half-duplex direction control output. See “Section 2.14,
Auto RS485 Half-duplex Control” on page 19 for complete details.
Logic 0 = RTS# output can be used for auto RTS hardware flow control or as a general purpose output.
Logic 1 = RTS# output enabled as the auto RS-485 half-duplex direction control output.
EFCR[3]: Reserved
EFCR[2]: Transmitter Disable
UART does not send serial data out on the TX output pin, but the TX FIFO will continue to receive data from
the CPU until full. Any data in the TSR will be sent out before the transmitter goes into disable state.
Logic 0 = Transmitter is enabled
Logic 1 = Transmitter is disabled
EFCR[1] = Receiver Disable
UART will stop receiving data immediately once this bit is set to a Logic 1. Any data that is being received in
the TSR will be received correctly and sent to the RX FIFO.
Logic 0 = Receiver is enabled
Logic 1 = Receiver is disabled
EFCR[0]: 9-bit or Multidrop Mode Enable
This bit enables 9-bit or Multidrop mode. See “Section 2.14, Auto RS485 Half-duplex Control” on page 19 for
complete details.
Logic 0 = Normal 8-bit Mode
Logic 1 = Enable 9-bit or Multidrop Mode
4.20 Baud Rate Generator Registers (DLL, DLM and DLD[3:0]) - Read/Write
These registers make-up the value of the baud rate divisor. The concatenation of the contents of DLM and
DLL is a 16-bit value is then added to DLD[3:0]/16 to achieve the fractional baud rate divisor. DLD must be
enabled via EFR bit-4 before it can be accessed. See “Section 2.6, Programmable Baud Rate Generator with
Fractional Divisor” on page 12.
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
DLD[5:4]: Sampling Rate Select
These bits select the data sampling rate. By default, the data sampling rate is 16X. The maximum data rate will
double if the 8X mode is selected and will quadruple if the 4X mode is selected. See Table 14 below.
DLD[7:6]: Reserved
4.21 Enhanced Feature Register (EFR)
Enhanced features are enabled or disabled using this register. Bits 0-3 provide single or dual consecutive
character software flow control selection (see Table 15). When the Xon1 and Xon2 and Xoff1 and Xoff2 modes
are selected, the double 8-bit words are concatenated into two sequential characters. Caution: note that
whenever changing the TX or RX flow control bits, always reset all bits back to logic 0 (disable) before
programming a new setting.
EFR[3:0]: Software Flow Control Select
Single character and dual sequential characters software flow control is supported. Combinations of software
flow control can be selected by programming these bits.
TABLE 14: SAMPLING RATE SELECT
DLD[5] DLD[4] SAMPLING RATE
0 0 16X
0 1 8X
1 X 4X
TABLE 15: SOFTWARE FLOW CONTROL FUNCTIONS
EFR BIT-3
CONT-3
EFR BIT-2
CONT-2
EFR BIT-1
CONT-1
EFR BIT-0
CONT-0 TRANSMIT AND RECEIVE SOFTWARE FLOW CONTROL
0 0 0 0 No TX and RX flow control (default and reset)
0 0 X X No transmit flow control
1 0 X X Transmit Xon1, Xoff1
0 1 X X Transmit Xon2, Xoff2
1 1 X X Transmit Xon1 and Xon2, Xoff1 and Xoff2
X X 0 0 No receive flow control
X X 1 0 Receiver compares Xon1, Xoff1
X X 0 1 Receiver compares Xon2, Xoff2
1 0 1 1 Transmit Xon1, Xoff1
Receiver compares Xon1 or Xon2, Xoff1 or Xoff2
0 1 1 1 Transmit Xon2, Xoff2
Receiver compares Xon1 or Xon2, Xoff1 or Xoff2
1 1 1 1 Transmit Xon1 and Xon2, Xoff1 and Xoff2,
Receiver compares Xon1 and Xon2, Xoff1 and Xoff2
0 0 1 1 No transmit flow control,
Receiver compares Xon1 and Xon2, Xoff1 and Xoff2
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
EFR[4]: Enhanced Function Bits Enable
Enhanced function control bit. This bit enables IER bits 4-7, ISR bits 4-5, FCR bits 4-5, MCR bits 2 and 5-7,
TCR, TLR and DLD to be modified. After modifying any enhanced bits, EFR bit-4 can be set to a logic 0 to latch
the new values. This feature prevents legacy software from altering or overwriting the enhanced functions once
set. Normally, it is recommended to leave it enabled, logic 1.
Logic 0 = modification disable/latch enhanced features. IER bits 4-7, ISR bits 4-5, FCR bits 4-5, MCR bits 2
and 5-7, and DLD are saved to retain the user settings. After a reset, the IER bits 4-7, ISR bits 4-5, FCR bits
4-5, MCR bits 5-7, and DLD are set to a logic 0 to be compatible with ST16C550 Mode (default).
Logic 1 = Enables the above-mentioned register bits to be modified by the user.
EFR[5]: Special Character Detect Enable
Logic 0 = Special character detect disabled (default).
Logic 1 = Special character detect enabled. The UART compares each incoming receive character with data
in the Xoff-2 register. If a match exists, the receive data will be transferred to FIFO and ISR bit-4 will be set to
indicate detection of the special character. Bit-0 corresponds with the LSB bit of the receive character. If flow
control is set for comparing Xon1, Xoff1 (EFR [1:0]= ‘10’) then flow control and special character work
normally. However, if flow control is set for comparing Xon2, Xoff2 (EFR[1:0]= ‘01’) then flow control works
normally, but Xoff2 will not go to the FIFO, and will generate an Xoff interrupt and a special character
interrupt, if enabled via IER bit-5.
EFR[6]: Auto RTS Flow Control Enable
RTS# output may be used for hardware flow control by setting EFR bit-6 to logic 1. When auto RTS is selected,
an interrupt will be generated when the receive FIFO is filled to the programmed trigger level and RTS de-
asserts HIGH at the programmed Halt Level. RTS# will return LOW when FIFO data falls below the
programmed Resume Level. The RTS# output must be asserted (LOW) before the auto RTS can take effect.
RTS# pin will function as a general purpose output when hardware flow control is disabled.
Logic 0 = Automatic RTS flow control is disabled (default).
Logic 1 = Enable Automatic RTS flow control.
EFR[7]: Auto CTS Flow Control Enable
Automatic CTS Flow Control.
Logic 0 = Automatic CTS flow control is disabled (default).
Logic 1 = Enable automatic CTS flow control. Data transmission stops when CTS# input de-asserts HIGH.
Data transmission resumes when CTS# returns LOW.
4.21.1 Software Flow Control Registers (XOFF1, XOFF2, XON1, XON2) - Read/Write
These registers are used as the programmable software flow control characters Xoff1, Xoff2, Xon1, and Xon2.
For more details, see Table 8.
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
NOTE: [1] Only resets to these values during a power up. They do not reset when the RESET# pin is asserted or during
software reset IOCont[3] = 1.
TABLE 16: UART RESET STATES
REGISTERS RESET STATE
DLM, DLL DLM = 0x00 and DLL = 0x01[1]
DLD Bits 7-0 = 0x00
RHR Bits 7-0 = 0xXX
THR Bits 7-0 = 0xXX
IER Bits 7-0 = 0x00
FCR Bits 7-0 = 0x00
ISR Bits 7-0 = 0x01
LCR Bits 7-0 = 0x1D
MCR Bits 7-0 = 0x00
LSR Bits 7-0 = 0x60
MSR Bits 3-0 = Logic 0
Bits 7-4 = Logic levels of the inputs inverted
SPR Bits 7-0 = 0xFF[1]
TCR Bits 7-0 = 0x0F
TLR Bits 7-0 = 0x00
TXLVL Bits 7-0 = 0x40
RXLVL Bits 7-0 = 0x00
IODir Bits 7-0 = 0x00
IOState Bits 7-0 = 0x00
IOIntEna Bits 7-0 = 0x00
IOCont Bits 7-0 = 0x00
EFCR Bits 7-0 = 0x00
EFR Bits 7-0 = 0x00
XON1 Bits 7-0 = 0x00[1]
XON2 Bits 7-0 = 0x00[1]
XOFF1 Bits 7-0 = 0x00[1]
XOFF2 Bits 7-0 = 0x00[1]
I/O SIGNALS RESET STATE
TX HIGH
RTS# HIGH
DTR# HIGH
IRQ# HIGH
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
5.0 ELECTRICAL CHARACTERISTICS
Test 1: The following inputs must remain steady at VCC or GND state to minimize sleep current: serial data,
serial clock, and all modem inputs are idle. Also, RX input must idle HIGH while asleep. Floating inputs will
result in sleep currents in the mA range.
ABSOLUTE MAXIMUM RATINGS
Power supply range 4V
Voltage at any pin GND - 0.3V to 4V
Operating temperature –40o to +85oC
Storage temperature –65o to +150oC
Package dissipation 500mW
TYPICAL PACKAGE THERMAL RESISTANCE DATA (MARGIN OF ERROR: ± 15%)
Thermal resistance (24-QFN) θJA = 38oC/W, θJC = 26oC/W
Thermal resistance (16-QFN) θJA = 40oC/W, θJC = 26oC/W
Thermal resistance (24-TSSOP) θJA = 84oC/W, θJC = 16oC/W
Thermal resistance (16-TSSOP) θJA = 105oC/W, θJC = 20oC/W
DC ELECTRICAL CHARACTERISTICS
TA = –40o to +85oC, VCC is 1.62V to 3.63V
SYMBOL PARAMETER
LIMITS
1.8V ±10%
MIN MAX
LIMITS
2.5V ±10%
MIN MAX
LIMITS
3.3V ±10%
MIN MAX
UNITS CONDITIONS
VILCK Clock input low level –0.3 0.3 –0.3 0.6 –0.3 0.6 V
VIHCK Clock input high level 1.4 VCC 1.8 VCC 2.4 VCC V
VIL Input low voltage –0.3 0.2 –0.3 0.5 –0.3 0.8 V
VIH Input high voltage 1.4 VCC 1.8 VCC 2.0 VCC V
VOL Output low voltage
0.4
0.4
0.4 V
V
IOL = 4mA
IOL = 2mA
IOL = 1.5mA
VOH Output high voltage
1.4
1.8
2.0 V
V
IOH = –1mA
IOH = –400µA
IOH = –200µA
IIL Input low leakage current ±10 ±10 ±10 µA
IIH Input high leakage current ±10 ±10 ±10 µA
CIN Input pin capacitance 5 5 5 pF
ICC Power supply current 250 250 500 µA XTAL1 = 2MHz
ISLEEP Sleep current 15 20 30 µA See Test 1
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
AC ELECTRICAL CHARACTERISTICS - UART CLOCK
Unless otherwise noted: TA = –40o to +85oC, VCC = 1.62 to 3.63V
SYMBOL PARAMETER
LIMITS
1.8V ±5%
MIN MAX
LIMITS
1.8V ±10%
MIN MAX
LIMITS
2.5V ±10%
MIN MAX
LIMITS
3.3V ±10%
MIN MAX
UNIT
XTAL1 UART crystal oscillator 24 24 24 24 MHz
ECLK UART external clock 32 24 50 64 MHz
TECLK External clock time period 1/ECLK 1/ECLK 1/ECLK 1/ECLK ns
FIGURE 20. CLOCK TIMING
External
Clock
VIHCK
VILCK
TECLK
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
AC ELECTRICAL CHARACTERISTICS - I2C-BUS TIMING SPECIFICATIONS
Unless otherwise noted: TA = –40o to +85oC, VCC = 1.62 to 3.63V
SYMBOL PARAMETER
STANDARD MODE
I2C-BUS
MIN MAX
FAST MODE
I2C-BUS
MIN MAX
UNIT
fSCL Operating frequency 0 100 0 400 kHz
TBUF Bus free time between STOP and START 4.7 1.3 s
THD;STA START condition hold time 4.0 0.6 s
TSU;STA START condition setup time 4.7 0.6 s
THD;DAT Data hold time 0 0 ns
TVD;ACK Data valid acknowledge 0.6 0.6 s
TVD;DAT SCL LOW to data out valid 0.6 0.6 ns
TSU;DAT Data setup time 250 150 ns
TLOW Clock LOW period 4.7 1.3 s
THIGH Clock HIGH period 4.0 0.6 s
TFClock/data fall time 300 300 ns
TRClock/data rise time 1000 300 ns
TSP Pulse width of spikes tolerance 0.5 0.5 s
TD1 I2C-bus GPIO output valid 0.2 0.2 s
TD2 I2C-bus modem input interrupt valid 0.2 0.2 s
TD3 I2C-bus modem input interrupt clear 0.2 0.2 s
TD4 I2C input pin interrupt valid 0.2 0.2 s
TD5 I2C input pin interrupt clear 0.2 0.2 s
TD6 I2C-bus receive interrupt valid 0.2 0.2 s
TD7 I2C-bus receive interrupt clear 0.2 0.2 s
TD8 I2C-bus transmit interrupt clear 1.0 0.5 s
TD15 SCL delay after reset 3 3 s
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
FIGURE 21. SCL DELAY AFTER RESET
FIGURE 22. I2C-BUS TIMING DIAGRAM
FIGURE 23. WRITE TO OUTPUT
TD15
RESET#
SCL
START
condition
(S)
Bit 7
MSB
(A7)
Bit 6
(A6)
Protocol
TBUF
TR
TSU;STA TLOW THIGH
1/FSCL
TF
SCL
THD;STA TSU;DAT THD;DAT
SDA
Bit 0
LSB
(R/W)
Acknowledge
(A)
STOP
condition
(P)
TVD;DAT
TSP
TVD;ACK TSU;STO
SLAVE
ADDRESS W A IOSTATE REG. A DATA ASDA
GPIOn
TD1
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
FIGURE 24. MODEM INPUT PIN INTERRUPT
FIGURE 25. GPIO PIN INTERRUPT
SLAVE
ADDRESS W A MSR REGISTER A DATAASDA
IRQ#
TD3
RA
SLAVE
ADDRESS
S
MODEM pin
TD2
SLAVE
ADDRESS W A IOSTATE REG. A DATAASDA
IRQ#
TD5
RA
SLAVE
ADDRESS
S
GPIOn
TD4
P
ACK from slave ACK from slave ACK from master
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
FIGURE 26. RECEIVE INTERRUPT
FIGURE 27. RECEIVE INTERRUPT CLEAR
FIGURE 28. TRANSMIT INTERRUPT CLEAR
D0 D1 D2 D3 D4 D5 D6 D7
Start bit Stop bit
Next
start
bit
TD6
RX
IRQ#
SLAVE
ADDRESS W A RHR A DATAASDA
IRQ#
TD7
RA
SLAVE
ADDRESS
SP
SLAVE
ADDRESS W A THR REGISTER A DATAASDA
IRQ#
TD8
ADATA
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
AC ELECTRICAL CHARACTERISTICS - SPI-BUS TIMING SPECIFICATIONS
Unless otherwise noted: TA = –40o to +85oC, VCC = 1.62 to 3.63V
SYMBOL PARAMETER
LIMITS
1.8V ±10%
MIN MAX
LIMITS
2.5V ±10%
MIN MAX
LIMITS
3.3V ±10%
MIN MAX
UNIT CONDITIONS
fSCL SPI clock frequency 8 16 18 MHz
TTR CS# HIGH to SO three-state time 100 100 100 ns CL = 70pF
TCSS CS# to SCL setup time 100 100 100 ns
TCSH CS# to SCL hold time 20 20 20 ns
TDO SCL fall to SO valid time 30 20 15 ns CL = 70pF
TDS SI to SCL setup time 30 20 15 ns
TDH SI to SCL hold time 10 10 10 ns
TCP SCL period time 125 63 55 ns TCH + TCL
TCH SCL HIGH time 62 31 27 ns
TCL SCL LOW time 62 31 27 ns
TCSW CS# HIGH pulse width 200 200 200 ns
TD9 SPI output data valid 200 200 200 ns
TD10 SPI modem output data valid 200 200 200 ns
TD11 SPI transmit interrupt clear 200 200 200 ns
TD12 SPI modem input interrupt clear 200 200 200 ns
TD13 SPI input pin interrupt clear 200 200 200 ns
TD14 SPI receive interrupt clear 200 200 200 ns
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
FIGURE 29. SPI-BUS TIMING
FIGURE 30. SPI WRITE MCR TO DTR OUTPUT SWITCH
TCSH TCSS
TDS
TDH
TCL TCH
CS#
SCLK
SI
SO
...
...
...
...
TCSH TCSW
TDO TTR
A3 A2 A1R/W A0 0 0 X D7 D6 D5 D4 D3 D2 D1 D0
CS#
SCLK
SI
GPIOx
TD9
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
FIGURE 31. SPI WRITE MCR TO DTR OUTPUT SWITCH
FIGURE 32. SPI WRITE THR TO CLEAR TX INT
A3 A2 A1R/W A0 0 0 X D7 D6 D5 D4 D3 D2 D1 D0
CS#
SCLK
SI
DTR#
(GPIO5)
TD10
A3 A2 A1R/W A0 0 0 X D7 D6 D5 D4 D3 D2 D1 D0
CS#
SCLK
SI
GPIOx
td11
IRQ #
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
FIGURE 33. READ MSR TO CLEAR MODEM INT
FIGURE 34. READ IOSTATE TO CLEAR GPIO INT
A3 A2 A1R/W A0 0 0 X
D7 D6 D5 D4 D3 D2 D1 D0
CS#
SCLK
SI
SO
TD12
IRQ#
A3 A2 A1R/W A0 0 0 X
D7 D6 D5 D4 D3 D2 D1 D0
CS#
SCLK
SI
SO
TD13
IRQ#
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
FIGURE 35. READ RHR TO CLEAR RX INT
A3 A2 A1R/W A0 0 0 X
D7 D6 D5 D4 D3 D2 D1 D0
CS#
SCLK
SI
SO
TD14
IRQ#
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
MECHANICAL DIMENSIONS (24 PIN QFN - 4 X 4 X 0.9 mm, 0.50 PITCH)
Revision: B
Drawing No.: POD-00000130
TOP VIEW
TERMINAL DETAILS
SIDE VIEW
BOTTOM VIEW
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
RECOMMENDED LAND PATTERN AND STENCIL (24 PIN QFN - 4 X 4 X 0.9 mm, 0.50 PITCH)
Revision: B
Drawing No.: POD-00000130
TYPICAL RECOMMENDED STENCIL
TYPICAL RECOMMENDED LAND PATTERN
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
MECHANICAL DIMENSIONS (16 PIN QFN - 4 X 4 X 0.9 mm, 0.65 PITCH)
Revision: A.1
Drawing No.: POD-00000140
TOP VIEW
TERMINAL DETAILS
SIDE VIEW
BOTTOM VIEW
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
RECOMMENDED LAND PATTERN AND STENCIL (16 PIN QFN - 4 X 4 X 0.9 mm, 0.65 PITCH)
Revision: A.1
Drawing No.: POD-00000140
TYPICAL RECOMMENDED STENCIL
TYPICAL RECOMMENDED LAND PATTERN
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
MECHANICAL DIMENSIONS (24 PIN TSSOP - 4.4 mm)
Revision: D
Drawing No.: POD-00000058
TOP VIEW
TERMINAL DETAILS
SIDE VIEW - 1
BOTTOM VIEW
©
SIDE VIEW - 2
©
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I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
RECOMMENDED LAND PATTERN AND STENCIL (24 PIN TSSOP)
Revision: D
Drawing No.: POD-00000058
TYPICAL RECOMMENDED STENCIL
TYPICAL RECOMMENDED LAND PATTERN
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REV. 1.1.2 I2C/SPI UART WITH 64-BYTE FIFO
MECHANICAL DIMENSIONS (16 PIN TSSOP - 4.4 mm)
Drawing No:
Revision: A
Side View
Top View
Front View
POD-00000117
60
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XR20M1170
I2C/SPI UART WITH 64-BYTE FIFO REV. 1.1.2
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REVISION HISTORY
DATE REVISION DESCRIPTION
September 2006 P1.0.0 Preliminary Datasheet.
October 2006 P1.0.1 Updated Thermal Resistance Data.
December 2006 P1.0.2 Added I2C/SPI timing diagrams.
May 2007 1.0.0 Final Datasheet. Updated power supply and sleep currents. Updated QFN package
drawing and added the parameter "k".
June 2011 1.0.1 Removed “DMA mode” since this is a legacy feature that is not supported in this
device. Added and updated maximum SPI clock frequency to the AC Electrical Char-
acteristics table for SPI-Bus Timing. Updated ordering information and removed ref-
erences to the discontinued 28-pin QFN package (PDN_11-0502-01).
July 2012 1.1.0 Clarified "OP2#" pin since the XR20M1170 does not have OP2# output pin.
Changed "AC Electrical Characteristics-UART Clock" table according to the PCN12-
0614-02.
July 2018 1.1.1 Updated to MaxLinear logo. Updated format and Ordering Information. Updated
capacitance in Figure 11.
June 2019 1.1.2 Corrected lead pitch on Land Pattern and Stencil.