EXAR XR16L784_05

XR16L784
xr
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
OCTOBER 2005
REV. 1.2.2
GENERAL DESCRIPTION
FEATURES
The XR16L7841 (784) is a quad Universal
Asynchronous Receiver and Transmitter (UART). The
device is designed for high bandwidth requirement in
communication systems. The global interrupt source
register provides a complete interrupt status
indication for all 4 channels to speed up interrupt
parsing. Each UART has its own 16C550 compatible
set of configuration registers, transmit and receive
FIFOs of 64 bytes, fully programmable transmit and
receive FIFO level triggers, transmit and receive
FIFO level counters, automatic RTS/CTS or DTR/
DSR hardware flow control with programmable
hysteresis, automatic software (Xon/Xoff) flow
control, IrDA (Infrared Data Association) encoder/
decoder, and a 16-bit general purpose timer/counter.
NOTE:
1 Covered by U.S. Patents #5,649,122 and #5,949,787
APPLICATIONS
• 2.97V to 5.5V operation with 5V Tolerant Inputs
• 8-bit Intel or Motorola Data Bus Interface
• Single Open Drain Interrupt output for all 4
channels
• Global Interrupt Source Registers for all channels
• 5G (Fifth Generation) “Flat” Register Set
• Each UART is Independently Controlled with:
■
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■
■
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• Remote Access Servers
• Ethernet Network to Serial Ports
• Network Management
• Factory Automation and Process Control
• Point-of-Sale Systems
• Multi-port RS-232/RS-422/RS-485 Cards
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16C550 Compatible Registers
64-byte Transmit and Receive FIFOs
Transmit and Receive FIFO Level Counters
Programmable TX and RX FIFO Trigger Levels
Automatic RTS/CTS or DTR/DSR Flow Control
Selectable RTS Flow Control Hysteresis
Automatic Xon/Xoff Software Flow Control
Automatic RS485 Half-duplex Control Output
with 16 Selectable Turn-around Delay
Infrared (IrDA 1.1) Data Encoder/Decoder
Programmable Data Rate with Prescaler
Up to 3.12 (16x) and 6.25 (8x) Mbps Data Rate
• A General Purpose 16-bit Timer/Counter
• Sleep Mode with Automatic Wake-up Indicator
• 64-pin LQFP Package (10x10x1.4 mm)
FIGURE 1. BLOCK DIAGRAM
*All Inputs are 5V Tolerant
(Except XTAL1)
2.97V to 5.5V VCC
GND
UART Channel 0
UART
Regs
A7:A0
D7:D0
IOR#
IOW#
CS#
INT#
Intel or
Motorola
Data
Bus
Interface
Device
Configuration
Register
s
BRG
64 Byte TX FIFO
TX &
RX
IR
ENDEC
64 Byte RX FIFO
UART Channel 1
UART Channel 2
16/68#
RST#
ENIR
TX0, RX0, DTR0#,
DSR0#, RTS0#,
CTS0#, CD0#, RI0#
16-bit
Timer/Counter
UART Channel 3
Crystal Osc/
Buffer
TX3, RX3, DTR3#,
DSR3#, RTS3#,
CTS3#, CD3#, RI3#
XTAL1
XTAL2
TMRCK
784BLK
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (510) 668-7000 • FAX (510) 668-7017 • www.exar.com
xr
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
CD2#
DSR2#
CTS2#
RX2
RTS2#
RI2#
XR16L784
64-LQFP
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33
ENIR
TMRCK
VCC
GND
TX3
DTR3#
RTS3#
RI3#
CD3#
DSR3#
CTS3#
RX3
RST#
16/68#
D7
D6
A6
A7
IOR#
IOW#
VCC
GND
D0
D1
D2
D3
D4
D5
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
A2
A3
A4
A5
49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64
XTAL2
XTAL1
GND
VCC
TX0
DTR0#
RTS0#
RI0#
CD0#
DSR0#
CTS0#
RX0
INT#
CS#
A0
A1
DSR1#
CTS1#
RX1
TX2
DTR2#
TX1
DTR1#
RTS1#
RI1#
CD1#
FIGURE 2. PIN OUT ASSIGNMENT
ORDERING INFORMATION
PART NUMBER
PACKAGE
OPERATING TEMPERATURE RANGE
DEVICE STATUS
XR16L784CV
64-Lead LQFP
0°C to +70°C
Active
XR16L784IV
64-Lead LQFP
-40°C to +85°C
Active
2
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
PIN DESCRIPTIONS
Pin Descriptions
NAME
PIN #
TYPE
DESCRIPTION
DATA BUS INTERFACE
A7-A0
6-1,64,63
I
Address data lines [7:0]. A0:A3 selects individual UART’s 16 configuration
registers, A4:A6 selects UART channel 0 to 3, and A7 selects the global
device configuration registers
D7:D0
18-11
IO
IOR#
7
I
When 16/68# pin is HIGH, it selects Intel bus interface and this input is read
strobe (active low). The falling edge instigates an internal read cycle and
retrieves the data byte from an internal register pointed by the address lines
[A7:A0], puts it on the data bus to allow the host processor to read it on the
leading edge.
When 16/68# pin is LOW, it selects Motorola bus interface and this input
should be connected to VCC.
IOW#
(R/W#)
8
I
When 16/68# pin is HIGH, it selects Intel bus interface and this input
becomes write strobe (active low). The falling edge instigates the internal
write cycle and the leading edge transfers the data byte on the data bus to an
internal register pointed by the address lines.
When 16/68# pin is LOW, it selects Motorola bus interface and this input
becomes read (logic 1) and write (logic 0) signal.
CS#
62
I
When 16/68# pin is HIGH, this input is chip select (active low) to enable the
XR16L784 device.
When 16/68# pin is LOW, this input becomes the read and write strobe
(active low) for the Motorola bus interface.
INT#
61
OD
Global interrupt output from XR16L784 (open drain, active low). This output
requires an external pull-up resistor (47K-100K ohms) to operate properly. It
may be shared with other devices in the system to form a single interrupt line
to the host processor and have the software driver polls each device for the
interrupt status.
Data bus lines (7:0] (bidirectional).
MODEM OR SERIAL I/O INTERFACE
TX0
53
O
UART channel 0 Transmit Data or infrared transmit data. Normal TXD output
idles HIGH while infrared TXD output idles LOW.
RX0
60
I
UART channel 0 Receive Data or infrared receive data. Normal RXD input
idles HIGH while infrared RXD input idles LOW. In the infrared mode, the
polarity of the incoming RXD signal can be selected via FCTR bit-4. If this bit
is a logic 0, a LOW on the RXD input is considered a mark and if this bit is a
logic 1, a HIGH on the RXD input is considered a space.
RTS0#
55
O
UART channel 0 Request to Send or general purpose output (active low).
This port must be asserted prior using for one of two functions:
1) auto RTS flow control, see EFR bit-6, MCR bits-1 & 2, FCTR bits 0-3 and
IER bit-6
2) Auto RS485 half-duplex direction control, see FCTR bit-5, MCR bit-2 and
MSR bits 4-7.
CTS0#
59
I
UART channel 0 Clear to Send or general purpose input (active low). It can be
used for auto CTS flow control, see EFR bit-7, MCR bit-2 and IER bit-7.
3
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
Pin Descriptions
NAME
PIN #
TYPE
DESCRIPTION
DTR0#
54
O
UART channel 0 Data Terminal Ready or general purpose output (active low).
This port must be asserted prior using for one of two functions:
1) auto DTR flow control, see EFR bit-6, FCTR bits-0 to 3, MCR bits-0 & 2,
and IER bit-6
2) Auto RS485 half-duplex direction control, see FCTR bit-5, MCR bit-2 and
MSR bit 4-7.
DSR0#
58
I
UART channel 0 Data Set Ready or general purpose input (active low). It can
be used for auto DSR flow control, see EFR bit-7, MCR bit-2 and IER bit-7.
CD0#
57
I
UART channel 0 Carrier Detect or general purpose input (active low).
RI0#
56
I
UART channel 0 Ring Indicator or general purpose input (active low).
TX1
48
O
UART channel 1 Transmit Data or infrared transmit data. Normal TXD output
idles HIGH while infrared TXD output idles LOW.
RX1
41
I
UART channel 1 Receive Data or infrared receive data. Normal RXD input
idles HIGH while infrared RXD input idles LOW. In the infrared mode, the
polarity of the incoming RXD signal can be selected via FCTR bit-4. If this bit
is a logic 0, a LOW on the RXD input is considered a mark and if this bit is a
logic 1, a HIGH on the RXD input is considered a space.
RTS1#
46
O
UART channel 1 Request to Send or general purpose output (active low).
See description of RTS0# pin.
CTS1#
42
I
UART channel 1 Clear to Send or general purpose input (active low). See
description of CTS0# pin.
DTR1#
47
O
UART channel 1 Data Terminal Ready or general purpose output (active low).
See description of DTS0# pin.
DSR1#
43
I
UART channel 1 Data Set Ready or general purpose input (active low). See
description of DSR0# pin.
CD1#
44
I
UART channel 1 Carrier Detect or general purpose input (active low).
RI1#
45
I
UART channel 1 Ring Indicator or general purpose input (active low).
TX2
40
O
UART channel 2 Transmit Data or infrared transmit data. Normal TXD output
idles HIGH while infrared TXD output idles LOW.
RX2
33
I
UART channel 2 Receive Data or infrared receive data. Normal RXD input
idles HIGH while infrared RXD input idles LOW. In the infrared mode, the
polarity of the incoming RXD signal can be selected via FCTR bit-4. If this bit
is a logic 0, a LOW on the RXD input is considered a mark and if this bit is a
logic 1, a HIGH on the RXD input is considered a space.
RTS2#
38
O
UART channel 2 Request to Send or general purpose output (active low).
See description of RTS0# pin.
CTS2#
34
I
UART channel 2 Clear to Send or general purpose input (active low). See
description of CTS0# pin.
DTR2#
39
O
UART channel 2 Data Terminal Ready or general purpose output (active low).
See description of DTS0# pin.
DSR2#
35
I
UART channel 2 Data Set Ready or general purpose input (active low). See
description of DSR0# pin.
CD2#
36
I
UART channel 2 Carrier Detect or general purpose input (active low).
RI2#
37
I
UART channel 2 Ring Indicator or general purpose intput (active low).
4
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
Pin Descriptions
NAME
PIN #
TYPE
DESCRIPTION
TX3
28
O
UART channel 3 Transmit Data or infrared transmit data. Normal TXD output
idles HIGH while infrared TXD output idles LOW.
RX3
21
I
UART channel 3 Receive Data or infrared receive data. Normal RXD input
idles HIGH while infrared RXD input idles LOW. In the infrared mode, the
polarity of the incoming RXD signal can be selected via FCTR bit-4. If this bit
is a logic 0, a LOW on the RXD input is considered a mark and if this bit is a
logic 1, a HIGH on the RXD input is considered a space.
RTS3#
26
O
UART channel 3 Request to Send or general purpose output (active low).
See description of RTS0# pin.
CTS3#
22
I
UART channel 3 Clear to Send or general purpose input (active low).d. See
description of CTS0# pin.
DTR3#
27
O
UART channel 3 Data Terminal Ready or general purpose output (active low).
See description of DTS0# pin.
DSR3#
23
I
UART channel 3 Data Set Ready or general purpose input (active low). See
description of DSR0# pin.
CD3#
24
I
UART channel 3 Carrier Detect or general purpose input (active low).
RI3#
25
I
UART channel 3 Ring Indicator or general purpose input (active low).
XTAL1
50
I
Crystal or external clock input. Caution: this input is not 5V tolerant.
XTAL2
49
O
Crystal or buffered clock output.
TMRCK
31
I
16-bit timer/counter external clock input.
ENIR
32
I
Infrared mode enable (active high). This pin is sampled during power up, following a hardware reset (RST#) or soft-reset (register RESET). It can be
used to start up all 8 UARTs in the infrared mode. The sampled logic state is
transferred to MCR bit-6 in the UART.
RST#
20
I
Reset (active low). The configuration and UART registers are reset to default
values, see Table-15.
16/68#
19
I
Intel or Motorola data bus interface select. HIGH selects Intel bus interface
and LOW selects Motorola interface. This input affects the functionality of
IOR#, IOW# and CS# pins.
VCC
9,30,52
+5V or +3.3V supply, all inputs are 5V tolerant except for XTAL1.
GND
10,29,51
Power supply common, ground.
ANCILLARY SIGNALS
NOTE: Pin type: I=Input, O=Output, IO= Input/output, OD=Output Open Drain.
5
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
1.0 DESCRIPTION
The XR16L784 (784) integrates the functions of 4 enhanced 16550 UARTs, a general purpose 16-bit timer/
counter and an on-chip oscillator. The device configuration registers include a set of four consecutive interrupt
source registers that provides interrupt-status for all 4 UARTs, timer/counter and a sleep wake up indicator.
Each UART channel has its own 16550 UART compatible configuration register set for individual channel
control, status, and data transfer. Additionally, each UART channel has 64-byte of transmit and receive FIFOs,
automatic RTS/CTS or DTR/DSR hardware flow control with hysteresis control, automatic Xon/Xoff and
special character software flow control, programmable transmit and receive FIFO trigger levels, FIFO level
counters, infrared encoder and decoder (IrDA ver 1.0), programmable baud rate generator with a prescaler of
divide by 1 or 4, and data rate up to 6.25 Mbps with 8X sampling clock rate or 3.125Mbps in the 16X rate. The
XR16L784 is a 5V and 3.3V device with 5 volt tolerant inputs (except XTAL1).
2.0 FUNCTIONAL DESCRIPTIONS
2.1
2.1.1
Device Reset
Hardware Reset
The RST# input resets the internal registers and the serial interface outputs in all 4 channels to their default
state (see Table 19). A LOW pulse of longer than 40 ns duration will be required to activate the reset function
in the device.
2.1.2
Software Reset
The internal registers of each UART can be reset by writing to the RESET register in the Device Configuration
Registers. For more details, see the RESET register description on page 23.
2.2
UART Channel Selection
The UART provides the user with the capability to bi-directionally transfer information between an external
CPU and an external serial communication device. A logic 0 on the chip select pins, CS#, allows the user to
select one of the UART channels to configure, send transmit data and/or unload receive data to/from the
UART. When address line A7 = 0, address lines A5:A4 are used to select one of the eight channels. See
Table 1 below for UART channel selection.
TABLE 1: UART CHANNEL SELECTION
2.3
A7
A6
A5
A4
FUNCTION
0
0
0
0
Channel 0 Selected
0
0
0
1
Channel 1 Selected
0
0
1
0
Channel 2 Selected
0
0
1
1
Channel 3 Selected
0
1
X
X
Reserved
Simultaneous Write to All Channels
During a write cycle, the setting of REGB bit-0 to a logic 1 will override the channel selection of address A5:A4
and allow a simultaneous write to all 4 UART channels when any channel is written to. This functional
capability allow the registers in all 8 UART channels to be modified concurrently, saving individual channel
initialization time. Caution should be considered, however, when using this capability. Any in-process serial
data transfer may be disrupted by changing an active channel’s mode. Also, REGB bit-0 should be reset to a
logic 0 before attempting to read from the UART.
6
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
2.4
INT# Ouput
The INT# interrupt output changes according to the operating mode and enhanced features setup. Table 2
and 3 summarize the operating behavior for the transmitter and receiver.
TABLE 2: INT# PIN OPERATION FOR TRANSMITTER
Auto RS485
Mode
FCR BIT-0 = 0
(FIFO DISABLED)
FCR BIT-0 = 1
(FIFO ENABLED)
INT# Pin
NO
HIGH = a byte in THR
LOW = THR empty
HIGH = FIFO above trigger level
LOW = FIFO below trigger level or FIFO empty
INT# Pin
YES
HIGH = a byte in THR
HIGH = FIFO above trigger level
LOW = transmitter empty LOW = FIFO below trigger level or transmitter empty
TABLE 3: INT# PIN OPERATION FOR RECEIVER
FCR BIT-0 = 0
(FIFO DISABLED)
INT# Pin
2.5
HIGH = no data
LOW = 1 byte
FCR BIT-0 = 1
(FIFO ENABLED)
HIGH = FIFO below trigger level
LOW = FIFO above trigger level
CRYSTAL OSCILLATOR / BUFFER
The 784 includes an on-chip oscillator (XTAL1 and XTAL2). The crystal oscillator provides the system clock to
the Baud Rate Generators (BRG) in each of the 8 UARTs, the 16-bit general purpose timer/counter and
internal logics. XTAL1 is the input to the oscillator or external clock buffer input with XTAL2 pin being the
output. For programming details, see “Section 2.6, Programmable Baud Rate Generator” on page 8.
The on-chip oscillator is designed to use an industry standard microprocessor crystal (parallel resonant,
fundamental frequency with 10-22 pF capacitance load, ESR of 20-120 ohms and 100ppm frequency
tolerance) connected externally between the XTAL1 and XTAL2 pins (see Figure 3). Alternatively, an external
clock can be connected to the XTAL1 pin to clock the internal 8 baud rate generators for standard or custom
rates. Typically, the oscillator connections are shown in Figure 3. For further reading on oscillator circuit please
see application note DAN108 on EXAR’s web site.
FIGURE 3. TYPICAL OSCILLATOR CONNECTIONS
R=300K to 400K
XTAL1
14.7456
MHz
XTAL2
C2
22-47pF
C1
22-47pF
7
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
2.6
REV. 1.2.2
Programmable Baud Rate Generator
A single Baud Rate Generator (BRG) is provided for the transmitter and receiver, allowing independent TX/RX
channel control. The programmable Baud Rate Generator is capable of operating with a crystal frequency of
up to 24 MHz. However, with an external clock input on XTAL1 pin and a 2K ohms pull-up resistor on XTAL2
pin (as shown in Figure 4) it can extend its operation up to 50 MHz (3.125 Mbps serial data rate) at room
temperature and 5.0V.
FIGURE 4. EXTERNAL CLOCK CONNECTION FOR EXTENDED DATA RATE
vcc
External Clock
XTAL1
gnd
VCC
R1
2K
XTAL2
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 -1) to obtain a 16X or 8X 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 and DLM registers) defaults to a random value upon power up. Therefore, the
BRG must be programmed during initialization to the operating data rate.
FIGURE 5. BAUD RATE GENERATOR
To Other
Channels
DLL and DLM
Registers
Prescaler
Divide by 1
XTAL1
XTAL2
Crystal
Osc/
Buffer
MCR Bit-7=0
(default)
Baud Rate
Generator
Logic
Prescaler
Divide by 4
8
MCR Bit-7=1
16X or 8X
Sampling
Rate Clock to
Transmitter
and Receiver
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
Programming the Baud Rate Generator Registers DLM and DLL provides the capability of selecting the
operating data rate. Table 4 shows the standard data rates available with a 14.7456 MHz crystal or external
clock at 16X clock rate. At 8X sampling rate, these data rates would double. When using a non-standard data
rate crystal or external clock, the divisor value can be calculated for channel ‘N’ with the following equation(s).
divisor (decimal) = (XTAL1 clock frequency / prescaler) / (serial data rate x 16), WHEN 8XMODE-BIT N IS 0
divisor (decimal) = (XTAL1 clock frequency / prescaler) / (serial data rate x 8), WHEN 8XMODE-BIT N IS 1
TABLE 4: TYPICAL DATA RATES WITH A 14.7456 MHZ CRYSTAL OR EXTERNAL CLOCK AT 16X SAMPLING
OUTPUT Data Rate OUTPUT Data Rate DIVISOR FOR 16x DIVISOR FOR 16x
MCR Bit-7=1
MCR Bit-7=0
Clock (Decimal) Clock (HEX)
DLM
PROGRAM
VALUE (HEX)
DLL
PROGRAM
VALUE (HEX)
DATA RATE
ERROR (%)
100
400
2304
900
09
00
0
600
2400
384
180
01
80
0
1200
4800
192
C0
00
C0
0
2400
9600
96
60
00
60
0
4800
19.2k
48
30
00
30
0
9600
38.4k
24
18
00
18
0
19.2k
76.8k
12
0C
00
0C
0
38.4k
153.6k
6
06
00
06
0
57.6k
230.4k
4
04
00
04
0
115.2k
460.8k
2
02
00
02
0
230.4k
921.6k
1
01
00
01
0
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 internal
clock. A bit time is 16 clock periods (see EMSR bit-7). 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 bit-5 and bit-6).
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 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.
9
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
FIGURE 6. TRANSMITTER OPERATION IN NON-FIFO MODE
Transmit
Holding
Register
(THR)
Data
Byte
THR Interrupt (ISR bit-1)
Enabled by IER bit-1
16X or 8X Clock
Transmit Shift Register (TSR)
M
S
B
L
S
B
TXNOFIFO1
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 7. TRANSMITTER OPERATION IN FIFO AND FLOW CONTROL MODE
Transmit
Data Byte
Transm it
FIFO
THR Interrupt (ISR bit-1) falls
below the programmed Trigger
Level and then when becomes
empty. FIFO is Enabled by FCR
bit-0=1
Auto CTS Flow Control (CTS# pin)
Flow Control Characters
(Xoff1/2 and Xon1/2 Reg.
Auto Software Flow Control
16X or 8X Clock
Transm it Data Shift Register
(TSR)
T XF IF O 1
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 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. After 8 clocks 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 3.74.6 character times. The RHR interrupt is enabled by IER bit-0.
10
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HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
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 8. RECEIVER OPERATION IN NON-FIFO MODE
16X or 8X Clock
Receive Data Shift
Register (RSR)
Error
Tags in
LSR bits
4:2
Receive
Data Byte
and Errors
Receive Data
Holding Register
(RHR)
Data Bit
Validation
Receive Data Characters
RHR Interrupt (ISR bit-2)
RXFIFO1
FIGURE 9. RECEIVER OPERATION IN FIFO AND AUTO RTS FLOW CONTROL MODE
16X or 8X Clock
Receive Data Shift
Register (RSR)
Data Bit
Validation
Example: - RX FIFO trigger level selected at 16 bytes
(See Note Below)
64 bytes by 11-bit
wide
FIFO
Error Tags
(64-sets)
Data falls to 8 RTS# re-asserts when data falls below the flow
Receive
Data FIFO
control trigger level to restart remote transmitter.
Enable by EFR bit-6=1, MCR bit-2.
FIFO Trigger=16 RHR Interrupt (ISR bit-2) programmed for
desired FIFO trigger level.
FIFO is Enabled by FCR bit-0=1
Error Tags in
LSR bits 4:2
Data fills to 24
Receive Data
Byte and Errors
Receive Data Characters
RTS# de-asserts when data fills above the flow
control trigger level to suspend remote transmitter.
Enable by EFR bit-6=1, MCR bit-2.
Receive
Data
RXFIFO1
NOTE: Table-B selected as Trigger Table for Figure 9 (Table 14).
11
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
2.9
REV. 1.2.2
THR and RHR Register Locations
The THR and RHR register addresses for channel 0 to channel 7 is shown in Table 5 below. The THR and
RHR for channels 0 to 3 are located at address 0x00, 0x10, 0x20 and 0x30 respectively. Transmit data byte is
loaded to the THR when writing to that address and receive data is unloaded from the RHR register when
reading that address. Both THR and RHR registers are 16C550 compatible in 8-bit format, so each bus
operation can only write or read in bytes.
TABLE 5: TRANSMIT AND RECEIVE DATA REGISTER, 16C550 COMPATIBLE
THR and RHR Address Locations For CH0 to CH3 (16C550 Compatible)
CH0 0x00 Write THR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
CH0 0x00 Read RHR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
CH1 0x10 Write THR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
CH1 0x10 Read RHR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
CH2 0x20 Write THR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
CH2 0x20 Read RHR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
CH3 0x30 Write THR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
CH3 0x30 Read RHR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
784THRRHR1
2.10
Automatic RTS/DTR Hardware Flow Control Operation
Automatic RTS/DTR flow control is used to prevent data overrun to the local receiver FIFO. The RTS#/DTR#
output pin is used to request remote unit to suspend/resume data transmission. The flow control features are
individually selected to fit specific application requirement (see Figure 10):
• Select RTS (and CTS) or DTR (and DSR) through MCR bit-2.
• Enable auto RTS/DTR flow control using EFR bit-6.
• The auto RTS or auto DTR function must be started by asserting the RTS# or DTR# output pin (MCR bit-1 or
bit-0 to a logic 1, respectively) after it is enabled.
• If using programmable RX FIFO trigger levels, hysteresis levels can be selected via FCTR bits 3-0.
With the Auto RTS function enabled, the RTS# output pin will not be de-asserted (HIGH) when the receive
FIFO reaches the programmed trigger level, but will be de-asserted when the FIFO reaches the next trigger
level for Trigger Tables A-C (See Table 14). The RTS# output pin will be asserted (LOW) again after the FIFO
is unloaded to the next trigger level below the programmed trigger level.
For Trigger Table D (or programmable trigger levels), the RTS# output pin is de-asserted when the the RX
FIFO level reaches the RX trigger level plus the hysteresis level and is asserted when the RX FIFO level falls
below the RX trigger level minus the hysteresis level.
However, even under these conditions, the 788 will continue to accept data until the receive FIFO is full if the
remote UART transmitter continues to send data.
• If used, enable RTS/DTR interrupt through IER bit-6 (after setting EFR bit-4). The UART issues an interrupt
when the RTS#/DTR# pin makes a transition: ISR bit-5 will be set to 1.
12
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
2.10.1
Auto CTS/DSR Flow Control
Automatic CTS/DSR flow control is used to prevent data overrun to the remote receiver FIFO. The CTS/DSR
pin is monitored to suspend/restart local transmitter. The flow control features are individually selected to fit
specific application requirement (see Figure 10):
• Select CTS (and RTS) or DSR (and DTR) through MCR bit-2.
• Enable auto CTS/DSR flow control using EFR bit-7.
With the Auto CTS or Auto DTR function enabled, the UART will suspend transmission as soon as the stop bit
of the character in the Transmit Shift Register has been shifted out. Transmission is resumed after the CTS#/
DTR# input is re-asserted (logic 0), indicating more data may be sent.
• If used, enable CTS/DSR interrupt through IER bit-7 (after setting EFR bit-4). The UART issues an interrupt
when the CTS#/DSR# pin makes a transition: ISR bit-5 will be set to a logic 1, and UART will suspend TX
transmissions as soon as the stop bit of the character in process is shifted out. Transmission is resumed
after the CTS#/DSR# input returns LOW, indicating more data may be sent.
FIGURE 10. AUTO RTS/DTR AND CTS/DSR FLOW CONTROL OPERATION
Local UART
UARTA
Remote UART
UARTB
RXA
Receiver FIFO
Trigger Reached
RTSA#
Auto RTS
Trigger Level
Receiver FIFO
Trigger Reached
RTSB#
Assert RTS# to Begin
Transmission
1
ON
Auto RTS
Trigger Level
10
OFF
ON
7
2
CTSB#
Auto CTS
Monitor
RXB
CTSA#
Auto CTS
Monitor
Transmitter
CTSB#
TXA
Transmitter
RTSA#
TXB
ON
3
8
OFF
6
Suspend
11
ON
TXB
Data Starts
4
Restart
9
RXA FIFO
INTA
(RXA FIFO
Interrupt)
Receive
RX FIFO
Data
Trigger Level
5
RTS High
Threshold
RTS Low
Threshold
12
RX FIFO
Trigger Level
RTSCTS1
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.
13
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
2.11
REV. 1.2.2
Auto Xon/Xoff (Software) Flow Control
When software flow control is enabled (See Table 18), the 784 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 784 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 784 will monitor the
receive data stream for a match to the Xon-1,2 character. If a match is found, the 784 will resume operation
and clear the flags (ISR bit-4).
Reset initially sets the contents of the Xon/Xoff 8-bit flow control registers to a logic 0. Following reset, any
desired Xon/Xoff value can be used for software flow control. Different conditions can be set to detect Xon/Xoff
characters (See Table 18) and suspend/resume transmissions. When double 8-bit Xon/Xoff characters are
selected, the 784 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 784 automatically
sends an Xoff message (when enabled) via the serial TX output to the remote modem. The 784 sends the Xoff1,2 characters two character times (= time taken to send two characters at the programmed baud rate) after
the receive FIFO crosses the programmed trigger level (for all trigger tables A-D). To clear this condition, the
784 will transmit the programmed Xon-1,2 characters as soon as receive FIFO is less than one trigger level
below the programmed trigger level (for Trigger Tables A, B, and C) or when receive FIFO is less than the
trigger level minus the hysteresis value (for Trigger Table D). This hysteresis value is the same as the Auto
RTS/DTR Hysteresis value in Table 17. Table 6 below explains this when Trigger Table-B (See Table 14) is
selected.
TABLE 6: AUTO XON/XOFF (SOFTWARE) FLOW CONTROL
RX TRIGGER LEVEL
INT PIN ACTIVATION
XOFF CHARACTER(S) SENT
(CHARACTERS IN RX FIFO)
XON CHARACTER(S) SENT
(CHARACTERS IN RX FIFO)
8
8
8*
0
16
16
16*
8
24
24
24*
16
28
28
28*
24
* After the trigger level is reached, an xoff character is sent after a short span of time (= time required to send 2
characters); for example, after 2.083ms has elapsed for 9600 baud and 10-bit word length setting.
2.12
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 784 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. Bit-0 in the Xon, Xoff
Registers corresponds with the LSB bit for the receive character.
14
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REV. 1.2.2
2.13
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
Auto RS485 Half-duplex Control
The auto RS485 half-duplex direction control changes the behavior of the transmitter when enabled by FCTR
bit-5. It asserts RTS# or DTR# (LOW) after a specified delay indicated in MSR[7:4] following the last stop bit of
the last character that has been transmitted. This helps in turning around the transceiver to receive the remote
station’s response. The delay optimizes the time needed for the last transmission to reach the farthest station
on a long cable network before switching off the line driver. This delay prevents undesirable line signal
disturbance that causes signal degradation. When the host is ready to transmit next polling data packet again,
it only has to load data bytes to the transmit FIFO. The transmitter automatically de-asserts RTS# or DTR#
output (HIGH) prior to sending the data. The auto RS485 half-duplex direction control also changes the
transmitter empty interrupt to TSR empty instead of THR empty.
2.14
Infrared Mode
Each UART in the 784 includes the infrared encoder and decoder compatible to the IrDA (Infrared Data
Association) version 1.0. The input pin ENIR conveniently activates all 8 UART channels to start up in the
infrared mode. Note that the ENIR pin is sampled when the RST# input is de-asserted. This global control pin
enables the MCR bit-6 function in every UART channel register. After power up or a reset, the software can
overwrite MCR bit-6 if so desired. ENIR and MCR bit-6 also disable the receiver while the transmitter is
sending data. This prevents echoed data from reaching the receiver. The global activation ENIR pin prevents
the infrared emitter from turning on and drawing large amount of current while the system is starting up. When
the infrared feature is enabled, the transmit data outputs, TX[3:0], would idle at logic zero level. Likewise, the
RX [3:0] inputs assume an idle level of logic zero.
The infrared encoder sends out a 3/16 of a bit wide HIGH-pulse for each “0” bit in the transmit data stream.
This signal encoding reduces the on-time of the infrared LED, hence reduces the power consumption. See
Figure 11.
The infrared decoder receives the input pulse from the infrared sensing diode on RX pin. Each time it senses a
light pulse, it returns a logic zero to the data bit stream. The decoder also accepts (when FCTR bit-4 = 1) an
inverted IR-encoded input signal. This option supports active low instead of normal active high pulse from
some infrared modules on the market.
15
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HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
FIGURE 11. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING
Character
TX Data
0
1
0
1
0
Stop
Start
Data Bits
1
0
1
1
0
Transmit
IR Pulse
(TX Pin)
1/2 Bit Time
Bit Time
3/16 Bit Time
IrEncoder-1
Receive
IR Pulse
(RX pin)
Bit Time
1/16 Clock Delay
1
0
1
0
0
Data Bits
1 1
0
1
Stop
0
Start
RX Data
Character
IRdecoder-
16
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REV. 1.2.2
2.15
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
Sleep Mode with Wake-Up Indicator
The 784 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 784 to enter sleep mode:
■ no interrupts pending for all 8 channels of the 784 (ISR bit-0 = 1)
■ SLEEP register = 0x0F
■ modem inputs are not toggling (MSR bits 0-3 = 0)
■ RX input pin of all 4 channels are idling HIGH
The 784 stops its crystal oscillator to conserve power in the sleep mode. User can check the XTAL2 pin for no
clock output as an indication that the device has entered the sleep mode.
The 784 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 784 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 784 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 in any channel. Also, a special interrupt is generated with an indication of no pending
interrupt. Reading INT0 will clear this special interrupt. The 784 will stay in the sleep mode of operation until it
is disabled by setting SLEEP = 0x00.
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.
17
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
2.16
REV. 1.2.2
Internal Loopback
Each UART channel 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 12 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 HIGH (idle or de-asserted state), and the CTS#, DSR#
CD# and RI# inputs are ignored.
FIGURE 12. INTERNAL LOOP BACK
VCC
TX [3:0]
Transmit Shift Register
(THR/FIFO)
Receive Shift Register
(RHR/FIFO)
RX [3:0]
VCC
RTS# [3:0]
Modem / General Purpose Control Logic
Internal Data Bus Lines and Control Signals
MCR bit-4=1
RTS#
CTS#
CTS# [3:0]
VCC
DTR# [3:0]
DTR#
DSR#
DSR# [3:0]
OP1#
RI#
OP2#
CD#
RI# [3:0]
CD# [3:0]
18
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
3.0 XR16L784 REGISTERS
The XR16L784 quad UART register set consists of the Device Configuration Registers that are accessible
directly from the data bus for programming general operating conditions of the UARTs and monitoring the
status of various functions. These functions include all 4 channel UART’s interrupt control and status, 16-bit
general purpose timer control and status, sleep mode, soft-reset, and device identification and revision. Also,
each UART channel has its own set of internal UART Configuration Registers for its own operation control,
status reporting and data transfer. These registers are mapped into a 256-byte of the data memory address
space. The following paragraphs describe all the registers in detail.
FIGURE 13. THE XR16L784 REGISTERS MAPPING
0x00-0F
Channel 0
0x10-1F
Channel 1
0x20-2F
Channel 2
0x30-3F
Channel 3
8-bit Data
Bus
Interface
UART[3:0] Configuration Registers
16550 Compatible and
Exar Enhanced Registers
0x40-7F
(reserved)
0x80-8F
INT0, INT1, INT2,
INT3, TIMER,
SLEEP, RESET
Device Configuration Registers
4 channel Interrupts,
16-bit Timer/Counter,
Sleep, Reset, DVID, DREV
784REGS
3.1
DEVICE CONFIGURATION REGISTER SET
The device configuration registers are directly accessible from the bus. This provides easy programming of
general operating parameters to the 784 UART and for monitoring the status of various functions. The device
configuration registers are mapped onto address 0x80-8F as shown on the register map in Table 8 and
Figure 13. These registers provide global controls and status of all 4 channel UARTs that include interrupt
status, 16-bit general purpose timer control and status, 8X or 16X sampling clock, sleep mode control, softreset control, simultaneous UART initialization, and device identification and revision.
.
TABLE 7: XR16L784 REGISTER SETS
ADDRESS [A7:A0]
UART CHANNEL SPACE
REFERENCE
0x00 - 0x0F
UART channel 0 Registers
(Table 11 & 12)
0x10 - 0x1F
UART channel 1 Registers
(Table 11 & 12)
0x20 - 0x2F
UART channel 2 Registers
(Table 11 & 12)
0x30 - 0x3F
UART channel 3 Registers
(Table 11 & 12)
0x40 - 0x7F
None
0x80 - 0x8F
Device Configuration Registers
COMMENT
First 8 registers are 16550 compatible
Reserved
(Table 8)
19
Interrupt registers and global controls
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
TABLE 8: DEVICE CONFIGURATION REGISTERS
ADDRESS READ/
REGISTER
[A7:A0] WRITE
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Rsvd
Rsvd
Rsvd
Rsvd
UART 3
UART 2
UART 1
UART 0
0x80
R
INT0
Source
0x81
R
INT1
UART 2 source
bit 1
bit 0
UART 1 interrupt source
bit 2
bit 1
bit 0
0x82
R
INT2
Rsvd
Rsvd
Rsvd
Rsvd
UART 3 interrupt source
bit 2
bit 1
bit 0
0x83
R
INT3
Rsvd
Rsvd
Rsvd
Rsvd
Rsvd
Rsvd
Rsvd
Rsvd
0x84
R/W
TIMER
CTRL
0
0
0
0
clock
source
function
select
start timer
enable
timer INT
0x85
R
TIMER
0
0
0
0
0
0
0
0
UART 0 interrupt source
bit 2
bit 1
bit 0
UART 2
bit 2
0x86
R/W TIMER LSB
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
0x87
R/W TIMER MSB
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
0x88
R/W
8X MODE
Rsvd
Rsvd
Rsvd
Rsvd
UART 3
UART 2
UART 1
UART 0
0x89
R
REG 1
0
0
0
0
0
0
0
0
0x8A
W
RESET
Rsvd
Rsvd
Rsvd
Rsvd
Reset
UART 3
Reset
UART 2
Reset
UART 1
Reset
UART 0
0x8B
R/W
SLEEP
Rsvd
Rsvd
Rsvd
Rsvd
Enable
sleep
UART 3
Enable
sleep
UART 2
Enable
sleep
UART 1
Enable
sleep
UART 0
0x8C
R
DREV
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
0x8D
R
DVID
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
0x8E
R/W
REG 2
0
0
0
0
0
0
0
Write to all
UARTs
20
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
3.1.1
The Global Interrupt Source Registers
The XR16L784 has a global interrupt source register set that consists of 4 consecutive registers [INT0, INT1,
INT2 and INT3]. Register INT3 is not used in the 784 UART, only in the 8-channel XR16L788. The 3 registers
are in the device configuration register address space.
INT3 (Rsvd)
[0x00]
INT2
[0x00]
INT1
[0x00]
INT0
[0x00]
All 4 registers default to logic zero (as indicated in square braces) for no interrupt pending. All 4 channel
interrupts are enabled or disabled in each channel’s IER register. INT0 shows individual status for each
channel while INT1 and INT2 show the details of the source of each channel’s interrupt with its unique 3-bit
encoding. Figure 14 shows the 4 interrupt registers in sequence for clarity. The 16-bit timer and sleep wakeup interrupts are masked in the device configuration registers, TIMERCNTL and SLEEP. An interrupt is
generated by the 784 when awakened from sleep if all 4 channels were placed in the sleep mode previously.
Reading INT0 will clear this wake-up interrupt.
Each bit in the INT0 register gives an indication of the channel that has requested service.
3.1.1.1
INT0 Channel Interrupt Indicator:
INT0 Register
Individual UART Channel Interrupt Status
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
Rsvd
Rsvd
Rsvd
Rsvd
Ch-3
Ch-2
Ch-1
Ch-0
For example, bit-0 represents channel 0 and bit-3 indicates channel 3. Bits 4 to 7 are reserved and remains at
logic zero. Logic one indicates the channel N [3:0] has called for service. The interrupt bit clears after reading
the appropiate register of the interrupting UART channel register (ISR, LSR and MSR). See Table 13 for
interrupt clearing details.
3.1.1.2
INT1 and INT2 Interrupt Source Locator
INT2 and INT1 provide a 12-bit (3 bits per channel) encoded interrupt indicator. Table 9 shows the 3 bit
encoding and their priority order. The 16-bit Timer time-out interrupt will show up only as a channel 0 interrupt .
For other channels, interrupt 7 is reserved.
.
FIGURE 14. THE GLOBAL INTERRUPT REGISTERS, INT0, INT1, INT2 AND INT3
Interrupt Registers,
INT0, INT1, INT2 and INT3
INT3 Register
Reserved
Bit
2
Bit
1
INT2 Register
Reserved
Bit
0
Bit
2
Bit
1
Reserved
Bit
0
Bit
2
Bit
1
Reserved
Bit
0
Bit
2
Bit
1
INT1 Register
Channel-3
Bit
0
Bit
2
Bit
1
Channel-2
Bit
0
Bit
2
Bit
1
Channel-1
Bit
0
Bit
2
Bit
1
Channel-0
Bit
0
Bit
2
Bit
1
Bit
0
INT0 Register
21
Rsvd Rsvd Rsvd Rsvd
Ch-3 Ch-2
Bit-7 Bit-6
Bit-3
Bit-5 Bit-4
Ch-1 Ch-0
Bit-2 Bit-1
Bit-0
xr
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
TABLE 9: UART CHANNEL [3:0] INTERRUPT SOURCE ENCODING AND CLEARING
PRIORITY BIT2 BIT1 BIT0
INTERRUPT SOURCE(S) AND CLEARING
x
0
0
0
None
1
0
0
1
RXRDY & RX Line Status (logic OR of LSR[4:1]). RXRDY INT clears by reading data in the
RX FIFO until it falls below the trigger level; RX Line Status INT cleared after reading LSR
register.
2
0
1
0
RXRDY Time-out: Cleared when the FIFO becomes empty.
3
0
1
1
TXRDY, THR or TSR (auto RS485 mode) empty, clears after reading ISR register.
4
1
0
0
MSR, RTS/CTS or DTR/DSR delta or Xoff/Xon or special character detected. The first two
clear after reading MSR register; Xoff/Xon or special char. detect INT clears after reading
ISR register.
5
1
0
1
Reserved.
6
1
1
0
Reserved.
7
1
1
1
TIMER Time-out, shows up as a channel 0 INT. It clears after reading the TIMERCNTL register. Reserved in other channels.
3.1.2
General Purpose 16-bit Timer/Counter. [TIMERMSB, TIMELSB, TIMER, TIMECNTL] (DEFAULT
0XXX-XX-00-00)
A 16-bit down-count timer for general purpose timer or counter. Its clock source may be selected from internal
crystal oscillator or externally on pin TMRCK. The timer can be set to be a single-shot for a one-time event or
re-triggerable for a periodic event. An interrupt may be generated in the INT Register when the timer times out.
It is controlled through 4 configuration registers [TIMERCNTL, TIMER, TIMELSB, TIMERMSB]. These
registers provide start/stop and re-triggerable or one-shot operation. The time-out output of the Timer can be
set to generate an interrupt for system or event alarm.
FIGURE 15. TIMER/COUNTER CIRCUIT.
TIMERMSB and TIMERLSB
(16-bit Value)
TMRCK
OSC. CLOCK
TIMERCNTL [3]
TIMERCNTL [1]
Time-out
16-Bit
Timer/Counter
1
0
Clock
Select
1
0
Timer Interrupt, Ch-0 INT=7
No Interrupt
Re-trigger
0
1
Start/Stop
TIMERCNTL [2]
Single/Re-triggerable
TIMERCNTL [0]
Timer Interrupt Enable
Single-shot
TABLE 10: TIMER CONTROL REGISTER
TIMERCNTL [0]
Logic 0 (default) disables Timer-Counter interrupt and logic one enables the interrupt, reading the
TIMERCNTL clears the interrupt.
TIMERCNLT [1]
Logic 0 (default) stops/pauses the timer and logic one starts/re-starts the timer/counter.
TIMERCNTL [2]
Logic0 (default) selects re-trigger timer function and logic one selects one-shot (timer function.
TIMERCNTL [3]
Logic 0 (default) selects internal and logic one selects external clock to the timer/counter.
TIMERCNTL [7:4]
Reserved (defaults to zero).
22
xr
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
TIMERCNTL Register
Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2
Rsvd
Rsvd
Rsvd
Rsvd
Clock
Single/
Select Re-trigger
Bit-1 Bit-0
Start/
Stop
INT
Enable
TIMER [7:0] (default 0x00): Reserved.
TIMERMSB [7:0] and TIMERLSB [7:0]
TIMERMSB and TIMERLSB form a 16-bit value. The least-significant bit of the timer is being bit [0] of the
TIMERLSB with most-significant-bit being bit [7] in TIMERMSB. Reading the TIMERCNTL register will clear its
interrupt. Default value is zero upon powerup and reset.
16-Bit Timer/Counter Programmable Registers
TIMERMSB Register
Bit-15
3.1.3
Bit-14
Bit-13
Bit-12
Bit-11
TIMERLSB Register
Bit-10
Bit-9
Bit-8
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
8XMODE [7:0] (default 0x00)
Each bit selects 8X or 16X sampling rate for that UART channel, bit-0 is channel 0. Logic 0 (default) selects
normal 16X sampling with logic one selects 8X sampling rate. Transmit and receive data rates will double by
selecting 8X.
8XMODE Register
Individual UART Channel 8X Clock Mode Enable
Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
Rsvd Rsvd Rsvd Rsvd Ch-3 Ch-2 Ch-1 Ch-0
3.1.4
REGA [7:0] reserved (default 0x00)
3.1.5
RESET [7:0] (default 0x00)
RESET Register
Individual UART Channel Reset Enable
Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
Rsvd Rsvd Rsvd Rsvd Ch-3 Ch-2 Ch-1 Ch-0
The 8-bit Reset register [RESET] provides the software with the ability to reset individual UART(s) when there
is a need. Each bit is self-resetting after it is written a logic 1 to perform a reset to that channel. All registers in
that channel will be reset to the default condition, see Table 19 for details. As an example, bit-0 =1 resets
UART channel 0 with bit-3=1 resets channel 3.
23
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
3.1.6
xr
REV. 1.2.2
SLEEP [7:0] - (default 0x00)
The 8-bit Sleep register enables each UART separately to enter Sleep mode. Sleep mode reduces power
consumption when the system needs to put the UART(s) to idle. The UART enters sleep mode when there is
no interrupt pending. When all 4 UARTs are put to sleep, the on-chip oscillator shuts off to further conserve
power. In this case, the quad UART is awakened by any of the UART channel on from a receive data byte or a
change on the modem port (CTS#, DSR#, CD# and RI#). The UART is ready after 32 crystal clocks to ensure
full functionality. Also, a special interrupt is generated with an indication of no pending interrupt. Reading INT0
will clear this wake-up interrupt. Logic 0 (default) and logic 1 disable and enable sleep mode respectively.
SLEEP Register
Individual UART Channel Sleep Enable
Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
Rsvd Rsvd Rsvd Rsvd Ch-3 Ch-2 Ch-1 Ch-0
3.1.7
Device Identification and Revision
There are 2 internal registers that provide device identification and revision, DVID and DREV registers. The 8bit content in the DVID register provides device identification. A return value of 0x24 from this register indicates
the device is a XR16L784. The DREV register returns a 8-bit value of 0x01 for revision A, 0x02 for revision B
and so on. This information is very useful to the software driver for identifying which device it is communicating
with and to keep up with revision changes.
DVID [7:0] (default 0x24)
Device identification for the type of UART. The upper nibble indicates it is a XR16L78x series with lower nibble
indicating the number of channels.
Examples:
XR16L784 = 0x24
XR16L788 = 0x28
DREV [7:0]
Revision number of the XR16L784. A 0x01 represents "revision-A" with 0x02 for rev-B and so forth.
3.1.8
REGB [7:0] - (default 0x00)
REGB register provides a control for simultaneous write to all 4 UARTs configuration registers or individually.
This is very useful for device intialization in the power up and reset routines.
REGB[0]
Logic 0 (default) write to each UART configuration registers individually.
Logic 1 enables simultaneous write to all 4 UARTs configuration register. Useful during device initialization.
REGB[7:1]
Reserved
24
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
3.2
UART CHANNEL CONFIGURATION REGISTERS
The first 8 registers are 16550 compatible with EXAR enhanced feature registers located on the upper 8
addresses. The 4 sets of UART configuration registers are decoded using address lines A0 to A3 as shown
below.
.
TABLE 11: UART CHANNEL CONFIGURATION REGISTERS
ADDRESS
A3
A2
A1
REGISTER
READ/WRITE
COMMENTS
A0
16550 COMPATIBLE REGISTERS
0
0
0
0
RHR - Receive Holding Register
Read-only
LCR[7] = 0
0
0
0
0
THR - Transmit Holding Register
Write-only
LCR[7] = 0
0
0
0
0
DLL - Div Latch Low
Read/Write
LCR[7] = 1
0
0
0
1
DLM - Div Latch High
Read/Write
LCR[7] = 1
0
0
0
1
IER - Interrupt Enable Register
Read/Write
LCR[7] = 0
0
0
1
0
ISR - Interrupt Status Register
Read-only
0
0
1
0
FCR - FIFO Control Register
Write-only
0
0
1
1
LCR - Line Control Register
Read/Write
0
1
0
0
MCR - Modem Control Register
Read/Write
0
1
0
1
LSR - Line Status Register
Read-only
0
1
1
0
MSR - Modem Status Register
Read-only
0
1
1
0
RS485 Turn-Around Delay Register
Write-only
0
1
1
1
SPR - Scratch Pad Register
Read/Write
ENHANCED REGISTERS
1
0
0
0
FCTR - Feature Control Register
Read/Write
1
0
0
1
EFR - Enhanced Function Register
Read/Write
1
0
1
0
TXCNT - Transmit FIFO Level Counter
Read-only
1
0
1
0
TXTRG - Transmit FIFO Trigger Level
Write-only
1
0
1
1
RXCNT - Receive FIFO Level Counter
Read-only
1
0
1
1
RXTRG - Receive FIFO Trigger Level
Write-only
1
1
0
0
Xoff-1 - Xoff Character 1
Write-only
1
1
0
0
Xchar
Read-only
1
1
0
1
Xoff-2 - Xoff Character 2
Write-only
1
1
1
0
Xon-1 - Xon Character 1
Write-only
1
1
1
1
Xon-2 - Xon Character 2
Write-only
25
Xon,Xoff Rcvd. Flags
xr
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
TABLE 12: UART CHANNEL CONFIGURATION REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED BY EFR BIT-4.
ADDRESS
A3-A0
REG
NAME
READ/
WRITE
BIT-7
BIT-6
BIT-5
BIT-4
BIT-3
BIT-2
BIT-1
BIT-0
COMMENT
0000
RHR
R
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
LCR[7]=0
0000
THR
W
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
LCR[7]=0
0000
DLL
R/W
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
LCR[7]=1
0001
DLM
R/W
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
LCR[7]=1
0001
IER
R/W
0
0
0
0
Modem
Status
Int.
Enable
RX Line
Status
Int.
Enable
TX
Empty
Int.
Enable
RX Data
Int.
Enable
INT
Source
Xoff/spe- Bit-3
cial char
INT
Source
Bit-2
INT
Source
Bit-1
INT
Source
Bit-0
TX FIFO RX FIFO
Reset
Reset
FIFOs
Enable
CTS/
RTS/
Xon/Xoff/
DSR# Int. DTR# Int. Sp. Char.
Enable
Enable
Int.
Enable
0010
ISR
R
FIFOs
Enable
FIFOs
Enable
0
DeltaFlow
Cntl
0010
FCR
W
0011
LCR
R/W
Divisor
Enable
Set TX
Break
Set Parity
0100
MCR
R/W
0
0
0
BRG
Prescaler
IR
Enable
0
RX FIFO RX FIFO TX FIFO TX FIFO
Trigger Trigger Trigger Trigger
Even
Parity
Internal
Lopback
XonAny Enable
DMA
Mode
Parity Stop Bits
Enable
OP22
OP12
RTS/
DTR
Flow Sel
Word
Length
Bit-1
Word
Length
Bit-0
RTS#
DTR#
Pin Con- Pin Control
trol
0101
LSR
R/W
RX FIFO
ERROR
TSR
Empty
THR
Empty
RX
Break
0110
MSR
R
CD
RI
DSR
CTS
Delta
CD#
Delta
RI#
Delta
DSR#
Delta
CTS#
MSR
W
RS485
DLY-3
RS485
DLY-2
RS485
DLY-1
RS485
DLY-0
0
0
0
0
0111
SPR
R/W
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
1000
FCTR
R/W
TRG
Table
Bit-1
TRG
Table
Bit-0
Auto
RS485
Enable
Invert IR
RX Input
1001
EFR
R/W
Auto
CTS/
DSR
Enable
Auto
RTS/
DTR
Enable
Special
Char
Select
Enable
IER [7:4],
ISR [5:4],
FCR[5:4],
MCR[7:5]
MSR[7:4]
Software
Flow
Cntl
Bit-3
Software
Flow
Cntl
Bit-2
Software
Flow
Cntl
Bit-1
Software
Flow
Cntl
Bit-0
1010
TXCNT
R
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
1010
TXTRG
W
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
26
RX
RX ParRX
RX Data
Framing ity Error Overrun Ready
Error
RTS/
RTS/
RTS/
RTS/
DTR
DTR
DTR
DTR
Hyst Bit- Hyst Bit- Hyst Bit- Hyst Bit3
2
1
0
User Data
xr
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
TABLE 12: UART CHANNEL CONFIGURATION REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED BY EFR BIT-4.
ADDRESS
A3-A0
REG
NAME
READ/
WRITE
BIT-7
BIT-6
BIT-5
BIT-4
BIT-3
BIT-2
BIT-1
BIT-0
1011
RXCNT
R
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
1011
RXTRG
W
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
1100
XCHAR
R
0
0
0
0
0
0
1100
XOFF1
W
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
1101
XOFF2
W
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
1110
XON1
W
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
1111
XON2
W
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
COMMENT
Xon Det. Xoff Det. Self-clear
Indicator Indicator after read
NOTE: MCR bits 2 and 3 (OP1 and OP2 outputs) are not available in the XR16L784. They are present for 16C550
compatibility during Internal loopback, see Figure 12.
4.0 INTERNAL REGISTER DESCRIPTIONS
4.1
Receive Holding Register (RHR) - Read Only
SEE”RECEIVER” ON PAGE 10.
4.2
Transmit Holding Register (THR) - Write Only
SEE”TRANSMITTER” ON PAGE 9.
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) register and
also encoded in INT (INT0-INT3) register in the Device Configuration Registers.
4.3.1
IER versus Receive FIFO Interrupt Mode Operation
When the receive FIFO (FCR BIT-0 = a logic 1) and receive interrupts (IER BIT-0 = logic 1) are enabled, the
RHR interrupts (see ISR bits 3 and 4) status will reflect the following:
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 XR16L788 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.
27
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
xr
REV. 1.2.2
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 interrupt is associated with bit-5 in the LSR register. An interrupt is issued whenever the THR becomes
empty or when data in the TX FIFO falls below the programmed trigger level.
• Logic 0 = Disable Transmit Holding Register empty interrupt (default).
• Logic 1 = Enable Transmit Holding Register empty interrupt.
IER[2]: Receive Line Status Interrupt Enable
If any of the LSR register bits 1, 2, 3 or 4 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 bits 1-4 generate an interrupt immediately when
the character has been received.
• 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]: Reserved.
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 software flow control, 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.
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.
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 queue up for next
service. No other interrupts are acknowledged until the pending interrupt is serviced. The Interrupt Source
Table, Table 13, shows the data values (bit 0-5) for the six prioritized interrupt levels and the interrupt sources
associated with each of these interrupt levels.
28
xr
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
4.4.1
Interrupt Generation:
• LSR is by any of the LSR bits 1, 2, 3 and 4.
• 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.
• Receive Xoff/Special character is by detection of a Xoff or Special character.
• CTS#/DSR# is when its transmitter toggles the input pin (from LOW to HIGH) during auto CTS/DSR flow
control enabled by EFR bit-7 and selection on MCR bit-2.
• RTS#/DTR# is when its receiver toggles the output pin (from LOW to HIGH) during auto RTS/DTR flow
control enabled by EFR bit-6 and selection on MCR bit-2.
4.4.2
Interrupt Clearing:
• LSR interrupt is cleared by a read to the LSR register.
• 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.
• Xoff interrupt is cleared by a read to ISR or when Xon character(s) is received.
• Special character interrupt is cleared by a read to ISR or after the next character is received.
• RTS#/DTR# and CTS#/DSR# status change interrupts are cleared by a read to the MSR register.
]
TABLE 13: INTERRUPT SOURCE AND PRIORITY LEVEL
PRIORITY
ISR REGISTER STATUS BITS
SOURCE OF THE 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
0
1
0
0
RXRDY (Received Data Ready)
3
0
0
1
1
0
0
RXRDY (Receive Data Time-out)
4
0
0
0
0
1
0
TXRDY (Transmitter Holding Register Empty)
5
0
0
0
0
0
0
MSR (Modem Status Register)
6
0
1
0
0
0
0
RXRDY (Received Xon/Xoff or Special character)
7
1
0
0
0
0
0
CTS#/DSR#, RTS#/DTR# change of state
X
0
0
0
0
0
1
None (default)
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[5:1]: Interrupt Status
These bits indicate the source for a pending interrupt at interrupt priority levels (See Table 13). See “Section
4.4.1, Interrupt Generation:” on page 29 and “Section 4.4.2, Interrupt Clearing:” on page 29 for details.
29
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
xr
REV. 1.2.2
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, set the transmit/receive FIFO trigger levels, and
select the DMA mode. The DMA, and FIFO modes are 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.
FCR[1]: RX FIFO Reset
This bit is only active when FCR bit-0 is active.
• 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 active.
• 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]: DMA Mode Select
This bit has no effect since TXRDY and RXRDY pins are not available in this device. It is provided for legacy
software.
• Logic 0 = Set DMA to mode 0 (default).
• Logic 1 = Set DMA to mode 1.
FCR[5:4]: Transmit FIFO Trigger Select
(logic 0 = default, TX trigger level = one)
The FCTR Bits 6-7 are associated with these 2 bits by selecting one of the four tables. The 4 user selectable
trigger levels in 4 tables are supported for compatibility reasons. These 2 bits set the trigger level for the
transmit FIFO interrupt. The UART will issue a transmit interrupt when the number of characters in the FIFO
falls below 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 14 below shows the selections.
FCR[7:6]: Receive FIFO Trigger Select
(logic 0 = default, RX trigger level =1)
The FCTR Bits 5-4 are associated with these 2 bits. 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 crosses the
trigger level. Table 14 shows the complete selections. Note that the receiver and the transmitter cannot use
different trigger tables. Whichever selection is made last applies to both the RX and TX side.
30
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HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
TABLE 14: TRANSMIT AND RECEIVE FIFO TRIGGER TABLE AND LEVEL SELECTION
TRIGGER
TABLE
FCTR
BIT-7
FCTR
BIT-6
Table-A
0
0
FCR
BIT-7
0
0
1
1
Table-B
0
Table-D
4.6
1
1
FCR
BIT-5
FCR
BIT-4
0
0
0
1
0
1
0
0
1
1
1
0
0
1
1
X
X
COMPATIBILITY
16C550, 16C2550,
16C2552, 16C554,
16C580
16
8
24
30
16C650A
8
16
32
56
16C654
8
16
24
28
0
0
1
0
1
TRANSMIT
TRIGGER
LEVEL
1 (default)
0
1
0
1
0
1
0
1
0
0
1
1
RECEIVE
TRIGGER LEVEL
1 (default)
4
8
14
1
0
0
1
1
Table-C
FCR
BIT-6
0
1
0
1
8
16
56
60
X
X
Programmable Programmable 16L2752, 16L2750,
via RXTRG
via TXTRG 16C2852, 16C850,
16C854, 16C864
register.
register.
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.
BIT-1
BIT-0
WORD LENGTH
0
0
5 (default)
0
1
6
1
0
7
1
1
8
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HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
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.
LENGTH
STOP BIT LENGTH
(BIT TIME(S))
0
5,6,7,8
1 (default)
1
5
1-1/2
1
6,7,8
2
WORD
BIT-2
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 15 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.
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 (default).
• Logic 1 = EVEN Parity is generated by forcing an even the number of logic 1’s in the transmitted character.
The receiver must be programmed to check the same format.
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.
TABLE 15: 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”
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’, logic 0, 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”, logic 0, for alerting the remote receiver of a line
break condition.
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
LCR[7]: Baud Rate Divisors Enable
Baud rate generator divisor (DLL/DLM) enable.
• Logic 0 = Data registers are selected (default).
• Logic 1 = Divisor latch registers are selected.
4.7
Modem Control Register (MCR) - Read/Write
The MCR register is used for controlling the modem interface signals or general purpose inputs/outputs.
MCR[0]: DTR# Output
The DTR# pin may be used for automatic hardware flow control enabled by EFR bit-6 and MCR bit-2=1. If the
modem interface is not used, this output may be used for general purpose.
• Logic 0 = Force DTR# output to a logic 1 (default).
• Logic 1 = Force DTR# output to a logic 0.
MCR[1]: RTS# Output
The RTS# pin may be used for automatic hardware flow control by enabled by EFR bit-6 and MCR bit-2=0. If
the modem interface is not used, this output may be used for general purpose.
• Logic 0 = Force RTS# output to a logic 1 (default).
• Logic 1 = Force RTS# output to a logic 0.
MCR[2]: RTS/CTS or DTR/DSR for Auto Flow Control
DTR# or RTS# auto hardware flow control select. This bit is in effect only when auto RTS/DTR is enabled by
EFR bit-6.
• Logic 0 = RTS# (RX side) and CTS# (TX side) pins are used for auto hardware flow control (default).
• Logic 1 = DTR# (RX side) and DSR# (TX side) pins are used for auto hardware flow control.
MCR[3]: Reserved
MCR[4]: Internal Loopback Enable
• Logic 0 = Disable loopback mode (default).
• Logic 1 = Enable local loopback mode, see loopback section and Figure 12.
MCR[5]: Xon-Any Enable
• Logic 0 = Disable Xon-Any function (default).
• Logic 1 = Enable Xon-Any function. In this mode any RX character received will enable Xon, resume data
transmission.
MCR[6]: Infrared Encoder/Decoder Enable
The state of this bit depends on the sampled logic level of pin ENIR during power up, following a hardware
reset (rising edge of RST# input). Afterward user can override this bit for desired operation.
• Logic 0 = Enable the standard modem receive and transmit character interface.
• Logic 1 = Enable infrared IrDA receive and transmit inputs/outputs. While in this mode, the TX/RX output/
input are routed to the infrared encoder/decoder. The data input and output levels will conform to the IrDA
infrared interface requirement. As such, while in this mode the infrared TX output will be a logic 0 during idle
data conditions. FCTR bit-4 may be selected to invert the RX input signal level going to the decoder for
infrared modules that provide rather an inverted output.
MCR[7]: Clock Prescaler Select
• 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.
33
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HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
4.8
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REV. 1.2.2
Line Status Register (LSR) - Read Only
This register provides the status of data transfers between the UART and the host. If IER bit-2 is set to a logic
1, an LSR interrupt will be generated immediately when any character in the RX FIFO has an error (parity,
framing, overrun, break).
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 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 Flag
• 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 Flag
• 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 Flag
• Logic 0 = No break condition (default).
• Logic 1 = The receiver received a break signal (RX was a logic 0 for one character frame time). In the FIFO
mode, only one break character is loaded into the FIFO. The break indication remains until the RX input
returns to the idle condition, “mark” or logic 1.
LSR[5]: Transmit Holding Register Empty Flag
This bit is the Transmit Holding Register Empty indicator. This bit indicates that the transmitter is ready to
accept a new character for transmission. In addition, this bit causes the UART to issue an interrupt to the host
when the THR interrupt enable is set. 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 at least 1 byte is written to the transmit FIFO.
LSR[6]: Transmit Shift Register Empty Flag
This bit is the Transmit Shift Register Empty indicator. 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 one whenever the transmit FIFO and transmit shift register are both empty.
LSR[7]: Receive FIFO Data Error Flag
• Logic 0 = No FIFO error (default).
• Logic 1 = An 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 the FIFO.
4.9
Modem Status Register (MSR) - Read Only
This register provides the current state of the modem interface signals, or other peripheral device that the
UART is connected. 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 as general
purpose inputs/outputs when they are not used with modem signals.
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
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 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 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 logic 0 to a logic 1, ending of the ringing signal. A modem status
interrupt will be generated if 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 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) and RTS/CTS flow control select (MCR bit-2). 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
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
This input may be used for auto DTR/DSR flow control function, see auto hardware flow control section.
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.
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
Modem Status Register (MSR) - Write Only
The upper four bits 4-7 of this register sets the delay in number of bits time for the auto RS485 turn around
from transmit to receive.
MSR [7:4]
When Auto RS485 feature is enabled (FCTR bit-5=1) and RTS# output is connected to the enable input of a
RS-485 transceiver. These 4 bits select from 0 to 15 bit-time delay after the end of the last stop-bit of the last
transmitted character. This delay controls when to change the state of RTS# output. This delay is very useful in
long-cable networks. Table 16 shows the selection. The bits are enabled by EFR bit-4.
35
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
TABLE 16: AUTO RS485 HALF-DUPLEX DIRECTION CONTROL DELAY FROM TRANSMIT-TO-RECEIVE
4.11
MSR[7]
MSR[6]
MSR[5]
MSR[4]
DELAY IN DATA BIT(S) TIME
0
0
0
0
0
0
0
0
1
1
0
0
1
0
2
0
0
1
1
3
0
1
0
0
4
9
1
0
1
5
0
1
1
0
6
0
1
1
1
7
1
0
0
0
8
1
0
0
1
9
1
0
1
0
10
1
0
1
1
11
1
1
0
0
12
1
1
0
1
13
1
1
1
0
14
1
1
1
1
15
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 reset or a power off-on cycle.
4.12
FEATURE CONTROL REGISTER (FCTR) - Read/Write
This register controls the UART enhanced functions that are not available on ST16C554 or ST16C654.
FCTR [3:0] - Auto RTS/DTR Flow Control Hysteresis Select
These bits select the auto RTS/DTR flow control hysteresis and only valid when TX and RX Trigger Table-D is
selected (FCTR bit-6 and 7 are set to logic 1). The RTS/DTR hysteresis is referenced to the RX FIFO trigger
level. After reset, these bits are set to logic 0 selecting the next FIFO trigger level for hardware flow control.
Table 17 below shows the 16 selectable hysteresis levels.
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
TABLE 17: 16 SELECTABLE HYSTERESIS LEVELS WHEN TRIGGER TABLE-D IS SELECTED
FCTR BIT-3
FCTR BIT-2
FCTR BIT-1
FCTR BIT-0
RTS/DTR HYSTERESIS
(CHARACTERS)
0
0
0
0
0
0
0
0
1
+/- 4
0
0
1
0
+/- 6
0
0
1
1
+/- 8
0
1
0
0
+/- 8
0
1
0
1
+/- 16
0
1
1
0
+/- 24
0
1
1
1
+/- 32
1
1
0
0
+/- 12
1
1
0
1
+/- 20
1
1
1
0
+/- 28
1
1
1
1
+/- 36
1
0
0
0
+/- 40
1
0
0
1
+/- 44
1
0
1
0
+/- 48
1
0
1
1
+/- 52
FCTR[4]: Infrared RX Input Logic Select
• Logic 0 = Select RX input as active high encoded IrDA data, normal, (default).
• Logic 1 = Select RX input as active low encoded IrDA data, inverted.
FCTR[5]: Auto RS485 Enable
Auto RS485 half duplex control enable/disable.
• Logic 0 = Standard ST16C550 mode. Transmitter generates an interrupt when transmit holding register
(THR) becomes empty. Transmit Shift Register (TSR) may still be shifting data bit out.
• Logic 1 = Enable Auto RS485 half duplex direction control. RTS# output changes its logic level from HIGH to
LOW when finished sending the last stop bit of the last character out of the TSR register. It changes from
LOW to HIGH when a data byte is loaded into the THR or transmit FIFO. The change to HIGH occurs prior
sending the start-bit. It also changes the transmitter interrupt from transmit holding to transmit shift register
(TSR) empty.
FCTR[7:6]: TX and RX FIFO Trigger Table Select
These 2 bits select the transmit and receive FIFO trigger level table A, B, C or D. When table A, B, or C is
selected the auto RTS flow control trigger level is set to "next FIFO trigger level" for compatibility to ST16C550
and ST16C650 series. RTS/DTR# triggers on the next level of the RX FIFO trigger level, in another word, one
FIFO level above and one FIFO level below. See in Table 14 for complete selection with FCR bit 4-5 and FCTR
bit 6-7, i.e. if Table C is used on the receiver with RX FIFO trigger level set to 56 bytes, RTS/DTR# output will
de-assert at 60 and re-assert at 16.
37
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
4.13
REV. 1.2.2
Enhanced Feature Register (EFR) - Read/Write
Enhanced features are enabled or disabled using this register. Bit 0-3 provide single or dual consecutive
character software flow control selection (see Table 18). 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.
TABLE 18: SOFTWARE FLOW CONTROL FUNCTIONS
EFR BIT-3
CONT-3
EFR BIT-2
CONT-2
EFR BIT-1
CONT-1
EFR BIT-0
CONT-0
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
TRANSMIT AND RECEIVE SOFTWARE FLOW CONTROL
EFR[3:0]: Software Flow Control Select
Combinations of software flow control can be selected by programming these bits.
EFR[4]: Enhanced Function Bits Enable
Enhanced function control bit. This bit enables the functions in IER bits 4-7, ISR bits 4-5, FCR bits 4-5, and
MCR bits 5-7 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, and MCR
bits 5-7 are saved to retain the user settings. After a reset, the IER bits 4-7, ISR bits 4-5, FCR bits 4-5, and
MCR bits 5-7 are set to a logic 0 to be compatible with ST16C554 mode (default).
• Logic 1 = Enables the enhanced functions. When this bit is set to a logic 1 all enhanced features are
enabled.
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REV. 1.2.2
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
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 Xoff-2 register. If a match exists, the received 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 for 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.
EFR[6]: Auto RTS or DTR Flow Control Enable
RTS#/DTR# output may be used for hardware flow control by setting EFR bit-6 to logic 1. When Auto RTS/
DTR is selected, an interrupt will be generated when the receive FIFO is filled to the programmed trigger level
and RTS/DTR# will de-assert (HIGH) at the next upper trigger or selected hysteresis level. RTS/DTR# will reassert (LOW) when FIFO data falls below the next lower trigger or selected hysteresis level (see FCTR bits 47). The RTS# or DTR# output must be asserted (LOW) before the auto RTS/DTR can take effect. The selection
for RTS# or DTR# is through MCR bit-2. RTS/DTR# pin will function as a general purpose output when
hardware flow control is disabled.
• Logic 0 = Automatic RTS/DTR flow control is disabled (default).
• Logic 1 = Enable Automatic RTS/DTR flow control.
EFR[7]: Auto CTS Flow Control Enable
Automatic CTS or DSR Flow Control.
• Logic 0 = Automatic CTS/DSR flow control is disabled (default).
• Logic 1 = Enable Automatic CTS/DSR flow control. Transmission stops when CTS/DSR# pin de-asserts
(HIGH). Transmission resumes when CTS/DSR# pin is asserted (LOW). The selection for CTS# or DSR# is
through MCR bit-2.
4.14
TXCNT[7:0]: Transmit FIFO Level Counter - Read Only
Transmit FIFO level byte count from 0x00 (zero) to 0x40 (64). This 8-bit register gives an indication of the
number of characters in the transmit FIFO. The FIFO level Byte count register is read only. The user can take
advantage of the FIFO level byte counter for faster data loading to the transmit FIFO., which reduces CPU
bandwidth requirements.
4.15
TXTRG [7:0]: Transmit FIFO Trigger Level - Write Only
An 8-bit value written to this register sets the TX FIFO trigger level from 0x00 (zero) to 0x40 (64). The TX FIFO
trigger level generates an interrupt whenever the data level in the transmit FIFO falls below this preset trigger
level.
4.16
RXCNT[7:0]: Receive FIFO Level Counter - Read Only
Receive FIFO level byte count from 0x00 (zero) to 0x40 (64). It gives an indication of the number of characters
in the receive FIFO. The FIFO level byte count register is read only. The user can take advantage of the FIFO
level byte counter for faster data unloading from the receiver FIFO, which reduces CPU bandwidth
requirements.
4.17
RXTRG[7:0]: Receive FIFO Trigger Level - Write Only
An 8-bit value written to this register, sets the RX FIFO trigger level from 0x00 (zero) to 0x40 (64). The RX
FIFO trigger level generates an interrupt whenever the receive FIFO level rises to this preset trigger level.
39
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
TABLE 19: UART RESET CONDITIONS
REGISTERS
RESET STATE
DLL
Bits 7-0 = 0xXX
DLM
Bits 7-0 = 0xXX
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 = 0x00
MCR
Bits 7-0 = 0x00
LSR
Bits 7-0 = 0x60
MSR
Bits 3-0 = logic 0
Bits 7-4 = logic levels of the inputs
SPR
Bits 7-0 = 0xFF
FCTR
Bits 7-0 = 0x00
EFR
Bits 7-0 = 0x00
TXCNT
Bits 7-0 = 0x00
TXTRG
Bits 7-0 = 0x00
RXCNT
Bits 7-0 = 0x00
RXTRG
Bits 7-0 = 0x00
XCHAR
Bits 7-0 = 0x00
XON1
Bits 7-0 = 0x00
XON2
Bits 7-0 = 0x00
XOFF1
Bits 7-0 = 0x00
XOFF2
Bits 7-0 = 0x00
I/O SIGNALS
RESET STATE
TX[ch-3:0]
HIGH
IRTX[ch-3:0]
LOW
RTS#[ch-3:0]
HIGH
DTR#[ch-3:0]
HIGH
40
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
ABSOLUTE MAXIMUM RATINGS
Power Supply Range
7 Volts
Voltage at Any Pin
-0.5 to 7V
Operating Temperature
-40o to +85o C
Storage Temperature
-65o to +150o C
Package Dissipation
500 mW
Thermal Resistance (10x10x1.4mm 64-LQFP)
θ-ja =70, θ-jc =14 oC/W
.
ELECTRICAL CHARACTERIISTICS
DC ELECTRICAL CHARACTERISTICS
TA=0o to 70oC (-40o to +85oC for industrial grade package), Vcc-3.3V and 5V +/-10% unless specified
PARAMETER
3.3V
MIN
MAX
5V
MIN
5V
MAX
UNITS
VILCK
Clock Input Low Voltage
-0.3
0.6
-0.5
0.6
V
VIHCK
Clock Input High Voltage
2.4
VCC
3.0
VCC
V
VIL
Input Low Voltage
-0.3
0.7
-0.5
0.8
V
VIH
Input High Voltage
2.0
6.0
2.0
6.0
V
0.4
V
Iout=4 mA at 3.3V
Iout=6 mA at 5V
V
Iout=-1 mA at 3.3V
Iout=-2 at 5V
SYMBOL
VOLCK
Clock Output (XTAL2) Low Voltage
VOHCK Clock Output (XTAL2) High Voltage
3.3
0.4
2.0
2.4
VOL
Output Low Voltage
See Figure 16
VOH
Output High Voltage
See Figure 17
CONDITION
IIL
Input Low Leakage Current
-10
-10
uA
IIH
Input High Leakage Current
10
10
uA
CIN
Input Pin Capacitance
5
5
pF
ICC
Power Supply Current
5
5
mA
External clock at 2MHz. A7-A0
at GND, all inputs at VCC or
GND and outputs unloaded
0.6
1.5
mA
Four UARTs asleep. A7-A0 at
GND, all inputs at VCC or GND
and outputs unloaded.
ISLEEP
Sleep Current
41
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
FIGURE 16. XR16L784 VOL SINK CURRENT CHART
XR16L784 Sink Current
26
24
22
20
18
IOL (mA)
16
14
VCC=5V
VCC=3.3V
12
10
8
6
4
2
0
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
VOL (V)
FIGURE 17. XR16L784 VOH SOURCE CURRENT CHART
XR16L784 Source Current
16
14
12
IOH (mA)
10
VCC=5V
8
VCC=3.3V
6
4
2
0
1.00
1.50
2.00
2.50
3.00
3.50
VOH (V)
42
4.00
4.50
5.00
xr
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
AC ELECTRICAL CHARACTERISTICS
TA=0O TO 70OC (-40O TO +85OC FOR INDUSTRIAL GRADE PACKAGE), VCC IS 2.97V TO 5.5V, 70 PF LOAD
WHERE APPLICABLE
SYMBOL
3,3V
MIN
PARAMETER
TC1,TC2 Clock Pulse Period
3.3V
MAX
10
5V
MIN
5V
MAX
8
UNITS
ns
TOSC
Oscillator Frequency
16
24
MHz
TECK
External Clock Frequency
33
50
MHz
TAS
Address Setup (16 Mode)
5
5
ns
TAH
Address Hold (16 Mode)
10
10
ns
TCS
Chip Select Width (16 Mode)
50
50
ns
TDY
Delay between CS# Active Cycles (16 Mode)
50
50
ns
TRD
Read Strobe Width (16 Mode)
50
50
ns
TWR
Write Strobe Width (16 Mode)
40
30
ns
TRDV
Read Data Valid (16 Mode)
35
25
ns
TWDS
Write Data Setup (16 Mode)
15
10
ns
TRDH
Read Data Hold (16 Mode)
TWDH
Write Data Hold (16 Mode)
15
10
ns
TADS
Address Setup (68 Mode)
10
5
ns
TADH
Address Hold (68 Mode)
10
10
ns
TRWS
R/W# Setup to CS# (68 Mode)
10
10
ns
TRDA
Read Data Access (68 mode)
35
25
ns
TRDH
Read Data Hold (68 mode)
TWDS
Write Data Setup (68 mode)
10
10
ns
TWDH
Write Data Hold (68 Mode)
10
10
ns
TRWH
CS# De-asserted to R/W# De-asserted (68 Mode)
10
10
ns
TCSL
CS# Width (68 Mode)
50
40
ns
TCSD
CS# Cycle Delay (68 Mode)
50
40
ns
TWDO
Delay from IOW# to Modem Output
50
50
ns
TMOD
Delay to set Interrupt from Modem Input
50
35
ns
TRSI
Delay To Reset Interrupt From IOR#
50
35
ns
TSSI
Delay From Stop To Set Interrupt
1
1
Bclk
TRRI
Delay From IOR# To Reset Interrupt
45
40
ns
Delay From Stop To Interrupt
45
40
ns
TWRI
Delay From IOW# To Reset Interrupt
45
40
ns
TRST
Reset Pulse
Bclk
Baud Clock
TSI
15
10
15
40
10
40
16X or 8X of data rate
43
ns
ns
ns
Hz
xr
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
FIGURE 18. 16 MODE (INTEL) DATA BUS READ AND WRITE TIMING
A0-A7
Valid Address
TAS
Valid Address
TAS
TAH
TCS
TAH
CS#
TDY
TRD
IOR#
TRDH
TRDV
Valid Data
D0-D7
TRDH
TRDV
Valid Data
16Read
16 Mode (Intel) Data Bus Read Timing
A0-A7
Valid Address
TAS
Valid Address
TAS
TAH
TCS
TAH
CS#
TDY
TWR
IOW#
TWDS
D0-D7
TWDH
Valid Data
TWDS
TWDH
Valid Data
16Write
16 Mode (Intel) Data Bus Write Timing
44
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
FIGURE 19. 68 MODE (MOTOROLA) DATA BUS READ AND WRITE TIMING
A0-A7
Valid Address
TADS
TCSL
Valid Address
TADH
CS#
TCSD
TRWS
TRWH
R/W#
TRDH
TRDA
Valid Data
D0-D7
Valid Data
68Read
68 Mode (Motorola) Data Bus Read Timing
A0-A7
Valid Address
TADS
TCSL
Valid Address
TADH
CS#
TCSD
TRWS
TRWH
R/W#
TWDS
D0-D7
TWDH
Valid Data
Valid Data
68Write
68 Mode (Motorola) Data Bus Write Timing
45
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
FIGURE 20. MODEM INPUT/OUTPUT PORT DELAY
Active
IOW#
T17D
Change of
State
RTS#
DTR#
Change of
State
CD#
CTS#
DSR#
Change of
State
Change of
State
T18D
T18D
Active
INT
Active
Active
T19D
Active
Active
IOR#
Active
T18D
Change of
State
RI#
Modem-1
FIGURE 21. RECEIVE INTERRUPT TIMING [NON-FIFO MODE]
RX
INT#
Start
Bit
D0:D7
Stop
Bit
D0:D7
1 Byte
in RHR
D0:D7
1 Byte
in RHR
T RR
T RR
IO R#
(Reading data
out of RHR)
46
1 Byte
in RHR
T RR
xr
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
FIGURE 22. TRANSMIT INTERRUPT TIMING [NON-FIFO MODE]
TX
S ta rt
B it
(U n lo a d in g )
IE R [1 ]
e n a b le d
S to p
B it
D 0 :D 7
D 0 :D 7
IS R is re a d
D 0 :D 7
IS R is re a d
IS R is re a d
IN T # *
TW RI
TW RI
TW RI
IO W #
(L o a d in g d a ta
in to T H R )
*T X in te rru p t is c le a re d w h e n th e IS R is re a d o r w h e n d a ta is lo a d e d in to th e T H R .
FIGURE 23. RECEIVE INTERRUPT TIMING [FIFO MODE]
Start
Bit
RX
S D0:D7
S D0:D7 T
D0:D7
S D0:D7 T
S D0:D7 T S D0:D7 T
S D0:D7 T
T SSI
INT#
RX FIFO drops
below RX
Trigger Level
RX FIFO fills up to RX
Trigger Level or RX Data
Tim eout
T RRI
T RR
IOR#
(Reading data out
of RX FIFO)
FIGURE 24. TRANSMIT INTERRUPT TIMING [FIFO MODE]
TX FIFO
Em pty
TX
Start
B it
S
(Unloading)
IER [1]
enabled
S top
Bit
D 0:D 7 T
Last Data B yte
Transm itted
S D 0:D 7
T S
T S
D 0:D 7 T
D0:D 7 T S D 0:D 7 T
T SI
ISR is read
INT#*
TX FIFO fills up
to trigger level
TW RI
TX FIFO drops
below trigger level
IO W #
(Loading data
into FIFO )
*TX interrupt is cleared when the ISR is read or when TX FIFO fills up to the trigger level.
47
ISR is read
S
D 0:D 7 T
xr
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
PACKAGE DIMENSIONS, 64-LQFP
D
D1
48
33
49
32
D1
64
17
1
16
B
e
A2
C
A
α
Seating Plane
A1
L
Note: The control dimension is the millimeter column
INCHES
MILLIMETERS
SYMBOL
MIN
MAX
MIN
MAX
A
0.055
0.063
1.40
1.60
A1
0.002
0.006
0.05
0.15
A2
0.053
0.057
1.35
1.45
B
0.007
0.011
0.17
0.27
C
0.004
0.008
0.09
0.20
D
0.465
0.480
11.80
12.20
D1
0.390
0.398
9.90
10.10
e
0.020 BSC
0.50 BSC
L
0.018
0.030
0.45
0.75
a
0×
7×
0×
7×
48
D
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REV. 1.2.2
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REVISION HISTORY
REVISION
DESCRIPTION
P1.0.0
Preliminary
1.0.1
Further clarification on A0-A7, RTS#, CTS#, DTR#, DSR# and ENIR pin description and throughout the
datasheet, change VIH from 2.2V to 2.4V at 5V, change VOH from 2.4V to 2.0 at 3.3V and from 4V to 2.4V at
5V, change ICC from 10 to 5mA and its test condition to 2MHz. clock, and ISLEEP to 0.6 and 1.5mA for 3.3V and
5V respectively. Revised the AC timing table.
1.0.2
Updated values of AC Electrical Characteristics (TAS, TAH, TCS, TRD, TADS, TADH, TWDS, TWDH). Added Exar’s
UART Technical Support E-mail address to first and last page.
1.1.0
(June 2003) Added Device Status to Ordering Information.
1.2.0
(June 2004) Clarified pin descriptions- changed from using logic 1 and logic 0 to HIGH (VCC) and LOW (GND)
for input and output pin descriptions. Added VOH vs. IOH and VOL vs. IOL curves (Figure 16 and
Figure 17). Clarified Transmit and Receive interrupt timing diagrams (Figure 21-Figure 24). DREV register was updated to 0x04 for devices with top mark date code of "D2 YYWW".
1.2.1
(February 2005) Corrected Trigger Table selection and programmable trigger level selection in Table 14.
1.2.2
(October 2005) Updated the 1.4mm-thick Quad Flat Pack package description from "TQFP" to "LQFP" to be
consistent with the JEDEC and Industry norms. Clarified wake-up interrupt in Sleep Mode description.
NOTICE
EXAR Corporation reserves the right to make changes to the products contained in this publication in order to
improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any
circuits described herein, conveys no license under any patent or other right, and makes no representation that
the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration
purposes and may vary depending upon a user’s specific application. While the information in this publication
has been carefully checked; no responsibility, however, is assumed for inaccuracies.
EXAR Corporation does not recommend the use of any of its products in life support applications where the
failure or malfunction of the product can reasonably be expected to cause failure of the life support system or
to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless
EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has
been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately
protected under the circumstances.
Copyright 2005 EXAR Corporation
Datasheet October 2005.
Send your UART technical inquiry with technical details to hotline: [email protected].
Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.
49
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
TABLE OF CONTENTS
GENERAL DESCRIPTION ............................................................................................... 1
APPLICATIONS ........................................................................................................................................... 1
FEATURES ................................................................................................................................................. 1
Figure 1. Block Diagram ....................................................................................................................... 1
Figure 2. Pin Out Assignment .............................................................................................................. 2
ORDERING INFORMATION ............................................................................................................................ 2
PIN DESCRIPTIONS ....................................................................................................... 3
1.0 DESCRIPTION ........................................................................................................................................ 6
2.0 Functional Descriptions ........................................................................................................................ 6
2.1 DEVICE RESET .............................................................................................................................................................. 6
2.1.1 Hardware Reset ....................................................................................................................... 6
2.1.2 Software Reset ......................................................................................................................... 6
2.2 UART CHANNEL SELECTION ......................................................................................................................................... 6
TABLE 1: UART CHANNEL SELECTION ...................................................................................................... 6
2.3 SIMULTANEOUS WRITE TO ALL CHANNELS ..................................................................................................................... 6
2.4 INT# OUPUT ................................................................................................................................................................ 7
TABLE 2: INT# PIN OPERATION FOR TRANSMITTER ................................................................................... 7
TABLE 3: INT# PIN OPERATION FOR RECEIVER ......................................................................................... 7
2.5 CRYSTAL OSCILLATOR / BUFFER .......................................................................................................................... 7
Figure 3. Typical oscillator connections ............................................................................................. 7
2.6 PROGRAMMABLE BAUD RATE GENERATOR .................................................................................................................... 8
Figure 4. External Clock Connection for Extended Data Rate .......................................................... 8
Figure 5. Baud Rate Generator ............................................................................................................. 8
TABLE 4: TYPICAL DATA RATES WITH A 14.7456 MHZ CRYSTAL OR EXTERNAL CLOCK AT 16X SAMPLING ... 9
2.7 TRANSMITTER ............................................................................................................................................................... 9
2.7.1 Transmit Holding Register (THR) - Write Only ......................................................................... 9
2.7.2 Transmitter Operation in non-FIFO Mode ................................................................................ 9
Figure 6. Transmitter Operation in non-FIFO Mode ......................................................................... 10
2.7.3 Transmitter Operation in FIFO Mode ..................................................................................... 10
Figure 7. Transmitter Operation in FIFO and Flow Control Mode ................................................... 10
2.8 RECEIVER ................................................................................................................................................................... 10
2.8.1 Receive Holding Register (RHR) - Read-Only ....................................................................... 11
Figure 8. Receiver Operation in non-FIFO Mode .............................................................................. 11
Figure 9. Receiver Operation in FIFO and Auto RTS Flow Control Mode ...................................... 11
2.9 THR AND RHR REGISTER LOCATIONS ........................................................................................................................ 12
TABLE 5: TRANSMIT AND RECEIVE DATA REGISTER, 16C550 COMPATIBLE .............................................. 12
2.10 AUTOMATIC RTS/DTR HARDWARE FLOW CONTROL OPERATION ................................................................................ 12
2.10.1 Auto CTS/DSR Flow Control ................................................................................................ 13
Figure 10. Auto RTS/DTR and CTS/DSR Flow Control Operation ................................................... 13
2.11 AUTO XON/XOFF (SOFTWARE) FLOW CONTROL ......................................................................................................... 14
TABLE 6: AUTO XON/XOFF (SOFTWARE) FLOW CONTROL ........................................................................ 14
2.12 SPECIAL CHARACTER DETECT .................................................................................................................................. 14
2.13 AUTO RS485 HALF-DUPLEX CONTROL ..................................................................................................................... 15
2.14 INFRARED MODE ....................................................................................................................................................... 15
Figure 11. Infrared Transmit Data Encoding and Receive Data Decoding ..................................... 16
2.15 SLEEP MODE WITH WAKE-UP INDICATOR .................................................................................................................. 17
2.16 INTERNAL LOOPBACK ................................................................................................................................................ 18
Figure 12. Internal Loop Back ............................................................................................................ 18
3.0 XR16L784 REGISTERS ........................................................................................................................ 19
Figure 13. The XR16L784 Registers Mapping ................................................................................... 19
3.1 DEVICE CONFIGURATION REGISTER SET ........................................................................................ 19
TABLE 7: XR16L784 REGISTER SETS ..................................................................................................... 19
TABLE 8: DEVICE CONFIGURATION REGISTERS ........................................................................................ 20
3.1.1 The Global Interrupt Source Registers ................................................................................... 21
I
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REV. 1.2.2
XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
Figure 14. The Global Interrupt Registers, INT0, INT1, INT2 and INT3 ........................................... 21
TABLE 9: UART CHANNEL [3:0] INTERRUPT SOURCE ENCODING AND CLEARING .................................... 22
3.1.2 General Purpose 16-bit Timer/Counter. [TIMERMSB, TIMELSB, TIMER, TIMECNTL] (default
0xXX-XX-00-00) ............................................................................................................................. 22
Figure 15. Timer/Counter circuit. ....................................................................................................... 22
TABLE 10: TIMER CONTROL REGISTER ............................................................................................... 22
3.1.3 8XMODE [7:0] (default 0x00) ............................................................................................... 23
3.1.4 REGA [7:0] reserved (default 0x00) ..................................................................................... 23
3.1.5 RESET [7:0] (default 0x00) .................................................................................................... 23
3.1.6 SLEEP [7:0] - (default 0x00) .................................................................................................. 24
3.1.7 Device Identification and Revision ......................................................................................... 24
3.1.8 REGB [7:0] - (default 0x00) ................................................................................................... 24
3.2 UART CHANNEL CONFIGURATION REGISTERS ................................................................................................. 25
TABLE 11: UART CHANNEL CONFIGURATION REGISTERS ........................................................... 25
TABLE 12: UART CHANNEL CONFIGURATION REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED
BY EFR BIT-4. ........................................................................................................................ 26
4.0 Internal Register Descriptions ........................................................................................................... 27
4.1 RECEIVE HOLDING REGISTER (RHR) - READ ONLY ..................................................................................................... 27
4.2 TRANSMIT HOLDING REGISTER (THR) - WRITE ONLY .................................................................................................. 27
4.3 INTERRUPT ENABLE REGISTER (IER) - READ/WRITE .................................................................................................... 27
4.3.1 IER versus Receive FIFO Interrupt Mode Operation ............................................................. 27
4.3.2 IER versus Receive/Transmit FIFO Polled Mode Operation ................................................. 27
4.4 INTERRUPT STATUS REGISTER (ISR) - READ ONLY ..................................................................................................... 28
4.4.1 Interrupt Generation: ............................................................................................................. 29
4.4.2 Interrupt Clearing: .................................................................................................................. 29
TABLE 13: INTERRUPT SOURCE AND PRIORITY LEVEL ............................................................................. 29
4.5 FIFO CONTROL REGISTER (FCR) - WRITE ONLY ........................................................................................................ 30
TABLE 14: TRANSMIT AND RECEIVE FIFO TRIGGER TABLE AND LEVEL SELECTION .................................. 31
4.6 LINE CONTROL REGISTER (LCR) - READ/WRITE .......................................................................................................... 31
TABLE 15: PARITY SELECTION ................................................................................................................ 32
4.7 MODEM CONTROL REGISTER (MCR) - READ/WRITE ....................................................................................................
4.8 LINE STATUS REGISTER (LSR) - READ ONLY ..............................................................................................................
4.9 MODEM STATUS REGISTER (MSR) - READ ONLY ........................................................................................................
4.10 MODEM STATUS REGISTER (MSR) - WRITE ONLY .....................................................................................................
33
34
34
35
TABLE 16: AUTO RS485 HALF-DUPLEX DIRECTION CONTROL DELAY FROM TRANSMIT-TO-RECEIVE ........ 36
4.11 SCRATCH PAD REGISTER (SPR) - READ/WRITE ................................................................................................. 36
4.12 FEATURE CONTROL REGISTER (FCTR) - READ/WRITE ..................................................................................... 36
TABLE 17: 16 SELECTABLE HYSTERESIS LEVELS WHEN TRIGGER TABLE-D IS SELECTED ....................... 37
4.13 ENHANCED FEATURE REGISTER (EFR) - READ/WRITE ............................................................................................... 38
TABLE 18: SOFTWARE FLOW CONTROL FUNCTIONS ................................................................................ 38
4.14 TXCNT[7:0]: TRANSMIT FIFO LEVEL COUNTER - READ ONLY ...................................................................................
4.15 TXTRG [7:0]: TRANSMIT FIFO TRIGGER LEVEL - WRITE ONLY ..................................................................................
4.16 RXCNT[7:0]: RECEIVE FIFO LEVEL COUNTER - READ ONLY .....................................................................................
4.17 RXTRG[7:0]: RECEIVE FIFO TRIGGER LEVEL - WRITE ONLY ....................................................................................
39
39
39
39
TABLE 19: UART RESET CONDITIONS .............................................................................................. 40
ABSOLUTE MAXIMUM RATINGS ................................................................................ 41
ELECTRICAL CHARACTERIISTICS ............................................................................. 41
DC ELECTRICAL CHARACTERISTICS ...............................................................................................
Figure 16. XR16L784 VOL Sink Current Chart ..................................................................................
Figure 17. XR16L784 VOH Source Current Chart .............................................................................
AC ELECTRICAL CHARACTERISTICS .........................................................................................................
Figure 18. 16 Mode (Intel) Data Bus Read and Write Timing ..........................................................
Figure 19. 68 Mode (Motorola) Data Bus Read and Write Timing ...................................................
Figure 20. Modem Input/Output Port Delay ......................................................................................
Figure 21. Receive Interrupt Timing [Non-FIFO Mode] ....................................................................
Figure 22. Transmit Interrupt Timing [Non-FIFO Mode] ..................................................................
II
41
42
42
43
44
45
46
46
47
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XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.2
Figure 23. Receive Interrupt Timing [FIFO Mode] ............................................................................ 47
Figure 24. Transmit Interrupt Timing [FIFO Mode] ........................................................................... 47
PACKAGE DIMENSIONS, 64-LQFP .............................................................................. 48
REVISION HISTORY .................................................................................................................................. 49
TABLE OF CONTENTS ..................................................................................................... I
III