XR16V2750IM-F [EXAR]
Serial I/O Controller, 2 Channel(s), 1MBps, CMOS, PQFP48, 7 X 7 MM, 1 MM HEIGHT, GREEN, TQFP-48;![XR16V2750IM-F](http://pdffile.icpdf.com/pdf1/p00111/img/icpdf/XR16V2750IM_602326_icpdf.jpg)
型号: | XR16V2750IM-F |
厂家: | ![]() |
描述: | Serial I/O Controller, 2 Channel(s), 1MBps, CMOS, PQFP48, 7 X 7 MM, 1 MM HEIGHT, GREEN, TQFP-48 先进先出芯片 |
文件: | 总51页 (文件大小:1074K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
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PRELIMINARY
XR16V2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
JUNE 2006
REV. P1.0.0
FEATURES
GENERAL DESCRIPTION
• 2.25 to 3.6 Volt Operation
• 5 Volt Tolerant Inputs
1
The XR16V2750 (V2750) is a high performance dual
universal asynchronous receiver and transmitter
(UART) with 64 byte TX and RX FIFOs. The device
operates from 2.25 to 3.6 volts with 5 Volt tolerant
inputs and is pin-to-pin compatible to Exar’s
ST16C2550 and XR16L2750. The V2750 register set
is identical to the XR16L2750 and is compatible to the
ST16C2550 and the XR16C2850 enhanced features.
It supports the Exar’s enhanced features of
programmable FIFO trigger level and FIFO level
counters, automatic hardware (RTS/CTS) and
software flow control, automatic RS-485 half duplex
direction control output and a complete modem
interface. Onboard registers provide the user with
operational status and data error flags. An internal
loopback capability allows system diagnostics.
Independent programmable baud rate generators are
provided in each channel to select data rates up to 8
Mbps at 3.3 Volt and 8X sampling clock. The V2750
is available in 48-pin TQFP and 32-pin QFN
packages.
• Pin-to-pin compatible to Exar’s XR16L2750 and
TI’s TL16C752B in the 48-TQFP package
• Two independent UART channels
■ Register set compatible to XR16L2750
■ Data rate of up to 8 Mbps at at 3.3 V, and
6.25 Mbps at 2.5 V with 8X sampling rate
■ Fractional Baud Rate Generator
■ Transmit and Receive FIFOs of 64 bytes
■ Programmable TX and RX FIFO Trigger Levels
■ Transmit and Receive FIFO Level Counters
■ Automatic Hardware (RTS/CTS) Flow Control
■ Selectable Auto RTS Flow Control Hysteresis
■ Automatic Software (Xon/Xoff) Flow Control
■ Automatic RS-485 Half-duplex Direction
Control Output via RTS#
■ Wireless Infrared (IrDA 1.0) Encoder/Decoder
■ Automatic sleep mode
NOTE: 1 Covered by U.S. Patent #5,649,122
APPLICATIONS
■ Full modem interface
• Portable Appliances
• Telecommunication Network Routers
• Ethernet Network Routers
• Device Identification and Revision
• Crystal oscillator (up to 32MHz) or external clock
(upto 64MHz) input
• 48-TQFP and 32-QFN packages
• Cellular Data Devices
• Factory Automation and Process Controls
FIGURE 1. XR16V2750 BLOCK DIAGRAM
* 5 Volt Tolerant Inputs
2.25 to 3.6 Volt VCC
A2:A0
D7:D0
GND
IOR#
IOW#
UART Channel A
TXA, RXA, DTRA#,
64 Byte TX FIFO
CSA#
CSB#
UART
DSRA#, RTSA#,
DTSA#, CDA#, RIA#,
OP2A#
Regs
IR
ENDEC
TX & RX
8-bit Data
Bus
Interface
INTA
INTB
BRG
64 Byte RX FIFO
TXRDYA#
TXRDYB#
RXRDYA#
RXRDYB#
TXB, RXB, DTRB#,
DSRB#, RTSB#,
CTSB#, CDB#, RIB#,
OP2B#
UART Channel B
(same as Channel A)
Reset
XTAL1
XTAL2
Crystal Osc/Buffer
2750BLK
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (510) 668-7000 • FAX (510) 668-7017 • www.exar.com
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
FIGURE 2. PIN OUT ASSIGNMENT
RESET
DTRB#
DTRA#
RTSA#
OP2A#
RXRDYA#
INTA
1
2
3
4
5
6
36
35
34
33
32
31
30
29
28
D5
D6
D7
RXB
RXA
XR16V2750
48-pin TQFP
TXRDYB#
TXA
7
INTB
TXB
8
9
A0
OP2B#
CSA#
CSB#
10
11
27 A1
A2
26
25
NC
NC 12
1
2
3
4
5
6
7
8
24 RESET
23 RTSA#
D6
D7
INTA
21 INTB
22
RXB
RXA
TXA
TXB
XR16V2750
32-pin QFN
A0
A1
A2
20
19
18
CSA#
CSB#
17 NC
ORDERING INFORMATION
PART NUMBER
PACKAGE
OPERATING TEMPERATURE RANGE
DEVICE STATUS
XR16V2750IL32
XR16V2750IM
32-pin QFN
-40°C to +85°C
-40°C to +85°C
Active
Active
48-Lead TQFP
2
PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
PIN DESCRIPTIONS
Pin Description
32-QFN
48-TQFP
PIN #
NAME
PIN #
TYPE
DESCRIPTION
DATA BUS INTERFACE
A2
A1
A0
18
19
20
26
27
28
I
Address data lines [2:0]. These 3 address lines select one of the inter-
nal registers in UART channel A/B during a data bus transaction.
D7
D6
D5
D4
D3
D2
D1
D0
2
3
I/O
Data bus lines [7:0] (bidirectional).
1
2
32
31
30
29
28
27
1
48
47
46
45
44
IOR#
14
19
I
I
Input/Output Read Strobe (active low). The falling edge instigates an
internal read cycle and retrieves the data byte from an internal register
pointed to by the address lines [A2:A0]. The data byte is placed on the
data bus to allow the host processor to read it on the rising edge.
IOW#
12
15
Input/Output Write Strobe (active low). The falling edge instigates an
internal write cycle and the rising edge transfers the data byte on the
data bus to an internal register pointed by the address lines.
CSA#
CSB#
INTA
7
8
10
11
30
I
I
UART channel A select (active low) to enable UART channel A in the
device for data bus operation.
UART channel B select (active low) to enable UART channel B in the
device for data bus operation.
22
O
UART channel A Interrupt output. The output state is defined by the
user through the software setting of MCR[3]. INTA is set to the active
mode and OP2A# output LOW when MCR[3] is set to a logic 1. INTA is
set to the three state mode and OP2A# output HIGH when MCR[3] is
set to a logic 0 (default). See MCR[3].
INTB
21
29
O
UART channel B Interrupt output. The output state is defined by the
user through the software setting of MCR[3]. INTB is set to the active
mode and OP2B# output LOW when MCR[3] is set to a logic 1. INTB is
set to the three state mode and OP2B# output HIGH when MCR[3] is
set to a logic 0 (default). See MCR[3].
TXRDYA#
RXRDYA#
TXRDYB#
-
-
-
43
31
6
O
O
O
UART channel A Transmitter Ready (active low). The output provides
the TX FIFO/THR status for transmit channel A. See Table 2. If it is not
used, leave it unconnected.
UART channel A Receiver Ready (active low). This output provides the
RX FIFO/RHR status for receive channel A. See Table 2. If it is not
used, leave it unconnected.
UART channel B Transmitter Ready (active low). The output provides
the TX FIFO/THR status for transmit channel B. See Table 3. If it is not
used, leave it unconnected.
3
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
Pin Description
32-QFN
PIN #
48-TQFP
PIN #
NAME
TYPE
DESCRIPTION
RXRDYB#
-
18
O
UART channel B Receiver Ready (active low). This output provides the
RX FIFO/RHR status for receive channel B. See Table 2. If it is not
used, leave it unconnected.
MODEM OR SERIAL I/O INTERFACE
TXA
5
7
O
UART channel A Transmit Data or infrared encoder data. Standard
transmit and receive interface is enabled when MCR[6] = 0. In this
mode, the TX signal will be HIGH during reset or idle (no data). Infrared
IrDA transmit and receive interface is enabled when MCR[6] = 1. In the
Infrared mode, the inactive state (no data) for the Infrared encoder/
decoder interface is LOW. If it is not used, leave it unconnected.
RXA
6
5
I
UART channel A Receive Data or infrared receive data. Normal receive
data input must idle HIGH. The infrared receiver pulses typically idles at
LOW but can be inverted by software control prior going in to the
decoder, see MCR[6] and FCTR[2]. If this pin is not used, tie it to VCC
or pull it high via a 100k ohm resistor.
RTSA#
CTSA#
23
25
33
38
O
I
UART channel A Request-to-Send (active low) or general purpose out-
put. This output must be asserted prior to using auto RTS flow control,
see EFR[6], MCR[1], FCTR[1:0], EMSR[5:4] and IER[6]. For auto
RS485 half-duplex direction control, see FCTR[3] and EMSR[3].
UART channel A Clear-to-Send (active low) or general purpose input.
It can be used for auto CTS flow control, see EFR[7], and IER[7]. This
input should be connected to VCC when not used.
DTRA#
DSRA#
-
-
34
39
O
I
UART channel A Data-Terminal-Ready (active low) or general purpose
output. If it is not used, leave it unconnected.
UART channel A Data-Set-Ready (active low) or general purpose input.
This input should be connected to VCC when not used. This input has
no effect on the UART.
CDA#
RIA#
-
-
-
40
41
32
I
I
UART channel A Carrier-Detect (active low) or general purpose input.
This input should be connected to VCC when not used. This input has
no effect on the UART.
UART channel A Ring-Indicator (active low) or general purpose input.
This input should be connected to VCC when not used. This input has
no effect on the UART.
OP2A#
O
Output Port 2 Channel A - The output state is defined by the user and
through the software setting of MCR[3]. INTA is set to the active mode
and OP2A# output LOW when MCR[3] is set to a logic 1. INTA is set to
the three state mode and OP2A# output HIGH when MCR[3] is set to a
logic 0. See MCR[3]. If INTA is used, this output should not be used as
a general output else it will disturb the INTA output functionality.
TXB
6
8
O
UART channel B Transmit Data or infrared encoder data. Standard
transmit and receive interface is enabled when MCR[6] = 0. In this
mode, the TX signal will be HIGH during reset or idle (no data). Infrared
IrDA transmit and receive interface is enabled when MCR[6] = 1. In the
Infrared mode, the inactive state (no data) for the Infrared encoder/
decoder interface is LOW. If it is not used, leave it unconnected.
4
PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
Pin Description
32-QFN
48-TQFP
PIN #
NAME
TYPE
DESCRIPTION
PIN #
RXB
3
4
I
UART channel B Receive Data or infrared receive data. Normal receive
data input must idle HIGH. The infrared receiver pulses typically idles at
logic 0 but can be inverted by software control prior going in to the
decoder, see MCR[6] and FCTR[2]. If this pin is not used, tie it to VCC
or pull it high via a 100k ohm resistor.
RTSB#
CTSB#
15
16
22
23
O
I
UART channel B Request-to-Send (active low) or general purpose out-
put. This port must be asserted prior to using auto RTS flow control,
see EFR[6], MCR[1], FCTR[1:0], EMSR[5:4] and IER[6]. For auto
RS485 half-duplex direction control, see FCTR[3] and EMSR[3].
UART channel B Clear-to-Send (active low) or general purpose input.
It can be used for auto CTS flow control, see EFR[7], and IER[7]. This
input should be connected to VCC when not used.
DTRB#
DSRB#
-
-
35
20
O
I
UART channel B Data-Terminal-Ready (active low) or general purpose
output. If it is not used, leave it unconnected.
UART channel B Data-Set-Ready (active low) or general purpose input.
This input should be connected to VCC when not used. This input has
no effect on the UART.
CDB#
RIB#
-
-
-
16
21
9
I
I
UART channel B Carrier-Detect (active low) or general purpose input.
This input should be connected to VCC when not used. This input has
no effect on the UART.
UART channel B Ring-Indicator (active low) or general purpose input.
This input should be connected to VCC when not used. This input has
no effect on the UART.
OP2B#
O
Output Port 2 Channel B - The output state is defined by the user and
through the software setting of MCR[3]. INTB is set to the active mode
and OP2B# output LOW when MCR[3] is set to a logic 1. INTB is set to
the three state mode and OP2B# output HIGH when MCR[3] is set to a
logic 0. See MCR[3]. If INTB is used, this output should not be used as
a general output else it will disturb the INTB output functionality.
ANCILLARY SIGNALS
XTAL1
XTAL2
RESET
10
11
24
13
14
36
I
O
I
Crystal or external clock input. Caution: this input is not 5V tolerant.
Crystal or buffered clock output.
Reset (active high) - A longer than 40 ns HIGH pulse on this pin will
reset the internal registers and all outputs. The UART transmitter output
will be held HIGH, the receiver input will be ignored and outputs are
reset during reset period (see Table 16).
VCC
26
42
17
Pwr
Pwr
2.25V to 3.6V power supply. All input pins, except XTAL1, are 5V toler-
ant.
GND
N.C.
13
Power supply common, ground.
No Connection.
9, 17
12, 24, 25,
37
Pin type: I=Input, O=Output, I/O= Input/output, OD=Output Open Drain.
5
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
1.0 PRODUCT DESCRIPTION
The XR16V2750 (V2750) integrates the functions of 2 enhanced 16C550 Universal Asynchronous Receiver
and Transmitter (UART). Each UART is independently controlled having its own set of device configuration
registers. The configuration registers set is 16550 UART compatible for control, status and data transfer.
Additionally, each UART channel has 64-bytes of transmit and receive FIFOs, automatic RTS/CTS 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 fractional baud rate generator with a prescaler of divide by 1 or 4, and data rate
up to 8 Mbps with 8X sampling clock rate or 4 Mbps in the 16X rate. The XR16V2750 is a 2.25 to 3.6V device
with 5 volt tolerant inputs. The V2750 is fabricated with an advanced CMOS process.
Enhanced Features
The V2750 DUART provides a solution that supports 64 bytes of transmit and receive FIFO memory, instead of
16 bytes in the ST16C2550 or one byte in the ST16C2450. The V2750 is designed to work with low supply
voltage and high performance data communication systems, that require fast data processing time. Increased
performance is realized in the V2750 by the larger transmit and receive FIFOs, FIFO trigger level control, FIFO
level counters and automatic flow control mechanism. This allows the external processor to handle more
networking tasks within a given time. For example, the ST16C2550 with a 16 byte FIFO, unloads 16 bytes of
receive data in 1.53 ms (This example uses a character length of 11 bits, including start/stop bits at 115.2
Kbps). This means the external CPU will have to service the receive FIFO at 1.53 ms intervals. However with
the 64 byte FIFO in the V2750, the data buffer will not require unloading/loading for 6.1 ms. This increases the
service interval giving the external CPU additional time for other applications and reducing the overall UART
interrupt servicing time. In addition, the programmable FIFO level trigger interrupt and automatic hardware/
software flow control is uniquely provided for maximum data throughput performance especially when
operating in a multi-channel system. The combination of the above greatly reduces the CPU’s bandwidth
requirement, increases performance, and reduces power consumption.
The V2750 supports a half-duplex output direction control signaling pin, RTS# A/B, to enable and disable the
external RS-485 transceiver operation. It automatically switches the logic state of the output pin to the receive
state after the last stop-bit of the last character has been shifted out of the transmitter. After receiving, the logic
state of the output pin switches back to the transmit state when a data byte is loaded in the transmitter. The
auto RS-485 direction control pin is not activated after reset. To activate the direction control function, user has
to set FCTR Bit-3 to “1”. This pin is normally high for receive state, low for transmit state.
Data Rate
The V2750 is capable of operation up to 4 Mbps at 3.3V with 16X internal sampling clock rate and 8 Mbps at
3.3V with 8X sampling clock rate. The device can operate with an external 32 MHz crystal at 2.5V on pins
XTAL1 and XTAL2, or external clock source of up to 64 MHz on XTAL1 pin. With a typical crystal of 14.7456
MHz and through a software option, the user can set the prescaler bit for data rates of up to 1.84 Mbps.
The rich feature set of the V2750 is available through the internal registers. Automatic hardware/software flow
control, selectable transmit and receive FIFO trigger levels, selectable TX and RX baud rates, infrared
encoder/decoder interface, modem interface controls, and a sleep mode are all standard features.
Following a power on reset or an external reset, the V2750 is software compatible with previous generation of
UARTs, 16C450, 16C550 and 16C650A as well as the 16C850.
6
PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
2.0 FUNCTIONAL DESCRIPTIONS
2.1
CPU Interface
The CPU interface is 8 data bits wide with 3 address lines and control signals to execute data bus read and
write transactions. The V2750 data interface supports the Intel compatible types of CPUs and it is compatible
to the industry standard 16C550 UART. No clock (oscillator nor external clock) is required to operate a data
bus transaction. Each bus cycle is asynchronous using CS#, IOR# and IOW# signals. Both UART channels
share the same data bus for host operations. The data bus interconnections are shown in Figure 3.
FIGURE 3. XR16V2750 DATA BUS INTERCONNECTIONS
VCC
VCC
D0
D1
D2
D3
D4
D5
D6
D7
D0
D1
D2
D3
D4
D5
D6
D7
TXA
RXA
DTRA#
RTSA#
CTSA#
DSRA#
UART
Channel A
Serial Interface of
RS-232, RS-485
A0
A1
A2
A0
A1
A2
CDA#
RIA#
OP2A#
IOR#
IOW#
IOR#
IOW#
TXB
RXB
CSA#
CSB#
UART_CSA#
UART_CSB#
DTRB#
RTSB#
CTSB#
DSRB#
CDB#
UART_INTA
UART_INTB
INTA
INTB
UART
Channel B
Serial Interface of
RS-232, RS-485
TXRDYA#
RXRDYA#
TXRDYB#
RXRDYB#
TXRDYA#
RXRDYA#
TXRDYB#
RXRDYB#
RIB#
OP2B#
UART_RESET
RESET
GND
2750int
2.2
5-Volt Tolerant Inputs
The V2750 can accept up to 5V inputs even when operating at 3.3V or 2.5V. But note that if the V2750 is
operating at 2.5V, its V may not be high enough to meet the requirements of the V of a CPU or a serial
OH
IH
transceiver that is operating at 5V. Caution: XTAL1 is not 5 volt tolerant.
2.3 Device Reset
The RESET input resets the internal registers and the serial interface outputs in both channels to their default
state (see Table 16). An active high pulse of longer than 40 ns duration will be required to activate the reset
function in the device.
2.4
Device Identification and Revision
The XR16V2750 provides a Device Identification code and a Device Revision code to distinguish the part from
other devices and revisions. To read the identification code from the part, it is required to set the baud rate
generator registers DLL and DLM both to 0x00 (DLD = 0xXX). Now reading the content of the DLM will provide
0x0A for the XR16V2750 and reading the content of DLL will provide the revision of the part; for example, a
reading of 0x01 means revision A.
2.5
Channel A and B 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 LOW signal on the chip select pins, CSA# or CSB#,
allows the user to select UART channel A or B to configure, send transmit data and/or unload receive data to/
from the UART. Selecting both UARTs can be useful during power up initialization to write to the same internal
7
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
registers, but do not attempt to read from both uarts simultaneously. Individual channel select functions are
shown in Table 1.
TABLE 1: CHANNEL A AND B SELECT
CSA#
CSB#
FUNCTION
1
0
1
0
1
1
0
0
UART de-selected
Channel A selected
Channel B selected
Channel A and B selected
2.6
Channel A and B Internal Registers
Each UART channel in the V2750 has a set of enhanced registers for control, monitoring and data loading and
unloading. The configuration register set is compatible to those already available in the standard single
16C550 and dual ST16C2550. These registers function as data holding registers (THR/RHR), interrupt status
and control registers (ISR/IER), a FIFO control register (FCR), receive line status and control registers (LSR/
LCR), modem status and control registers (MSR/MCR), programmable data rate (clock) divisor registers (DLL/
DLM/DLD), and a user accessible Scratchpad Register (SPR).
Beyond the general 16C2550 features and capabilities, the V2750 offers enhanced feature registers (EMSR,
FLVL, EFR, Xon/Xoff 1, Xon/Xoff 2, FCTR, TRG, FC) that provide automatic RTS and CTS hardware flow
control, Xon/Xoff software flow control, automatic RS-485 half-duplex direction output enable/disable, FIFO
trigger level control, and FIFO level counters. All the register functions are discussed in full detail later in
“Section 3.0, UART Internal Registers” on page 21.
2.7
DMA Mode
The device does not support direct memory access. The DMA Mode (a legacy term) in this document doesn’t
mean “direct memory access” but refers to data block transfer operation. The DMA mode affects the state of
the RXRDY# A/B and TXRDY# A/B output pins. The transmit and receive FIFO trigger levels provide additional
flexibility to the user for block mode operation. The LSR bits 5-6 provide an indication when the transmitter is
empty or has an empty location(s) for more data. The user can optionally operate the transmit and receive
FIFO in the DMA mode (FCR bit-3=1). When the transmit and receive FIFO are enabled and the DMA mode is
disabled (FCR bit-3 = 0), the V2750 is placed in single-character mode for data transmit or receive operation.
When DMA mode is enabled (FCR bit-3 = 1), the user takes advantage of block mode operation by loading or
unloading the FIFO in a block sequence determined by the programmed trigger level. In this mode, the V2750
sets the TXRDY# pin when the transmit FIFO becomes full, and sets the RXRDY# pin when the receive FIFO
becomes empty. The following table shows their behavior. Also see Figures 17 through 22.
TABLE 2: TXRDY# AND RXRDY# OUTPUTS IN FIFO AND DMA MODE
FCR BIT-0=0
PINS
FCR BIT-0=1 (FIFO ENABLED)
(FIFO DISABLED)
FCR Bit-3 = 0
FCR Bit-3 = 1
(DMA Mode Disabled)
(DMA Mode Enabled)
RXRDY# A/B LOW = 1 byte.
HIGH = no data.
LOW = at least 1 byte in FIFO.
HIGH = FIFO empty.
HIGH to LOW transition when FIFO reaches the
trigger level, or time-out occurs.
LOW to HIGH transition when FIFO empties.
TXRDY# A/B LOW = THR empty. LOW = FIFO empty.
LOW = FIFO has at least 1 empty location.
HIGH = byte in THR. HIGH = at least 1 byte in FIFO. HIGH = FIFO is full.
8
PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
2.8
INTA and INTB Outputs
The INTA and INTB interrupt output changes according to the operating mode and enhanced features setup.
Table 3 and 4 summarize the operating behavior for the transmitter and receiver. Also see Figures 17
through 22.
TABLE 3: INTA AND INTB PINS OPERATION FOR TRANSMITTER
Auto RS485
Mode
FCR BIT-0 = 0
FCR BIT-0 = 1 (FIFO ENABLED)
LOW = FIFO above trigger level
(FIFO DISABLED)
INTA/B Pin
INTA/B Pin
NO
LOW = a byte in THR
HIGH = THR empty
HIGH = FIFO below trigger level or FIFO empty
YES
LOW = a byte in THR
LOW = FIFO above trigger level
HIGH = transmitter empty
HIGH = FIFO below trigger level or transmitter empty
TABLE 4: INTA AND INTB PIN OPERATION FOR RECEIVER
FCR BIT-0 = 0
FCR BIT-0 = 1
(FIFO DISABLED)
(FIFO ENABLED)
INTA/B Pin
LOW = no data
HIGH = 1 byte
LOW = FIFO below trigger level
HIGH = FIFO above trigger level
2.9
Crystal Oscillator or External Clock Input
The V2750 includes an on-chip oscillator (XTAL1 and XTAL2) to produce a clock for both UART sections in the
device. The CPU data bus does not require this clock for bus operation. The crystal oscillator provides a
system clock to the Baud Rate Generators (BRG) section found in each of the UART. XTAL1 is the input to the
oscillator or external clock buffer input with XTAL2 pin being the output. Please note that the input XTAL1 is not
5V tolerant and so the maximum at the pin should be VCC. For programming details, see ““Section 2.10,
Programmable Baud Rate Generator with Fractional Divisor” on page 10.”
FIGURE 4. TYPICAL OSCILLATOR CONNECTIONS
XTAL1
XTAL2
R1
0-120 Ω
(Optional)
R2
500 ΚΩ − 1 ΜΩ
1.8432 MHz
to
Y1
24 MHz
C1
C2
22-47 pF
22-47 pF
9
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
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 100 ppm frequency
tolerance) connected externally between the XTAL1 and XTAL2 pins (see Figure 4). The programmable Baud
Rate Generator is capable of operating with a crystal oscillator frequency of up to 32 MHz at 2.5V. However,
with an external clock input on XTAL1 pin, it can extend its operation up to 64 MHz (8 Mbps serial data rate) at
3.3V with an 8X sampling rate. For further reading on the oscillator circuit please see the Application Note
DAN108 on the EXAR web site at http://www.exar.com.
2.10 Programmable Baud Rate Generator with Fractional Divisor
Each UART has its own Baud Rate Generator (BRG) with a prescaler for the transmitter and receiver. The
prescaler is controlled by a software bit in the MCR register. The MCR register bit-7 sets the prescaler to divide
the input crystal or external clock by 1 or 4. The output of the prescaler clocks to the BRG. The BRG further
divides this clock by a programmable divisor between 1 and (216 - 0.0625) in increments of 0.0625 (1/16) to
obtain a 16X 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, DLM and DLD registers) defaults to the value
of ’1’ (DLL = 0x01, DLM = 0x00 and DLD = 0x00) upon reset. Therefore, the BRG must be programmed during
initialization to the operating data rate. The DLL and DLM registers provide the integer part of the divisor and
the DLD register provides the fractional part of the dvisior. Only the four lower bits of the DLD are implemented
and they are used to select a value from 0 (for setting 0000) to 0.9375 or 15/16 (for setting 1111). Programming
the Baud Rate Generator Registers DLL, DLM and DLD provides the capability for selecting the operating data
rate. Table 5 shows the standard data rates available with a 24MHz crystal or external clock at 16X clock rate.
If the pre-scaler is used (MCR bit-7 = 1), the output data rate will be 4 times less than that shown in Table 5. At
8X sampling rate, these data rates would double. Also, when using 8X sampling mode, please note that the bit-
time will have a jitter (+/- 1/16) whenever the DLD is non-zero and is an odd number. When using a non-
standard data rate crystal or external clock, the divisor value can be calculated with the following equation(s):
Required Divisor (decimal) = (XTAL1 clock frequency / prescaler) / (serial data rate x 16), with 16X mode EMSR[7] = 1
Required Divisor (decimal) = (XTAL1 clock frequency / prescaler / (serial data rate x 8), with 8X mode EMSR[7] = 0
The closest divisor that is obtainable in the V2750 can be calculated using the following formula:
ROUND( (Required Divisor - TRUNC(Required Divisor) )*16)/16 + TRUNC(Required Divisor), where
DLM = TRUNC(Required Divisor) >> 8
DLL = TRUNC(Required Divisor) & 0xFF
DLD = ROUND( (Required Divisor-TRUNC(Required Divisor) )*16)
In the formulas above, please note that:
TRUNC (N) = Integer Part of N. For example, TRUNC (5.6) = 5.
ROUND (N) = N rounded towards the closest integer. For example, ROUND (7.3) = 7 and ROUND (9.9) = 10.
A >> B indicates right shifting the value ’A’ by ’B’ number of bits. For example, 0x78A3 >> 8 = 0x0078.
10
PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
FIGURE 5. BAUD RATE GENERATOR
To Other
Channel
DLL, DLM and DLD
Registers
MCR Bit-7=0
(default)
Prescaler
Divide by 1
16X or 8X
Sampling
Rate Clock
to Transmitter
and Receiver
Crystal
Osc/
Buffer
XTAL1
XTAL2
Fractional Baud
Rate Generator
Logic
Prescaler
Divide by 4
MCR Bit-7=1
TABLE 5: TYPICAL DATA RATES WITH A 24 MHZ CRYSTAL OR EXTERNAL CLOCK AT 16X SAMPLING
Required
Output Data
Rate
DIVISOR FOR
16x Clock
(Decimal)
DIVISOR
OBTAINABLE IN
V2750
DLM PROGRAM DLL PROGRAM DLD PROGRAM DATA ERROR
VALUE (HEX)
VALUE (HEX)
VALUE (HEX)
RATE (%)
400
2400
3750
625
3750
625
E
2
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
A6
71
38
9C
96
4E
3C
34
27
1E
1A
14
F
0
0
8
4
0
2
0
1
1
0
1
0
0
0
C
8
B
8
0
0
C
4
0
0
A
8
0
0
4800
312.5
156.25
150
312 8/16
156 4/16
150
0
9600
0
10000
19200
25000
28800
38400
50000
57600
75000
100000
115200
153600
200000
225000
230400
250000
300000
400000
460800
500000
750000
921600
1000000
0
78.125
60
78 2/16
60
0
0
52.0833
39.0625
30
52 1/16
39 1/16
30
0.04
0
0
26.0417
20
26 1/16
20
0.08
0
15
15
0
13.0208
9.7656
7.5
13
D
0.16
0.16
0
9 12/16
7 8/16
6 11/16
6 8/16
6
9
7
6.6667
6.5104
6
6
0.31
0.16
0
6
6
5
5
5
0
3.75
3 12/16
3 4/16
3
3
0
3.2552
3
3
0.16
0
3
2
2
2
0
1.6276
1.5
1 10/16
1 8/16
1
0.16
0
1
11
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
2.11 Transmitter
The transmitter section comprises of an 8-bit Transmit Shift Register (TSR) and 64 bytes of FIFO which
includes a byte-wide Transmit Holding Register (THR). TSR shifts out every data bit with the 16X/8X internal
clock. A bit time is 16 (8) 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).
2.11.1 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.
2.11.2 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.
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
(EMSR Bit-7)
M
S
B
L
S
B
Transmit Shift Register (TSR)
TXNOFIFO1
2.11.3 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.
12
PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
FIGURE 7. TRANSMITTER OPERATION IN FIFO AND FLOW CONTROL MODE
Transmit
FIFO
Transmit
Data Byte
THR Interrupt (ISR bit-1) falls
below the programmed Trigger
Level and then when becomes
empty. FIFO is Enabled by FCR
bit-0=1
Auto CTS Flow Control (CTS# pin)
Flow Control Characters
(Xoff1/2 and Xon1/2 Reg.
Auto Software Flow Control
16X or 8X Clock
(EMSR bit-7)
Transmit Data Shift Register
(TSR)
TXFIFO1
2.12 Receiver
The receiver section contains an 8-bit Receive Shift Register (RSR) and 64 bytes of FIFO which includes a
byte-wide Receive Holding Register (RHR). The RSR uses the 16X/8X clock (EMSR bit-7) for timing. It verifies
and validates every bit on the incoming character in the middle of each data bit. On the falling edge of a start or
false start bit, an internal receiver counter starts counting at the 16X/8X clock rate. After 8 clocks (or 4 if 8X) the
start bit period should be at the center of the start bit. At this time the start bit is sampled and if it is still a logic
0 it is validated. Evaluating the start bit in this manner prevents the receiver from assembling a false character.
The rest of the data bits and stop bits are sampled and validated in this same manner to prevent false framing.
If there were any error(s), they are reported in the LSR register bits 2-4. Upon unloading the receive data byte
from RHR, the receive FIFO pointer is bumped and the error tags are immediately updated to reflect the status
of the data byte in RHR register. RHR can generate a receive data ready interrupt upon receiving a character
or delay until it reaches the FIFO trigger level. Furthermore, data delivery to the host is guaranteed by a
receive data ready time-out interrupt when data is not received for 4 word lengths as defined by LCR[1:0] plus
12 bits time. This is equivalent to 3.7-4.6 character times. The RHR interrupt is enabled by IER bit-0.
2.12.1 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.
13
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
FIGURE 8. RECEIVER OPERATION IN NON-FIFO MODE
16X or 8X Clock
(EMSR bit-7)
Receive Data Shift
Data Bit
Register (RSR)
Validation
Receive Data Characters
Error
Receive
Data Byte
and Errors
Receive Data
Holding Register
(RHR)
Tags in
LSR bits
4:2
RHR Interrupt (ISR bit-2)
RXFIFO1
FIGURE 9. RECEIVER OPERATION IN FIFO AND AUTO RTS FLOW CONTROL MODE
16X or 8X Clock
(EMSR bit-7)
Receive Data Shift
Register (RSR)
Data Bit
Validation
Receive Data Characters
Example
- RX FIFO trigger level selected at 16
:
bytes
(See Note Below)
RTS# re-asserts when data falls below the flow
control trigger level to restart remote transmitter.
Enable by EFR bit-6=1, MCR bit-1.
64 bytes by 11-bit
wide
Data falls to
8
FIFO
Receive
Data FIFO
FIFO
Trigger=16
RHR Interrupt (ISR bit-2) programmed for
desired FIFO trigger level.
FIFO is Enabled by FCR bit-0=1
Data fills to
24
RTS# de-asserts when data fills above the flow
control trigger level to suspend remote transmitter.
Enable by EFR bit-6=1, MCR bit-1.
Receive
Data
Receive Data
Byte and Errors
RXFIFO1
NOTE: Table-B selected as Trigger Table for Figure 9 (Table 10).
14
PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
2.13 Auto RTS (Hardware) Flow Control
Automatic RTS hardware flow control is used to prevent data overrun to the local receiver FIFO. The RTS#
output is used to request remote unit to suspend/resume data transmission. The auto RTS flow control
features is enabled to fit specific application requirement (see Figure 10):
• Enable auto RTS flow control using EFR bit-6.
• The auto RTS function must be started by asserting RTS# output pin (MCR bit-1 to logic 1 after it is enabled).
If using the Auto RTS interrupt:
• Enable RTS interrupt through IER bit-6 (after setting EFR bit-4). The UART issues an interrupt when the
RTS# pin makes a transition from low to high: ISR bit-5 will be set to logic 1.
2.14
Auto RTS Hysteresis
The V2750 has a new feature that provides flow control trigger hysteresis while maintaining compatibility with
the XR16C850, ST16C650A and ST16C550 family of UARTs. With the Auto RTS function enabled, an interrupt
is generated when the receive FIFO reaches the programmed RX trigger level. The RTS# pin will not be forced
HIGH (RTS off) until the receive FIFO reaches the upper limit of the hysteresis level. The RTS# pin will return
LOW after the RX FIFO is unloaded to the lower limit of the hysteresis level. Under the above described
conditions, the V2750 will continue to accept data until the receive FIFO gets full. The Auto RTS function is
initiated when the RTS# output pin is asserted LOW (RTS On). Table 13 shows the complete details for the
Auto RTS# Hysteresis levels. Please note that this table is for programmable trigger levels only (Table D). The
hysteresis values for Tables A-C are the next higher and next lower trigger levels in the corresponding table.
2.15
Auto CTS Flow Control
Automatic CTS flow control is used to prevent data overrun to the remote receiver FIFO. The CTS# input is
monitored to suspend/restart the local transmitter. The auto CTS flow control feature is selected to fit specific
application requirement (see Figure 10):
• Enable auto CTS flow control using EFR bit-7.
If using the Auto CTS interrupt:
• Enable CTS interrupt through IER bit-7 (after setting EFR bit-4). The UART issues an interrupt when the
CTS# pin is de-asserted (HIGH): ISR bit-5 will be set to 1, and UART will suspend transmission as soon as
the stop bit of the character in process is shifted out. Transmission is resumed after the CTS# input is re-
asserted (LOW), indicating more data may be sent.
15
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
FIGURE 10. AUTO RTS AND CTS FLOW CONTROL OPERATION
Local UART
UARTA
Remote UART
UARTB
RXA
TXB
Receiver FIFO
Trigger Reached
Transmitter
RTSA#
TXA
CTSB#
RXB
Auto RTS
Trigger Level
Auto CTS
Monitor
Receiver FIFO
Trigger Reached
Transmitter
CTSA#
RTSB#
Auto CTS
Monitor
Auto RTS
Trigger Level
Assert RTS# to Begin
Transmission
1
10
11
ON
ON
ON
RTSA#
OFF
OFF
7
2
ON
3
CTSB#
TXB
8
Restart
9
Data Starts
6
Suspend
4
RXA FIFO
Receive
Data
RX FIFO
12
RTS High
Threshold
RTS Low
Threshold
5
RX FIFO
Trigger Level
Trigger Level
INTA
(RXA FIFO
Interrupt)
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 con-
tinues 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 trans-
mit 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.
16
PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
2.16 Auto Xon/Xoff (Software) Flow Control
When software flow control is enabled (See Table 15), the V2750 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 V2750 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 V2750 will monitor the
receive data stream for a match to the Xon-1,2 character. If a match is found, the V2750 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 0x00. Following reset the user can
write any Xon/Xoff value desired for software flow control. Different conditions can be set to detect Xon/Xoff
characters (See Table 15) and suspend/resume transmissions. When double 8-bit Xon/Xoff characters are
selected, the V2750 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 V2750 automatically
sends an Xoff message via the serial TX output to the remote modem. The V2750 sends the Xoff-1,2
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). To clear this condition, the V2750 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 Hysteresis
value in Table 14. Table 6 below explains this when Trigger Table-B (See Table 10) is selected.
TABLE 6: AUTO XON/XOFF (SOFTWARE) FLOW CONTROL
XOFF CHARACTER(S) SENT
(CHARACTERS IN RX FIFO)
XON CHARACTER(S) SENT
(CHARACTERS IN RX FIFO)
RX TRIGGER LEVEL
INT PIN ACTIVATION
8
8
8*
0
8
16
24
28
16
24
28
16*
24*
28*
16
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.
2.17
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 V2750 compares each incoming receive character with Xoff-2 data. If a match exists, the received data will
be transferred to FIFO and ISR bit-4 will be set to indicate detection of special character. Although the Internal
Register Table shows Xon, Xoff Registers with eight bits of character information, the actual number of bits is
dependent on the programmed word length. Line Control Register (LCR) bits 0-1 defines the number of
character bits, i.e., either 5 bits, 6 bits, 7 bits, or 8 bits. The word length selected by LCR bits 0-1 also
determines the number of bits that will be used for the special character comparison.
2.18
Auto RS485 Half-duplex Control
The auto RS485 half-duplex direction control changes the behavior of the transmitter when enabled by FCTR
bit-3. By default, it de-asserts RTS# (HIGH) output 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. 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 re-asserts RTS# (LOW) output prior to sending the data. The RS485 half-duplex
direction control output can be inverted by enabling EMSR bit-3.
17
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
2.19 Infrared Mode
The V2750 UART includes the infrared encoder and decoder compatible to the IrDA (Infrared Data
Association) version 1.0. The IrDA 1.0 standard that stipulates the infrared encoder sends out a 3/16 of a bit
wide HIGH-pulse for each “0” bit in the transmit data stream. This signal encoding reduces the on-time of the
infrared LED, hence reduces the power consumption. See Figure 11 below.
The infrared encoder and decoder are enabled by setting MCR register bit-6 to a ‘1’. When the infrared feature
is enabled, the transmit data output, TX, idles at logic zero level. Likewise, the RX input assumes an idle level
of logic zero from a reset and power up, see Figure 11.
Typically, the wireless infrared decoder receives the input pulse from the infrared sensing diode on the RX pin.
Each time it senses a light pulse, it returns a logic 1 to the data bit stream. However, this is not true with some
infrared modules on the market which indicate a logic 0 by a light pulse. So the V2750 has a provision to invert
the input polarity to accommodate this. In this case user can enable FCTR bit-2 to invert the input signal.
FIGURE 11. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING
Character
Data Bits
1
1
1
1
1
0
0
0
0
0
TX Data
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
1
1 1
1
0
0
0
0
0
RX Data
Data Bits
Character
IRdecoder-
18
PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
2.20
Sleep Mode with Auto Wake-Up
The V2750 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 V2750 to enter sleep mode:
■ no interrupts pending for both channels of the V2750 (ISR bit-0 = 1)
■ sleep mode of both channels are enabled (IER bit-4 = 1)
■ modem inputs are not toggling (MSR bits 0-3 = 0)
■ RX input pins are idling HIGH
The V2750 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 V2750 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 V2750 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 V2750 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 from channel A or B. The V2750 will stay in the sleep mode of operation until it is
disabled by setting IER bit-4 to a logic 0.
If the address lines, data bus lines, IOW#, IOR#, CSA#, CSB#, and modem input lines remain steady when the
V2750 is in sleep mode, the maximum current will be in the microamp range as specified in the DC Electrical
Characteristics on page 40. If the input lines are floating or are toggling while the V2750 is in sleep mode, the
current can be up to 100 times more. If any of those signals are toggling or floating, then an external buffer
would be required to keep the address, data and control lines steady to achieve the low current. As an
alternative, please refer to the XR16L2751 which is pin-to-pin and software compatible with the V2750 but with
(some additional pins and) the PowerSave feature that eliminates any unnecessary external buffer.
A word of caution: owing to the starting up delay of the crystal oscillator after waking up from sleep mode, the
first few receive characters may be lost. The number of characters lost during the restart also depends on your
operating data rate. More characters are lost when operating at higher data rate. Also, it is important to keep
RX A/B inputs idling HIGH or “marking” condition during sleep mode to avoid receiving a “break” condition
upon the restart. This may occur when the external interface transceivers (RS-232, RS-485 or another type)
are also put to sleep mode and cannot maintain the “marking” condition. To avoid this, the designer can use a
47k-100k ohm pull-up resistor on the RXA and RXB pins.
19
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
2.21 Internal Loopback
The V2750 UART provides an internal loopback capability for system diagnostic purposes. The internal
loopback mode is enabled by setting MCR register bit-4 to logic 1. All regular UART functions operate normally.
Figure 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 while the CTS#, DSR# CD# and RI# inputs are ignored.
Caution: the RX input pin must be held HIGH during loopback test else upon exiting the loopback test the
UART may detect and report a false “break” signal. Also, Auto RTS/CTS flow control is not supported during
internal loopback.
FIGURE 12. INTERNAL LOOP BACK IN CHANNEL A AND B
VCC
TXA/TXB
Transmit Shift Register
(THR/FIFO)
MCR bit-4=1
Receive Shift Register
(RHR/FIFO)
RXA/RXB
VCC
RTSA#/RTSB#
RTS#
CTS#
CTSA#/CTSB#
VCC
DTRA#/DTRB#
DTR#
DSR#
DSRA#/DSRB#
OP1#
RI#
RIA#/RIB#
VCC
OP2A#/OP2B#
OP2#
CD#
CDA#/CDB#
20
PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
3.0 UART INTERNAL REGISTERS
Each of the UART channel in the V2750 has its own set of configuration registers selected by address lines A0,
A1 and A2 with CSA# or CSB# selecting the channel. The complete register set is shown on Table 7 and
Table 8.
TABLE 7: UART CHANNEL A AND B UART INTERNAL REGISTERS
ADDRESSES
REGISTER
READ/WRITE
COMMENTS
A2 A1 A0
16C550 COMPATIBLE REGISTERS
0
0 0
RHR - Receive Holding Register
Read-only
Write-only
LCR[7] = 0
THR - Transmit Holding Register
0
0
0
0 0
0 1
1 0
DLL - Divisor LSB
Read/Write
Read/Write
Read/Write
LCR[7] = 1, LCR ≠ 0xBF
DLM - Divisor MSB
DLD - Divisor Fractional
LCR[7] = 1, LCR ≠ 0xBF,
EFR[4] = 1
0
0
0
0
0 0
0 1
0 1
1 0
DREV - Device Revision Code
DVID - Device Identification Code
IER - Interrupt Enable Register
Read-only
Read-only
Read/Write
DLL, DLM = 0x00,
LCR[7] = 1, LCR ≠ 0xBF
LCR[7] = 0
ISR - Interrupt Status Register
FCR - FIFO Control Register
Read-only
Write-only
LCR ≠ 0xBF
0
1
1
1
1
1
1
1 1
0 0
0 1
1 0
1 1
1 1
1 1
LCR - Line Control Register
Read/Write
Read/Write
Read-only
Read-only
Read/Write
Read-only
Write-only
MCR - Modem Control Register
LSR - Line Status Register
LCR ≠ 0xBF
MSR - Modem Status Register
SPR - Scratch Pad Register
LCR ≠ 0xBF, FCTR[6] = 0
LCR ≠ 0xBF, FCTR[6] = 1
FLVL - RX/TX FIFO Level Counter Register
EMSR - Enhanced Mode Select Register
ENHANCED REGISTERS
0
0 0
TRG - RX/TX FIFO Trigger Level Register
FC - RX/TX FIFO Level Counter Register
Write-only
Read-only
0
0
1
1
1
1
0 1
1 0
0 0
0 1
1 0
1 1
FCTR - Feature Control Register
EFR - Enhanced Function Register
Xon-1 - Xon Character 1
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
LCR = 0xBF
Xon-2 - Xon Character 2
Xoff-1 - Xoff Character 1
Xoff-2 - Xoff Character 2
21
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
.
TABLE 8: INTERNAL REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED WHEN EFR BIT-4=1
ADDRESS
A2-A0
REG
READ/
WRITE
BIT-7
BIT-6
BIT-5
BIT-4
BIT-3
BIT-2
BIT-1
BIT-0
COMMENT
NAME
16C550 Compatible Registers
0 0 0
0 0 0
0 0 1
RHR
THR
IER
RD
WR
Bit-7
Bit-7
0/
Bit-6
Bit-6
0/
Bit-5
Bit-5
0/
Bit-4
Bit-4
0/
Bit-3
Bit-3
Bit-2
Bit-2
Bit-1
Bit-1
Bit-0
Bit-0
RD/WR
Modem RXLine
Stat. Int.
Enable
TX
Empty
Int
RX
Data
Int.
LCR[7]=0
Stat.
Int.
CTS Int. RTS Int. Xoff Int.
Enable Enable Enable
Sleep
Mode
Enable
Enable Enable Enable
0 1 0
0 1 0
ISR
RD
FIFOs
Enabled Enabled
FIFOs
0/
0/
INT
INT
INT
INT
Source Source Source Source
Bit-3
INT
INT
Bit-2
Bit-1
Bit-0
Source Source
Bit-5
Bit-4
LCR ≠ 0xBF
FCR
WR RXFIFO RXFIFO
Trigger Trigger
0/
0/
DMA
Mode
Enable
TX
FIFO
Reset Reset
RX
FIFOs
FIFO Enable
TXFIFO TXFIFO
Trigger Trigger
0 1 1
1 0 0
LCR RD/WR Divisor Set TX Set Par-
Even
Parity
Parity
Enable
Stop
Bits
Word
Length Length
Bit-1 Bit-0
Word
Enable
Break
ity
MCR RD/WR
0/
0/
0/
Internal OP2#/INT Rsrvd RTS# DTR#
Lopback Output
Output Output
Control Control
(OP1#)
BRG
Pres-
caler
IR Mode XonAny
ENable
Enable
Enable
LCR ≠ 0xBF
1 0 1
LSR
RD
RD
RX FIFO THR &
THR
Empty
RX
Break
RX Fram-
ing Error Parity Over-
RX
RX
RX
Data
Ready
Global
Error
TSR
Empty
Error
run
Error
1 1 0
1 1 1
MSR
CD#
RI#
DSR#
Input
CTS#
Input
Delta
CD#
Delta
RI#
Delta
DSR# CTS#
Delta
Input
Input
SPR RD/WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0 LCR ≠ 0xBF
FCTR[6]=0
1 1 1
EMSR
WR
16X
LSR
Error
Inter-
rupt.
Imd/Dly#
Auto
Auto
Auto
RS485
Output
Inversion
Rsrvd Rx/Tx Rx/Tx
FIFO FIFO
Count Count
Sam-
pling
Rate
RTS
Hyst.
RTS
Hyst.
bit-3
bit-2
LCR ≠ 0xBF
FCTR[6]=1
Mode
1 1 1
FLVL
RD
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
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PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
TABLE 8: INTERNAL REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED WHEN EFR BIT-4=1
ADDRESS
A2-A0
REG
READ/
WRITE
BIT-7
BIT-6
BIT-5
BIT-4
BIT-3
BIT-2
BIT-1
BIT-0
COMMENT
NAME
Baud Rate Generator Divisor
LCR[7]=1
0 0 0
0 0 1
0 1 0
DLL RD/WR
DLM RD/WR
DLD RD/WR
Bit-7
Bit-7
0
Bit-6
Bit-6
0
Bit-5
Bit-5
0
Bit-4
Bit-4
0
Bit-3
Bit-3
Bit-3
Bit-2
Bit-2
Bit-2
Bit-1
Bit-1
Bit-1
Bit-0
Bit-0
Bit-0
LCR ≠ 0xBF
LCR[7]=1
LCR ≠ 0xBF
EFR[4] = 1
0 0 0
0 0 1
DREV
DVID
RD
RD
Bit-7
0
Bit-6
0
Bit-5
0
Bit-4
0
Bit-3
1
Bit-2
0
Bit-1
1
Bit-0
0
LCR[7]=1
LCR≠ 0xBF
DLL=0x00
DLM=0x00
Enhanced Registers
0 0 0
0 0 0
0 0 1
TRG
FC
WR
RD
Bit-7
Bit-7
Bit-6
Bit-6
Bit-5
Bit-5
Bit-4
Bit-4
Bit-3
Bit-3
Bit-2
Bit-2
Bit-1
Bit-1
Bit-0
Bit-0
FCTR RD/WR RX/TX SCPAD
Trig
Table
Bit-1
Trig
Table
Bit-0
Auto
RX IR
Input
Inv.
Auto
RTS
Hyst
Bit-1
Auto
RTS
Hyst
Bit-0
Mode
Swap
RS485
Direction
Control
Enable
0 1 0
EFR RD/WR
Auto
CTS
Enable Enable
Auto
RTS
Special
Char
Select
Soft-
ware
Flow
Cntl
Soft-
ware
Flow
Cntl
Soft-
ware
Flow
Cntl
Soft-
ware
Flow
Cntl
IER [7:4],
ISR [5:4],
FCR[5:4],
LCR=0XBF
MCR[7:5],
DLD
Bit-2
Bit-1
Bit-0
Bit-3
1 0 0
1 0 1
1 1 0
1 1 1
XON1 RD/WR
XON2 RD/WR
XOFF1 RD/WR
XOFF2 RD/WR
Bit-7
Bit-7
Bit-7
Bit-7
Bit-6
Bit-6
Bit-6
Bit-6
Bit-5
Bit-5
Bit-5
Bit-5
Bit-4
Bit-4
Bit-4
Bit-4
Bit-3
Bit-3
Bit-3
Bit-3
Bit-2
Bit-2
Bit-2
Bit-2
Bit-1
Bit-1
Bit-1
Bit-1
Bit-0
Bit-0
Bit-0
Bit-0
4.0 INTERNAL REGISTER DESCRIPTIONS
4.1 Receive Holding Register (RHR) - Read- Only
SEE”RECEIVER” ON PAGE 13.
4.2 Transmit Holding Register (THR) - Write-Only
SEE”TRANSMITTER” ON PAGE 12.
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).
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4.3.1 IER versus Receive FIFO Interrupt Mode Operation
When the receive FIFO (FCR BIT-0 = 1) and receive interrupts (IER BIT-0 = 1) are enabled, the RHR interrupts
(see ISR bits 2 and 3) status will reflect the following:
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 XR16V2750 in the FIFO
polled mode of operation. Since the receiver and transmitter have separate bits in the LSR either or both can
be used in the polled mode by selecting respective transmit or receive control bit(s).
A. LSR BIT-0 indicates there is data in RHR or RX FIFO.
B. LSR BIT-1 indicates an overrun error has occurred and that data in the FIFO may not be valid.
C. LSR BIT 2-4 provides the type of receive data errors encountered for the data byte in RHR, if any.
D. LSR BIT-5 indicates THR is empty.
E. LSR BIT-6 indicates when both the transmit FIFO and TSR are empty.
F. LSR BIT-7 indicates a data error in at least one character in the RX FIFO.
IER[0]: RHR Interrupt Enable
The receive data ready interrupt will be issued when RHR has a data character in the non-FIFO mode or when
the receive FIFO has reached the programmed trigger level in the FIFO mode.
• Logic 0 = Disable the receive data ready interrupt (default).
• Logic 1 = Enable the receiver data ready interrupt.
IER[1]: THR Interrupt Enable
This bit enables the Transmit Ready interrupt which is issued whenever the THR becomes empty in the non-
FIFO mode or when data in the FIFO falls below the programmed trigger level in the FIFO mode. If the THR is
empty when this bit is enabled, an interrupt will be generated.
• Logic 0 = Disable Transmit Ready interrupt (default).
• Logic 1 = Enable Transmit Ready interrupt.
IER[2]: Receive Line Status Interrupt Enable
If any of the LSR register bits 1, 2, 3 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 bit-1 generates an interrupt immediately when the
character has been received. LSR bits 2-4 generate an interrupt when the character with errors is read out of
the FIFO (default). Instead, LSR bits 2-4 can be programmed to generate an interrupt immediately, by setting
EMSR bit-6 to a logic 1.
• 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.
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IER[4]: Sleep Mode Enable (requires EFR bit-4 = 1)
• Logic 0 = Disable Sleep Mode (default).
• Logic 1 = Enable Sleep Mode. See Sleep Mode section for further details.
IER[5]: Xoff Interrupt Enable (requires EFR bit-4=1)
• Logic 0 = Disable the software flow control, receive Xoff interrupt (default).
• Logic 1 = Enable the receive Xoff interrupt. See Software Flow Control section for details.
IER[6]: RTS# Output Interrupt Enable (requires EFR bit-4=1)
• Logic 0 = Disable the RTS# interrupt (default).
• Logic 1 = Enable the RTS# interrupt. The UART issues an interrupt when the RTS# pin makes a transition
from low to high.
IER[7]: CTS# Input Interrupt Enable (requires EFR bit-4=1)
• Logic 0 = Disable the CTS# interrupt (default).
• Logic 1 = Enable the CTS# interrupt. The UART issues an interrupt when CTS# pin makes a transition from
low to high.
4.4
Interrupt Status Register (ISR) - Read-Only
The UART provides multiple levels of prioritized interrupts to minimize external software interaction. The
Interrupt Status Register (ISR) provides the user with six interrupt status bits. Performing a read cycle on the
ISR will give the user the current highest pending interrupt level to be serviced, others are queued up to be
serviced next. No other interrupts are acknowledged until the pending interrupt is serviced. The Interrupt
Source Table, Table 9, shows the data values (bit 0-5) for the interrupt priority levels and the interrupt sources
associated with each of these interrupt levels.
4.4.1
Interrupt Generation:
• LSR is by any of the LSR bits 1, 2, 3 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# is when its transmitter toggles the input pin (from LOW to HIGH) during auto CTS flow control.
• RTS# is when its receiver toggles the output pin (from LOW to HIGH) during auto RTS flow control.
4.4.2
Interrupt Clearing:
• LSR interrupt is cleared by 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# and CTS# flow control interrupts are cleared by a read to the MSR register.
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REV. P1.0.0
]
TABLE 9: INTERRUPT SOURCE AND PRIORITY LEVEL
PRIORITY
ISR REGISTER STATUS BITS
SOURCE OF INTERRUPT
LEVEL
BIT-5
BIT-4
BIT-3
BIT-2
BIT-1
BIT-0
1
2
3
4
5
6
7
-
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
0
1
1
1
0
0
0
0
0
1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
1
LSR (Receiver Line Status Register)
RXRDY (Receive Data Time-out)
RXRDY (Received Data Ready)
TXRDY (Transmit Ready)
MSR (Modem Status Register)
RXRDY (Received Xoff or Special character)
CTS#, RTS# change of state
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[3:1]: Interrupt Status
These bits indicate the source for a pending interrupt at interrupt priority levels (See Interrupt Source Table 9).
ISR[4]: Xoff/Xon or Special Character Interrupt Status
This bit is set when EFR[4] = 1 and IER[5] = 1. ISR bit-4 indicates that the receiver detected a data match of
the Xoff character(s). If this is an Xoff interrupt, it can be cleared by a read to the ISR. If it is a special character
interrupt, it can be cleared by reading ISR or it will automatically clear after the next character received.
ISR[5]: RTS#/CTS# Interrupt Status
This bit is enabled when EFR[4] = 1. ISR bit-5 indicates that the CTS# or RTS# has been de-asserted.
ISR[7:6]: FIFO Enable Status
These bits are set to a logic 0 when the FIFOs are disabled. They are set to a logic 1 when the FIFOs are
enabled.
4.5
FIFO Control Register (FCR) - Write-Only
This register is used to enable the FIFOs, clear the FIFOs, 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 a ‘1’.
• 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.
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HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
FCR[2]: TX FIFO Reset
This bit is only active when FCR bit-0 is a ‘1’.
• 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
Controls the behavior of the TXRDY# and RXRDY# pins. See DMA operation section for details.
• Logic 0 = Normal Operation (default).
• Logic 1 = DMA Mode.
FCR[5:4]: Transmit FIFO Trigger Select (requires EFR bit-4=1)
(logic 0 = default, TX trigger level = 1)
These 2 bits set the trigger level for the transmit FIFO. The UART will issue a transmit interrupt when the
number of 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 10 below shows the selections. EFR bit-4
must be set to ‘1’ before these bits can be accessed. 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.
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 10 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.
27
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REV. P1.0.0
TABLE 10: TRANSMIT AND RECEIVE FIFO TRIGGER TABLE AND LEVEL SELECTION
TRANSMIT
TRIGGER
LEVEL
TRIGGER FCTR FCTR
FCR
BIT-7
FCR
BIT-6
FCR
BIT-5
FCR
BIT-4
RECEIVE
TRIGGER LEVEL
COMPATIBILITY
TABLE
BIT-5
BIT-4
Table-A
0
0
0
0
1 (default)
16C550, 16C2550,
16C2552, 16C554,
16C580
0
0
1
1
0
1
0
1
1 (default)
4
8
14
Table-B
Table-C
Table-D
0
1
1
1
0
1
0
0
1
1
0
1
0
1
16
8
16C650A
24
30
0
0
1
1
0
1
0
1
8
16
24
28
0
0
1
1
0
1
0
1
8
16C654
16
32
56
0
0
1
1
0
1
0
1
8
16
56
60
X
X
X
X
Programmable Programmable 16L2752, 16C2850,
16C2852, 16C850,
16C854, 16C864
via TRG
via TRG
register.
register.
FCTR[7] = 0.
FCTR[7] = 1.
4.6
Line Control Register (LCR) - Read/Write
The Line Control Register is used to specify the asynchronous data communication format. The word or
character length, the number of stop bits, and the parity are selected by writing the appropriate bits in this
register.
LCR[1:0]: TX and RX Word Length Select
These two bits specify the word length to be transmitted or received.
BIT-1
BIT-0
WORD LENGTH
0
0
1
1
0
1
0
1
5 (default)
6
7
8
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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.
STOP BIT LENGTH
(BIT TIME(S))
WORD
LENGTH
BIT-2
0
1
1
5,6,7,8
5
1 (default)
1-1/2
2
6,7,8
LCR[3]: TX and RX Parity Select
Parity or no parity can be selected via this bit. The parity bit is a simple way used in communications for data
integrity check. See Table 11 for parity selection summary below.
• Logic 0 = No parity.
• Logic 1 = A parity bit is generated during the transmission while the receiver checks for parity error of the
data character received.
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 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 11: PARITY SELECTION
LCR BIT-5 LCR BIT-4 LCR BIT-3
PARITY SELECTION
No parity
X
0
0
1
1
X
0
1
0
1
0
1
1
1
1
Odd parity
Even parity
Force parity to mark, “1”
Forced parity to space, “0”
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LCR[6]: Transmit Break Enable
When enabled, the Break control bit causes a break condition to be transmitted (the TX output is forced to a
“space", LOW state). This condition remains, until disabled by setting LCR bit-6 to a logic 0.
• Logic 0 = No TX break condition (default).
• Logic 1 = Forces the transmitter output (TX) to a “space”, LOW, for alerting the remote receiver of a line
break condition.
LCR[7]: Baud Rate Divisors Enable
Baud rate generator divisor (DLL, DLM and DLD) enable.
• Logic 0 = Data registers are selected (default).
• Logic 1 = Divisor latch registers are selected.
4.7
Modem Control Register (MCR) or General Purpose Outputs Control - Read/Write
The MCR register is used for controlling the serial/modem interface signals or general purpose inputs/outputs.
MCR[0]: DTR# Output
The DTR# pin is a modem control output. If the modem interface is not used, this output may be used as a
general purpose output.
• Logic 0 = Force DTR# output HIGH (default).
• Logic 1 = Force DTR# output LOW.
MCR[1]: RTS# Output
The RTS# pin is a modem control output and may be used for automatic hardware flow control by enabled by
EFR bit-6. The RTS# pin can also be used for Auto RS485 Half-Duplex direction control enabled by FCTR bit-
3. If the modem interface is not used, this output may be used as a general purpose output.
• Logic 0 = Force RTS# HIGH (default).
• Logic 1 = Force RTS# LOW.
MCR[2]: Reserved
OP1# is not available as an output pin on the V2750. But it is available for use during Internal Loopback Mode.
In the Loopback Mode, this bit is used to write the state of the modem RI# interface signal.
MCR[3]: OP2# Output / INT Output Enable
This bit enables or disables the operation of INT, interrupt output. If INT output is not used, OP2# can be used
as a general purpose output.
• Logic 0 = INT (A-B) outputs disabled (three state mode) and OP2# output set HIGH(default).
• Logic 1 = INT (A-B) outputs enabled (active mode) and OP2# output set LOW.
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 (requires EFR bit-4=1)
• Logic 0 = Disable Xon-Any function (default).
• Logic 1 = Enable Xon-Any function. In this mode, any RX character received will resume transmit operation.
The RX character will be loaded into the RX FIFO, unless the RX character is an Xon or Xoff character and
the V2750 is programmed to use the Xon/Xoff flow control.
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MCR[6]: Infrared Encoder/Decoder Enable (requires EFR bit-4=1)
• Logic 0 = Enable the standard modem receive and transmit input/output interface (default).
• Logic 1 = Enable infrared IrDA receive and transmit inputs/outputs. The TX/RX output/input are routed to the
infrared encoder/decoder. The data input and output levels conform to the IrDA infrared interface
requirement. While in this mode, the infrared TX output will be idling LOW. SEE”INFRARED MODE” ON
PAGE 18.
MCR[7]: Clock Prescaler Select (requires EFR bit-4=1)
• Logic 0 = Divide by one. The input clock from the crystal or external clock is fed directly to the Programmable
Baud Rate Generator without further modification, i.e., divide by one (default).
• Logic 1 = Divide by four. The prescaler divides the input clock from the crystal or external clock by four and
feeds it to the Programmable Baud Rate Generator, hence, data rates become one forth.
4.8
Line Status Register (LSR) - Read Only
This register provides the status of data transfers between the UART and the host.
LSR[0]: Receive Data Ready Indicator
• Logic 0 = No data in receive holding register or FIFO (default).
• Logic 1 = Data has been received and is saved in the receive holding register or FIFO.
LSR[1]: Receiver Overrun Error Flag
• Logic 0 = No overrun error (default).
• Logic 1 = Overrun error. A data overrun error condition occurred in the receive shift register. This happens
when additional data arrives while the FIFO is full. In this case the previous data in the receive shift register
is overwritten. Note that under this condition the data byte in the receive shift register is not transferred into
the FIFO, therefore the data in the FIFO is not corrupted by the error.
LSR[2]: Receive Data Parity Error Tag
• Logic 0 = No parity error (default).
• Logic 1 = Parity error. The receive character in RHR does not have correct parity information and is suspect.
This error is associated with the character available for reading in RHR.
LSR[3]: Receive Data Framing Error Tag
• Logic 0 = No framing error (default).
• Logic 1 = Framing error. The receive character did not have a valid stop bit(s). This error is associated with
the character available for reading in RHR.
LSR[4]: Receive Break Error Tag
• Logic 0 = No break condition (default).
• Logic 1 = The receiver received a break signal (RX was LOW for at least one character frame time). In the
FIFO mode, only one break character is loaded into the FIFO.
LSR[5]: Transmit Holding Register Empty Flag
This bit is the Transmit Holding Register Empty indicator. The THR bit is set to a logic 1 when the last data byte
is transferred from the transmit holding register to the transmit shift register. The bit is reset to logic 0
concurrently with the data loading to the transmit holding register by the host. In the FIFO mode this bit is set
when the transmit FIFO is empty, it is cleared when the transmit FIFO contains at least 1 byte.
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LSR[6]: THR and TSR Empty Flag
This bit is set to a logic 1 whenever the transmitter goes idle. It is set to logic 0 whenever either the THR or
TSR contains a data character. In the FIFO mode this bit is set to a logic 1 whenever the transmit FIFO and
transmit shift register are both empty.
LSR[7]: Receive FIFO Data Error Flag
• Logic 0 = No FIFO error (default).
• Logic 1 = A global indicator for the sum of all error bits in the RX FIFO. At least one parity error, framing error
or break indication is in the FIFO data. This bit clears when there is no more error(s) in any of the bytes in the
RX FIFO.
4.9
Modem Status Register (MSR) - Read Only
This register provides the current state of the modem interface input signals. Lower four bits of this register are
used to indicate the changed information. These bits are set to a logic 1 whenever a signal from the modem
changes state. These bits may be used for general purpose inputs when they are not used with modem
signals.
MSR[0]: Delta CTS# Input Flag
• Logic 0 = No change on CTS# input (default).
• Logic 1 = The CTS# input has changed state since the last time it was monitored. A modem status interrupt
will be generated if 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 LOW to HIGH, 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). 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
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.
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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 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.
4.11 Enhanced Mode Select Register (EMSR)
This register replaces SPR (during a Write) and is accessible only when FCTR[6] = 1.
EMSR[1:0]: Receive/Transmit FIFO Level Count (Write-Only)
When Scratchpad Swap (FCTR[6]) is asserted, EMSR bits 1-0 controls what mode the FIFO Level Counter is
operating in.
TABLE 12: SCRATCHPAD SWAP SELECTION
FCTR[6] EMSR[1] EMSR[0]
Scratchpad is
0
1
1
1
X
X
0
1
X
0
1
1
Scratchpad
RX FIFO Level Counter Mode
TX FIFO Level Counter Mode
Alternate RX/TX FIFO Counter Mode
During Alternate RX/TX FIFO Level Counter Mode, the first value read after EMSR bits 1-0 have been
asserted will always be the RX FIFO Level Counter. The second value read will correspond with the TX FIFO
Level Counter. The next value will be the RX FIFO Level Counter again, then the TX FIFO Level Counter and
so on and so forth.
EMSR[2]: Reserved
EMSR[3]: Automatic RS485 Half-Duplex Control Output Inversion
• Logic 0 = RTS# output is LOW during TX and HIGH during RX (default, compatible with 16C2850).
• Logic 1 = RTS# output is HIGH during TX and LOW during RX.
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EMSR[5:4]: Extended RTS Hysteresis
TABLE 13: AUTO RTS HYSTERESIS
RTS#
HYSTERESIS
(CHARACTERS)
EMSR
BIT-5
EMSR
BIT-4
FCTR
BIT-1
FCTR
BIT-0
0
0
0
0
0
0
0
0
0
0
1
1
0
1
0
1
0
±4
±6
±8
0
0
0
0
1
1
1
1
0
0
1
1
0
1
0
1
±8
±16
±24
±32
1
1
1
1
0
0
0
0
0
0
1
1
0
1
0
1
±40
±44
±48
±52
1
1
1
1
1
1
1
1
0
0
1
1
0
1
0
1
±12
±20
±28
±36
EMSR[6]: LSR Interrupt Mode
• Logic 0 = LSR Interrupt Delayed (for 16C2550 compatibility, default). LSR bits 2, 3, and 4 will generate an
interrupt when the character with the error is in the RHR.
• Logic 1 = LSR Interrupt Immediate. LSR bits 2, 3, and 4 will generate an interrupt as soon as the character is
received into the FIFO.
EMSR[7]: 16X Sampling Rate Mode
Logic 0 = 8X Sampling Rate.
Logic 1 = 16X Sampling Rate (default).
4.12 FIFO Level Register (FLVL) - Read-Only
The FIFO Level Register replaces the Scratchpad Register (during a Read) when FCTR[6] = 1. Note that this is
not identical to the FIFO Data Count Register which can be accessed when LCR = 0xBF.
FLVL[7:0]: FIFO Level Register
This register provides the FIFO counter level for the RX FIFO or the TX FIFO or both depending on EMSR[1:0].
See Table 12 for details.
4.13 Baud Rate Generator Registers (DLL, DLM and DLD) - Read/Write
These registers make-up the value of the baud rate divisor. The concatenation of the contents of DLM and
DLL is a 16-bit value is then added to DLD/16 to achieve the fractional baud rate divisor. DLD must be enabled
via EFR bit-4 before it can be accessed. SEE”PROGRAMMABLE BAUD RATE GENERATOR WITH
FRACTIONAL DIVISOR” ON PAGE 10.
4.14 Device Identification Register (DVID) - Read Only
This register contains the device ID (0x0A for XR16V2750). Prior to reading this register, DLL and DLM should
be set to 0x00 (DLD = 0xXX).
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4.15 Device Revision Register (DREV) - Read Only
This register contains the device revision information. For example, 0x01 means revision A. Prior to reading
this register, DLL and DLM should be set to 0x00 (DLD = 0xXX).
4.16 Trigger Level Register (TRG) - Write-Only
User Programmable Transmit/Receive Trigger Level Register. If both the programmable TX and RX trigger
levels are used, the TX trigger levels must be set before the RX trigger levels.
TRG[7:0]: Trigger Level Register
These bits are used to program desired trigger levels when trigger Table-D is selected. FCTR bit-7 selects
between programming the RX Trigger Level (a logic 0) and the TX Trigger Level (a logic 1).
4.17 RX/TX FIFO Level Count Register (FC) - Read-Only
This register is accessible when LCR = 0xBF. Note that this register is not identical to the FIFO Level Count
Register which is located in the general register set when FCTR bit-6 = 1 (Scratchpad Register Swap). It is
suggested to read the FIFO Level Count Register at the Scratchpad Register location when FCTR bit-6 = 1.
See Table 12.
FC[7:0]: RX/TX FIFO Level Count
Receive/Transmit FIFO Level Count. Number of characters in Receiver FIFO (FCTR[7] = 0) or Transmitter
FIFO (FCTR[7] = 1) can be read via this register. Reading this register is not recommended when transmitting
or receiving data.
4.18
Feature Control Register (FCTR) - Read/Write
This register controls the XR16V2750 functions that are not available in ST16C2450 or ST16C2550.
FCTR[1:0]: RTS Hysteresis
User selectable RTS# hysteresis levels for hardware flow control application. After reset, these bits are set to
“0” to select the next trigger level for hardware flow control. See Table 13 for more details.
FCTR[2]: IrDa RX Inversion
• Logic 0 = Select RX input as encoded IrDa data (Idle state will be LOW).
• Logic 1 = Select RX input as inverted encoded IrDa data (Idle state will be HIGH).
FCTR[3]: Auto RS-485 Direction Control
• Logic 0 = Standard ST16C550 mode. Transmitter generates an interrupt when transmit holding register
becomes empty and transmit shift register is shifting data out.
• Logic 1 = Enable Auto RS485 Direction Control function. The direction control signal, RTS# pin, changes its
output logic state from LOW to HIGH one bit time after the last stop bit of the last character is shifted out.
Also, the Transmit interrupt generation is delayed until the transmitter shift register becomes empty. The
RTS# output pin will automatically return to a LOW when a data byte is loaded into the TX FIFO. However,
RTS# behavior can be inverted by setting EMSR[3] = 1.
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FCTR[5:4]: Transmit/Receive Trigger Table Select
See Table 10 for more details.
REV. P1.0.0
TABLE 14: TRIGGER TABLE SELECT
FCTR
BIT-5
FCTR
BIT-4
TABLE
0
0
1
1
0
1
0
1
Table-A (TX/RX)
Table-B (TX/RX)
Table-C (TX/RX)
Table-D (TX/RX)
FCTR[6]: Scratchpad Swap
• Logic 0 = Scratch Pad register is selected as general read and write register. ST16C550 compatible mode.
• Logic 1 = FIFO Level Count register (Read-Only), Enhanced Mode Select Register (Write-Only). Number of
characters in transmit or receive FIFO can be read via scratch pad register when this bit is set. Enhanced
Mode Select Register is selected when it is written into.
FCTR[7]: Programmable Trigger Register Select
If using both programmable TX and RX trigger levels, TX trigger levels must be set before RX trigger levels.
• Logic 0 = Registers TRG and FC selected for RX.
• Logic 1 = Registers TRG and FC selected for TX.
4.19 Enhanced Feature Register (EFR)
Enhanced features are enabled or disabled using this register. Bit 0-3 provide single or dual consecutive
character software flow control selection (see Table 15). When the Xon1 and Xon2 and Xoff1 and Xoff2 modes
are selected, the double 8-bit words are concatenated into two sequential characters. Caution: note that
whenever changing the TX or RX flow control bits, always reset all bits back to logic 0 (disable) before
programming a new setting.
EFR[3:0]: Software Flow Control Select
Single character and dual sequential characters software flow control is supported. Combinations of software
flow control can be selected by programming these bits.
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TABLE 15: SOFTWARE FLOW CONTROL FUNCTIONS
EFR BIT-3
EFR BIT-2
CONT-2
EFR BIT-1
CONT-1
EFR BIT-0
CONT-0
TRANSMIT AND RECEIVE SOFTWARE FLOW CONTROL
CONT-3
0
0
1
0
1
X
X
X
1
0
0
0
1
1
X
X
X
0
0
X
X
X
X
0
1
0
1
0
X
X
X
X
0
0
1
1
No TX and RX flow control (default and reset)
No transmit flow control
Transmit Xon1, Xoff1
Transmit Xon2, Xoff2
Transmit Xon1 and Xon2, Xoff1 and Xoff2
No receive flow control
Receiver compares Xon1, Xoff1
Receiver compares Xon2, Xoff2
Transmit Xon1, Xoff1
Receiver compares Xon1 or Xon2, Xoff1 or Xoff2
0
1
0
1
1
0
1
1
1
1
1
1
Transmit Xon2, Xoff2
Receiver compares Xon1 or Xon2, Xoff1 or Xoff2
Transmit Xon1 and Xon2, Xoff1 and Xoff2,
Receiver compares Xon1 and Xon2, Xoff1 and Xoff2
No transmit flow control,
Receiver compares Xon1 and Xon2, Xoff1 and Xoff2
EFR[4]: Enhanced Function Bits Enable
Enhanced function control bit. This bit enables IER bits 4-7, ISR bits 4-5, FCR bits 4-5, MCR bits 5-7, and DLD
to be modified. After modifying any enhanced bits, EFR bit-4 can be set to a logic 0 to latch the new values.
This feature prevents legacy software from altering or overwriting the enhanced functions once set. Normally, it
is recommended to leave it enabled, logic 1.
• Logic 0 = modification disable/latch enhanced features. IER bits 4-7, ISR bits 4-5, FCR bits 4-5, MCR bits 5-
7, and DLD are saved to retain the user settings. After a reset, the IER bits 4-7, ISR bits 4-5, FCR bits 4-5,
MCR bits 5-7, and DLD are set to a logic 0 to be compatible with ST16C550 mode (default).
• Logic 1 = Enables the above-mentioned register bits to be modified by the user.
EFR[5]: Special Character Detect Enable
• Logic 0 = Special Character Detect Disabled (default).
• Logic 1 = Special Character Detect Enabled. The UART compares each incoming receive character with
data in Xoff-2 register. If a match exists, the receive data will be transferred to FIFO and ISR bit-4 will be set
to indicate detection of the special character. Bit-0 corresponds with the LSB bit of the receive character. If
flow control is set for comparing Xon1, Xoff1 (EFR [1:0]= ‘10’) then flow control and special character work
normally. However, if flow control is set for comparing Xon2, Xoff2 (EFR[1:0]= ‘01’) then flow control works
normally, but Xoff2 will not go to the FIFO, and will generate an Xoff interrupt and a special character
interrupt, if enabled via IER bit-5.
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EFR[6]: Auto RTS Flow Control Enable
RTS# output may be used for hardware flow control by setting EFR bit-6 to logic 1. When Auto RTS is
selected, an interrupt will be generated when the receive FIFO is filled to the programmed trigger level and
RTS de-asserts HIGH at the next upper trigger level or hysteresis level. RTS# will return LOW when FIFO data
falls below the next lower trigger level. The RTS# output must be asserted (LOW) before the auto RTS can
take effect. RTS# pin will function as a general purpose output when hardware flow control is disabled.
• Logic 0 = Automatic RTS flow control is disabled (default).
• Logic 1 = Enable Automatic RTS flow control.
EFR[7]: Auto CTS Flow Control Enable
Automatic CTS Flow Control.
• Logic 0 = Automatic CTS flow control is disabled (default).
• Logic 1 = Enable Automatic CTS flow control. Data transmission stops when CTS# input de-asserts HIGH.
Data transmission resumes when CTS# returns LOW.
4.19.1 Software Flow Control Registers (XOFF1, XOFF2, XON1, XON2) - Read/Write
These registers are used as the programmable software flow control characters xoff1, xoff2, xon1, and xon2.
For more details, see Table 6.
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TABLE 16: UART RESET CONDITIONS FOR CHANNEL A AND B
REGISTERS
RESET STATE
DLM, DLL
DLM = 0x00 and DLL = 0x01. Only resets to these values during a power up.
They do not reset when the Reset Pin is asserted.
DLD
RHR
THR
IER
Bits 7-0 = 0x00
Bits 7-0 = 0xXX
Bits 7-0 = 0xXX
Bits 7-0 = 0x00
Bits 7-0 = 0x00
Bits 7-0 = 0x01
Bits 7-0 = 0x00
Bits 7-0 = 0x00
Bits 7-0 = 0x60
FCR
ISR
LCR
MCR
LSR
MSR
Bits 3-0 = Logic 0
Bits 7-4 = Logic levels of the inputs inverted
SPR
EMSR
FLVL
Bits 7-0 = 0xFF
Bits 7-0 = 0x80
Bits 7-0 = 0x00
Bits 7-0 = 0x00
Bits 7-0 = 0x00
Bits 7-0 = 0x00
Bits 7-0 = 0x00
Bits 7-0 = 0x00
Bits 7-0 = 0x00
RESET STATE
HIGH
EFR
XON1
XON2
XOFF1
XOFF2
FC
I/O SIGNALS
TX
OP2#
HIGH
RTS#
HIGH
DTR#
HIGH
RXRDY#
TXRDY#
INT
HIGH
LOW
Three-State Condition
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ABSOLUTE MAXIMUM RATINGS
Power Supply Range
Voltage at Any Pin
4 Volts
GND-0.3V to 5.5V
o
o
Operating Temperature
-40 to +85 C
o
o
Storage Temperature
Package Dissipation
-65 to +150 C
500 mW
TYPICAL PACKAGE THERMAL RESISTANCE DATA (MARGIN OF ERROR: ± 15%)
o
o
Thermal Resistance (48-TQFP)
Thermal Resistance (32-QFN)
theta-ja =59 C/W, theta-jc = 16 C/W
o
o
theta-ja = 33 C/W, theta-jc = 22 C/W
ELECTRICAL CHARACTERISTICS
DC ELECTRICAL CHARACTERISTICS
TA=-40O TO +85OC, VCC IS 2.25V TO 3.6V
LIMITS
2.5V
LIMITS
SYMBOL
PARAMETER
3.3V
UNITS
CONDITIONS
MIN
MAX
MIN
MAX
V
Clock Input Low Level
Clock Input High Level
Input Low Voltage
-0.3
0.4
VCC
0.5
-0.3
0.6
V
V
V
V
ILCK
V
2.0
-0.3
1.8
2.4
-0.3
2.0
VCC
0.7
IHCK
V
IL
V
Input High Voltage
Output Low Voltage
5.5
5.5
IH
V
0.4
V
V
I
I
= 6 mA
= 4 mA
OL
OL
OL
0.4
V
Output High Voltage
2.4
V
V
I
I
= -4 mA
= -2 mA
OH
OH
OH
1.8
I
Input Low Leakage Current
Input High Leakage Current
Input Pin Capacitance
Power Supply Current
Sleep Current
±10
±10
5
±10
±10
5
uA
uA
pF
IL
I
IH
C
IN
I
1.5
15
2.5
30
mA
uA
Ext Clk = 2MHz
See Test 1
CC
I
SLEEP
Test 1: The following inputs must remain steady at VCC or GND state to minimize Sleep current: A0-A2, D0-
D7, IOR#, IOW#, CSA#, CSB# and all modem inputs. Also, RXA and RXB inputs must idle HIGH while asleep.
Floating inputs will result in sleep currents in the mA range. For PowerSave feature that isolates address, data
and control signals, please see the XR16V2751 datasheet.
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AC ELECTRICAL CHARACTERISTICS
UNLESS OTHERWISE NOTED: TA=-40O TO +85OC, VCC=2.25 - 3.63V, 70 PF LOAD WHERE APPLICABLE
LIMITS
LIMITS
SYMBOL
PARAMETER
2.5V ± 10%
3.3V ± 10%
UNIT
MIN
MAX
MIN
MAX
XTAL1
ECLK
UART Crystal Oscillator
32
50
24
64
MHz
MHz
ns
External Clock
T
External Clock Time Period
10
0
7
0
ECLK
T
Address Setup Time
ns
ns
AS
T
Address Hold Time
0
0
AH
T
T
T
Chip Select Width
75
75
75
65
65
65
ns
CS
RD
DY
IOR# Strobe Width
ns
Read Cycle Delay
ns
T
Data Access Time
70
30
60
15
ns
RDV
T
Data Disable Time
0
0
ns
DD
T
IOW# Strobe Width
75
75
10
5
65
65
10
5
ns
WR
T
T
T
Write Cycle Delay
ns
DY
DS
DH
Data Setup Time
ns
Data Hold Time
ns
T
T
Delay From IOW# To Output
Delay To Set Interrupt From MODEM Input
Delay To Reset Interrupt From IOR#
Delay From Stop To Set Interrupt
Delay From IOR# To Reset Interrupt
Delay From Stop To Interrupt
Delay From Initial INT Reset To Transmit Start
Delay From IOW# To Reset Interrupt
Delay From Stop To Set RXRDY#
Delay From IOR# To Reset RXRDY#
Delay From IOW# To Set TXRDY#
Delay From Center of Start To Reset TXRDY#
Reset Pulse Width
50
50
50
1
50
50
50
1
ns
WDO
MOD
ns
T
ns
RSI
SSI
RRI
T
Bclk
ns
T
45
45
24
45
1
45
45
24
45
1
T
ns
SI
T
8
8
Bclk
ns
INT
T
T
WRI
SSR
Bclk
ns
T
45
45
8
45
45
8
RR
T
ns
WT
T
T
Bclk
ns
SRT
RST
40
40
Bclk
Baud Clock
16X or 8X of data rate
Hz
41
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
FIGURE 13. CLOCK TIMING
TECLK
TECL
TECH
VIH
External
Clock
VIL
FIGURE 14. MODEM INPUT/OUTPUT TIMING FOR CHANNELS A & B
IOW #
Active
TW DO
RTS#
DTR#
Change of state
Change of state
CD#
CTS#
DSR#
Change of state
Change of state
TMOD
TMOD
INT
Active
Active
Active
Active
TRSI
IOR#
Active
Active
TMOD
Change of state
RI#
42
PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
FIGURE 15. DATA BUS READ TIMING
A0-A2
Valid Address
Valid Address
TAS
TAS
TAH
TAH
TCS
TCS
CSA#/
CSB#
TDY
TRD
TRD
IOR#
TDD
TDD
TRDV
TRDV
D0-D7
Valid Data
Valid Data
RDTm
FIGURE 16. DATA BUS WRITE TIMING
A0-A2
Valid Address
TCS
Valid Address
TCS
TAS
TAS
TAH
TAH
CSA#/
CSB#
TDY
TWR
TWR
IOW#
TDH
TDH
TDS
Valid Data
TDS
Valid Data
D0-D7
16Write
43
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
FIGURE 17. RECEIVE READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B
RX
Stop
Bit
Start
Bit
D0:D7
D0:D7
D0:D7
TSSR
TSSR
TSSR
1 Byte
1 Byte
1 Byte
in RHR
in RHR
in RHR
INT
TSSR
TSSR
TSSR
Active
Data
Active
Data
Active
Data
RXRDY#
Ready
Ready
Ready
TRR
TRR
TRR
IOR#
(Reading data
out of RHR)
RXNFM
FIGURE 18. TRANSMIT READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B
TX
Stop
Bit
Start
Bit
D0:D7
D0:D7
D0:D7
IER[1]
enabled
ISR is read
ISR is read
ISR is read
INT*
TWRI
TWRI
TWRI
TSRT
TSRT
TSRT
TXRDY#
TWT
TWT
TWT
IOW#
(Loading data
into THR)
*INT is cleared when the ISR is read or when data is loaded into the THR.
TXNonFIFO
44
PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
FIGURE 19. RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA DISABLED] FOR CHANNELS A & B
Start
Bit
RX
S
S
D0:D7
S
S
S
T
S
D0:D7
D0:D7
T
D0:D7
TSSI
D0:D7
T
D0:D7
T
D0:D7
T
Stop
Bit
RX FIFO drops
below RX
Trigger Level
INT
TSSR
FIFO
Empties
RX FIFO fills up to RX
Trigger Level or RX Data
Timeout
RXRDY#
First Byte is
Received in
RX FIFO
TRRI
TRR
IOR#
(Reading data out
of RX FIFO)
RXINTDMA#
FIGURE 20. RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA ENABLED] FOR CHANNELS A & B
Start
Bit
Stop
Bit
RX
S
S
S
S
T
D0:D7
D0:D7
D0:D7
T
D0:D7
TSSI
D0:D7
S
T
S
D0:D7
T
D0:D7
T
RX FIFO drops
below RX
Trigger Level
INT
RX FIFO fills up to RX
Trigger Level or RX Data
Timeout
TSSR
FIFO
Empties
RXRDY#
TRRI
TRR
IOR#
(Reading data out
of RX FIFO)
RXFIFODMA
45
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
FIGURE 21. TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE DISABLED] FOR CHANNELS A & B
Stop
Bit
Start
Bit
Last Data Byte
Transmitted
TX FIFO
Empty
TX
(Unloading)
T
S
S
S
T
S
T
S
D0:D7
D0:D7
T
S D0:D7
T
D0:D7
T
D0:D7
D0:D7
T
ISR is read
TSI
IER[1]
enabled
ISR is read
TSRT
INT*
TX FIFO
Empty
TX FIFO fills up
to trigger level
TX FIFO drops
below trigger level
TWRI
Data in
TX FIFO
TXRDY#
TWT
IOW#
(Loading data
into FIFO)
*INT is cleared when the ISR is read or when TX FIFO fills up to the trigger level.
TXDMA#
FIGURE 22. TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE ENABLED] FOR CHANNELS A & B
Stop
Bit
Start
Bit
Last Data Byte
Transmitted
TX
(Unloading)
S
S
D0:D7
D0:D7
T
D0:D7
S
D0:D7
S
D0:D7
S
D0:D7
T
S D0:D7
T
T
T
T
IER[1]
enabled
ISR Read
ISR Read
TSI
TSRT
INT*
TX FIFO fills up
to trigger level
TX FIFO drops
below trigger level
TWRI
At least 1
empty location
in FIFO
TX FIFO
Full
TXRDY#
TWT
IOW#
(Loading data
into FIFO)
*INT cleared when the ISR is read or when TX FIFO fills up to trigger level.
TXDMA
46
PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
PACKAGE DIMENSIONS (48 PIN TQFP - 7 X 7 X 1 mm)
D
D
1
36
25
37
24
D
1
D
48
13
1
1
2
B
e
A2
C
A
Seating
Plane
A1
α
L
Note: The control dimension is the millimeter column
INCHES MILLIMETERS
MAX
SYMBOL
MIN
MIN
MAX
1.20
0.15
A
0.039
0.002
0.047
0.006
1.00
0.05
A
A
1
2
0.037
0.041
0.95
1.05
B
0.007
0.004
0.346
0.272
0.011
0.008
0.362
0.280
0.17
0.09
8.80
6.90
0.27
0.20
9.20
7.10
C
D
D
1
e
L
a
0.020 BSC
0.50 BSC
0.018
0.030
0.45
0.75
0°
7°
0°
7°
47
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
PACKAGE DIMENSIONS (32 PIN QFN - 5 X 5 X 0.9 mm)
D2
D
D
D2
L
b
e
Note: The actual center pad is
metallic and the size (D2) is
device-dependent with a typical
tolerance of 0.3mm
A1
Steating Plane
A
A3
Note: The control dimension is in millimeter.
INCHES
MILLIMETERS
SYMBOL
MIN
MAX
0.039
0.002
0.010
0.201
0.150
0.012
MIN
MAX
1.00
0.05
0.25
5.10
3.80
0.30
A
A1
A3
D
0.031
0.000
0.006
0.193
0.138
0.007
0.80
0.00
0.15
4.90
3.50
0.18
D2
b
e
0.0197 BSC
0.012 0.020
0.50 BSC
L
0.30
0.50
48
PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REVISION HISTORY
DATE
REVISION
DESCRIPTION
June 2006
P1.0.0
Preliminary Datasheet.
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 2006 EXAR Corporation
Datasheet June 2006.
Send your UART technical inquiry with technical details to hotline: uarttechsupport@exar.com.
Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.
49
XR16V2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
TABLE OF CONTENTS
GENERAL DESCRIPTION ................................................................................................ 1
APPLICATIONS............................................................................................................................................... 1
FEATURES .................................................................................................................................................... 1
FIGURE 1. XR16V2750 BLOCK DIAGRAM ......................................................................................................................................... 1
FIGURE 2. PIN OUT ASSIGNMENT ..................................................................................................................................................... 2
ORDERING INFORMATION................................................................................................................................ 2
PIN DESCRIPTIONS ........................................................................................................ 3
1.0 PRODUCT DESCRIPTION....................................................................................................................... 6
2.0 FUNCTIONAL DESCRIPTIONS............................................................................................................... 7
2.1 CPU INTERFACE................................................................................................................................................. 7
FIGURE 3. XR16V2750 DATA BUS INTERCONNECTIONS ................................................................................................................... 7
2.2 5-VOLT TOLERANT INPUTS .............................................................................................................................. 7
2.3 DEVICE RESET ................................................................................................................................................... 7
2.4 DEVICE IDENTIFICATION AND REVISION........................................................................................................ 7
2.5 CHANNEL A AND B SELECTION....................................................................................................................... 7
TABLE 1: CHANNEL A AND B SELECT ............................................................................................................................................... 8
2.6 CHANNEL A AND B INTERNAL REGISTERS ................................................................................................... 8
2.7 DMA MODE.......................................................................................................................................................... 8
TABLE 2: TXRDY# AND RXRDY# OUTPUTS IN FIFO AND DMA MODE ............................................................................................. 8
2.8 INTA AND INTB OUTPUTS................................................................................................................................. 9
TABLE 3: INTA AND INTB PINS OPERATION FOR TRANSMITTER ........................................................................................................ 9
TABLE 4: INTA AND INTB PIN OPERATION FOR RECEIVER ............................................................................................................... 9
2.9 CRYSTAL OSCILLATOR OR EXTERNAL CLOCK INPUT................................................................................ 9
FIGURE 4. TYPICAL OSCILLATOR CONNECTIONS................................................................................................................................. 9
2.10 PROGRAMMABLE BAUD RATE GENERATOR WITH FRACTIONAL DIVISOR.......................................... 10
FIGURE 5. BAUD RATE GENERATOR ............................................................................................................................................... 11
TABLE 5: TYPICAL DATA RATES WITH A 24 MHZ CRYSTAL OR EXTERNAL CLOCK AT 16X SAMPLING ................................................... 11
2.11 TRANSMITTER................................................................................................................................................ 12
2.11.1 TRANSMIT HOLDING REGISTER (THR) - WRITE ONLY......................................................................................... 12
2.11.2 TRANSMITTER OPERATION IN NON-FIFO MODE.................................................................................................. 12
FIGURE 6. TRANSMITTER OPERATION IN NON-FIFO MODE .............................................................................................................. 12
2.11.3 TRANSMITTER OPERATION IN FIFO MODE ........................................................................................................... 12
FIGURE 7. TRANSMITTER OPERATION IN FIFO AND FLOW CONTROL MODE ..................................................................................... 13
2.12 RECEIVER ....................................................................................................................................................... 13
2.12.1 RECEIVE HOLDING REGISTER (RHR) - READ-ONLY ............................................................................................ 13
FIGURE 8. RECEIVER OPERATION IN NON-FIFO MODE .................................................................................................................... 14
FIGURE 9. RECEIVER OPERATION IN FIFO AND AUTO RTS FLOW CONTROL MODE ......................................................................... 14
2.13 AUTO RTS (HARDWARE) FLOW CONTROL ................................................................................................ 15
2.14 AUTO RTS HYSTERESIS............................................................................................................................... 15
2.15 AUTO CTS FLOW CONTROL........................................................................................................................ 15
FIGURE 10. AUTO RTS AND CTS FLOW CONTROL OPERATION....................................................................................................... 16
2.16 AUTO XON/XOFF (SOFTWARE) FLOW CONTROL...................................................................................... 17
TABLE 6: AUTO XON/XOFF (SOFTWARE) FLOW CONTROL ............................................................................................................... 17
2.17 SPECIAL CHARACTER DETECT.................................................................................................................. 17
2.18 AUTO RS485 HALF-DUPLEX CONTROL ..................................................................................................... 17
2.19 INFRARED MODE ........................................................................................................................................... 18
FIGURE 11. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING .......................................................................... 18
2.20 SLEEP MODE WITH AUTO WAKE-UP.......................................................................................................... 19
2.21 INTERNAL LOOPBACK................................................................................................................................. 20
FIGURE 12. INTERNAL LOOP BACK IN CHANNEL A AND B ................................................................................................................ 20
3.0 UART INTERNAL REGISTERS ............................................................................................................. 21
TABLE 7: UART CHANNEL A AND B UART INTERNAL REGISTERS ....................................................................................... 21
TABLE 8: INTERNAL REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED WHEN EFR BIT-4=1 ......................................... 22
4.0 INTERNAL REGISTER DESCRIPTIONS............................................................................................... 23
4.1 RECEIVE HOLDING REGISTER (RHR) - READ- ONLY .................................................................................. 23
4.2 TRANSMIT HOLDING REGISTER (THR) - WRITE-ONLY ............................................................................... 23
4.3 INTERRUPT ENABLE REGISTER (IER) - READ/WRITE................................................................................. 23
4.3.1 IER VERSUS RECEIVE FIFO INTERRUPT MODE OPERATION ............................................................................... 24
4.3.2 IER VERSUS RECEIVE/TRANSMIT FIFO POLLED MODE OPERATION.................................................................. 24
I
PRELIMINARY
XR16V2750
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
4.4 INTERRUPT STATUS REGISTER (ISR) - READ-ONLY .................................................................................. 25
4.4.1 INTERRUPT GENERATION: ........................................................................................................................................ 25
4.4.2 INTERRUPT CLEARING: ............................................................................................................................................. 25
TABLE 9: INTERRUPT SOURCE AND PRIORITY LEVEL ....................................................................................................................... 26
4.5 FIFO CONTROL REGISTER (FCR) - WRITE-ONLY ........................................................................................ 26
TABLE 10: TRANSMIT AND RECEIVE FIFO TRIGGER TABLE AND LEVEL SELECTION .......................................................................... 28
4.6 LINE CONTROL REGISTER (LCR) - READ/WRITE ........................................................................................ 28
TABLE 11: PARITY SELECTION ........................................................................................................................................................ 29
4.7 MODEM CONTROL REGISTER (MCR) OR GENERAL PURPOSE OUTPUTS CONTROL - READ/WRITE . 30
4.8 LINE STATUS REGISTER (LSR) - READ ONLY.............................................................................................. 31
4.9 MODEM STATUS REGISTER (MSR) - READ ONLY ....................................................................................... 32
4.10 SCRATCH PAD REGISTER (SPR) - READ/WRITE ....................................................................................... 33
4.11 ENHANCED MODE SELECT REGISTER (EMSR)......................................................................................... 33
TABLE 12: SCRATCHPAD SWAP SELECTION .................................................................................................................................... 33
TABLE 13: AUTO RTS HYSTERESIS ................................................................................................................................................ 34
4.12 FIFO LEVEL REGISTER (FLVL) - READ-ONLY ............................................................................................ 34
4.13 BAUD RATE GENERATOR REGISTERS (DLL, DLM AND DLD) - READ/WRITE ....................................... 34
4.14 DEVICE IDENTIFICATION REGISTER (DVID) - READ ONLY....................................................................... 34
4.15 DEVICE REVISION REGISTER (DREV) - READ ONLY................................................................................. 35
4.16 TRIGGER LEVEL REGISTER (TRG) - WRITE-ONLY.................................................................................... 35
4.17 RX/TX FIFO LEVEL COUNT REGISTER (FC) - READ-ONLY ....................................................................... 35
4.18 FEATURE CONTROL REGISTER (FCTR) - READ/WRITE .......................................................................... 35
TABLE 14: TRIGGER TABLE SELECT ............................................................................................................................................... 36
4.19 ENHANCED FEATURE REGISTER (EFR) ..................................................................................................... 36
TABLE 15: SOFTWARE FLOW CONTROL FUNCTIONS ........................................................................................................................ 37
4.19.1 SOFTWARE FLOW CONTROL REGISTERS (XOFF1, XOFF2, XON1, XON2) - READ/WRITE.............................. 38
TABLE 16: UART RESET CONDITIONS FOR CHANNEL A AND B ............................................................................................ 39
ABSOLUTE MAXIMUM RATINGS ................................................................................. 40
TYPICAL PACKAGE THERMAL RESISTANCE DATA (MARGIN OF ERROR: ± 15%) 40
ELECTRICAL CHARACTERISTICS............................................................................... 40
DC ELECTRICAL CHARACTERISTICS............................................................................................................. 40
TA=-40o to +85oC, Vcc is 2.25V to 3.6V ............................................................................................................... 40
AC ELECTRICAL CHARACTERISTICS............................................................................................................. 41
Unless otherwise noted: TA=-40o to +85oC, Vcc=2.25 - 3.63V, 70 pF load where applicable................................ 41
FIGURE 13. CLOCK TIMING............................................................................................................................................................. 42
FIGURE 14. MODEM INPUT/OUTPUT TIMING FOR CHANNELS A & B ................................................................................................. 42
FIGURE 16. DATA BUS WRITE TIMING ............................................................................................................................................ 43
FIGURE 15. DATA BUS READ TIMING.............................................................................................................................................. 43
FIGURE 17. RECEIVE READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B ......................................................... 44
FIGURE 18. TRANSMIT READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B ....................................................... 44
FIGURE 19. RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA DISABLED] FOR CHANNELS A & B........................................ 45
FIGURE 20. RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA ENABLED] FOR CHANNELS A & B......................................... 45
FIGURE 21. TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE DISABLED] FOR CHANNELS A & B ........................... 46
FIGURE 22. TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE ENABLED] FOR CHANNELS A & B ............................ 46
PACKAGE DIMENSIONS (48 PIN TQFP - 7 X 7 X 1 mm) .................................................................................. 47
PACKAGE DIMENSIONS (32 PIN QFN - 5 X 5 X 0.9 mm).............................................. 48
REVISION HISTORY ..................................................................................................................................... 49
TABLE OF CONTENTS ..................................................................................................... I
II
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