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NOVEMBER 2005
XR16C2850
2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
REV. 2.1.3
GENERAL DESCRIPTION
The XR16C28501 (2850) is an enhanced dual universal asynchronous receiver and transmitter (UART). Enhanced features include 128 bytes of TX and RX FIFOs, programmable TX and RX FIFO trigger level, FIFO level counters, automatic (RTS/ CTS) hardware and (Xon/Xoff) software flow control, automatic RS-485 half duplex direction control output and data rates up to 6.25 Mbps at 5V and 8X sampling clock. Onboard status registers provide the user with operational status and data error flags. An internal loopback capability allows system diagnostics. The 2850 has a full modem interface and can operate at 2.97V to 5.5V and is pin-to-pin compatible to Exar's ST16C2550 and XR16C2750 except the 48-TQFP package. The 2850 register set is compatible to the industry standard ST16C2550 and is available in 48pin TQFP and 44-pin PLCC packages.
NOTE:
1 Covered by U.S. Patent #5,649,122 and #5,949,787
FEATURES Added feature in devices with a top mark date code of "F2 YYWW" and newer:

5V tolerant inputs 0 ns address hold time (TAH)
* Pin-to-pin compatible and functionally compatible to
Exar's ST16C2550 and XR16L2750 and TI's TL16C752B in the 48-TQFP package
* Pin-alike Exar's XR16L2750 and ST16C2550 48TQFP package but with additional CLK8/16, CLKSEL and HDCNTL inputs
* Two independent UART channels

APPLICATIONS
* Portable Appliances * Telecommunication Network Routers * Ethernet Network Routers * Cellular Data Devices * Factory Automation and Process Controls
Register set compatible to 16C550 Up to 6.25 Mbps at 5V, and 4 Mbps at 3.3V Transmit and Receive FIFOs of 128 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 Auto RS-485 Half-duplex Direction Control Wireless Infrared (IrDA 1.0) Encoder/Decoder Full modem interface
* Device Identification and Revision * Crystal oscillator or external clock input * Industrial and commercial temperature ranges * 48-TQFP and 44-PLCC packages
FIGURE 1. XR16C2850 BLOCK DIAGRAM
A2:A0 D7:D0 IOR# IOW# CSA# CSB# INTA INTB TXRDYA# TXRDYB# RXRDYA# RXRDYB# HDCNTL# CLKSEL CLK8/16 Reset 8-bit Data Bus Interface UART Channel A UART Regs BRG 128 Byte TX FIFO TX & RX IR ENDEC
2.97V to 5.5V VCC GND TXA, RXA, DTRA#, DSRA#, RTSA#, DTSA#, CDA#, RIA#, OP2A#
128 Byte RX FIFO TXB, RXB, DTRB#, DSRB#, RTSB#, CTSB#, CDB#, RIB#, OP2B# XTAL1 XTAL2
UART Channel B (same as Channel A)
Crystal Osc/Buffer
Exar Corporation 48720 Kato Road, Fremont CA, 94538 * (510) 668-7000 * FAX (510) 668-7017 * www.exar.com
XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS FIGURE 2. PIN OUT ASSIGNMENT
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REV. 2.1.3
TXRDYA#
48
VCC
45
43
42
41
40
38
47
46
44
39
37
HDCNTL#
DSRA#
RIA#
D2
D1
D0
CTSA#
D4
D3
CDA#
D5 D6 D7 RXB RXA TXRDYB# TXA TXB OP2B#
1 2 3 4 5 6 7 8 9
36 35 34 33
RESET DTRB# DTRA# RTSA# OP2A# RXRDYA# INTA INTB A0 A1 A2 CLKSEL
XR16C2850 48-pin TQFP
32 31 30 29 28 27 26 25
CSA# 10 CSB# 11 NC 12 15 13 18 19 20 22 16 14 17 21 23 CTSB# 24 CLK8/16
GND
DSRB#
RXRDYB#
RTSB#
CDB#
XTAL2
IOW#
XTAL1
IOR#
RIB#
TXRDYA#
DSRA# 41
44
43
42
40
6
5
4
3
2
1
CTSA#
CDA#
RIA#
VCC
D4
D3
D2
D1
D0
D5 D6 D7 RXB RXA
7 8 9 10 11
39 38 37 36
RESET DTRB# DTRA# RTSA#
TXRDYB# 12 TXA TXB 13 14
XR16C2850 44-pin PLCC
35 OP2A# 34 33 32 31 RXRDYA# INTA INTB A0
OP2B# 15 CSA# 16 CSB# 17 XTAL1 18 XTAL2 19 IOW# 20 CDB# 21 GND 22 RXRDYB# 23 IOR# 24 DSRB# 25 RIB# 26 RTSB# 27 CTSB# 28
30 A1 29 A2
ORDERING INFORMATION
PART NUMBER XR16C2850CJ XR16C2850CM XR16C2850IJ XR16C2850IM PACKAGE 44-Lead PLCC 48-Lead TQFP 44-Lead PLCC 48-Lead TQFP OPERATING TEMPERATURE RANGE 0C to +70C 0C to +70C Active Active DEVICE STATUS
-40C to +85C Active -40C to +85C Active
2
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REV. 2.1.3
XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
PIN DESCRIPTIONS
NAME 44-PLCC PIN # 48-TQFP PIN # TYPE DESCRIPTION
DATA BUS INTERFACE A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 IOR# 29 30 31 9 8 7 6 5 4 3 2 24 26 27 28 3 2 1 48 47 46 45 44 19 I Address data lines [2:0]. These 3 address lines select one of the internal registers in UART channel A/B during a data bus transaction. Data bus lines [7:0] (bidirectional).
I/O
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. 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. 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. 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 is LOW when MCR[3] is set to a logic 1. INTA is set to the three state mode and OP2A# is HIGH when MCR[3] is set to a logic 0 (default). See MCR[3]. If this output is not used, leave it unconnected. 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 is LOW when MCR[3] is set to a logic 1. INTB is set to the three state mode and OP2B# is HIGH when MCR[3] is set to a logic 0 (default). See MCR[3]. If this output is not used, leave it unconnected.
IOW#
20
15
I
CSA# CSB# INTA
16 17 33
10 11 30
I I O
INTB
32
29
O
TXRDYA#
1
43
O
UART channel A Transmitter Ready (active low). The output provides the TX FIFO/THR status for transmit channel A. See Table 2. If this output 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 this output 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 2. If this output is not used, leave it unconnected.
RXRDYA#
34
31
O
TXRDYB#
12
6
O
3
XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
NAME RXRDYB# 44-PLCC PIN # 23 48-TQFP PIN # 18 TYPE O DESCRIPTION
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REV. 2.1.3
UART channel B Receiver Ready (active low). This output provides the RX FIFO/RHR status for receive channel B. See Table 2. If this output is not used, leave it unconnected.
MODEM OR SERIAL I/O INTERFACE TXA 13 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 isLOW. If this output is not used, leave it unconnected. UART channel A Receive Data or infrared receive data. Normal receive data input must idle HIGH. The infrared receiver pulses typically idles 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. UART channel A Request-to-Send (active low) or general purpose output. 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]. If this output is not used, leave it unconnected. 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. UART channel A Data-Terminal-Ready (active low) or general purpose output. If this output 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. UART channel A Carrier-Detect (active low) or general purpose input. This input should be connected to VCC when not used. UART channel A Ring-Indicator (active low) or general purpose input. This input should be connected to VCC when not used. 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 is LOW when MCR[3] is set to a logic 1. INTA is set to the three state mode and OP2A# is HIGH when MCR[3] is set to a logic 0. See MCR[3]. This output can only be used as a general purpose output when interrupts are not used, otherwise it will disturb the INTA output functionality. If this output is not used, leave it unconnected. 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 this output is not used, leave it unconnected.
RXA
11
5
I
RTSA#
36
33
O
CTSA#
40
38
I
DTRA# DSRA# CDA# RIA# OP2A#
37 41 42 43 35
34 39 40 41 32
O I I I O
TXB
14
8
O
4
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
48-TQFP PIN # 4 TYPE I DESCRIPTION UART channel B Receive Data or infrared receive data. Normal receive data input must idle HIGH. The infrared receiver pulses typically idles 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. UART channel B Request-to-Send (active low) or general purpose output. 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]. If this output is not used, leave it unconnected. 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. UART channel B Data-Terminal-Ready (active low) or general purpose output. If this output 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. 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. 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 is LOW when MCR[3] is set to a logic 1. INTB is set to the three state mode and OP2B# is HIGH when MCR[3] is set to a logic 0. See MCR[3]. This output can only be used as a general purpose output when interrupts are not used, otherwise it will disturb the INTB output functionality. If this output is not used, leave it unconnected.
NAME RXB
44-PLCC PIN # 10
RTSB#
27
22
O
CTSB#
28
23
I
DTRB# DSRB#
38 25
35 20
O I
CDB#
21
16
I
RIB#
26
21
I
OP2B#
15
9
O
ANCILLARY SIGNALS XTAL1 XTAL2 HDCNTL# 18 19 13 14 37 I O I Crystal or external clock input. Crystal or buffered clock output. RS-485 half duplex directional control for channel A and B (active low). Connect to VCC for normal RTS# function and connect to GND for RS485 half duplex direction control. RTS# pin goes LOW for transmit and HIGH for receive during RS-485 mode. This pin is wire "OR-ed" with FCTR[3]. If this pin is connected to VCC, the function of the RTS# pin can be controlled via FCTR[3]. If this pin is connected to GND, the RTS# pin will always be the RS-485 half duplex direction control and can not be controlled via FCTR[3]. See FCTR[3].
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
NAME CLKSEL 44-PLCC PIN # 48-TQFP PIN # 25 TYPE I DESCRIPTION
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REV. 2.1.3
Clock Pre-scaler select. Connect to VCC for divide by 1 and GND for divide by 4. MCR[7] can override the state of this pin following reset or initialization. See Figure 6 and MCR[7]. Transmit/Receive data sampling rate. Connect to VCC for normal 16X sampling clock (standard baud rates) or GND for 8X sampling clock to double the standard baud rates. 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 at logic 1, the receiver input will be ignored and outputs are reset during reset period (see Table 16). 2.97V to 5.5V power supply. All inputs are 5V tolerant for devices with top mark date code of "F2 YYWW" and newer. Power supply common, ground. No Connection.
CLK8/16
-
24
I
RESET
39
36
I
VCC GND N.C.
44 22 none
42 17 12
Pwr Pwr
Pin type: I=Input, O=Output, I/O= Input/output, OD=Output Open Drain.
6
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REV. 2.1.3
XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
1.0 PRODUCT DESCRIPTION The XR16C2850 (2850) integrates the functions of 2 enhanced 16C550 Universal Asynchrounous 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 128-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 baud rate generator with a prescaler of divide by 1 or 4, and data rate up to 6.25 Mbps with 8X sampling clock rate (available only in the 48-pin TQFP package) or 3.125Mbps in the 16X rate. The XR16C2850 is a 5V and 3.3V device. The 2850 is fabricated with an advanced CMOS process. Enhanced Features The 2850 DUART provides a solution that supports 128 bytes of transmit and receive FIFO memory, instead of 64 bytes provided in the XR16L2750 and 16 bytes in the ST16C2550, or one byte in the ST16C2450. The 2850 is designed to work with high performance data communication systems, that require fast data processing time. Increased performance is realized in the 2850 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 115.2Kbps). This means the external CPU will have to service the receive FIFO at 1.53 ms intervals. However with the 128 byte FIFO in the 2850, the data buffer will not require unloading/loading for 12.2 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 2850 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 2850 is capable of operation up to 3.125 Mbps at 5V with 16X internal sampling clock rate, and 6.25 Mbps at 5V with 8X sampling clock rate (available only on the 48-pin package). The device can operate with an external 24 MHz crystal on pins XTAL1 and XTAL2, or external clock source of up to 50 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 2850 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 2850 is software compatible with previous generation of UARTs, 16C2450, 16C2550 and 16L2750.
7
XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS 2.0 FUNCTIONAL DESCRIPTIONS 2.1 CPU Interface
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REV. 2.1.3
The CPU interface is 8 data bits wide with 3 address lines and control signals to execute data bus read and write transactions. The 2850 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. XR16C2850 DATA BUS INTERCONNECTIONS
D 0 D 1 D 2 D 3 D 4 D 5 D 6 D 7 A0 A1 A2 IOR # IOW# U T_C AR SA# U T_C AR SB# U T_IN AR TA U T_IN AR TB TXR YA# D RD XR YA# TXR YB# D RD XR YB# U T_R AR ESET
D 0 D 1 D 2 D 3 D 4 D 5 D 6 D 7 A0 A1 A2 IOR # IOW# C SA# C SB# IN TA IN TB TXR YA# D RD XR YA# TXR YB# D RD XR YB# R ESET
VC C TXA R XA D A# TR UT AR C hannel A R TSA# C TSA# D A# SR C A# D R IA# OP2A#
VC C
Serial Interface of R S-232, R S-485
TXB R XB D B# TR UT AR C hannel B R TSB# C TSB# D B# SR C B# D R IB# OP2B# Serial Interface of R S232, R S-485
GN D 2750int
.
2.2
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. 2.3 Device Identification and Revision The XR16C2850 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. Now reading the content of the DLM will provide 0x12 for the XR16C2850 and reading the content of DLL will provide the revision of the part; for example, a reading of 0x01 means revision A. 2.4 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 logic 0 on 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 registers, but do not attempt to read from both uarts simultaneously. Individual channel select functions are shown in Table 1.
8
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
TABLE 1: CHANNEL A AND B SELECT
CSA# 1 0 1 0 CSB# 1 1 0 0 FUNCTION UART de-selected Channel A selected Channel B selected Channel A and B selected
2.5
Channel A and B Internal Registers
Each UART channel in the 2850 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), and a user accessible scratchpad register (SPR). Beyond the general 16C2550 features and capabilities, the 2850 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. 2.6 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 2850 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 2850 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 20 through 25. TABLE 2: TABLE 2TXRDY# AND RXRDY# OUTPUTS IN FIFO AND DMA MODE
PINS FCR BIT-0=0 (FIFO DISABLED) FCR BIT-0=1 (FIFO ENABLED) FCR Bit-3 = 0 (DMA Mode Disabled) RXRDY# A/B LOW = 1 byte HIGH = no data TXRDY# A/B LOW = THR empty HIGH = byte in THR LOW = at least 1 byte in FIFO HIGH = FIFO empty LOW = FIFO empty HIGH = at least 1 byte in FIFO FCR Bit-3 = 1 (DMA Mode Enabled) HIGH to LOW transition when FIFO reaches the trigger level, or timeout occurs. LOW to HIGH transition when FIFO empties. LOW = FIFO has at least 1 empty location HIGH = FIFO is full
9
XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS 2.7 INTA and INTB Ouputs
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The INTA and INTB interrupt output output changes according to the operating mode and enahnced features setup. Table 3 and 4 summarize the operating behavior for the transmitter and receiver. Also see Figures 20 through 25. TABLE 3: INTA AND INTB PINS OPERATION FOR TRANSMITTER
Auto RS485 Mode INTA/B Pin INTA/B Pin NO YES FCR BIT-0 = 0 (FIFO DISABLED) LOW = a byte in THR HIGH = THR empty LOW = a byte in THR HIGH = transmitter empty FCR BIT-0 = 1 (FIFO ENABLED) LOW = FIFO above trigger level HIGH = FIFO below trigger level or FIFO empty LOW = FIFO above trigger level HIGH = FIFO below trigger level or transmitter empty
TABLE 4: INTA AND INTB PIN OPERATION FOR RECEIVER
FCR BIT-0 = 0 (FIFO DISABLED) INTA/B Pin LOW = no data HIGH = 1 byte FCR BIT-0 = 1 (FIFO ENABLED) LOW = FIFO below trigger level HIGH = FIFO above trigger level
2.8
Crystal Oscillator or External Clock Input
The 2850 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. SEE"PROGRAMMABLE BAUD RATE GENERATOR" ON PAGE 11. FIGURE 4. TYPICAL OSCILLATOR CONNECTIONS
XTAL1
XTAL2 R1 0-120 (Optional) 1.8432 MHz to 24 MHz
R2 500 - 1 Y1 C1 22-47 pF C2 22-47 pF
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). Alternatively, an external clock can be connected to the XTAL1 pin to clock the internal baud rate generator for standard or custom rates.
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
Typical oscillator connections are shown in Figure 4. For further reading on oscillator circuit please see application note DAN108 on EXAR's web site. 2.9 Programmable Baud Rate Generator A single Baud Rate Generator (BRG) is provided for the transmitter and receiver, allowing independent TX/RX channel control. The programmable Baud Rate Generator is capable of operating with a crystal frequency of up to 24 MHz. However, with an external clock input on XTAL1 pin and a 2K ohms pull-up resistor on XTAL2 pin (as shown in Figure 5) it can extend its operation up to 50 MHz (3.125 Mbps serial data rate and 16X sampling) at room temperature and 5.0V. FIGURE 5. EXTERNAL CLOCK CONNECTION FOR EXTENDED DATA RATE
vcc gnd
External Clock
XTAL1
VCC R1 2K XTAL2
Each UART also has their own prescaler along with the BRG. The prescaler is controlled by CLKSEL hardware pin or 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 and can override the CLKSEL pin following reset. The clock output of the prescaler goes to the BRG. The BRG further divides this clock by a programmable divisor between 1 and (216 -1) to obtain a 16X sampling rate clock of the serial data rate. The sampling rate clock is used by the transmitter for data bit shifting and receiver for data sampling. FIGURE 6. BAUD RATE GENERATOR AND PRESCALER
DLL and DLM Registers Prescaler Divide by 1 XTAL1 XTAL2 Crystal Osc/ Buffer Prescaler Divide by 4 MCR Bit-7=0 (default) Baud Rate Generator Logic MCR Bit-7=1 16X Sampling Rate Clock to Transmitter
Programming the Baud Rate Generator Registers DLM and DLL provides the capability of selecting the operating data rate. Table 5 shows the standard data rates available with a 14.7456 MHz crystal or external clock at 16X sampling rate clock rate. A 16X sampling clock is typically used. However, user can select the 8X sampling clock rate mode to double the operating data rate. When using a non-standard data rate crystal or external clock, the divisor value can be calculated for DLL/DLM with the following equation.
11
XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
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REV. 2.1.3
divisor (decimal) = (XTAL1 clock frequency / prescaler) / (serial data rate x 16), with CLK8/16 pin = 1 divisor (decimal) = (XTAL1 clock frequency / prescaler) / (serial data rate x 8), with CLK8/16 pin = 0
TABLE 5: TYPICAL DATA RATES WITH A 14.7456 MHZ CRYSTAL OR EXTERNAL CLOCK
OUTPUT Data Rate OUTPUT Data Rate DIVISOR FOR 16x DIVISOR FOR 16x MCR Bit-7=1 MCR Bit-7=0 Clock (Decimal) Clock (HEX) (DEFAULT) 100 600 1200 2400 4800 9600 19.2k 38.4k 57.6k 115.2k 230.4k 400 2400 4800 9600 19.2k 38.4k 76.8k 153.6k 230.4k 460.8k 921.6k 2304 384 192 96 48 24 12 6 4 2 1 900 180 C0 60 30 18 0C 06 04 02 01 DLM PROGRAM VALUE (HEX) 09 01 00 00 00 00 00 00 00 00 00 DLL PROGRAM VALUE (HEX) 00 80 C0 60 30 18 0C 06 04 02 01 DATA RATE ERROR (%) 0 0 0 0 0 0 0 0 0 0 0
2.10
Transmitter
The transmitter section comprises of an 8-bit Transmit Shift Register (TSR) and 128 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 CLK8/16 pin description). 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). 2.10.1 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 128 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. 2.10.2 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.
12
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
FIGURE 7. TRANSMITTER OPERATION IN NON-FIFO MODE
Data Byte
Transmit Holding Register (THR)
THR Interrupt (ISR bit-1) Enabled by IER bit-1
16X or 8X Clock Transmit Shift Register (TSR)
M S B L S B
TXNOFIFO1
2.10.3
Transmitter Operation in FIFO Mode
The host may fill the transmit FIFO with up to 128 bytes of transmit data. The THR empty flag (LSR bit-5) is set whenever the FIFO is empty. The THR empty flag can generate a transmit empty interrupt (ISR bit-1) when the amount of data in the FIFO falls below its programmed trigger level. The transmit empty interrupt is enabled by IER bit-1. The TSR flag (LSR bit-6) is set when TSR/FIFO becomes empty. FIGURE 8. TRANSMITTER OPERATION IN FIFO AND FLOW CONTROL MODE
Transmit Data Byte
Transmit FIFO
THR Interrupt (ISR bit-1) falls below the programm ed Trigger Level and then when becom es em pty. FIFO is Enabled by FCR bit-0=1
Auto CTS Flow Control (CTS# pin) Flow Control Characters (Xoff1/2 and Xon1/2 Reg. Auto Software Flow Control
16X or 8X Clock
Transm it Data Shift Register (TSR)
T XF IF O 1
13
XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS 2.11 Receiver
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REV. 2.1.3
The receiver section contains an 8-bit Receive Shift Register (RSR) and 128 bytes of FIFO which includes a byte-wide Receive Holding Register (RHR). The RSR uses the 16X/8X clock (CLK8/16 pin) 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. 2.11.1 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 128 bytes by 11-bits wide, the 3 extra bits are for the 3 error tags to be reported in LSR register. When the FIFO is enabled by FCR bit-0, the RHR contains the first data character received by the FIFO. After the RHR is read, the next character byte is loaded into the RHR and the errors associated with the current data byte are immediately updated in the LSR bits 2-4. FIGURE 9. RECEIVER OPERATION IN NON-FIFO MODE
16X or 8X Clock Receive Data Shift Register (RSR) Data Bit Validation
Receive Data Characters
Receive Data Byte and Errors
Error Tags in LSR bits 4:2
Receive Data Holding Register (RHR)
RHR Interrupt (ISR bit-2)
RXFIFO1
14
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
FIGURE 10. RECEIVER OPERATION IN FIFO AND AUTO RTS FLOW CONTROL MODE
16X or 8X Clock
Receive Data Shift Register (RSR)
Data Bit Validation
Receive Data Characters
128 bytes by 11-bit wide FIFO
Example: - RX FIFO trigger level selected at 16 bytes (See Note Below) Data falls to 8 Error Tags (128-sets)
Receive Data FIFO
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. RHR Interrupt (ISR bit-2) programmed for desired FIFO trigger level. FIFO is Enabled by FCR bit-0=1 RTS# de-asserts when data fills above the flow control trigger level to suspend remote transmitter. Enable by EFR bit-6=1, MCR bit-1.
FIFO Trigger=16
Data fills to 24 Error Tags in LSR bits 4:2
Receive Data Byte and Errors
Receive Data
RXFIFO1
NOTE: Table-B selected as Trigger Table for Figure 10 (Table 10).
2.12
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 11):
* 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).
With the Auto RTS function enabled, the RTS# output pin will not be de-asserted (HIGH) when the receive FIFO reaches the programmed trigger level, but will be de-asserted when the FIFO reaches the next trigger level (See Table 10). The RTS# output pin will be asserted (LOW) again after the FIFO is unloaded to the next trigger level below the programmed trigger level. However, even under these conditions, the 2850 will continue to accept data until the receive FIFO is full if the remote UART transmitter continues to send data.
* Enable RTS interrupt through IER bit-6 (after setting EFR bit-4). The UART issues an interrupt when the
RTS# pin is de-asserted (HIGH) during Auto RTS flow control mode: ISR bit-5 will be set to logic 1. 2.13 Auto RTS Hysteresis The 2850 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 2850 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.
15
XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS 2.14 Auto CTS Flow Control
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REV. 2.1.3
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 11):
* Enable auto CTS flow control using EFR bit-7.
With the Auto CTS function enabled, the UART will suspend transmission as soon as the stop bit of the character in the Transmit Shift Register has been shifted out. Transmission is resumed after the CTS# input is re-asserted (LOW), indicating more data may be sent.
* 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) during Auto CTS flow control mode: ISR bit-5 will be set to 1. FIGURE 11. AUTO RTS AND CTS FLOW CONTROL OPERATION
Local UART UARTA Receiver FIFO Trigger Reached Auto RTS Trigger Level Transmitter Auto CTS Monitor RXA TXB Remote UART UARTB Transmitter Auto CTS Monitor Receiver FIFO Trigger Reached Auto RTS Trigger Level
RTSA# TXA
CTSB# RXB
CTSA# Assert RTS# to Begin Transmission 1 ON 2 7 ON 3 8 OFF
RTSB#
RTSA# CTSB# TXB
OFF
10 11
ON ON
Data Starts 4 RXA FIFO INTA (RXA FIFO Interrupt) Receive RX FIFO Data Trigger Level 5
6
Suspend
Restart 9
RTS High Threshold
RTS Low Threshold
12
RX FIFO Trigger Level
RTSCTS1
The local UART (UARTA) starts data transfer by asserting RTSA# (1). RTSA# is normally connected to CTSB# (2) of remote UART (UARTB). CTSB# allows its transmitter to send data (3). TXB data arrives and fills UARTA receive FIFO (4). When RXA data fills up to its receive FIFO trigger level, UARTA activates its RXA data ready interrupt (5) and continues to receive and put data into its FIFO. If interrupt service latency is long and data is not being unloaded, UARTA monitors its receive data fill level to match the upper threshold of RTS delay and de-assert RTSA# (6). CTSB# follows (7) and request UARTB transmitter to suspend data transfer. UARTB stops or finishes sending the data bits in its transmit shift register (8). When receive FIFO data in UARTA is unloaded to match the lower threshold of RTS delay (9), UARTA re-asserts RTSA# (10), CTSB# recognizes the change (11) and restarts its transmitter and data flow again until next receive FIFO trigger (12). This same event applies to the reverse direction when UARTA sends data to UARTB with RTSB# and CTSA# controlling the data flow.
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
2.15
Auto Xon/Xoff (Software) Flow Control
When software flow control is enabled (See Table 15), the 2850 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 2850 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 2850 will monitor the receive data stream for a match to the Xon-1,2 character. If a match is found, the 2850 will resume operation and clear the flags (ISR bit-4). Reset initially sets the contents of the Xon/Xoff 8-bit flow control registers to a logic 0. Following reset, any desired Xon/Xoff value can be used for software flow control. Different conditions can be set to detect Xon/Xoff characters (See Table 15) and suspend/resume transmissions. When double 8-bit Xon/Xoff characters are selected, the 2850 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 2850 automatically sends an Xoff message (when enabled) via the serial TX output to the remote modem. The 2850 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 A-D). To clear this condition, the 2850 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 13. Table 6 below explains this when Trigger Table-B (See Table 10) is selected. TABLE 6: AUTO XON/XOFF (SOFTWARE) FLOW CONTROL
RX TRIGGER LEVEL 8 16 24 28 INT PIN ACTIVATION 8 16 24 28 XOFF CHARACTER(S) SENT (CHARACTERS IN RX FIFO) 8* 16* 24* 28* XON CHARACTER(S) SENT (CHARACTERS IN RX FIFO) 0 8 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.
2.16
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 2850 compares each incoming receive character with Xoff-2 data. If a match exists, the received data will be transferred to FIFO and ISR bit-4 will be set to indicate detection of special character. Although the Internal Register Table shows Xon, Xoff Registers with eight bits of character information, the actual number of bits is dependent on the programmed word length. Line Control Register (LCR) bits 0-1 defines the number of character bits, i.e., either 5 bits, 6 bits, 7 bits, or 8 bits. The word length selected by LCR bits 0-1 also determines the number of bits that will be used for the special character comparison. Bit-0 in the Xon, Xoff Registers corresponds with the LSB bit for the receive character. 2.17 Auto RS485 Half-duplex Control The auto RS485 half-duplex direction control changes the behavior of the transmitter when enabled by FCTR bit-3. It de-asserts RTS# output (HIGH) 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# output (LOW) prior sending the data.
17
XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS 2.18 Infrared Mode
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REV. 2.1.3
The 2850 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 HIGHpulse 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 12 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 12. 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 2850 has a provision to invert the input polarity to accomodate this. In this case user can enable FCTR bit-2 to invert the input signal. FIGURE 12. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING
Character Start Stop 1 1 0 1 1/2 Bit Time 3/16 Bit Time
IrEncoder-1
Data Bits 1 0 1 0 0
TX Data
0
Transmit IR Pulse (TX Pin) Bit Time
Receive IR Pulse (RX pin)
Bit Time 1/16 Clock Delay
RX Data
0 Start
1
0
1
0
0
11
0
1 Stop
IRdecoder-
Data Bits Character
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
2.19
Sleep Mode with Auto Wake-Up
The 2850 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 2850 to enter sleep mode: no interrupts pending for both channels of the 2850 (ISR bit-0 = 1) sleep mode of both channels are enabled (IER bit-4 = 1) modem inputs are not toggling (MSR bits 0-3 = 0) RX input pin of both channels are idling at a logic 1 The 2850 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 2850 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 2850 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 2850 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 2850 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 2850 is in sleep mode, the maximum current will be in the microamp range as specified in the DC Electrical Characteristics on page 38. If the input lines are floating or are toggling while the 2850 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. 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
XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS 2.20 Internal Loopback
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REV. 2.1.3
The 2850 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 13 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 pin is held HIGH or mark condition while RTS# and DTR# are de-asserted, and CTS#, DSR# CD# and RI# inputs are ignored. Caution: the RX input must be held HIGH during loopback test else upon exiting the loopback test the UART may detect and report a false "break" signal. FIGURE 13. INTERNAL LOOP BACK IN CHANNELS A AND B
VCC Transmit Shift Register (THR/FIFO) MCR bit-4=1 Internal Data Bus Lines and Control Signals Receive Shift Register (RHR/FIFO) VCC RTS# Modem / General Purpose Control Logic RTSA#/RTSB# TXA/TXB
RXA/RXB
CTS# VCC DTR# DSR# OP1# RI# VCC OP2# CD#
CTSA#/CTSB# DTRA#/DTRB#
DSRA#/DSRB# RIA#/RIB# OP2A#/OP2B#
CDA#/CDB#
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
3.0 UART INTERNAL REGISTERS Each of the UART channel in the 2850 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
A2,A1,A0 ADDRESSES REGISTER READ/WRITE COMMENTS
16C550 COMPATIBLE REGISTERS 0 0 0 0 0 0 0 0 1 1 1 1 1 1 00 00 01 00 01 01 10 11 00 01 10 11 11 11 RHR - Receive Holding Register THR - Transmit Holding Register DLL - Div Latch Low Byte DLM - Div Latch High Byte DREV - Device Revision Code DVID - Device Identification Code IER - Interrupt Enable Register ISR - Interrupt Status Register FCR - FIFO Control Register LCR - Line Control Register MCR - Modem Control Register LSR - Line Status Register Reserved MSR - Modem Status Register Reserved SPR - Scratch Pad Register FLVL - TX/RX FIFO Level Counter Register EMSR - Enhanced Mode Select Register ENHANCED REGISTERS 0 0 0 1 1 1 1 00 01 10 00 01 10 11 TRG - TX/RX FIFO Trigger Level Reg FC - TX/RX FIFO Level Counter Register FCTR - Feature Control Reg EFR - Enhanced Function Reg Xon-1 - Xon Character 1 Xon-2 - Xon Character 2 Xoff-1 - Xoff Character 1 Xoff-2 - Xoff Character 2 Write-only Read-only Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write LCR = 0xBF Read-only Write-only Read/Write Read/Write Read-only Read-only Read/Write Read-only Write-only Read/Write Read/Write Read-only Write-only Read-only Write-only Read/Write Read-only Write-only LCR[7] = 0, FCTR[6] = 0 LCR[7] = 0, FCTR[6] = 1 LCR[7] = 0 LCR[7] = 0 LCR[7] = 0
LCR[7] = 1, LCR 0xBF DLL, DLM = 0x00, LCR[7] = 1, LCR 0xBF
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
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REV. 2.1.3
TABLE 8: INTERNAL REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED WHEN EFR BIT-4=1
ADDRESS A2-A0 REG NAME READ/ WRITE BIT-7 BIT-6 BIT-5 BIT-4 BIT-3 BIT-2 BIT-1 BIT-0 COMMENT
16C550 Compatible Registers 000 000 001 RHR THR IER RD WR RD/WR Bit-7 Bit-7 0/ CTS# Int. Enable 010 ISR RD Bit-6 Bit-6 0/ RTS# Int. Enable Bit-5 Bit-5 0/ Xoff Int.. Enable 0/ INT Source Bit-5 0/ Bit-4 Bit-4 0/ Sleep Mode Enable 0/ INT Source Bit-4 0/ Bit-3 Bit-3 Bit-2 Bit-2 Bit-1 Bit-1 Bit-0 Bit-0
Modem RX Line TX RX Status Int. Status- Empty Data Int. Enable Int. Int. Enable Enable Enable INT Source Bit-3 INT INT INT Source Source Source Bit-2 Bit-1 Bit-0 LCR[7] = 0
FIFOs FIFOs Enabled Enabled
010
FCR
WR
RX FIFO RX FIFO Trigger Trigger
TX FIFO TX FIFO Trigger Trigger Set Parity 0/ Even Parity
DMA Mode Enable Parity Enable
TX FIFO Reset Stop Bits
RX FIFO Reset
FIFOs Enable
011
LCR
RD/WR
Divisor Enable 0/ BRG Prescaler
Set TX Break 0/
Word Word Length Length Bit-1 Bit-0
100
MCR
RD/WR
Internal OP2#/INT Rsvd RTS# DTR# Lopback Output (OP1#) Output Output IR Mode XonAny Enable Enable Control Control ENable THR & TSR Empty RI# Input Bit-6 Rsvd THR Empty RX Break RX Framing Error RX Parity Error Delta RI# Bit-2 Rsvd RX Overrun Error Delta DSR# Bit-1 Rx/Tx FIFO Count RX Data Ready Delta CTS# Bit-0 Rx/Tx FIFO Count LCR[7] = 0 FCTR[6]=0 LCR[7] = 0
101
LSR
RD
RX FIFO Global Error CD# Input Bit-7 Rsvd
110 111 111
MSR SPR EMSR
RD RD/WR WR
DSR# Input Bit-5 Auto RTS Hyst. bit-3 Bit-5
CTS# Input Bit-4 Auto RTS Hyst. bit-2 Bit-4
Delta CD# Bit-3 Rsvd
LCR[7] = 0 FCTR[6]=1
111
FLVL
RD
Bit-7
Bit-6
Bit-3
Bit-2
Bit-1
Bit-0
Baud Rate Generator Divisor 000 001 DLL DLM RD/WR RD/WR 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 LCR[7] = 1 LCR 0xBF
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
TABLE 8: INTERNAL REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED WHEN EFR BIT-4=1
ADDRESS A2-A0 000 001 REG NAME DREV DVID READ/ WRITE RD RD BIT-7 Bit-7 0 BIT-6 Bit-6 0 BIT-5 Bit-5 0 BIT-4 Bit-4 1 BIT-3 Bit-3 0 BIT-2 Bit-2 0 BIT-1 Bit-1 1 BIT-0 Bit-0 0 COMMENT LCR[7] = 1 LCR 0xBF DLL=0x00 DLM=0x00
Enhanced Registers 000 000 001 TRG FC WR RD Bit-7 Bit-7 RX/TX Mode Bit-6 Bit-6 SCPAD Swap Bit-5 Bit-5 Trig Table Bit-1 Special Char Select Bit-4 Bit-4 Trig Table Bit-0
Enable IER [7:4], ISR [5:4], FCR[5:4], MCR[7:5]
Bit-3 Bit-3 Auto RS485 Direction Control Software Flow Cntl Bit-3 Bit-3 Bit-3 Bit-3 Bit-3
Bit-2 Bit-2 RX IR Input Inv.
Bit-1 Bit-1 Auto RTS Hyst Bit-1 Software Flow Cntl Bit-1 Bit-1 Bit-1 Bit-1 Bit-1
Bit-0 Bit-0 Auto RTS Hyst Bit-0 Software Flow Cntl Bit-0 Bit-0 Bit-0 Bit-0 Bit-0
FCTR RD/WR
010
EFR
RD/WR
Auto CTS Enable
Auto RTS Enable
Software Flow Cntl Bit-2 Bit-2 Bit-2 Bit-2 Bit-2
LCR=0XBF
100 101 110 111
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
4.0 INTERNAL REGISTER DESCRIPTIONS 4.1 4.2 4.3 Receive Holding Register (RHR) - Read- Only Transmit Holding Register (THR) - Write-Only Interrupt Enable Register (IER) - Read/Write SEE"RECEIVER" ON PAGE 14. SEE"TRANSMITTER" ON PAGE 12. The Interrupt Enable Register (IER) masks the interrupts from receive data ready, transmit empty, line status and modem status registers. These interrupts are reported in the Interrupt Status Register (ISR). 4.3.1 IER versus Receive FIFO Interrupt Mode Operation When the receive FIFO (FCR BIT-0 = 1) and receive interrupts (IER BIT-0 = 1) are enabled, the RHR interrupts (see ISR bits 2 and 3) status will reflect the following: 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.
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS 4.3.2 IER versus Receive/Transmit FIFO Polled Mode Operation
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When FCR BIT-0 equals a logic 1 for FIFO enable; resetting IER bits 0-3 enables the XR16C2850 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 nonFIFO 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 bits 1-4 generate an interrupt immediately when the character has been received.
* Logic 0 = Disable the receiver line status interrupt (default). * Logic 1 = Enable the receiver line status interrupt.
IER[3]: Modem Status Interrupt Enable
* Logic 0 = Disable the modem status register interrupt (default). * Logic 1 = Enable the modem status register interrupt.
IER[4]: Sleep Mode Enable (requires EFR bit-4 = 1)
* Logic 0 = Disable Sleep Mode (default). * Logic 1 = Enable Sleep Mode. See Sleep Mode section for complete 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 software flow control, receive Xoff interrupt. See Software Flow Control section for
details. IER[6]: RTS# Output Interrupt Enable (requires EFR bit-4=1)
* Logic 0 = Disable the RTS# interrupt (default). * Logic 1 = Enable the RTS# interrupt. The UART issues an interrupt when the RTS# pin makes a transition
from LOW to HIGH.
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
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 enabled
by EFR bit-7.
* RTS# is when its receiver toggles the output pin (from LOW to HIGH) during auto RTS flow control enabled
by EFR bit-6. 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.
]
TABLE 9: INTERRUPT SOURCE AND PRIORITY LEVEL
PRIORITY LEVEL 1 2 3 4 5 6 BIT-5 0 0 0 0 0 0 ISR REGISTER STATUS BITS BIT-4 0 0 0 0 0 1 BIT-3 0 1 0 0 0 0 BIT-2 1 1 1 0 0 0 BIT-1 1 0 0 1 0 0 BIT-0 0 0 0 0 0 0 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) SOURCE OF INTERRUPT
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS TABLE 9: INTERRUPT SOURCE AND PRIORITY LEVEL
PRIORITY LEVEL 7 BIT-5 1 0 ISR REGISTER STATUS BITS BIT-4 0 0 BIT-3 0 0 BIT-2 0 0 BIT-1 0 0 BIT-0 0 1 CTS#, RTS# change of state None (default)
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SOURCE OF INTERRUPT
ISR[0]: Interrupt Status
* Logic 0 = An interrupt is pending and the ISR contents may be used as a pointer to the appropriate interrupt
service routine.
* Logic 1 = No interrupt pending (default condition).
ISR[5:1]: Interrupt Status These bits indicate the source for a pending interrupt at interrupt priority levels (See Table 9). See "Section 4.4.1, Interrupt Generation:" on page 25 and "Section 4.4.2, Interrupt Clearing:" on page 25 for details. 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. 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.
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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 (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. TABLE 10: TRANSMIT AND RECEIVE FIFO TRIGGER TABLE AND LEVEL SELECTION
TRIGGER TABLE Table-A FCTR BIT-5 0 FCTR BIT-4 0 0 0 1 1 Table-B 0 1 0 1 0 1 0 0 1 1 0 0 1 1 Table-C 1 0 0 1 0 1 0 0 1 1 0 0 1 1 Table-D 1 1 X 0 1 0 1 X X X 0 1 0 1 8 16 56 60 Programmable Programmable 16L2752, 16L2750, 16C2852, 16C850, via TRG via TRG 16C854, 16C864 register. register. FCTR[7] = 0. FCTR[7] = 1. 0 1 0 1 8 16 24 28 8 16 32 56 16C654 FCR BIT-7 FCR BIT-6 FCR BIT-5 0 FCR
BIT-4
RECEIVE TRIGGER LEVEL
TRANSMIT TRIGGER LEVEL 1 (default)
COMPATIBILITY 16C550, 16C2550, 16C2552, 16C554, 16C580
0 1 (default) 4 8 14
16 8 24 30
16C650A
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS 4.6 Line Control Register (LCR) - Read/Write
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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 0 0 1 1 BIT-0 0 1 0 1 WORD LENGTH 5 (default) 6 7 8
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.
BIT-2 0 1 1 WORD
LENGTH
STOP BIT LENGTH (BIT TIME(S)) 1 (default) 1-1/2 2
5,6,7,8 5 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.
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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 X 0 0 1 1 LCR BIT-4 X 0 1 0 1 LCR BIT-3 0 1 1 1 1 PARITY SELECTION No parity Odd parity Even parity Force parity to mark, "1" Forced parity to space, "0"
LCR[6]: Transmit Break Enable When enabled, the Break control bit causes a break condition to be transmitted (the TX output is forced to a "space', 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) 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 enabled by EFR bit-6. The RTS# output must be asserted before the auto RTS can take effect. If the modem interface is not used, this output may be used as a general purpose output.
* Logic 0 = Force RTS# output HIGH (default). * Logic 1 = Force RTS# output LOW. If auto RTS flow control is enabled, it will take effect after this bit has
been set. MCR[2]: Reserved OP1# is not available as an output pin on the 2850. 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.
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS MCR[3]: OP2# Output / INT Output Enable
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This bit enables and 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 is HIGH (default). * Logic 1 = INT (A-B) outputs enabled (active mode) and OP2# output is LOW.
MCR[4]: Internal Loopback Enable
* Logic 0 = Disable loopback mode (default). * Logic 1 = Enable local loopback mode, see loopback section and Figure 13.
MCR[5]: Xon-Any Enable
* Logic 0 = Disable Xon-Any function (for 16C550 compatibility, 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 2850 is programmed to use the Xon/Xoff flow control. MCR[6]: Infrared Encoder/Decoder Enable
* 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 LOW during idle data conditions. MCR[7]: Clock Prescaler Select
* Logic 0 = Divide by one. The input clock from the crystal or external clock is fed directly to the Programmable
Baud Rate Generator without further modification, i.e., divide by one (default).
* Logic 1 = Divide by four. The prescaler divides the input clock from the crystal or external clock by four and
feeds it to the Programmable Baud Rate Generator, hence, data rates become one forth. 4.8 Line Status Register (LSR) - Read Only This register provides the status of data transfers between the UART and the host. If IER bit-2 is set to a logic 1, an LSR interrupt will be generated immediately when any character in the RX FIFO has an error (parity, framing, overrun, break). LSR[0]: Receive Data Ready Indicator
* Logic 0 = No data in receive holding register or FIFO (default). * Logic 1 = Data has been received and is saved in the receive holding register or FIFO.
LSR[1]: Receiver Overrun 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. If IER bit-2 is set, an interrupt will be generated immediately. 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.
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
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 a logic 0 for at least one character frame time). In the
FIFO mode, only one break character is loaded into the FIFO. The break indication remains until the RX input returns to the idle condition, "mark" or HIGH. LSR[5]: Transmit Holding Register Empty Flag This bit is the Transmit Holding Register Empty indicator. The THR bit is set to a logic 1 when the last data byte is transferred from the transmit holding register to the transmit shift register. The bit is reset to logic 0 concurrently with the data loading to the transmit holding register by the host. In the FIFO mode this bit is set when the transmit FIFO is empty, it is cleared when the transmit FIFO contains at least 1 byte. LSR[6]: THR and TSR Empty Flag This bit is set to a logic 1 whenever the transmitter goes idle. It is set to logic 0 whenever either the THR or TSR contains a data character. In the FIFO mode this bit is set to a logic 1 whenever the transmit FIFO and transmit shift register are both empty. 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 logic 0 to a logic 1, ending of the ringing signal. A modem status
interrupt will be generated if MSR interrupt is enabled (IER bit-3). MSR[3]: Delta CD# Input Flag
* Logic 0 = No change on CD# input (default). * Logic 1 = Indicates that the CD# input has changed state since the last time it was monitored. A modem
status interrupt will be generated if MSR interrupt is enabled (IER bit-3).
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS MSR[4]: CTS Input Status
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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. 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 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] 0 1 1 1 1 EMSR[1] X 0 0 1 1 EMSR[0] Scratchpad is X 0 1 0 1 Scratchpad RX FIFO Counter Mode TX FIFO Counter Mode RX FIFO Counter Mode Alternate RX/TX FIFO Counter Mode
During Alternate RX/TX FIFO Counter Mode, the first value read after EMSR bits 1-0 have been asserted will always be the RX FIFO Counter. The second value read will correspond with the TX FIFO Counter. The next value will be the RX FIFO Counter again, then the TX FIFO Counter and so on and so forth. EMSR[3:2]: Reserved
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
EMSR[5:4]: Extended RTS Hysteresis TABLE 13: EXTENDED RTS HYSTERESIS
EMSR BIT-5 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 EMSR BIT-4 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 FCTR BIT-1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 FCTR BIT-0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 RTS# HYSTERESIS (CHARACTERS) 0 4 6 8 8 16 24 32 40 44 48 52 12 20 28 36
EMSR[7:6]: Reserved 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 and DLM) - Read/Write The concatenation of the contents of DLM and DLL gives the 16-bit divisor value which is used to calculate the baud rate:
* Baud Rate = (Clock Frequency / 16) / Divisor
See MCR bit-7 and the baud rate table also. 4.14 Device Identification Register (DVID) - Read Only This register contains the device ID (0x12 for XR16C2850). Prior to reading this register, DLL and DLM should be set to 0x00. 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.
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS 4.16 Trigger Level / FIFO Data Count Register (TRG) - Write-Only User Programmable Transmit/Receive Trigger Level Register. TRG[7:0]: Trigger Level Register
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REV. 2.1.3
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 FIFO Data Count Register (FC) - Read-Only This register is accessible when LCR = 0xBF. Note that this register is not identical to the FIFO Level Register which is located in the general register set when FCTR bit-6 = 1. FC[7:0]: FIFO Data Count Register Transmit/Receive FIFO Count. Number of characters in Transmit (FCTR[7] = 1) or Receive FIFO (FCTR[7] = 0) can be read via this register. 4.18 Feature Control Register (FCTR) - Read/Write This register controls the XR16C2850 new functions that are not available in ST16C550 or ST16C650A. 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 This bit controls the functionality of the RTS# output if HDCNTL# is connected to VCC. If HDCNTL# is connected to GND, then the RTS# output will function as the RS-485 half-duplex direction control signal.
* 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 logic low when a data byte is loaded into the TX FIFO. FCTR[5:4]: Transmit/Receive Trigger Table Select See Table 10 for more details. TABLE 14: TRIGGER TABLE SELECT
FCTR BIT-5 0 0 1 1 FCTR BIT-4 0 1 0 1 TABLE 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 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.
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FCTR[7]: Programmable Trigger Register Select
* 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. TABLE 15: SOFTWARE FLOW CONTROL FUNCTIONS
EFR BIT-3 CONT-3 0 0 1 0 1 X X X 1 0 1 0 EFR BIT-2 CONT-2 0 0 0 1 1 X X X 0 1 1 0 EFR BIT-1 CONT-1 0 X X X X 0 1 0 1 1 1 1 EFR BIT-0 CONT-0 0 X X X X 0 0 1 1 1 1 1 TRANSMIT AND RECEIVE SOFTWARE FLOW CONTROL 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 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, and MCR bits 5-7 to be modified. After modifying any enhanced bits, EFR bit-4 can be set to a logic 0 to latch the new values. This feature prevents legacy software from altering or overwriting the enhanced functions once set. Normally, it is recommended to leave it enabled, logic 1.
* Logic 0 = modification disable/latch enhanced features. IER bits 4-7, ISR bits 4-5, FCR bits 4-5, and MCR
bits 5-7 are saved to retain the user settings. After a reset, the IER bits 4-7, ISR bits 4-5, FCR bits 4-5, and MCR bits 5-7are 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.
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS EFR[5]: Special Character Detect Enable
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* 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. 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 to a logic 1 at the next upper trigger level or hysteresis level. RTS# will return to a logic 0 when FIFO data falls below the next lower trigger level. The RTS# output must be asserted (logic 0) 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 to logic
1. Data transmission resumes when CTS# returns to a logic 0. 4.20 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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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS TABLE 16: UART RESET CONDITIONS FOR CHANNEL A AND B
REGISTERS DLL DLM RHR THR IER FCR ISR LCR MCR LSR MSR SPR EMSR FLVL EFR XON1 XON2 XOFF1 XOFF2 FC I/O SIGNALS TX OP2# RTS# DTR# RXRDY# TXRDY# INT HIGH HIGH HIGH HIGH HIGH LOW Three-State Condition Bits 7-0 = 0xXX Bits 7-0 = 0xXX 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 Bits 3-0 = Logic 0 Bits 7-4 = Logic levels of the inputs inverted Bits 7-0 = 0xFF 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 Bits 7-0 = 0x00 RESET STATE RESET STATE
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
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ABSOLUTE MAXIMUM RATINGS
Power Supply Range Voltage at Any Pin Operating Temperature Storage Temperature Package Dissipation 7 Volts GND-0.3 V to 7 V -40o to +85oC -65o to +150oC 500 mW
TYPICAL PACKAGE THERMAL RESISTANCE DATA (MARGIN OF ERROR: 15%)
Thermal Resistance (48-TQFP) Thermal Resistance (44-PLCC) theta-ja =59oC/W, theta-jc = 16oC/W theta-ja = 50oC/W, theta-jc = 21oC/W
ELECTRICAL CHARACTERISTICS
DC ELECTRICAL CHARACTERISTICS UNLESS OTHERWISE NOTED: TA=0O TO 70OC (-40O TO +85OC FOR INDUSTRIAL GRADE PACKAGE), VCC IS 2.97V TO 5.5V
SYMBOL VILCK VIHCK VIHCK VIL VIH VIH VOLCK VOHCK VOL VOH IIL IIH CIN ICC ISLEEP PARAMETER Clock Input Low Level Clock Input High Level (top mark date code of "DC YYWW" and older) Clock Input High Level (top mark date code of "F2 YYWW" and newer) Input Low Voltage Input High Voltage (top mark date code of "DC YYWW" and older) Input High Voltage (top mark date code of "F2 YYWW" and newer) Clock Output (XTAL2) Low Voltage 0.4 Clock Output (XTAL2) High Voltage 2.0 Output Low Voltage Output High Voltage Input Low Leakage Current Input High Leakage Current Input Pin Capacitance Power Supply Current Sleep Current See Figure 14. See Figure 15. 10 10 5 1.2 30 10 10 5 3 100 uA uA pF mA uA See Test 1 2.4 V LIMITS 3.3V MIN MAX -0.3 2.4 2.4 -0.3 2.0 2.0 0.6 VCC 5.5 0.8 VCC 5.5 LIMITS 5.0V MIN MAX -0.5 3.0 3.0 -0.5 2.2 2.0 0.6 VCC 5.5 0.8 VCC 5.5 0.4 UNITS V V V V V V V IOL = 6 mA IOL = 4 mA IOH = -6 mA IOH = -1 mA CONDITIONS
Test 1: The following inputs should remain steady at VCC or GND state to minimize Sleep current: A0-A2, D0-D7, IOR#, IOW#, CSA# and CSB#. Also, RXA and RXB inputs must idle at logic 1 state while asleep.
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
FIGURE 14. XR16C2850 VOL SINK CURRENT CHART
XR16C2850 Sink Current
22 20 18 16 14 IOL (mA) 12 10 8 6 4 2 0 0.00 0.10 0.20 0.30 0.40 0.50 VOL (V) 0.60 0.70 0.80 0.90 1.00
VCC=5V VCC=3.3V
FIGURE 15. XR16C2850 VOH SOURCE CURRENT CHART
XR16C2850 Source Current
12
10
8
IOH (mA)
6
VCC=5V VCC=3.3V
4
2
0 1.00 1.50 2.00 2.50 3.00 VOH (V) 3.50 4.00 4.50 5.00
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
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AC ELECTRICAL CHARACTERISTICS
TA=0O TO 70OC (-40O TO +85OC FOR INDUSTRIAL GRADE PACKAGE), VCC IS 2.90V TO 5.5V, 70 PF LOAD
WHERE APPLICABLE
SYMBOL CLK OSC OSC TAS TAH TAH TCS TRD TDY TRDV TDD TWR TDY TDS TDH TWDO TMOD TRSI TSSI TRRI TSI TINT TWRI TSSR TRR TWT TSRT
PARAMETER MIN Clock Pulse Duration Oscillator Frequency External Clock Frequency Address Setup Time Address Hold Time (top mark date code of "DC YYWW" and older) Address Hold Time (top mark date code of "F2 YYWW" and newer) Chip Select Width IOR# Strobe Width Read Cycle Delay Data Access Time Data Disable Time IOW# Strobe Width Write Cycle Delay Data Setup Time Data Hold Time 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# 8 0 40 40 20 5 5 10 0 66 35 40 30
LIMITS 3.3 MAX MIN 20 8 33 0 5 0 50 25 30 35 25 0 25 30 15 5 50 40 40 1 45 45 24 45 1 45 45 8 8
LIMITS 5.0 MAX
UNIT ns 24 50 MHz MHz ns ns ns ns ns ns 25 15 ns ns ns ns ns ns 40 35 35 1 40 40 24 40 1 40 40 8 ns ns ns Bclk ns ns Bclk ns Bclk ns ns Bclk
CONDITIONS
100 pF load 100 pF load 100 pF load
100 pF load
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
AC ELECTRICAL CHARACTERISTICS
TA=0O TO 70OC (-40O TO +85OC FOR INDUSTRIAL GRADE PACKAGE), VCC IS 2.90V TO 5.5V, 70 PF LOAD
WHERE APPLICABLE
SYMBOL TRST N Bclk
PARAMETER MIN Reset Pulse Width Baud Rate Divisor Baud Clock 40 1
LIMITS 3.3 MAX MIN 40 216-1 1
LIMITS 5.0 MAX
UNIT ns
CONDITIONS
216-1
Hz
16X or 8X of data rate
FIGURE 16. CLOCK TIMING
CLK EXTERNAL CLOCK OSC CLK
FIGURE 17. MODEM INPUT/OUTPUT TIMING FOR CHANNELS A & B
IOW # Active T W DO RTS# DTR# Change of state Change of state
CD# CTS# DSR# T MOD INT
Change of state
Change of state T MO D
Active T RSI
Active
Active
IOR#
Active
Active
Active T M OD
RI#
Change of state
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS FIGURE 18. DATA BUS READ TIMING
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A0-A2 TAS
Valid Address TAS
Valid Address
TCS CSA#/ CSB#
TAH
TCS
TAH
TDY TRD IOR# TDD Valid Data TDD Valid Data TRD
TRDV D0-D7
TRDV
RDTm
FIGURE 19. DATA BUS WRITE TIMING
A0-A2 TAS
Valid Address TAS
Valid Address
TCS CSA#/ CSB#
TAH
TCS
TAH
TDY TWR IOW# TWR
TDS D0-D7 Valid Data
TDH
TDS Valid Data
TDH
16Write
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
FIGURE 20. RECEIVE READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B
RX
Start Bit Stop Bit TSSR 1 Byte in RHR TSSR Active Data Ready TRR
D0:D7
D0:D7 TSSR 1 Byte in RHR TSSR Active Data Ready TRR
D0:D7 TSSR 1 Byte in RHR TSSR Active Data Ready TRR
INT
RXRDY#
IOR#
(Reading data out of RHR)
RXNFM
FIGURE 21. TRANSMIT READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B
TX
Start Bit Stop Bit
(Unloading) IER[1] enabled
D0:D7
D0:D7
D0:D7
ISR is read
ISR is read
ISR is read
INT*
TWRI TSRT TWRI TSRT TWRI 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
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
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FIGURE 22. RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA DISABLED] FOR CHANNELS A & B
Start Bit
RX
S D0:D7 Stop Bit
S D0:D7 T
D0:D7
TSSI
S D0:D7 T
S D0:D7 T S D0:D7 T
S D0:D7 T
RX FIFO drops below RX Trigger Level
INT
TSSR
RXRDY# First Byte is Received in RX FIFO IOR#
(Reading data out of RX FIFO)
RX FIFO fills up to RX Trigger Level or RX Data Timeout
FIFO Empties
TRRI
TRR
RXINTDMA#
FIGURE 23. RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA ENABLED] FOR CHANNELS A & B
Start Bit
Stop Bit S D0:D7 T
RX
S D0:D7
D0:D7
TSSI
S D0:D7 T
S D0:D7 T S D0:D7 T
S D0:D7 T
RX FIFO drops below RX Trigger Level
INT RX FIFO fills up to RX Trigger Level or RX Data Timeout RXRDY#
TSSR
FIFO Empties
TRRI
TRR
IOR#
(Reading data out of RX FIFO)
RXFIFODMA
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
FIGURE 24. TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE DISABLED] FOR CHANNELS A & B
Start Bit Stop Bit
TX FIFO Empty
Last Data Byte Transmitted S D0:D7 T S D0:D7 T TSI T S D0:D7 T S D0:D7 T ISR is read TSRT S D0:D7 T
TX
(Unloading) IER[1] enabled
S D0:D7 T ISR is read
INT*
TX FIFO fills up to trigger level TX FIFO drops below trigger level
TX FIFO Empty TWRI
TXRDY#
Data in TX FIFO
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 25. TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE ENABLED] FOR CHANNELS A & B
Start Bit
Stop Bit
Last Data Byte Transmitted D0:D7 S D0:D7 T S D0:D7 T S D0:D7 T S D0:D7 T ISR Read
TX
(Unloading) IER[1] enabled
S D0:D7 T S D0:D7 T ISR Read
TSRT
TSI
INT*
TX FIFO fills up to trigger level TWRI TX FIFO Full TX FIFO drops below trigger level At least 1 empty location in FIFO
TXRDY#
TWT
IOW#
(Loading data into FIFO)
*INT cleared when the ISR is read or when TX FIFO fills up to trigger level.
TXDMA
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
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PACKAGE DIMENSIONS (48 PIN TQFP - 7 X 7 X 1 mm)
D D1 36 25
37
24
D1
D
48
13
1 B A2 e
1 2
C Seating Plane A A1
L
Note: The control dimension is the millimeter column INCHES SYMBOL A A1 A2 B C D D1 e L a MIN 0.039 0.002 0.037 0.007 0.004 0.346 0.272 MAX 0.047 0.006 0.041 0.011 0.008 0.362 0.280 MILLIMETERS MIN 1.00 0.05 0.95 0.17 0.09 8.80 6.90 MAX 1.20 0.15 1.05 0.27 0.20 9.20 7.10
0.020 BSC 0.018 0x 0.030 7x
0.50 BSC 0.45 0x 0.75 7x
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
PACKAGE DIMENSIONS (44 PIN PLCC)
44 LEAD PLASTIC LEADED CHIP CARRIER (PLCC)
Rev. 1.00
D D1 21 44 45 x H 2 45 x H 1 C Seating Plane A2
B1
D
D1
D3
B
D2
e
R D3 A1 A
Note: The control dimension is the millimeter column INCHES SYMBOL A A1 A2 B B1 C D D1 D2 D3 e H1 H2 R MIN 0.165 0.090 0.020 0.013 0.026 0.008 0.685 0.650 0.590 MAX 0.180 0.120 --0.021 0.032 0.013 0.695 0.656 0.630 MILLIMETERS MIN 4.19 2.29 0.51 0.33 0.66 0.19 17.40 16.51 14.99 MAX 4.57 3.05 --0.53 0.81 0.32 17.65 16.66 16.00
0.500 typ. 0.050 BSC 0.042 0.042 0.025 0.056 0.048 0.045
12.70 typ. 1.27 BSC 1.07 1.07 0.64 1.42 1.22 1.14
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
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PACKAGE DIMENSIONS (40 PIN PDIP)
40
21 E1
1 D
20 E A2 A1 C
Seating Plane
A L B e B1
eA eB
Note: The control dimension is the millimeter column INCHES SYMBOL A A1 A2 B B1 C D E E1 e eA eB L a MIN 0.160 0.015 0.125 0.014 0.030 0.008 1.98 0.600 0.485 MAX 0.250 0.070 0.195 0.024 0.070 0.014 2.095 0.625 0.580 MILLIMETERS MIN 4.06 0.38 3.18 0.36 0.76 0.20 50.29 15.24 12.32 MAX 6.35 1.78 4.95 0.56 1.78 0.38 53.21 15.88 14.73
0.100 BSC 0.600 BSC 0.600 0.115 0x 0.700 0.200 15x
2.54 BSC 15.24 BSC 15.24 2.92 0x 17.78 5.08 15x
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
REVISION HISTORY
Date February 2000 April 2002 Revision Rev 1.0.0 Rev 2.0.0 Initial datasheet. Changed to standard style format. Internal Registers are described in the order they are listed in the Internal Register Table. Clarified timing diagrams. Corrected Auto RTS Hysteresis table. Renamed Rclk (Receive Clock) to Bclk (Baud Clock) and timing symbols. Added TAH, TCS and OSC. Changed to single column format. Added device status to ordering information. Clarified sleep mode conditions. Clarified pin descriptions- changed from using logic 1 and logic 0 to HIGH (VCC) and LOW (GND) for input and output pin descriptions. Added VOL sink current and VOH source current charts (Figure 14 and Figure 15). Devices with top mark date code of "F2 YYWW" and newer have 5V tolerant inputs (except for XTAL1) and have 0 ns address hold time (TAH). DREV register was updated to 0x06. Corrected datasheet to show that all inputs are 5V tolerant (including XTAL1) in devices with top mark date code of "F2 YYWW" and newer. Removed discontinued 40-pin PDIP from Ordering Information. Corrected part numbers in Ordering Information. Description
May 2004
Rev 2.1.0
February 2005 August 2005 November 2005
Rev 2.1.1 Rev 2.1.2 Rev 2.1.3
NOTICE EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a user's specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. Copyright 2005 EXAR Corporation Datasheet November 2005. 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.
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TABLE OF CONTENTS
GENERAL DESCRIPTION .................................................................................................1
APPLICATIONS................................................................................................................................................1 FEATURES .....................................................................................................................................................1
FIGURE 1. XR16C2850 BLOCK DIAGRAM......................................................................................................................................... 1 FIGURE 2. PIN OUT ASSIGNMENT ..................................................................................................................................................... 2 ORDERING INFORMATION.................................................................................................................................2
PIN DESCRIPTIONS .........................................................................................................3
1.0 PRODUCT DESCRIPTION .....................................................................................................................7 2.0 FUNCTIONAL DESCRIPTIONS .............................................................................................................8
2.1 CPU INTERFACE .............................................................................................................................................. 8
FIGURE 3. XR16C2850 DATA BUS INTERCONNECTIONS ................................................................................................................. 8
2.2 DEVICE RESET ................................................................................................................................................ 8 2.3 DEVICE IDENTIFICATION AND REVISION ..................................................................................................... 8 2.4 CHANNEL A AND B SELECTION .................................................................................................................... 8
TABLE 1: CHANNEL A AND B SELECT ............................................................................................................................................... 9
2.5 CHANNEL A AND B INTERNAL REGISTERS ................................................................................................ 9 2.6 DMA MODE ....................................................................................................................................................... 9
TABLE 2: TABLE 2TXRDY# AND RXRDY# OUTPUTS IN FIFO AND DMA MODE ................................................................................ 9
2.7 INTA AND INTB OUPUTS .............................................................................................................................. 10
TABLE 3: INTA AND INTB PINS OPERATION FOR TRANSMITTER ...................................................................................................... 10 TABLE 4: INTA AND INTB PIN OPERATION FOR RECEIVER ............................................................................................................. 10
2.8 CRYSTAL OSCILLATOR OR EXTERNAL CLOCK INPUT ........................................................................... 10
FIGURE 4. TYPICAL OSCILLATOR CONNECTIONS............................................................................................................................... 10
2.9 PROGRAMMABLE BAUD RATE GENERATOR ........................................................................................... 11
FIGURE 5. EXTERNAL CLOCK CONNECTION FOR EXTENDED DATA RATE .......................................................................................... 11 FIGURE 6. BAUD RATE GENERATOR AND PRESCALER ..................................................................................................................... 11 TABLE 5: TYPICAL DATA RATES WITH A 14.7456 MHZ CRYSTAL OR EXTERNAL CLOCK ...................................................................... 12
2.10 TRANSMITTER ............................................................................................................................................. 12
2.10.1 2.10.2 FIGURE 7. 2.10.3 FIGURE 8. TRANSMIT HOLDING REGISTER (THR) - WRITE ONLY ....................................................................................... 12 TRANSMITTER OPERATION IN NON-FIFO MODE ................................................................................................ 12 TRANSMITTER OPERATION IN NON-FIFO MODE .............................................................................................................. 13 TRANSMITTER OPERATION IN FIFO MODE ......................................................................................................... 13 TRANSMITTER OPERATION IN FIFO AND FLOW CONTROL MODE ..................................................................................... 13
2.11 RECEIVER .................................................................................................................................................... 14
2.11.1 RECEIVE HOLDING REGISTER (RHR) - READ-ONLY .......................................................................................... 14 FIGURE 9. RECEIVER OPERATION IN NON-FIFO MODE .................................................................................................................... 14 FIGURE 10. RECEIVER OPERATION IN FIFO AND AUTO RTS FLOW CONTROL MODE ....................................................................... 15
2.12 AUTO RTS (HARDWARE) FLOW CONTROL ............................................................................................. 15 2.13 AUTO RTS HYSTERESIS ............................................................................................................................ 15 2.14 AUTO CTS FLOW CONTROL ...................................................................................................................... 16
FIGURE 11. AUTO RTS AND CTS FLOW CONTROL OPERATION....................................................................................................... 16
2.15 AUTO XON/XOFF (SOFTWARE) FLOW CONTROL ................................................................................... 17
TABLE 6: AUTO XON/XOFF (SOFTWARE) FLOW CONTROL ............................................................................................................... 17
2.16 SPECIAL CHARACTER DETECT ............................................................................................................... 17 2.17 AUTO RS485 HALF-DUPLEX CONTROL .................................................................................................. 17 2.18 INFRARED MODE ........................................................................................................................................ 18
FIGURE 12. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING .......................................................................... 18
2.19 2.20
SLEEP MODE WITH AUTO WAKE-UP ....................................................................................................... 19 INTERNAL LOOPBACK .............................................................................................................................. 20
FIGURE 13. INTERNAL LOOP BACK IN CHANNELS A AND B .............................................................................................................. 20
3.0 UART INTERNAL REGISTERS ...........................................................................................................21
TABLE 7: TABLE 8: UART CHANNEL A AND B UART INTERNAL REGISTERS...................................................................................... 21 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 ............................................................................. 23 4.3.2 IER VERSUS RECEIVE/TRANSMIT FIFO POLLED MODE OPERATION ................................................................ 24
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XR16C2850 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
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 ....................................................................................................................... 25
4.5 FIFO CONTROL REGISTER (FCR) - WRITE-ONLY ..................................................................................... 26
TABLE 10: TRANSMIT AND RECEIVE FIFO TRIGGER TABLE AND LEVEL SELECTION .......................................................................... 27
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 4.8 LINE STATUS REGISTER (LSR) - READ ONLY ........................................................................................... 4.9 MODEM STATUS REGISTER (MSR) - READ ONLY .................................................................................... 4.10 SCRATCH PAD REGISTER (SPR) - READ/WRITE .................................................................................... 4.11 ENHANCED MODE SELECT REGISTER (EMSR) ...................................................................................... 4.12 4.13 4.14 4.15 4.16 4.17 4.18 FIFO LEVEL REGISTER (FLVL) - READ-ONLY ......................................................................................... BAUD RATE GENERATOR REGISTERS (DLL AND DLM) - READ/WRITE .............................................. DEVICE IDENTIFICATION REGISTER (DVID) - READ ONLY .................................................................... DEVICE REVISION REGISTER (DREV) - READ ONLY .............................................................................. TRIGGER LEVEL / FIFO DATA COUNT REGISTER (TRG) - WRITE-ONLY ............................................. FIFO DATA COUNT REGISTER (FC) - READ-ONLY ................................................................................. FEATURE CONTROL REGISTER (FCTR) - READ/WRITE .......................................................................
29 30 31 32 32 33 33 33 33 34 34 34
TABLE 12: SCRATCHPAD SWAP SELECTION .................................................................................................................................... 32 TABLE 13: EXTENDED RTS HYSTERESIS ........................................................................................................................................ 33
TABLE 14: TRIGGER TABLE SELECT ............................................................................................................................................... 34
4.19 ENHANCED FEATURE REGISTER (EFR) .................................................................................................. 35
TABLE 15: SOFTWARE FLOW CONTROL FUNCTIONS ........................................................................................................................ 35
4.20 SOFTWARE FLOW CONTROL REGISTERS (XOFF1, XOFF2, XON1, XON2) - READ/WRITE ................ 36
TABLE 16: UART RESET CONDITIONS FOR CHANNEL A AND B............................................................................................ 37
ABSOLUTE MAXIMUM RATINGS .................................................................................. 38 TYPICAL PACKAGE THERMAL RESISTANCE DATA (MARGIN OF ERROR: 15%) 38 ELECTRICAL CHARACTERISTICS................................................................................ 38
DC ELECTRICAL CHARACTERISTICS.............................................................................................................. 38
FIGURE 14. XR16C2850 VOL SINK CURRENT CHART ................................................................................................................... 39 FIGURE 15. XR16C2850 VOH SOURCE CURRENT CHART ............................................................................................................. 39
AC ELECTRICAL CHARACTERISTICS.............................................................................................................. 40 TA=0O TO 70OC (-40O TO +85OC FOR INDUSTRIAL GRADE PACKAGE), VCC IS 2.90V TO 5.5V, 70 PF LOAD WHERE APPLICABLE ................................................................................................................................................. 40
FIGURE 16. FIGURE 17. FIGURE 19. FIGURE 18. FIGURE 20. FIGURE 21. FIGURE 22. FIGURE 23. FIGURE 24. FIGURE 25. CLOCK TIMING............................................................................................................................................................. 41 MODEM INPUT/OUTPUT TIMING FOR CHANNELS A & B ................................................................................................. 41 DATA BUS WRITE TIMING ............................................................................................................................................ 42 DATA BUS READ TIMING .............................................................................................................................................. 42 RECEIVE READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B ......................................................... 43 TRANSMIT READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B ....................................................... 43 RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA DISABLED] FOR CHANNELS A & B........................................ 44 RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA ENABLED] FOR CHANNELS A & B......................................... 44 TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE DISABLED] FOR CHANNELS A & B ........................... 45 TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE ENABLED] FOR CHANNELS A & B ............................ 45
PACKAGE DIMENSIONS (48 PIN TQFP - 7 X 7 X 1 mm)................................................ 46 PACKAGE DIMENSIONS (44 PIN PLCC) ....................................................................... 47 PACKAGE DIMENSIONS (40 PIN PDIP) ........................................................................ 48
REVISION HISTORY ...................................................................................................................................... 49
TABLE OF CONTENTS ............................................................................................................ I
II

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