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XR16C872

Dual UART with 1284 Parallel Port and Plug-and-Play Controller

Exar Corporation 

XR16C872

Preliminary

PIN DESCRIPTION (CONT'D)

Symbol

DTRA#,

DTRB#

Pin #

65

55

Type

O

RTSA#,

66

O

RTSB#

56

CTSA#,

67,

I

CTSB#

57

DSRA#,

68,

I

DSRB#

58

CDA#,

69,

I

CDB#

59

RIA#,

70,

I

RIB#

60

VCC

GND

25,35,42

62,90

PWR

16,26,36,43 PWR

61,77,98

Pin Description

Data Terminal Ready A/B or general purpose output. DTRA/B# are active

low and associated with UARTchannel A and B. A logic 0 on indicates that

UART A/B is ready. This pin is controlled via the MCR register for channel A/B.

Setting MCR bit-0 to logic 1 puts the output pin to logic 0. This pin will be a logic 1

after writing a logic 0 to MCR bit-0. This pin has no effect on the UART

transmitter or receiver.

Request to Send A/B or general purpose output. RTSA/B# are active low

outputs and associated with UART channels A/B. Writing a logic 1 to MCR

bit-1sets the pin to a logic 0 and requests remote unit to send data. After a

reset this pin is set to a logic 1. When auto RTS flow control is enabled (EFR

bit-6=1), a logic 0 asks remote modem to send data and a logic 1 requests

to suspend. The user must assert RTS# after enabling auto RTS flow control.

Clear to Send A/B or general purpose input. CTSA/B# are active low

inputs and associated with UART channels A and B. A logic 0 indicates

the remote modem is ready for data. A level change on this input pin will

generate a status change interrupt (MSR bit-0). When auto CTS flow

control is enabled, a logic 1 suspends local data transmission and a logic 0

restarts the local transmitter.

Data Set Read A/B or general purpose input. DSRA/B# are active low inputs

and associated with UARTchannel A and B. A logic 0 on indicates the modem

is ready for data exchange with the UART. A logic level change on this input

pin will generate a status change interrupt (MSR bit-1).This pin has no effect

on the UART’s transmit or receive operation.

Carrier Detect A/B or general purpose input. CDA/B# are active low inputs and

associated with UART channels A and B. A logic 0 on this pin indicates a

carrier signal has been detected by the modem. A logic level change on this

input pin will generate a status change interrupt (MSR bit-3). This pin has no

effect on the UART’s transmit or receive operation.

Ring Indicator A/B or general purpose input. RIA/B# are active low inputs

and associated with UART channels A and B. A logic 0 on indicates the

modem has received a ringing signal from the telephone line. A logic 1

transition on this input pin will generate a status change interrupt (MSR

bit-2). This pin has no effect on UART's transmit or receive operation.

+5 Volts power supply.

Signal ground.

Rev. P1.00

8

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