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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

Pin # Type Pin Description

IOCHRDY

20 OT24 Input/Output Channel Ready. IOCHRDY is a three-state active high output with

an internal weak pull-up resistor. This pin goes low when 1284 parallel port

requires additional clock during a read or write cycle.

TC

91

I

Terminal Count. TC is an active high input during DMA cycle and when

DACK# is low to indicate data transfer is complete.

RESET

1

I

System Reset. Reset is an active high input. A 40ns minimum pulse will reset

the internal registers and outputs to the default state. The TX output is at logic 1

and RX input is internally held at logic 1 during reset. See XR16C872 Reset

Conditions for details.

XTAL1

76

I

Crystal Oscillator Input. A 22.1184 MHz crystal must be connected to this input

and XTAL2 pin to form an internal oscillator circuit which provides the main

clock to the the baud rate generators. An external clock of same frequency

may be used instead.

XTAL2

75

O

Crystal Oscillator Output. The other side of the crystal is connected to this pin

to form an internal crystal oscillator.

EED

73

Bidir EED is a bi-directional serial data bus to the external 93C46 EEPROM.

EECLK

72

O

EECLK is a 500KHz clock output to the external EEPROM for serial data timing

reference.

EECS

71

Bidir EEPROM Chip Select. EECS is an active high output to the external EEPROM.

During Manual configuration mode, a logic 1 input will bypass the internal

divide-by-3 clock circuit to the two UARTs.

MAN#

74

I

1284 CONTROLLER INTERFACE

PD7-PD0

32-34 IOP14

37-41

Manual Configuration Select. MAN# is an active low input that enables S1-S5

for selection of COM1-4 and LPT1-2 or in embedded applications.

Parallel Data Bus. PD0-PD7 are three-state bi-directional data lines to the

parallel port. PD0 is the least significant bit with PD7 being the most

significant bit. PD0-PD7 are high current drive outputs and can connect to

the printer/parallel connector without external buffers.

ACK#

51

IP24 Acknowledge. ACK# is an active low input with with an internal weak pull-up.

It can be a general purpose input or line printer acknowledge signal. A logic

0 from the parallel/printer indicates successful data transfer to the print buffer.

AUTOFD#

46 IOP14 AutoLineFeed. AUTOFD# is an active low tri-state with an internal weak pull-

up. It can be a general purpose I/O or automatic line feed. When this signal

is low the printer should automatically line feed after each printed line.

Rev. P1.00

6

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