6-6

ST78C34

Rev. 3.00

SYMBOL DESCRIPTION

Symbol

Pin

Signal

Pin Description

40

44

type

-ERROR

1

1

I

General purpose input or line printer error (active low, with internal

pull-up). This is an output from the printer to indicate an error by

holding it low during error condition.

SLCT

2

2

I

General purpose input or line printer selected (active high, with

internal pull-up). This is an output from the printer to indicate that

the line printer has been selected.

BUSY

3

3

I

General purpose input or line printer busy (active high, with internal

pull-up). An output from the printer to indicate printer is not ready

to accept data.

-ACK

4

4

I

General purpose input or line printer acknowledge (active low, with

internal pull-up). An output from the printer to indicate that data has

been accepted successfully.

PE

5

5

I

General purpose input or line printer paper empty (active high, with

internal pull-up). An output from the printer to indicate out of paper.

INTSEL

6

8

I

Interrupt select mode. The external -ACK can be selected as an

interrupt source by connecting this pin to the VCC or left open.

Connecting this pin to GND will set the interrupt to latched mode,

reading the status register resets the INT output.

D0-D7

14-7

16-9

I/O

Bi-directional data bus. Eight bit, three state data bus to transfer

information to or from the CPU. D0 is the least significant bit of

the data bus.

INT

16

19

O

Interrupt output (selectable active low or high). To signal the state

of the printer port. This pin tracks the -ACK input pin, When -ACK

is low INT is low and when -ACK is high INT is high if selected as

active low interrupt.

XTAL1

17

20

I

Crystal input 1 or external clock input. A crystal can be connected

to this pin and XTAL2 pin to utilize the internal oscillator circuit. An

external clock can be used to clock oscillator circuit.

XTAL2

18

21

O

Crystal input 2 or buffered clock output. See XTAL1.

-CS

19

22

I

Chip select (active low). A low at this pin enables the ST78C34 /

CPU data transfer operation.