6-7

ST78C34

Rev. 3.00

SYMBOL DESCRIPTION

Symbol

Pin

Signal

Pin Description

40

44

type

GND

20

23

O

Signal and power ground.

RESET

21

24

I

Master reset (active high). A high on this pin will reset all the

outputs and internal registers.

-STROBE

22

25

I/O

General purpose I/O or strobe output (open drain active low, with

internal pull-up). To transfer latched data to the external peripheral

or printer.

-AUTOFDXT

23

26

I/O

General purpose I/O or line printer auto feed (open drain active

low, with internal pull-up). To signal the printer for continuous form

feed.

INIT

24

27

I/O

General purpose I/O or line printer initialize (open drain active

high, with internal pull-up). To signal the line printer to enter

internal initialization routine.

-SLCTIN

25

28

I/O

General purpose I/O or line printer select (open drain active low,

with internal pull-up). To select the line printer.

GND

26

30

O

Power and signal ground.

PD0-PD7

27-34

31-38

I/O

Bi-directional parallel ports (three state). To transfer data in or out

of the ST78C34 parallel port. PD7-PD0 are latched during output

mode.

A0-A1

36-37

40-41

I

Address lines. To select internal registers.

-IOW

38

42

I

Write strobe (active low). A low on this pin will transfer the contents

of the CPU data bus to the addressed register.

-IOR

39

43

I

Read strobe (active low). A low level on this pin transfers the

contents of the ST78C34 data bus to the CPU.

VCC

40

44

I

Power supply input.