971

HS-82C55ARH

Pin Description

SYMBOL

PIN

NUMBERS

TYPE

DESCRIPTION

PA0-7

1-4, 37-40

I/O

Port A: General purpose I/O Port. Data direction and mode is determined by the contents

of the Control Word.

PB0-7

18-25

I/O

Port B: General purpose I/O port. See Port A.

PC0-3

14-17

I/O

Port C (Lower): Combination I/O port and control port associated with Port B. See Port A.

PC4-7

10-13

I/O

Port C (Upper): Combination I/O Port and control port associated with Port A. See Port A.

D0-7

27-34

I/O

Bidirectional Data Bus: Three-State data bus enabled as an input when CS and WR are

low and as an output when CS and RD are low.

VDD

26

I

VDD: The +5V power supply pin. A 0.1

µF capacitor between pins 26 and 7 is recommend-

ed for decoupling.

GND

7

I

Ground.

CS

6

I

Chip Select: A “low” on this input pin enables the communication between the

HS-82C55ARH and the CPU.

RD

5

I

Read: A “low” on this input pin enables the HS-82C55ARH to send the data or status

information to the CPU on the data bus. In essence, it allows the CPU to “read from” the

HS-82C55ARH.

WR

36

I

Write: A “low” on this input pin enables the CPU to write data or control words into the

HS-82C55ARH.

A0 and A1

8, 9

I

Port Select 0 and Port Select 1: These input signals, in conjunction with the RD and WR

inputs, control the selection of one of the three ports or the control word registers. They are

normally connected to the Least Significant Bits of the address bus (A0 and A1).

Reset

35

I

Reset: A “high” on this input clears the control register and all ports (A, B, C) are set to the

input mode. “Bus hold” devices internal to the HS-82C55ARH will hold the I/O port inputs

to a logic “1” state with a maximum hold current of 400

µA.

Functional Diagram

GROUP A

CONTROL

POWER

SUPPLIES

DATA

BUS

BUFFER

GROUP B

CONTROL

READ/WRITE

CONTROL

LOGIC

RD

WR

A1

A0

RESET

CS

D7 - D0

BIDIRECTIONAL

DATA BUS

+5V

GND

8-BIT INTERNAL

DATA BUS

GROUP B

PORT B

(8)

GROUP B

PORT C

LOWER (4)

GROUP A

PORT C

UPPER (4)

GROUP A

PORT A

(8)

I/O

PA7 - PA0

I/O

PC7 - PC4

I/O

PC3 - PC0

I/O

PB7 - PB0

Spec Number

518060