Diamond Systems 16-Channel 12-Bit Analog Output PC/104 Module user manual 82C55A Pin Description

PIN

SYMBOL

NUMBER

TYPE

DESCRIPTION

VCC

26

VCC: The +5V power supply pin. A 0.1μF capacitor between pins 26 and 7 is

recommended for decoupling.

GND

7

GROUND

D0-D7

27-34

I/O

DATA BUS: The Data Bus lines are bidirectional three-state pins connected to the

system data bus.

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 with the “Bus Hold” circuitry turned on.

6

I

CHIP SELECT: Chip select is an active low input used to enable the 82C55A onto the

CS

Data Bus for CPU communications.

5

I

READ: Read is an active low input control signal used by the CPU to read status

RD

information or data via the data bus.

36

I

WRITE: Write is an active low input control signal used by the CPU to load control

WR

words and data into the 82C55A.

A0-A1

8, 9

I

ADDRESS: These input signals, in conjunction with the

and

inputs, control

RD

WR

the selection of one of the three ports or the control word register. A0 and A1 are

normally connected to the least significant bits of the Address Bus A0, A1.

PA0-PA7

1-4, 37-40

I/O

PORT A: 8-bit input and output port. Both bus hold high and bus hold low circuitry are

present on this port.

PB0-PB7

18-25

I/O

PORT B: 8-bit input and output port. Bus hold high circuitry is present on this port.

PC0-PC7

10-17

I/O

PORT C: 8-bit input and output port. Bus hold circuitry is present on this port.

POWER

+5V

GROUP A

I/O

PORT A

PA7-PA0

SUPPLIES

GND

GROUP A

(8)

CONTROL

GROUP A

I/O

PORT C

BI-DIRECTIONAL

PC7-PC4

UPPER

DATA BUS

(4)

DATA BUS

D7-D0

BUFFER

GROUP B

8-BIT

I/O

INTERNAL

PORT C

PC3-PC0

DATA BUS

LOWER

(4)

RD

READ

WR

GROUP B

WRITE

A1

CONTROL

CONTROL

GROUP B

I/O

LOGIC

PORT B

PB7-PB0

A0

(8)

RESET

CS