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IA8255

Programmable Peripheral Interface Adapter

Copyright

© 1999, InnovASIC Inc.

Customer Specific IC Solutions

The IA8255 is a programmable peripheral interface adapter mega-function designed to be

functionally equivalent to the Intel 8255A and Harris 82C55A devices. This function has 24 I/O

signals programmable in two groups of 12. Three modes of operation allow the following:

•

Basic Input/Output (Mode 0) - Port A, Port B, Port C (upper), and Port C (lower) can be

independently configured as inputs or outputs to read or hold static data. Outputs are

latched, but inputs are not latched.

•

Strobed Input/Output (Mode 1) - Port A and Port B can be independently configured as

strobed input or output buses. Signals from Port C are dedicated as control signals for data

handshaking.

•

Bidirectional Bus (Mode 2) - Port A can also be configured as a bidirectional bus, with the

majority of Port C providing the control signals. In this case, Port B is still capable of

implementing one of the previous described modes.

A block diagram is shown in Figure 1.

Functional Block Diagram

Figure 1

DATA BUS

BUFFER

GROUP A

CONTROL

GROUP B

CONTROL

8 BIT INTERNAL

DATA BUS

GROUP A

PORT A

(8)

GROUP A

PORT C

UPPER (4)

GROUP B

PORT C

LOWER

(4)

GROUP B

PORT B

(8)

CONTROL

REGISTER AND

LOGIC

A0

A1

CS_n

RESET

RD_n

WR_n

D7:D0

I/O

PA7:PA0

I/O

PC7:PC4

I/O

PC3:PC0

I/O

PB7:PB0