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8255

Programmable Peripheral Interface (PPI) / 24 line I/O interface

8255
Category: Other | Datasheet

Description

The Intel 8255A (8255) is a general purpose programmable I/O device designed for use with Intel microprocessors. It has 24 1/0 pins which may be individually programmed in 2 groups of 12 and used in 3 major modes of operation. In the first mode (MODE 0), each group of 12 I/O pins may be programmed in sets of 4 to be input or output. In MODE 1, the second mode, each group may be programmed to have 8 lines of input or output. Of the remaining 4 pins, 3 are used for handshaking and interrupt control signals. The third mode of operation (MODE 2) is a bidirectional bus mode which uses 8 lines for a bidirectional bus, and 5 lines, borrowing one from the other group, for handshaking.

Pinout

Pin Signal Dir Name
1 PA3 Input/Output Port A bit 3
2 PA2 Input/Output Port A bit 2
3 PA1 Input/Output Port A bit 1
4 PA0 Input/Output Port A bit 0
5 RD# Input Read Input
6 CS# Input Chip Select
7 GND Power Ground
8 A1 Input Port Address 1
9 A0 Input Port Address 0
10 PC7 Input/Output Port C bit 7
11 PC6 Input/Output Port C bit 6
12 PC5 Input/Output Port C bit 5
13 PC4 Input/Output Port C bit 4
14 PC0 Input/Output Port C bit 0
15 PC1 Input/Output Port C bit 1
16 PC2 Input/Output Port C bit 2
17 PC3 Input/Output Port C bit 3
18 PB0 Input/Output Port B bit 0
19 PB1 Input/Output Port B bit 1
20 PB2 Input/Output Port B bit 2
21 PB3 Input/Output Port B bit 3
22 PB4 Input/Output Port B bit 4
23 PB5 Input/Output Port B bit 5
24 PB6 Input/Output Port B bit 6
25 PB7 Input/Output Port B bit 7
26 VCC Power Power supply (+5V)
27 D7 Input/Output Data Bus bit 7
28 D6 Input/Output Data Bus bit 6
29 D5 Input/Output Data Bus bit 5
30 D4 Input/Output Data Bus bit 4
31 D3 Input/Output Data Bus bit 3
32 D2 Input/Output Data Bus bit 2
33 D1 Input/Output Data Bus bit 1
34 D0 Input/Output Data Bus bit 0
35 RESET Input Reset Input
36 WR# Input Write Input
37 PA7 Input/Output Port A bit 7
38 PA6 Input/Output Port A bit 6
39 PA5 Input/Output Port A bit 5
40 PA4 Input/Output Port A bit 4

Registers

Addr A0 A1 Register
0 0 0 Port A
1 1 0 Port B
2 0 1 Port C
3 1 1 Control

 

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