8255 Programmable Peripheral I/O

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The 8255A is a general-purpose programmable l/O device designed for use with Intel microprocessors. It has 24 O 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 /0 pins may be programmed in sets of 4 to be input or output. In MODE1, the second mode, each group may be programmed to have 8 lines of input or output.

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8255 Pinout

8255 Pin Configuration

Pin Number	Pin Name	Description
1-4	PA0-PA3	Port A
5	RD	Read (Active Low)
6	CS	Chip Select (Active Low)
7	GND	Ground
8	A0	Address Input
9	A1	Address Input
10-17	PC0-PC7	Port C
18-25	PB0-PB7	Port B
26	Vcc	+5V Power Supply
27-34	D0-D7	Data Bus
35	RESET	Reset Input
36	WR	Write (Active Low)
37-40	PA4-PA7	Port A