8255A - Programmable peripheral interface


PA3	1 •	40	PA4
PA2	2	39	PA5
PA1	3	38	PA6
PA0	4	37	PA7
RD	5	36	WR
CS	6	35	RESET
GND	7	34	D0
A1	8	33	D1
A0	9	32	D2
PC7	10	31	D3
PC6	11	30	D4
PC5	12	29	D5
PC4	13	28	D6
PC0	14	27	D7
PC1	15	26	Vcc
PC2	16	25	PB7
PC3	17	24	PB6
PB0	18	23	PB5
PB1	19	22	PB4
PB2	20	21	PB3

Pin	Symbol	Description
1	PA3	port A
2	PA2	port A
3	PA1	port A
4	PA0	port A
5	RD	read enable (active low)
6	CS	chip select (active low)
7	GND	ground
8	A1	address input
9	A0	address input
10	PC7	port C
11	PC6	port C
12	PC5	port C
13	PC4	port C
14	PC0	port C
15	PC1	port C
16	PC2	port C
17	PC3	port C
18	PB0	port B
19	PB1	port B
20	PB2	port B
21	PB3	port B
22	PB4	port B
23	PB5	port B
24	PB6	port B
25	PB7	port B
26	Vcc	supply voltage
27	D7	data bus
28	D6	data bus
29	D5	data bus
30	D4	data bus
31	D3	data bus
32	D2	data bus
33	D1	data bus
34	D0	data bus
35	RESET	reset (active high)
36	WR	write enable (active low)
37	PA7	port A
38	PA6	port A
39	PA5	port A
40	PA4	port A

Notes

Control word:

Bit 0	Port C lower bits; 1=input, 0=output
Bit 1	Port B; 1=input, 0=output
Bit 2	Group B mode selection
Bit 3	Port C upper bits; 1=input, 0=output
Bit 4	Port A; 1=input, 0=output
Bits 5-6	Group A mode selection
Bit 7	1=mode set, 0=bit set/reset

When bit 7 of control word is set to 1, the rest of the bits have the following functions:

Bit 0 1=set bit, 0=clear bit

Bits 1-3 specify bit to modify (0-7)

Note: Data is maintained by an independent source and accuracy is not guaranteed. Check with the manufacturer's datasheet for up-to-date information.

Bit 0	1=set bit, 0=clear bit
Bits 1-3	specify bit to modify (0-7)