8254 - Programmable interval timer


D7	1 •	24	Vcc
D6	2	23	WR
D5	3	22	RD
D4	4	21	CS
D3	5	20	A1
D2	6	19	A0
D1	7	18	CLK 2
D0	8	17	OUT 2
CLK 0	9	16	GATE 2
OUT 0	10	15	CLK 1
GATE 0	11	14	GATE 1
GND	12	13	OUT 1

Pin	Symbol	Description
1	D7	data bus
2	D6	data bus
3	D5	data bus
4	D4	data bus
5	D3	data bus
6	D2	data bus
7	D1	data bus
8	D0	data bus
9	CLK 0	counter 0 clock input
10	OUT 0	counter 0 output
11	GATE 0	counter 0 gate input
12	GND	ground
13	OUT 1	counter 1 output
14	GATE 1	counter 1 gate input
15	CLK 1	counter 1 clock input
16	GATE 2	counter 2 gate input
17	OUT 2	counter 2 output
18	CLK 2	counter 2 clock input
19	A0	address bus
20	A1	address bus
21	CS	chip select (active low)
22	RD	read enable (active low)
23	WR	write enable (active low)
24	Vcc	supply voltage

Specifications

(typical values under recommended operating conditions, unless specified)

Parameter	Value	Unit
Maximum clock input frequency	8 (8254) 10 (8254-2)	MHz

Notes

Register 00: counter 0 value
Register 01: counter 1 value
Register 10: counter 2 value
Register 11: control word
Control word:

Bit 0 0=binary (16 bits), 1=BCD (4 decades)

Bits 1-3 mode select

Bits 4-5 read/write mode

Bits 6-7 select counter/read-back mode
Mode 0: interrupt on terminal count
Mode 1: hardware retriggerable one-shot
Mode 2: rate generator
Mode 3: square wave
Mode 4: software triggered strobe
Mode 5: hardware triggered strobe (retriggerable)

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	0=binary (16 bits), 1=BCD (4 decades)
Bits 1-3	mode select
Bits 4-5	read/write mode
Bits 6-7	select counter/read-back mode