8254 データシートの表示（PDF） - Intel

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8254

PROGRAMMABLE INTERVAL TIMER

Intel 

8254

Symbol

D7 – D0

CLK 0

OUT 0

GATE 0

GND

VCC

WR

RD

CS

A1 A0

CLK 2

OUT 2

GATE 2

CLK 1

GATE 1

OUT 1

Pin

No

1–8

9

10

11

12

24

23

22

21

20 – 19

18

17

16

15

14

13

Type

IO

I

O

I

I

I

I

I

I

O

I

I

I

O

Table 1 Pin Description

Name and Function

DATA Bi-directional three state data bus lines connected to system

data bus

CLOCK 0 Clock input of Counter 0

OUTPUT 0 Output of Counter 0

GATE 0 Gate input of Counter 0

GROUND Power supply connection

POWER a5V power supply connection

WRITE CONTROL This input is low during CPU write operations

READ CONTROL This input is low during CPU read operations

CHIP SELECT A low on this input enables the 8254 to respond to

RD and WR signals RD and WR are ignored otherwise

ADDRESS Used to select one of the three Counters or the Control

Word Register for read or write operations Normally connected to

the system address bus

A1

A0

Selects

0

0

Counter 0

0

1

Counter 1

1

0

Counter 2

1

1

Control Word Register

CLOCK 2 Clock input of Counter 2

OUT 2 Output of Counter 2

GATE 2 Gate input of Counter 2

CLOCK 1 Clock input of Counter 1

GATE 1 Gate input of Counter 1

OUT 1 Output of Counter 1

FUNCTIONAL DESCRIPTION

General

The 8254 is a programmable interval timer counter

designed for use with Intel microcomputer systems

It is a general purpose multi-timing element that can

be treated as an array of I O ports in the system

software

The 8254 solves one of the most common problems

in any microcomputer system the generation of ac-

curate time delays under software control Instead of

setting up timing loops in software the programmer

configures the 8254 to match his requirements and

programs one of the counters for the desired delay

After the desired delay the 8254 will interrupt the

CPU Software overhead is minimal and variable

length delays can easily be accommodated

Some of the other counter timer functions common

to microcomputers which can be implemented with

the 8254 are

 Real time clock

 Event-counter

 Digital one-shot

 Programmable rate generator

 Square wave generator

 Binary rate multiplier

 Complex waveform generator

 Complex motor controller

Block Diagram

DATA BUS BUFFER

This 3-state bi-directional 8-bit buffer is used to in-

terface the 8254 to the system bus (see Figure 3)

2

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