82C54 datasheet(5/18 Pages) INTEL

5 / 18 page

82C54

OPERATIONAL DESCRIPTION

General

After power-up the state of the 82C54 is undefined

The Mode count value and output of all Counters

are undefined

How each Counter operates is determined when it is

programmed Each Counter must be programmed

before it can be used Unused counters need not be

programmed

Programming the 82C54

Counters are programmed by writing a Control Word

and then an initial count The control word format is

shown in Figure 7

All Control Words are written into the Control Word

Control Word itself specifies which Counter is being

programmed

By contrast initial counts are written into the Coun-

ters not the Control Word Register The A1 A0 in-

puts are used to select the Counter to be written

into The format of the initial count is determined by

the Control Word used

Control Word Format

A1 A0 e 11 CS e 0RD e 1WR e 0

SC1

SC0

RW1

RW0

BCD

Select Counter

SC1

SC0

Select Counter 0

Select Counter 1

Select Counter 2

Read-Back Command

(See Read Operations)

ReadWrite

RW1 RW0

Counter Latch Command (see Read

Operations)

ReadWrite least significant byte only

ReadWrite most significant byte only

ReadWrite least significant byte first

then most significant byte

NOTE

Don’t care bits (X) should be 0 to insure

compatibility with future Intel products

MODE

Mode 0

Mode 1

Mode 2

Mode 3

Mode 4

Mode 5

BCD

Binary Counter 16-bits

Binary Coded Decimal (BCD) Counter

(4 Decades)

Figure 7 Control Word Format

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