ID82C54【PDF 19/22 页】IC OSC PROG TIMER 8MHZ 24DIP

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82C54

Functional Description

General

The 82C54 is a programmable interval timer/counter

designed for use with 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 82C54 solves one of the most common problems in any

microcomputer system, the generation of accurate time

delays under software control. Instead of setting up timing

loops in software, the programmer configures the 82C54 to

match his requirements and programs one of the counters

for the desired delay. After the desired delay, the 82C54 will

interrupt the CPU. Software overhead is minimal and

variable length delays can easily be accommodated.

Some of the other computer/timer functions common to

microcomputers which can be implemented with the 82C54

are:

Real time clock

Event counter

Digital one-shot

Programmable rate generator

Square wave generator

Binary rate multiplier

Complex waveform generator

Complex motor controller

Data Bus Buffer

This three-state, bi-directional, 8-bit buffer is used to

interface the 82C54 to the system bus (see Figure 1).

Read/Write Logic

The Read/Write Logic accepts inputs from the system bus and

generates control signals for the other functional blocks of the

82C54. A1 and A0 select one of the three counters or the

Control Word Register to be read from/written into. A “low” on

the RD input tells the 82C54 that the CPU is reading one of the

counters. A “low” on the WR input tells the 82C54 that the CPU

is writing either a Control Word or an initial count. Both RD and

WR are qualified by CS; RD and WR are ignored unless the

82C54 has been selected by holding CS low.

Control Word Register

The Control Word Register (Figure 2) is selected by the

Read/Write Logic when A1, A0 = 11. If the CPU then does a

write operation to the 82C54, the data is stored in the

Control Word Register and is interpreted as a Control Word

used to define the Counter operation.

The Control Word Register can only be written to; status

information is available with the Read-Back Command.

Counter 0, Counter 1, Counter 2

These three functional blocks are identical in operation, so

only a single Counter will be described. The internal block

diagram of a signal counter is shown in Figure 3. The

counters are fully independent. Each Counter may operate

in a different Mode.

The Control Word Register is shown in the figure; it is not

part of the Counter itself, but its contents determine how the

Counter operates.

CONTROL

WORD

REGISTER

COUNTER

INTERNAL

OUT 2

GATE 2

CLK 2

OUT 1

GATE 1

CLK 1

OUT 0

GATE 0

CLK 0

D7 - D0

FIGURE 1. DATA BUS BUFFER AND READ/WRITE LOGIC

FUNCTIONS

DATA/

BUS

BUFFER

READ/

WRITE

LOGIC

READ/

WRITE

LOGIC

DATA/

BUS

BUFFER

INTERNAL

BUS

OUT 2

GATE 2

CLK 2

OUT 1

GATE 1

CLK 1

OUT 0

GATE 0

CLK 0

D7 - D0

FIGURE 2. CONTROL WORD REGISTER AND COUNTER

FUNCTIONS

CONTROL

WORD

REGISTER

COUNTER

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