4 timer/counter operation, Counter 0 counter 1 counter 2, 8254 timer/counter – ADLINK ACL-8216 User Manual

Page 46

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38 Operation Theorem

4.4 Timer/Counter

Operation

The ACL-8216 has an interval timer/counter 8254 on board. It offers 3
independent 16-bit programmable down counters; counter 1 and counter 2
are cascaded together for A/D timer pacer trigger of A/D conversion. and
counter 0 is free for your applications. The following figure shows the 8254
timer/counter connection.

Counter 0

Counter 1

Counter 2

CLK0

GATE0

OUT0

CLK1

GATE1

CLK2

GATE2

OUT1

OUT2

2MHz

Oscillator

Vcc

A/D Trigge

CN3 Pin-34

CN3 Pin-37

CN3 Pin-33

CN3 Pin-1

CN3 Pin-35

INT

EXT

8254 Timer/Counter

The clock source of counter 0 can be internal or external, while the gate can
be controlled externally and the output is send to the connector CN3. As to
counter 0 and counter 1, the clock source is internally fixed, while the gate
can be controlled externally and the output is send to the connector CN3 too.
All the timer/ counter signals are TTL compatible.

The 8254 Timer / Counter Chip

The Intel (NEC) 8254 contains three independent, programmable, multi-
mode 16 bit counter/timers. The three independent 16 bit counters can be
clocked at rates from DC to 5 MHz. Each counter can be individually
programmed with 6 different operating modes by appropriately formatted
control words. The most commonly uses for the 8254 in microprocessor
based system are:

• Pprogrammable baud rate generator
• event

counter

• binary rate multiplier
• real-time

clock

• digital

one-shot

• motor

control

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