ADLINK ACL-8112 Series - Manual (Page 55)

Operation Theory
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5.4 Timer/Counter Operation
The ACL-8112 has an 8254 interval timer/counter on board. Refer to section
3.5 for signal connection and the configuration of the counter.
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 systems are:
• programmable baud rate generator
• event
counter
• binary rate multiplier
• real-time
clock
• digital
one-shot
• motor
control
For more information about the 8254 , please refer to the NEC
Microprocessors and peripherals or Intel Microsystems Components
Handbook.
Pacer Trigger Source
Counter 1 and 2 are cascaded together to generate a timer pacer trigger for
the A/D conversion. The frequency of the pacer trigger is software
controllable. The maximum pacer signal rate is 2MHz/4=500K which
exceeds the maximum A/D conversion rate of the ACL-8112. The minimum
signal rate is 2MHz/65535/65535, which is a very slow frequency that user
may never use.
General Purpose Timer/ Counter
Counter 0 is free for user applications. The clock source, gate control signal
and the output signal are sent via CN3. The general purpose timer / counter
can be used as an event counter, used for measuring frequency or other
functions. See the 'Timer/Counter Applications' section for examples.