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Chapter 5
PCI-1712/1712L User’s Manual
Advantech Co., Ltd.
www.advantech.com
5.4 Counter/Timer Features
The PCI-1712/1712L features multifunction counter/timer functions
with one-shot, rate generation, frequency measurement and pulse
width measurement. There are two 8254 counter chips in PCI-1712/
1712L, and each chip has 3 multifunction counters. The first counter
chip (chip 1) is specified for AI and AO functions, and can’t be used
by user. The second counter chip (chip 2) is reserved for user, and the
following section describes its features.
The PCI-1712/1712L uses the 82C54 programmable timer/counter chip
includes 3 independent 16-bit down counters: counter 0, counter 1 and
counter 2. Each counter has clock input, gate input and pulse output. It
can be programmed to count from 2 up to 65535.
For detailed information, Intel
®
82C54 User’s Manual is available by
accessing the following path on CD-ROM:
\Document\Intel 82C54 manual.pdf
Clock sources
The following clock sources are available for the user counters, and
they are available to set its active edge as rising edge or falling edge:
q Internal clock
User can specify the internal clock as the clock source through
software, and choose among four frequency options: 10MHz, 1MHz,
100kHz and 10kHz of the on-board crystal oscillator. For detailed
information, please refer to Appendix D.14 Counter gate and clock
control/status.
q External clock
The external clock is useful when you want to pace counter/timer
operations at rates not available with the internal clock or if you want
to pace at uneven internals. User can specify an external clock as the
clock source through software. User could connect the external clock
to the PCI-1712/1712L through the PCLD-8712 screw-terminal wiring
board that corresponds to each counter/timer.
q Internally cascaded clock
You can also route the clock output signal from one user counter to the
clock input signal of the next user counter to internally cascade the
counters. In this way, you can create a 32-bit or even a 48-bit counter
without externally cascading multiple counters together. When user
wants to cascade the counters, please follow the round-robin order of