Appendix D. 82C54 Counter Function - Advantech PCI-1755 User Manual

Appendix D. 82C54 Counter Function

D.1 Overview
The PCI-1755 uses one Intel 82C54 compatible programmable interval timer/counter chip.
The popular 82C54 offers three independent 16-bit counters, counter 0, counter 1 and
counter 2. Each counter has a clock input, control gate and an output. You can program
each counter for maximum count values from 2 to 65535.
The 82C54 has a maximum input clock frequency of 10 MHz. The PCI-1755 provides 10
MHz input frequencies to the counter chip from an on-board crystal oscillator.
Counter 0
On the PCI-1755 counter 0 can be a 16-bit timer or an event counter, selectable by users.
When the clock source is set as an internal source, counter 0 is a 16-bit timer; when set as
an external source, then counter 0 is an event counter and the clock source comes from
CNT0_CLK. The counter is controlled by CNT0_GATE. When CNT0_GATE input is
high, counter 0 will begin to count.
Counter 1 & 2
Counter 1 and counter 2 of the counter chip are cascaded to create a 32-bit timer for the
pacer trigger. A low-to-high edge of counter 2 output (PACER_OUT) will trigger an A/D
conversion. At the same time, you can use this signal as a synchronous signal for other
applications.
65