Advantech PCI-1751U, User Manual

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PCI-1751U User’s Manual 30
A.3.4 MODE 3 – Square Wave Generator
This mode is similar to Mode 2, except that the output will remain high
until one half of the count has been completed (for even numbers), and
will go low for the other half of the count. This is accomplished by
decreasing the counter by two on the falling edge of each clock pulse.
When the counter reaches the terminal count, the state of the output is
changed, the counter is reloaded with the full count and the whole process
is repeated.
If the count is odd and the output is high, the first clock pulse (after the
count is loaded ) decrements the count by 1. Subsequent clock pulses dec-
rement the count by 2. After time-out, the output goes low and the full
count is reloaded. The first clock pulse (following the reload) decrements
the counter by 3. Subsequent clock pulses decrement the count by two
until time-out, then the whole process is repeated. In this way, if the count
is odd, the output will be high for (N+1)/2 counts and low for (N-1)/2
counts.
A.3.5 MODE 4 – Software Triggered Strobe
After the mode is set, the output will be high. When the count is loaded,
the counter will begin counting. On terminal count, the output will go low
for one input clock period then go high again.
If you reload the count register during counting, the new count will be
loaded on the next CLK pulse. The count will be inhibited while the
GATE input is low.
A.3.6 MODE 5 – Hardware Triggered Strobe
The counter will start counting after the rising edge of the trigger input
and will go low for one clock period when the terminal count is reached.
The counter is retriggerable.