User manual

Frequency measurement
This approach is a particular fit for a high frequency signal.
Standard Clock
Unknown Signal
CLK
OUT GATE
Counter 0 Counter 1
GATE OUT
CLK
Figure 3-4: Frequency measurement
Implementing this measurement needs two counters. One for the up
cycle period, another for the down cycle period. Adding them together
gives the total period. The duty cycle can also be calculated by dividing
the up period by the total period. Connect the unknown signal to each
counter's Gate. Apply a standard clock to each counter. Counter 0
counts the up cycle. Counter 1 counts the down cycle. In PCI-1780,
wiring is simple. Only connect the unknown signal to counter 0, and use
the register to select the gate source. Counter 0 select the "Gate N",
counter 1 select the "Gate N-1". Apply the standard clock to both
counters by clock source select register. It could change the clock for
different measurement range. Counter 0 set as "Mode O" and gate
polarity is positive.
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