Chapter 8 Counters
© National Instruments Corporation 8-3 NI USB-621x User Manual
You can route the pause trigger to the Gate input of the counter. You can
configure the counter to pause counting when the pause trigger is high or
when it is low. Figure 8-3 shows an example of on-demand edge counting
with a pause trigger.
Figure 8-3. Single Point Edge Counting with Pause Trigger
Buffered (Sample Clock) Edge Counting
With buffered edge counting (edge counting using a sample clock), the
counter counts the number of edges on the Source input after the counter is
armed. The value of the counter is sampled on each active edge of a sample
clock. A USB Signal Stream transfers the sampled values to host memory.
The count values returned are the cumulative counts since the counter
armed event; that is, the sample clock does not reset the counter.
You can route the counter sample clock to the Gate input of the counter. You
can configure the counter to sample on the rising or falling edge of the
sample clock.
Figure 8-4 shows an example of buffered edge counting. Notice that
counting begins when the counter is armed, which occurs before the first
active edge on Gate.
Figure 8-4. Buffered (Sample Clock) Edge Counting
Counter Armed
SOURCE
Pause Trigger
(Pause when Low)
Counter Value
1 0 0 5 4 3 2
3
6
3
Counter Armed
SOURCE
Sample Clock
(Sample on Rising Edge)
Counter Value
Buffer
1 0 7 6 3 4 5 2
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