Non-Cumulative Buffered Edge Counting; Controlling The Direction Of Counting - National Instruments NI USB-621x User Manual

Chapter 9 Counters
NI USB-621x User Manual

Non-Cumulative Buffered Edge Counting

Non-cumulative edge counting is similar to buffered (sample clock) edge
counting. However, the counter resets after each active edge of the Sample
Clock. You can route the Sample Clock to the Gate input of the counter.
Figure 9-5 shows an example of non-cumulative buffered edge counting.
Sample Clock
(Sample on
Rising Edge)
SOURCE
Counter Value
Buffer
Figure 9-5. Non-Cumulative Buffered Edge Counting
Notice that the first count interval begins when the counter is armed, which
occurs before the first active edge on Gate.
Note that if you are using an external signal as the Source, at least one
Source pulse should occur between each active edge of the Gate signal.
This condition ensures that correct values are returned by the counter. If this
condition is not met, consider using duplicate count prevention, described
in the Duplicate Count Prevention

Controlling the Direction of Counting

In edge counting applications, the counter can count up or down. You can
configure the counter to do the following:
• Always count up
• Always count down
• Count up when the Counter n B input is high; count down when it is
low
For information about connecting counter signals, refer to the
Counter/Timer Pinouts
Counter
Armed
0 1 2 1 2
2
section.
section.
9-4
3 1 2 3 1
2 2
3 3
3
Default
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