Counter Input Applications; Counting Edges; Single Point (On-Demand) Edge Counting - National Instruments Data Acquisition Device NI USB-621x User Manual

Chapter 8 Counters

Counter Input Applications

Counting Edges

NI USB-621x User Manual
The counters have seven input signals, although in most applications only
a few inputs are used.
For information about connecting counter signals, refer to the
Counter/Timer Pinouts
In edge counting applications, the counter counts edges on its Source
after the counter is armed. You can configure the counter to count rising
or falling edges on its Source input. You also can control the direction of
counting (up or down).
The counter values can be read on demand or with a sample clock.

Single Point (On-Demand) Edge Counting

With single point (on-demand) edge counting, the counter counts the
number of edges on the Source input after the counter is armed. On-demand
refers to how the software can read the counter contents at any time without
disturbing the counting process. Figure 8-2 shows an example of single
point edge counting.
Counter Armed
SOURCE
Counter Value
Figure 8-2. Single Point (On-Demand) Edge Counting
You also can use a pause trigger to pause (or gate) the counter. When the
pause trigger is active, the counter ignores edges on its Source input. When
the pause trigger is inactive, the counter counts edges normally.
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.
section.
0 1 2
8-2
Default
3 4 5
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