also can control the direction of counting (up or down), as described in the Controlling the
Direction of Counting section. The counter values can be read on demand or with a sample
clock.
Refer to the following sections for more information about edge counting options:
• Single Point (On-Demand) Edge Counting
• Buffered (Sample Clock) Edge Counting
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 the fact that software can read
the counter contents at any time without disturbing the counting process. The following figure
shows an example of single point edge counting.
Figure 50. Single Point (On-Demand) Edge Counting
Counter Armed
SOURCE
Counter Value 10 5432
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. The following figure shows
an example of on-demand edge counting with a pause trigger.
Figure 51. Single Point (On-Demand) Edge Counting with Pause Trigger
Counter Armed
SOURCE
Pause Trigger
(Pause When Low)
Counter Value
10 0 5432
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 and stored in the FIFO. The sampled values
will be transferred to host memory using a high-speed data stream.
78 | ni.com | cRIO-904x User Manual
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