5-4 | ni.comChapter 5 CountersYou 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 countercounts edges normally.You can route the pause trigger to the Gate input of the counter. You can configure the counterto pause counting when the pause trigger is high or when it is low. Figure 5-3 shows an exampleof on-demand edge counting with a pause trigger.Figure 5-3. Single Point (On-Demand) Edge Counting with Pause TriggerBuffered (Sample Clock) Edge CountingWith buffered edge counting (edge counting using a sample clock), the counter countsthe number of edges on the Source input after the counter is armed. The value of the counteris sampled on each active edge of a sample clock and stored in the FIFO. The STC3 transfers thesampled values to host memory using a high-speed data stream.The count values returned are the cumulative counts since the counter armed event. That is, thesample clock does not reset the counter. You can configure the counter to sample on the risingor falling edge of the sample clock.Figure 5-4 shows an example of buffered edge counting. Notice that counting begins when thecounter is armed, which occurs before the first active edge on Sample Clock.Figure 5-4. Buffered (Sample Clock) Edge CountingCounter ArmedSOURCEPause Trigger(Pause When Low)Counter Value 10 0 5432363Counter ArmedSOURCESample Clock(Sample on Rising Edge)Counter ValueBuffer10 763 4 52
