National Instruments Data Acquisition Device NI USB-621x User Manual

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National Instruments Data Acquisition Device NI USB-621x User Manual Manual pdf 98 page image

Chapter 8 Counters© National Instruments Corporation 8-5 NI USB-621x User ManualFigure 8-5 shows an example of a single pulse-width measurement.Figure 8-5. Single Pulse-Width MeasurementBuffered Pulse-Width MeasurementBuffered pulse-width measurement is similar to single pulse-widthmeasurement, but buffered pulse-width measurement takes measurementsover multiple pulses.The counter counts the number of edges on the Source input while the Gateinput remains active. On each trailing edge of the Gate signal, the counterstores the count in a hardware save register. A USB Signal Stream transfersthe stored values to host memory.Figure 8-6 shows an example of a buffered pulse-width measurement.Figure 8-6. Buffered Pulse-Width MeasurementNote that if you are using an external signal as the Source, at least oneSource pulse should occur between each active edge of the Gate signal.This condition ensures that correct values are returned by the counter. If thisSOURCEGATECounter ValueHW Save Register1022SOURCEGATECounter ValueBuffer10 33 2212 3 32