7-6 | ni.comChapter 7 CountersFigure 7-7 shows an example of a single period measurement.Figure 7-7. Single Period MeasurementBuffered Period MeasurementBuffered period measurement is similar to single period measurement, but buffered periodmeasurement measures multiple periods.The counter counts the number of rising (or falling) edges on the Source input between each pairof active edges on the Gate input. At the end of each period on the Gate signal, the counter storesthe count in a hardware save register. A DMA controller transfers the stored values to hostmemory.The counter begins when it is armed. The arm usually occurs in the middle of a period of theGate input. So the first value stored in the hardware save register does not reflect a full period ofthe Gate input. In most applications, this first point should be discarded.Figure 7-8 shows an example of a buffered period measurement.Figure 7-8. Buffered Period MeasurementNote that if you are using an external signal as the Source, at least one Source pulse should occurbetween each active edge of the Gate signal. This condition ensures that correct values arereturned by the counter. If this condition is not met, consider using duplicate count prevention,described in the Duplicate Count Prevention section.SOURCEGATECounter ValueHW Save Register10 354 52SOURCEGATECounter ValueBuffer11 2 332 331 12 22 2332 (Discard) (Discard) (Discard)3Counter ArmedArtisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
