5-10 | ni.comChapter 5 CountersRefer to the Pulse versus Semi-Period Measurements section for information about thedifferences between semi-period measurement and pulse measurement.Single Semi-Period MeasurementSingle semi-period measurement is equivalent to single pulse-width measurement.Implicit Buffered Semi-Period MeasurementIn implicit buffered semi-period measurements, on each edge of the Gate signal, the counterstores the count in the FIFO. The STC3 transfers the sampled values to host memory using ahigh-speed data stream.The counter begins counting when it is armed. The arm usually occurs between edges on theGate input. You can select whether to read the first active low or active high semi period usingthe CI.SemiPeriod.StartingEdge property in NI-DAQmx.Figure 5-11 shows an example of an implicit buffered semi-period measurement.Figure 5-11. Implicit Buffered Semi-Period MeasurementFor information about connecting counter signals, refer to the Default Counter/Timer Routingsection.Pulse versus Semi-Period MeasurementsIn hardware, pulse measurement and semi-period are the same measurement. Both measure thehigh and low times of a pulse. The functional difference between the two measurements is howthe data is returned. In a semi-period measurement, each high or low time is considered one pointof data and returned in units of seconds or ticks. In a pulse measurement, each pair of high andlow times is considered one point of data and returned as a paired sample in units of frequencyand duty cycle, high and low time or high and low ticks. When reading data, 10 points in asemi-period measurement will get an array of five high times and five low times. When you read10 points in a pulse measurement, you get an array of 10 pairs of high and low times.Also, pulse measurements support sample clock timing while semi-period measurements do not.123133SOURCEGATECounter ValueBuffer1 3221 113120CounterArmedStartingEdge
