Chapter 7 CountersNI 6232/6233 User Manual 7-8 ni.comof rising (or falling) edges occurring on the Source input between the twoactive edges of the Gate signal.You can calculate the period of the Gate input by multiplying the period ofthe Source signal by the number of edges returned by the counter.Single Period MeasurementWith single period measurement, the counter counts the number of rising(or falling) edges on the Source input occurring between two active edgesof the Gate input. On the second active edge of the Gate input, the counterstores the count in a hardware save register and ignores other edges on theGate and Source inputs. Software then can read the stored count.Figure 7-8 shows an example of a single period measurement.Figure 7-8. Single Period MeasurementBuffered Period MeasurementBuffered period measurement is similar to single period measurement, butbuffered period measurement measures multiple periods.The counter counts the number of rising (or falling) edges on the Sourceinput between each pair of active edges on the Gate input. At the end ofeach period on the Gate signal, the counter stores the count in a hardwaresave register. A DMA controller transfers the stored values to host memory.The counter begins when it is armed. The arm usually occurs in the middleof a period of the Gate input. So the first value stored in the hardware saveregister does not reflect a full period of the Gate input. In most applications,this first point should be discarded.Figure 7-9 shows an example of a buffered period measurement.SOURCEGATECounter ValueHW Save Register10 354 52
