© National Instruments | 5-5NI cDAQ-9181/9184/9188/9191 User ManualControlling the Direction of CountingIn edge counting applications, the counter can count up or down. You can configure the counterto do the following:• Always count up• Always count down• Count up when the Counter 0 B input is high; count down when it is lowFor information about connecting counter signals, refer to the Default Counter/Timer Routingsection.Pulse-Width MeasurementIn pulse-width measurements, the counter measures the width of a pulse on its Gate input signal.You can configure the counter to measure the width of high pulses or low pulses on the Gatesignal.You can route an internal or external periodic clock signal (with a known period) to the Sourceinput of the counter. The counter counts the number of rising (or falling) edges on the Sourcesignal while the pulse on the Gate signal is active.You can calculate the pulse width by multiplying the period of the Source signal by the numberof edges returned by the counter.A pulse-width measurement will be accurate even if the counter is armed while a pulse train isin progress. If a counter is armed while the pulse is in the active state, it will wait for the nexttransition to the active state to begin the measurement.Refer to the following sections for more information about cDAQ chassis pulse-widthmeasurement options:• Single Pulse-Width Measurement• Implicit Buffered Pulse-Width Measurement• Sample Clocked Buffered Pulse-Width Measurement
