Chapter 8 CountersNI USB-621x User Manual 8-18 ni.comTwo-Signal Edge-Separation MeasurementTwo-signal edge-separation measurement is similar to pulse-widthmeasurement, except that there are two measurement signals—Aux andGate. An active edge on the Aux input starts the counting and an activeedge on the Gate input stops the counting. You must arm a counter to begina two edge separation measurement.After the counter has been armed and an active edge occurs on the Auxinput, the counter counts the number of rising (or falling) edges on theSource. The counter ignores additional edges on the Aux input.The counter stops counting upon receiving an active edge on the Gate input.The counter stores the count in a hardware save register.You can configure the rising or falling edge of the Aux input to be the activeedge. You can configure the rising or falling edge of the Gate input to bethe active edge.Use this type of measurement to count events or measure the time thatoccurs between edges on two signals. This type of measurement issometimes referred to as start/stop trigger measurement, second gatemeasurement, or A-to-B measurement.Single Two-Signal Edge-Separation MeasurementWith single two-signal edge-separation measurement, the counter countsthe number of rising (or falling) edges on the Source input occurringbetween an active edge of the Gate signal and an active edge of the Auxsignal. The counter then stores the count in a hardware save register andignores other edges on its inputs. Software then reads the stored count.
