Contents
NI 6238/6239 User Manual viii ni.com
Chapter 7Counters
Counter Input Applications...........................................................................................7-3
Counting Edges...............................................................................................7-3
Single Point (On-Demand) Edge Counting......................................7-3
Buffered (Sample Clock) Edge Counting.........................................7-4
Non-Cumulative Buffered Edge Counting.......................................7-5
Controlling the Direction of Counting..............................................7-5
Pulse-Width Measurement..............................................................................7-6
Single Pulse-Width Measurement....................................................7-6
Buffered Pulse-Width Measurement................................................7-6
Period Measurement.......................................................................................7-7
Single Period Measurement..............................................................7-8
Buffered Period Measurement..........................................................7-8
Semi-Period Measurement..............................................................................7-9
Single Semi-Period Measurement....................................................7-9
Buffered Semi-Period Measurement................................................7-10
Frequency Measurement.................................................................................7-10
Method 1—Measure Low Frequency with One Counter................. 7-10
Method 1b—Measure Low Frequency with One Counter
(Averaged).....................................................................................7-11
Method 2—Measure High Frequency with Two Counters.............. 7-12
Method 3—Measure Large Range of Frequencies Using Two
Counters.........................................................................................7-13
Choosing a Method for Measuring Frequency.................................7-14
Position Measurement.....................................................................................7-16
Measurements Using Quadrature Encoders......................................7-16
Measurements Using Two Pulse Encoders...................................... 7-18
Two-Signal Edge-Separation Measurement...................................................7-19
Single Two-Signal Edge-Separation Measurement..........................7-19
Buffered Two-Signal Edge-Separation Measurement......................7-20
Counter Output Applications.........................................................................................7-21
Simple Pulse Generation.................................................................................7-21
Single Pulse Generation....................................................................7-21
Single Pulse Generation with Start Trigger......................................7-21
Retriggerable Single Pulse Generation.............................................7-22
Pulse Train Generation....................................................................................7-23
Continuous Pulse Train Generation..................................................7-23
Frequency Generation.....................................................................................7-24
Using the Frequency Generator........................................................7-24
Frequency Division.........................................................................................7-25
Pulse Generation for ETS...............................................................................7-25