Chapter 2 Function Reference — CTR_Ev Read
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National Instruments Corporation 2-95 NI-DAQ FRM for PC Compatibles
Using This Function
CTR_EvRead reads the current value of the counter without disturbing the counting process
and returns the value in count. CTR_EvRead also performs overflow detection and returns the
overflow status i n overflow. Overflow detection and the significance of count depend on the
counter configuration.
Special Considerations for Overflow Detection
For NI-DAQ to detect an overflow condition, you must conf igure th e counter for TC toggl ed
output type and positive output polarity, and then you must configure the counter to stop
counting on overflow (cont = 0 in the CTR_EvCount call). If these conditions are not met, the
value of overflow is meaningless. If more than one counter is concatenated for event-counting
applications, you should configure the lower-order counters to continue counting when
overflow occurs, and overflow detection is only meaningful for the highest order counter.
count, returned by CTR_EvRead for the lower-order counters, then represents the module
65,536 event count. See Event-Counting Applications in Chapter 3, Software Overview, in the
NI-DAQ User Manual for PC Compatibles for more information.