National Instruments Data Acquisition Device NI USB-621x - Manual (Page 130)

Chapter 8 Counters
© National Instruments Corporation 8-37 NI USB-621x User Manual
Figure 8-33. Duplicate Count Prevention Example
Even if the Source pulses are long, the counter increments only once for
each Source pulse.
Normally, the counter value and Counter n Internal Output signals change
synchronously to the Source signal. With duplicate count prevention, the
counter value and Counter n Internal Output signals change synchronously
to the 80 MHz Timebase.
Enabling Duplicate Count Prevention in NI-DAQmx
Duplicate count prevention is automatically used with USB-621x devices.
Disabling duplicate count prevention is not supported.
Gate
0
7 7
6 7 0 1
Counter detects
rising Gate edge.
Source
Counter Value
Buffer
Counter value
increments only
one time for each
Source pulse.
80 MHz Timebase