National Instruments PCI-6238, Руководство пользователя

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Chapter 7 Counters
© National Instruments Corporation 7-37 NI 6238/6239 User Manual
Figure 7-32. Duplicate Count Example
Example Application That Prevents Duplicate Count
With duplicate count prevention enabled, the counter synchronizes both the
Source and Gate signals to the 80 MHz Timebase. By synchronizing to the
timebase, the counter detects edges on the Gate even if the Source does not
pulse. This enables the correct current count to be stored in the buffer even
if no Source edges occur between Gate signals, as shown in Figure 7-33.
Figure 7-33. 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
Gate
Source
Counter Value
Buffer 7
6 7 1
No Source edge, so no
value written to buffer.
Gate
Source
80 MHz Timebase
Counter Value
Buffer
0
7 7
6 7 0 1
Counter detects
rising Gate edge.
Counter value
increments only
one time for each
Source pulse.