National Instruments Eight-slot USB Chassis NI cDAQ-9172 - Manual (Page 72)

NI cDAQ-9172 User Guide and Specifications 72 ni.com
Example Application That Works Incorrectly
(Duplicate Counting)
In Figure 44, after the first rising edge of Gate, no Source pulses occur,
which means that the counter does not write the correct data to the buffer.
Figure 44. 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 45.
Figure 45. Duplicate Count Prevention Example
Gate
7
6 7 1
No Source edge, so no
value written to buffer.
Source
Counter Value
Buffer
Gate
0
7 7
6 7 0 1
Counter detects
rising Gate edge.
Counter value
increments only
one time for each
Source pulse.
Buffer
Source
80 MHz Timebase
Counter Value