Buffered Semi-Period Measurement - National Instruments USB-621 Series User Manual

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Buffered Semi-Period Measurement

In buffered semi-period measurement, on each edge of the Gate signal, the
counter stores the count in a hardware save register. A USB Signal Stream
transfers the stored values to host memory.
The counter begins counting on the first active edge of the Gate after it is
armed. The arm usually occurs between edges on the Gate input. The
counter does not store a value for this incomplete semi-period.
Figure 8-9 shows an example of a buffered semi-period measurement.
Counter Armed
GATE
SOURCE
Counter Value
Buffer
Figure 8-9. Buffered Semi-Period Measurement
Note that if you are using an external signal as the Source, at least one
Source pulse should occur between each active edge of the Gate signal.
This condition ensures that correct values are returned by the counter. If this
condition is not met, the counter returns a zero. Refer to the
Count Prevention section for more information.
For information about connecting counter signals, refer to the
Counter/Timer Pinouts
0 1 2
section.
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