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Chapter 5
Counters
Pulse versus Semi-Period Measurements
section for information about the
differences between semi-period measurement and pulse measurement.
Single Semi-Period Measurement
Single semi-period measurement is equivalent to single pulse-width measurement.
Implicit Buffered Semi-Period Measurement
In implicit buffered semi-period measurements, on each edge of the Gate signal, the counter
stores the count in the FIFO. The STC3 transfers the sampled values to host memory using a
high-speed data stream.
The counter begins counting when it is armed. The arm usually occurs between edges on the
Gate input. You can select whether to read the first active low or active high semi period using
the
CI.SemiPeriod.StartingEdge
property in NI-DAQmx.
Figure 5-11 shows an example of an implicit buffered semi-period measurement.
Figure 5-11.
Implicit Buffered Semi-Period Measurement
For information about connecting counter signals, refer to the
section.
Pulse versus Semi-Period Measurements
In hardware, pulse measurement and semi-period are the same measurement. Both measure the
high and low times of a pulse. The functional difference between the two measurements is how
the data is returned. In a semi-period measurement, each high or low time is considered one point
of data and returned in units of seconds or ticks. In a pulse measurement, each pair of high and
low times is considered one point of data and returned as a paired sample in units of frequency
and duty cycle, high and low time or high and low ticks. When reading data, 10 points in a
semi-period measurement will get an array of five high times and five low times. When you read
10 points in a pulse measurement, you get an array of 10 pairs of high and low times.
Also, pulse measurements support sample clock timing while semi-period measurements do not.
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