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Chapter 7
Counters
You can calculate the pulse width by multiplying the period of the Source signal by the number
of edges returned by the counter.
A pulse-width measurement will be accurate even if the counter is armed while a pulse train is
in progress. If a counter is armed while the pulse is in the active state, it will wait for the next
transition to the active state to begin the measurement.
Refer to the following sections for more information about M Series pulse-width measurement
options:
•
Single Pulse-Width Measurement
•
Buffered Pulse-Width Measurement
Single Pulse-Width Measurement
With single pulse-width measurement, the counter counts the number of edges on the Source
input while the Gate input remains active. When the Gate input goes inactive, the counter stores
the count in a hardware save register and ignores other edges on the Gate and Source inputs.
Software then reads the stored count.
Figure 7-5 shows an example of a single pulse-width measurement.
Figure 7-5.
Single Pulse-Width Measurement
Buffered Pulse-Width Measurement
Buffered pulse-width measurement is similar to single pulse-width measurement, but buffered
pulse-width measurement takes measurements over multiple pulses.
The counter counts the number of edges on the Source input while the Gate input remains active.
On each trailing edge of the Gate signal, the counter stores the count in a hardware save register.
A DMA controller transfers the stored values to host memory.
S
OURCE
GATE
Co
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nter V
a
l
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e
HW
Sa
ve Regi
s
ter
1
0
2
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