Chapter 7 Counters
© National Instruments 7-25 X Series User Manual
the channel B goes low to enter the reload phase, the increment occurs first.
The reload occurs within one maximum timebase period after the reload
phase becomes true. After the reload occurs, the counter continues to count
as before. The figure illustrates channel Z reload with X4 decoding.
Figure 7-21. Channel Z Reload with X4 Decoding
Measurements Using Two Pulse Encoders
The counter supports two pulse encoders that have two channels—channels
A and B.
The counter increments on each rising edge of channel A. The counter
decrements on each rising edge of channel B, as shown in Figure 7-22.
Figure 7-22. Measurements Using Two Pulse Encoders
For information about connecting counter signals, refer to the Default
Counter/Timer Pinouts section.
Buffered (Sample Clock) Position Measurement
With buffered position measurement (position measurement using a
sample clock), the counter increments based on the encoding used after the
counter is armed. The value of the counter is sampled on each active edge
of a sample clock. A DMA controller transfers the sampled values to host
memory. The count values returned are the cumulative counts since the
Ch A
Ch B
Counter Value
56
A = 0
B = 0
Z = 1
Ch Z
Max Timebase
890 21743
Ch A
Ch B
Counter Value2 3 54 344
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