Chapter 7
Counters
©
National Instruments Corporation
7-17
For information about connecting counter signals, refer to the
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
counter armed event; that is, the sample clock does not reset the counter.
You can route the counter sample clock to the Gate input of the counter.
You can configure the counter to sample on the rising or falling edge of the
sample clock.
Figure 7-19 shows an example of a buffered edge X1 position
measurement.
Figure 7-19.
Buffered Position Measurement
Two-Signal Edge-Separation Measurement
Two-signal edge-separation measurement is similar to pulse-width
measurement, except that there are two measurement signals—Aux and
Gate. An active edge on the Aux input starts the counting and an active
edge on the Gate input stops the counting. You must arm a counter to begin
a two edge separation measurement.
After the counter has been armed and an active edge occurs on the Aux
input, the counter counts the number of rising (or falling) edges on the
Source. The counter ignores additional edges on the Aux input.
The counter stops counting upon receiving an active edge on the Gate input.
The counter stores the count in a hardware save register.
1
4
1
Ch A
Ch B
4
1
0
2
5
Co
u
nt
B
u
ffer
Sa
mple Clock
(
Sa
mple on Ri
s
ing Edge)
Co
u
nter
Armed
