Chapter 7
Counters
©
National Instruments
7-11
X Series User Manual
Fig
u
re 7-10 shows an example of a sample clocked b
u
ffered p
u
lse
meas
u
rement.
Figure 7-10.
Sample Clocked Buffered Pulse Measurement
Hardware-Timed Single Point Pulse Measurement
A hardware-timed single point (HWTSP) p
u
lse meas
u
rement has the same
behavior as a sample clocked b
u
ffered p
u
lse meas
u
rement.
Note
If a p
u
lse does not occ
u
r between sample clocks, an overr
u
n error will occ
u
r.
Note
(NI USB-634
x
/635
x
/636
x
Devices)
X Series USB devices do not s
u
pport
hardware-timed single point (HWTSP) operations.
For information abo
u
t connecting co
u
nter signals, refer to the
Default
Counter/Timer Pinouts
section.
Pulse versus Semi-Period Measurements
In hardware, p
u
lse meas
u
rement and semi-period are the same
meas
u
rement. Both meas
u
re the high and low times of a p
u
lse. The
f
u
nctional difference between the two meas
u
rements is how the data is
ret
u
rned. In a semi-period meas
u
rement, each high or low time is
considered one point of data and ret
u
rned in
u
nits of seconds or ticks. In a
p
u
lse meas
u
rement, each pair of high and low times is considered one point
of data and ret
u
rned as a paired sample in
u
nits of freq
u
ency and d
u
ty cycle,
high and low time or high and low ticks. When reading data, 10 points in a
semi-period meas
u
rement will get an array of five high times and five low
times. When yo
u
read 10 points in a p
u
lse meas
u
rement, yo
u
get an array
of 10 pairs of high and low times.
Co
u
nter
Armed
G
a
te
S
o
u
rce
H L
2 2
H L
2 2
3 3
Sa
mple
Clock
S
1
S
2
B
u
ffer
2
2
3
3
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