Chapter 8
Counters
©
National Instruments Corporation
8-9
Buffered Semi-Period Measurement
In b
u
ffered semi-period meas
u
rement, on each edge of the Gate signal, the
co
u
nter stores the co
u
nt in a hardware save register. A USB Signal Stream
transfers the stored val
u
es to host memory.
The co
u
nter begins co
u
nting on the first active edge of the Gate after it is
armed. The arm
u
s
u
ally occ
u
rs between edges on the Gate inp
u
t. The
co
u
nter does not store a val
u
e for this incomplete semi-period.
Fig
u
re 8-9 shows an example of a b
u
ffered semi-period meas
u
rement.
Figure 8-9.
Buffered Semi-Period Measurement
Note that if yo
u
are
u
sing an external signal as the So
u
rce, at least one
So
u
rce p
u
lse sho
u
ld occ
u
r between each active edge of the Gate signal.
This condition ens
u
res that correct val
u
es are ret
u
rned by the co
u
nter. If this
condition is not met, the co
u
nter ret
u
rns a zero. Refer to the
section for more information.
For information abo
u
t connecting co
u
nter signals, refer to the
section.
3
1
2
3
1
3
S
OURCE
GATE
Co
u
nter V
a
l
u
e
B
u
ffer
1
3
2
2
1 1
1
3
1
2
0
Co
u
nter Armed
