Chapter 2
Device Overview
©
National Instruments
2-7
Even if the So
u
rce p
u
lses are long, the co
u
nter increments only once for
each so
u
rce p
u
lse.
Normally, the co
u
nter and Co
u
nter
n
Internal O
u
tp
u
t signals change
synchrono
u
sly to the So
u
rce signal. With d
u
plicate co
u
nt prevention, the
co
u
nter val
u
e and Co
u
nter
n
Internal O
u
tp
u
t signals change synchrono
u
sly
to the maxim
u
m onboard timebase.
Notice that d
u
plicate co
u
nt prevention sho
u
ld only be
u
sed if the freq
u
ency
of the So
u
rce signal is one-fo
u
rth of the maxim
u
m onboard timebase.
Enabling Duplicate Count Prevention in NI-DAQmx
Yo
u
can enable d
u
plicate co
u
nt prevention in NI-DAQmx by setting the
Enable Duplicate Count Prevention
attrib
u
te/property. For specific
information on finding the
Enable Duplicate Count Prevention
attrib
u
te/property, refer to the help file for the API yo
u
are
u
sing. Refer to
the
NI-DAQmx Help
for more information.
When to Use Duplicate Count Prevention
Use d
u
plicate co
u
nt prevention for b
u
ffered meas
u
rements that
u
se an
external Ctr
n
So
u
rce signal and the freq
u
ency of the signal is less than or
eq
u
al to one-fo
u
rth of the maxim
u
m onboard timebase. Use this mode if
yo
u
are
u
sing a low freq
u
ency or yo
u
expect zero Ctr
n
So
u
rce edges
between s
u
ccessive edges of the Ctr
n
Gate signal.
Yo
u
sho
u
ld
u
se d
u
plicate co
u
nt prevention if the following conditions are
tr
u
e:
•
Yo
u
are making a b
u
ffered co
u
nter inp
u
t meas
u
rement.
•
Yo
u
are
u
sing an external signal (s
u
ch as PFI
x
) as the co
u
nter So
u
rce.
•
The freq
u
ency of the external so
u
rce is one-fo
u
rth of the maxim
u
m
onboard timebase.
•
Yo
u
can have the co
u
nter val
u
e and o
u
tp
u
t to change synchrono
u
sly
with the maxim
u
m onboard timebase.
In all other cases, yo
u
sho
u
ld
not
enable d
u
plicate co
u
nt prevention.
When Not to Use Duplicate Count Prevention
Use d
u
plicate co
u
nter prevention only for b
u
ffered meas
u
rements with an
external Ctr
n
So
u
rce signal. Do not
u
se it when the Ctr
n
So
u
rce signal is
greater than one-fo
u
rth of the maxim
u
m timebase.
Summary of Contents for PCI-6601
Page 1: ...PCI 6601...
