Chapter 4
Analog Input
©
National Instruments
4-29
X Series User Manual
Using an External Source
Use one of the following external signals as the so
u
rce of AI Sample Clock:
•
PFI <0..15>
•
RTSI <0..7>
•
PXI_STAR
•
PXIe-DSTAR<A,B>
•
Analog Comparison Event (an analog trigger)
Routing AI Sample Clock Signal to an Output Terminal
Yo
u
can ro
u
te AI Sample Clock o
u
t to any PFI <0..15>, RTSI <0..7>, or
PXIe-DSTARC terminal. This p
u
lse is always active high.
All PFI terminals are config
u
red as inp
u
ts by defa
u
lt.
Other Timing Requirements
Yo
u
r DAQ device only acq
u
ires data d
u
ring an acq
u
isition. The device
ignores AI Sample Clock when a meas
u
rement acq
u
isition is not in
progress. D
u
ring a meas
u
rement acq
u
isition, yo
u
can ca
u
se yo
u
r DAQ
device to ignore AI Sample Clock
u
sing the AI Pa
u
se Trigger signal.
A co
u
nter/timing engine on yo
u
r device internally generates AI Sample
Clock
u
nless yo
u
select some external so
u
rce. AI Start Trigger starts this
co
u
nter and either software or hardware can stop it once a finite acq
u
isition
completes. When
u
sing the AI timing engine, yo
u
also can specify a
config
u
rable delay from AI Start Trigger to the first AI Sample Clock
p
u
lse. By defa
u
lt, this delay is set to two ticks of the AI Sample Clock
Timebase signal.
When
u
sing an externally generated AI Sample Clock, yo
u
m
u
st ens
u
re the
clock signal is consistent with respect to the timing req
u
irements of
AI Convert Clock. Fail
u
re to do so may res
u
lt in a scan overr
u
n and will
ca
u
se an error. Refer to the
AI Convert Clock Signal
section for more
information abo
u
t the timing req
u
irements between AI Convert Clock and
AI Sample Clock.
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