Chapter 4
Analog Input
©
National Instruments
4-59
X Series User Manual
Routing AI Start Trigger to an Output Terminal
Yo
u
can ro
u
te AI Start Trigger o
u
t to any PFI <0..15>, RTSI <0..7>, or
PXIe-DSTARC terminal. The o
u
tp
u
t is an active high p
u
lse. All PFI
terminals are config
u
red as inp
u
ts by defa
u
lt.
The device also
u
ses AI Start Trigger to initiate pretriggered DAQ
operations. In most pretriggered applications, a software trigger generates
AI Start Trigger. Refer to the
AI Reference Trigger Signal
section for a
complete description of the
u
se of AI Start Trigger and AI Reference
Trigger in a pretriggered DAQ operation.
AI Reference Trigger Signal
Use AI Reference Trigger (ai/ReferenceTrigger) signal to stop a
meas
u
rement acq
u
isition. To
u
se a reference trigger, specify a b
u
ffer of
finite size and a n
u
mber of pretrigger samples (samples that occ
u
r before
the reference trigger). The n
u
mber of posttrigger samples (samples that
occ
u
r after the reference trigger) desired is the b
u
ffer size min
u
s the
n
u
mber of pretrigger samples.
Note
(NI USB-6356/6366 Devices)
Yo
u
can select the b
u
ffer on the host or on the
NI USB-6356/6366 device. To enable a Reference Trigger to Onboard Memory, set the
AI Data Transfer Req
u
est Condition property in NI-DAQmx to When Acq
u
isition
Complete.
Once the acq
u
isition begins, the DAQ device writes samples to the b
u
ffer.
After the DAQ device capt
u
res the specified n
u
mber of pretrigger samples,
the DAQ device begins to look for the reference trigger condition. If the
reference trigger condition occ
u
rs before the DAQ device capt
u
res the
specified n
u
mber of pretrigger samples, the DAQ device ignores the
condition.
If the b
u
ffer becomes f
u
ll, the DAQ device contin
u
o
u
sly discards the oldest
samples in the b
u
ffer to make space for the next sample. This data can be
accessed (with some limitations) before the DAQ device discards it. Refer
to the KnowledgeBase doc
u
ment,
Can a Pretriggered Acquisition be
Continuous?
, for more information. To access this KnowledgeBase, go to
ni.com/info
and enter the Info Code
rdcanq
.
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