Chapter 6
Digital I/O
X Series User Manual
6-10
ni.com
Using an Analog Source
When yo
u
u
se an analog trigger so
u
rce, the acq
u
isition begins on the first
rising or falling edge of the Analog Comparison Event signal.
Routing DI Start Trigger to an Output Terminal
Yo
u
can ro
u
te DI 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 DI Start Trigger to initiate pretriggered DAQ
operations. In most pretriggered applications, a software trigger generates
DI Start Trigger. Refer to the
DI Reference Trigger Signal
section for a
complete description of the
u
se of DI Start Trigger and DI Reference
Trigger in a pretriggered DAQ operation.
DI Reference Trigger Signal
Use the DI Reference Trigger (di/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.
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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