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AI Reference Trigger Signal
© National Instruments Corporation
Using an Analog Source
When you use an analog trigger source, the acquisition begins on the first
rising edge of the Analog Comparison Event signal.
Routing AI Start Trigger to an Output Terminal
You can route ai/StartTrigger out to any PFI <0..15> or RTSI <0..7>
terminal.
The output is an active high pulse.
All PFI terminals are configured as inputs by default.
The device also uses ai/StartTrigger to initiate pretriggered DAQ
operations. In most pretriggered applications, a software trigger generates
ai/StartTrigger. Refer to the AI Reference Trigger Signal section for a
complete description of the use of ai/StartTrigger and ai/ReferenceTrigger
in a pretriggered DAQ operation.
Use a reference trigger (ai/ReferenceTrigger) signal to stop a measurement
acquisition. To use a reference trigger, specify a buffer of finite size and a
number of pretrigger samples (samples that occur before the reference
trigger). The number of posttrigger samples (samples that occur after the
reference trigger) desired is the buffer size minus the number of pretrigger
samples.
Once the acquisition begins, the DAQ device writes samples to the buffer.
After the DAQ device captures the specified number of pretrigger samples,
the DAQ device begins to look for the reference trigger condition. If the
reference trigger condition occurs before the DAQ device captures the
specified number of pretrigger samples, the DAQ device ignores the
condition.
If the buffer becomes full, the DAQ device continuously discards the oldest
samples in the buffer 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 document, Can a Pretriggered Acquisition be
Continuous?, for more information. To access this KnowledgeBase, go to
and enter the info code
ni.com/info
rdcanq
4-37
Chapter 4
Analog Input
.
M Series User Manual
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