Using An Analog Source; Routing Ai Start Trigger To An Output Terminal; Using A Time Source; Ai Reference Trigger Signal - National Instruments NI cRIO-905x Series User Manual

The source also can be one of several other internal signals on your cRIO controller. Refer to
the "Device Routing in MAX" topic in the NI-DAQmx Help or the LabVIEW Help for more
information.

Using an Analog Source

Some C Series modules can generate a trigger based on an analog signal. In NI-DAQmx, this
is called the Analog Comparison Event. When you use an analog trigger source for Start
Trigger, 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 the Start Trigger signal to any output PFI terminal. The output is an active high
pulse.

Using a Time Source

To use the Start Trigger signal with a time source, configure a specific time in NI-DAQmx.
Refer to the "Timestamps" and "Time Triggering" topics in the NI-DAQmx Help for more
information on accessing time-based features in the NI-DAQmx API.

AI Reference Trigger Signal

Use a reference trigger 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 cRIO controller writes samples to the buffer. After the cRIO
controller captures the specified number of pretrigger samples, the cRIO controller begins to
look for the reference trigger condition. If the reference trigger condition occurs before the
cRIO controller captures the specified number of pretrigger samples, the controller ignores the
condition.
If the buffer becomes full, the cRIO controller 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 cRIO controller discards it. Refer to the Can a Pretriggered Acquisition be
Continuous? document for more information. To access this document, go to ni.com/info and
enter the Info Code .
rdcanq
When the reference trigger occurs, the cRIO controller continues to write samples to the buffer
until the buffer contains the number of posttrigger samples desired. The figure below shows
the final buffer.
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