Reference Trigger Final Buffer; Routing The Reference Trigger Signal To An Output Terminal - National Instruments cRIO-904 Series User Manual

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.
Figure 35. Reference Trigger Final Buffer
Reference Trigger
Pretrigger Samples Posttrigger Samples
Complete Buffer
Using a Digital Source
To use a reference trigger with a digital source, specify a source and a rising or falling edge.
Either PFI or one of several internal signals on the cRIO controller can provide the source.
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, the acquisition stops on the first rising or falling edge
of the Analog Comparison Event signal, depending on the trigger properties.

Routing the Reference Trigger Signal to an Output Terminal

You can route a reference trigger to any output PFI terminal. Reference Trigger is active high
by default.
cRIO-904x User Manual | © National Instruments | 51