Using an Internal Source
To use DI Sample Clock with an internal source, specify the signal source and the polarity of
the signal. Use the following signals as the source:
• it Sample Clock
• ot Sample Clock
• Counter n Internal Output
• Frequency Output
• DI Change Detection Output
Several other internal signals can be routed to DI Sample Clock. Refer to the "Device Routing
in MAX" topic in the NI-DAQmx Help or the LabVIEW Help for more information.
Using an External Source
You can route the following signals as DI Sample Clock:
• Any PFI terminal
• Analog Comparison Event (an analog trigger)
You can sample data on the rising or falling edge of DI Sample Clock.
Routing DI Sample Clock to an Output Terminal
You can route DI Sample Clock to any output PFI terminal. The PFI circuitry inverts the
polarity of DI Sample Clock before driving the PFI terminal.
DI Start Trigger Signal
Use the DI Start Trigger signal to begin a measurement acquisition. A measurement
acquisition consists of one or more samples. If you do not use triggers, begin a measurement
with a software command. Once the acquisition begins, configure the acquisition to stop in one
of the following ways:
• When a certain number of points has been sampled (in finite mode)
• After a hardware reference trigger (in finite mode)
• With a software command (in continuous mode)
An acquisition that uses a start trigger (but not a reference trigger) is sometimes referred to as
a posttriggered acquisition. That is, samples are measured only after the trigger.
When you are using an internal sample clock, you can specify a delay from the start trigger to
the first sample.
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.
NI cRIO-905x User Manual | © National Instruments | 53
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