Use the DI Start Trigger (di/StartTrigger) 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 Digital Source

To use DI Start Trigger with a digital source, specify a source and a rising or falling edge. Use the following signals as the source:

  • Any PFI terminal on an installed C Series module
  • Counter n Internal Output

The source also can be one of several other internal signals on the cDAQ chassis. 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 DI Start Trigger, the acquisition begins on the first rising edge of the Analog Comparison Event signal.

Note Depending on the C Series module capabilities, you may need two modules to utilize analog triggering. Using a Time Source To use the Start Trigger signal with a time source, specify 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. Routing DI Start Trigger to an Output Terminal You can route DI Start Trigger to any output PFI terminal on an installed C Series module. The output is an active high pulse.