You can use the AI Start Trigger (ai/StartTrigger) signal to begin a measurement acquisition. A measurement acquisition consists of one or more samples. If you do not use triggers, you begin a measurement with a software command. After the acquisition begins, you can configure the acquisition to stop:
To use ai/StartTrigger with a digital source, you specify a source and an edge. The source can be an external signal connected to any PFI or RTSI <0..6> pin. The source can also be one of several internal signals on your DAQ device. Refer to Device Routing in MAX in the NI-DAQmx Help for more information.
Also, specify whether the measurement acquisition begins on the rising edge or falling edge of the ai/StartTrigger signal.
The following figure shows the timing requirements of the ai/StartTrigger source.
When you use an analog trigger source, the acquisition begins on the first rising edge of the Analog Comparison Event signal.
You can configure the PFI 0/AI START TRIG pin to output the ai/StartTrigger signal. The output pin reflects the ai/StartTrigger signal regardless of what signal you specify as its source.
The output is an active high pulse. The following figure shows the timing behavior of the PFI 0/AI START TRIG pin when the pin is an output.
The PFI 0/AI START TRIG pin is configured as an input by default.
When acquisitions use a start trigger without a reference trigger, they are posttrigger acquisitions because data is acquired only after the trigger. The device also uses ai/StartTrigger to initiate pretrigger DAQ operations. In most pretrigger applications, a software trigger generates ai/StartTrigger. Refer to AI Reference Trigger Signal for a complete description of the use of ai/StartTrigger and ai/ReferenceTrigger in a pretrigger DAQ operation.