- DAQ M Series NI USB-621x User Manual

Triggering

A trigger is a signal that causes an action, such as starting or stopping the

acquisition of data. When you configure a trigger, you must decide how you

want to produce the trigger and the action you want the trigger to cause. All

M Series devices support internal software triggering, as well as external

digital triggering. For information about the different actions triggers can

perform for each sub-system of the device, refer to the following sections:

• The Analog Input Digital Triggering section of Chapter 4, Analog

Input

• The Analog Output Digital Triggering section of Chapter 7, Analog

Output

• The Counter Triggering section of Chapter 9, Counters

Triggering with a Digital Source

Your DAQ device can generate a trigger on a digital signal. You must

specify a source and an edge. The digital source can be any input PFI signal.

The edge can be either the rising edge or falling edge of the digital signal.

A rising edge is a transition from a low logic level to a high logic level. A

falling edge is a high to low transition.

Figure 14-1 shows a falling-edge trigger.

Figure 14-1. Falling-Edge Trigger

5 V

0 V

Falling Edge Initiates Acquisition

Digital Trigger