14

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 14-1shows a falling-edge trigger.

5 V

Digital Trigger

0 V

Falling Edge Initiates Acquisition

Figure 14-1.Falling-Edge Trigger

© National Instruments Corporation

14-1

NI USB-621x User Manual