Triggering; Triggering With A Digital Source - National Instruments Data Acquisition Device NI USB-621x User Manual

Triggering

Triggering with a Digital Source

© National Instruments Corporation
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 USB-621x 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
Input
• The Analog Output Digital Triggering
Output
• The Counter Triggering
Your USB-621x 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 12-1 shows a falling-edge
trigger.
Digital Trigger
12-1
section of Chapter 4,
section of Chapter 5,
section of Chapter 8,
5 V
Falling Edge Initiates Acquisition
Figure 12-1. Falling-Edge Trigger
12
Analog
Analog
Counters
0 V
NI USB-621x User Manual