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Archived: The Definitions of Digital Trigger A, Digital Trigger B, and Digital Trigger A&B

This document has been archived and is no longer updated by National Instruments

Note: This page is about NI-DAQ also known as Traditional NI-DAQ (Legacy). NI-DAQmx replaced Traditional NI-DAQ (Legacy) in 2003. NI strongly recommends using NI-DAQmx for new designs and migrating existing Traditional NI-DAQ (Legacy) applications to NI-DAQmx. Please review the Getting Started with NI-DAQmx guide for more information on migration.

Primary Software: Driver Software>>NI-DAQ
Primary Software Version: 7.0
Primary Software Fixed Version: N/A
Secondary Software: N/A

I want to use a TTL digital trigger pulse to start data acquisition on my DAQ board. I noticed there are two types of triggers: Digital Trigger A, Digital Trigger B. Which digital trigger setting should I use?

Digital Trigger A is normally used as a start trigger. When using Digital Trigger A, data will not be acquired until the trigger signal is received.

Digital Trigger B is called the reference trigger (stop trigger in NI-DAQ 6.9.3 and below). Digital Trigger B should be used when pretrigger scans are desired. When using this trigger, as soon as the software start command is received, data is acquired into a circular buffer of the same size as the specified pretrigger scans. When Digital Trigger B is signaled, data continues to be acquired in a second, normal buffer until the requested total number of scans are acquired (post trigger scans = total requested scans - pretrigger scans). The returned buffer will contain the pretrigger scans and the posttrigger scans, concatenated and in the proper order.

One can also combine the behaviors using both triggers: Digital A&B. In this mode, no data is taken until Trigger A is received. When it is received, pretrigger scans are taken until such time as Trigger B is received, and the posttrigger scans are completed.

Related Links:
White Paper: Tips and Techniques in Data Acquisition Triggering - NI-DAQmx
NI Community: Generate Digital Pulse with Digital Start Trigger
Example Program: NI-DAQmx: Continuous Acquisition With a Digital Start Trigger
Example Program: NI-DAQmx: Acquire Waveform with an External Scan Clock and a Software Analog Trigger
Developer Zone Tutorial: Measurement Studio DAQ Triggering in Visual Basic for E Series DAQ Devices


Report Date: 01/31/1996
Last Updated: 04/11/2016
Document ID: 0HU7KPTA

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