Asynchronously Reading the AI Read Drop-In Replacement

AI Read.vi is a synchronous operation that monopolizes the thread it runs in until the data requested is received. This example uses the scan backlog to implement a drop-in replacement, AI Read (Asynchronous).vi, which reads the replacement asynchronously and allows other operations to obtain CPU time while waiting for data.

This type of operation can also be implemented using DAQ occurrences, but not as simply as replacing the existing AI Read.vi with this AI Read (Asynchronous).vi. Refer to the block diagram and documentation in VI Properties for more information on implementation.

NOTE: Due to the operation of this VI, you must wire a positive time-out period of sufficient duration for your operation so it will function properly. If you leave the default input of -1 wired, you will receive a -10800 error every time you try to run it.

Requirements

Filename: 1083.zip

Software Requirements

Application Software: LabVIEW Full Development System 5.0
Language(s): LabVIEW

Hardware Requirements

Hardware Group: Multifunction DAQ (MIO)
Driver: Traditional NI-DAQ (Legacy) 6.5.0

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Asynch AI Read doesn't always work
Asynch AI Read doesn't work the same in all cases, nor as desired for slow scanning SCXI apps.) I tried it using a DAQ board, and I love it. However, I tried it scanning 3 SCXI modules @ 1 hz, and 'AI Readwith#scans=0' does not pick up the just-completed scan at the exact time it comes in. It seems to need about 50-200 milliseconds after the scan is completed to indicate the existence of the scan in the scan backlog. Be aware of this if you're planning to use the 1Hz rate from the Asynch AI Read as a timing basis for the rest of your program.
- Alan R. Bentz, Kodak. alan.bentz@kodak.com - May 16, 2003