Multifunction DAQ

Showing results for 
Search instead for 
Did you mean: 

Timing / execution control for DAQmx channels

I have a PCI-6251 DAQ board and running LV 2009. I have modified to my needs 2 of the DAQmx Output example VI's (Cont Gen Voltage WFM-Int


I place both VI's in my main window, one configured for ao:0 and the other set to ao:1, and am monitoring ao:0 and ao:1 outputs with a dual channel oscope.

When I run the main window I get a waveform out on ao:0 only. Then I stop it, run again, and I get a signal on ao:1 only. Stop and run, then get the idea.


I tried putting them both in a while loop and the behavior is the same.


Do I need to do something with the execution control? or is this a DAQmx problem? Perhaps sample clock related? I noticed the sub-VI within the above mentioned VI has Sample Clock settings but I do not understand the options. Or is it related to the DAQmx Write block, which has another set of options I haven't fully grasped yet.


Any ideas or help is greatly appreciated.



0 Kudos
Message 1 of 3

The SubVI I mentioned is Waveform Buffer Generation (Multi).vi which has a number of sample options. I am trying to find the manual now...

I'm hoping there is some simple thing I have overlooked...

0 Kudos
Message 2 of 3

You must not have automatic error handling on or are ignoring the errors you get.


You have made a common mistake and one I've already answered a couple of times this week (and once today). You simply cannot have more than one task running at the same time for the same resource. You have to have a single task with multiple channels defined. that means no more than one start task, timing function, DAQmx Write, etc. The only thing you are allowed is multiple DAQmx Create channels and they would have to use the same task.

0 Kudos
Message 3 of 3