Labview ignores all but 1 Daq Assistant, how can I avoid this?

Question

When I am putting together my block diagram, I use the DAQ Assistant to orchestrate everything.  Then when I go to create another DAQ Assistant instance, LabVIEW seems to ignore the first one.  It appears as though I can only use one DAQ Assistant at a time in my VIs, is this the case?  I am a bit of a novice, is there an easy way to avoid this, or change the orginal DAQ Assistant into some other form so I can use another DAQ Assistant for developing another part of my VI?
I have looked long and hard for a good explanation of the difference between Tasks and Virtual Channels and while I have found efforts at explaining it, I do not understand.  I see that I can convert my DAQ Assistant into a task, but then I have a task output which does not help me (I need a data output for my VI).
I am sure this is obvious to someone that has done it a million times, but I just can't find an answer wading through all of the knowledge base information or the LabVIEW help.
Thanks a bunch!
~milqman

Answer 1

Hello milq,
That following tutorial that Novatron linked you earlier is an awesome resource for becoming familiar with programming with the NI-DAQmx.
Learn 10 Functions in NI-DAQmx and Solve 80% of Data Acquisition Applications
An important point to take away from this tutorial is that you can either create a DAQmx task using the wizard-style interfaces provided by the DAQ Assistant and within Measurement & Automation Explorer (MAX), or you can programmatically create and configure your DAQ Task in your LabVIEW code using the DAQmx Create Virtual Channel VI, DAQmx Timing VI, etc.  When you create a new DAQmx Task using the wizard-style interface, you are configuring all of the settings for your task manually.  When you use that DAQmx Task in LabVIEW (with a DAQmx Task Control or Constant), you are referencing all of those configuration options you've manually set.  To actually perform a read or write operation based on those settings, you need to wire the DAQmx Task into the 'task in' input of a DAQmx Read or DAQmx Write VI. 
So for your analog input operation, you can wire the task directly into a DAQmx Read VI.  In the DAQmx Read VI, you'll want to select the type of task your reading from in the drop down box (Analog), if your reading from a single or multiple channels (1 Chan or N Chan), and if taking just one or multiple measurements with each call to the DAQmx Read VI (1 Samp or N Samp)
For your digital output operation, you'll want to configure a separate digital output task, and wire it directly to a DAQmx Write VI.  Again, select the type of task your writing to (Digital), if your writing to a single or multiple channels, and if you want to perform a single write or multiple writes.
To help with getting started with DAQmx programming in LabVIEW, I would highly recommend taking a look at the DAQmx example located in the LabVIEW Example Finder (Help > Find Examples).  A difference you'll note in these examples is that all the task configurations that you have been making with the wizard-style DAQ Assistant are done programmatically with the DAQmx Create Channel and DAQmx Timing VI.  I hope this helps and good luck!
Travis G.
Applications Engineering
National Instruments
www.ni.com/support
Message Edited by Travis G. on 06-21-2006 05:23 PM
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AnalogInDigitalOut.Jpg ‏21 KB