Can I create a task that includes 2 C series modules?

Question

I am trying to create a single task that includes 2 NI-9425 C series modules but when I wire the physical channel constant "Mod3/port0, Mod4/port0" into the DAQmx Create Virtual Channel.vi I receive error -200086 which states physical channel range syntax in the input string is invalid because multiple devices were listed in the string.  It is my understanding from LabView help that multidevice tasks are allowed.  Also according to this KB article http://digital.ni.com/public.nsf/allkb/CF85114C6025C84C862571C000722DDA multi-device tasks are supported for S Series devices, C Series, and DSA devices, and according to this KB article http://digital.ni.com/public.nsf/websearch/78E44565FD87E7D686257108007F94F8?OpenDocument I have formatted my physical channel constant correctly.
Can someone please explain why I am getting this error when all indications are that this should be a simple thing to do?
My C series modules are in slots 3 and 4 in a cDAQ-9188 chassis, I am currently running LabView 8.5.1, with Windows XP
Thank you,
Eric
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Answer 1

Hi Eric,
I'm afraid that you can't configure hardware timing with the NI 9425 in CompactDAQ. The NI 9425 data sheet explains: "The NI 9425 is a static digital module, so you can use it to perform software-timed or static operations only when installed in an NI CompactDAQ chassis."
For AI, AO, and counters, daisy chaining multiple calls to DAQmx Create Channel is equivalent to specifying a list of physical channels, but for DIO it's different. A single DIO virtual channel can contain multiple physical channels (lines). It would be completely reasonable to assume that specifying a list of lines with "one channel for all lines" would cause DAQmx to put all of the lines in a single virtual channel, but due to how it's implemented in the DAQmx framework, this is not possible when the lines are on multiple devices. It would also be reasonable to assume that if DAQmx couldn't put all of the lines in a single virtual channel, then it would create one virtual channel per device, but that's also not how it's implemented--it returns the error that you received.
Instead, here are two approaches to putting all 64 lines in one task. Either one should work.
Approach A: Create a single task, containing two virtual channels (MyChan0 and MyChan1). MyChan0 contains cDAQ1Mod3/port0/line0:31 and MyChan1 contains cDAQ1Mod4/port0/line0:31. The Digital 2D Bool NChan 1Samp read VI returns a 2x32 array of Booleans. To flatten this into a 1D 64-element array, you need to use Reshape Array or some other method.
The DAQmx Task >> Channels property is there to show that there are two virtual channels named MyChan0 and MyChan1. Also, I used a for-loop to show that you don't have to hardcode multiple calls to DAQmx Create Channel. The "one channel for all lines" constant is redundant because that is the default.
Approach B: Create a single task, containing 64 virtual channels (MyChan0 through MyChan63). This uses the "one channel for each line" constant, which is not the default. MyChan0 contains cDAQ1Mod3/port0/line0, MyChan1 contains cDAQ1Mod3/port0/line1, etc. The Digital 1D Bool NChan 1Samp read VI returns a 1D 64-element array of Booleans. If you used the Digital 2D Bool NChan 1Samp VI instead, you would get a 64x1 array because there are 64 virtual channels containing 1 line each.
Brad
Brad Keryan
NI R&D