Unable to create Start Trigger for counter input tasks

[Axiom]

Hi,

Hardware: PCI-6602

Software: DAQmx 7.4 Ansi C API

I'm having some trouble configuring a start trigger for counter input tasks.  After creating the task and with counter input channel (any measurement type) I call DAQmxCfgDigEdgeStartTrig( ) specifying one of the PFI lines (say '/Dev1/PFI2') as the trigger source terminal.  This call always returns  "Error -200452 : Specifed property is not supported by the device or is not applicable to the task".  I have also tried configuring timing before the trigger but that does not make any difference.  One thing I've noticed is that this same error does not occur for counter output (pulse generation) tasks.  Any help with this problem would be much appreciated.

Thanks,

Jeff   

[Kevin_Price]

Jeff,

Hi again.  This one stumped me for a while too when I was transitioning to DAQmx.  It may be documented somewhere, but it didn't make itself obvious.

Counter input operations use a different triggering method/mechanism that's referred to as an "arm start" trigger.  I work in LV so I don't know the C syntax, but try searching for "arm start" in your docs. 

(For other readers: in LV, this cannot be setup with the regular DAQmx Trigger vi.  You must use a DAQmx Trigger Property Node and specify your settings there.)

-Kevin P. 

[Axiom]

Thanks again Kevin for pointing me in the right direction .

For anyone interested, a digital edge arm start trigger for counter input tasks can be configured in C using:

DAQmxSetArmStartTrigType(taskHandle, DAQmx_Val_DigEdge);

The trigger source terminal and active edge can then be modified with:

DAQmxSetDigEdgeArmStartTrigSrc() and DAQmxGetDigEdgeArmStartTrigEdge().

The initial confusion was due in part to a knowledge base article (http://digital.ni.com/public.nsf/allkb/9C657EE63C9D07A686256F6D0062AC66) which suggests that both an arm start trigger and a (regular) start trigger can be used with TIO devices.  While this may be true for counter output tasks, the (regular) start trigger does not appear to be applicable to counter input tasks.

Jeff

[Ryan_V[DE]]

Spot on, Jeff. I'll see what I can do to eliminate some confusion in that KB.

Regards,