How can I Synchronize two counters in CVI using NI-DAQmx

Question

Hi, I am new to NI-DAQmx, and I would like to program counting of random digital pulses using two counters in LabWindowsCVI and a PCI6229 multifunction card. I have the evaluation copy for CVI 7.1
I would like to set counter0, to count pulses from the 10MHz clock, to generate a single pulse (duration in the few ms timescale), that will gate counter1 in the same card.
When I try to route the output from counter0 to the gate of counter1 I get an error code
(-89137, "The specified route can not be satisfied because it requires resources that are currently in use by another route").
How can one do the equivalent of the "Select_Signal()" in the traditional NI-DAQ?"
I have also a hard time seting the counter0 to actually count a number of clock cycles from the 10 MHz clock.
What is the NI-DAQmx equivalent of the function "GPCTR_Change_Parameter()" to program a counter to count a predefined number of clock cycles?
Any suggestions are welcome.
Fundadero

Answer 1

Hi Fundadero-
It sounds like you're programming for an M Series card with counter operations and need a bit of help with DAQmx functions.
In order to count edges of the 10MHz reference clock you will need to use a format similar to that found in the CVI shipping example "CntDigEv.prj." This is found in the NI Example Finder (Help>>Find Examples) under Hardware Input and Output>>DAQmx>>Counter Measurements>>Count Digital Events. In order to measure pulses from a source rather than the default input terminal (ctrXsource where X is the counter number), you will need to use the function DAQmxSetCICountEdgesTerm(taskhandle char[] counter, char source terminal) as follows:
DAQmxErrChk (DAQmxCreateTask("",&taskHandle));
DAQmxErrChk (DAQmxCreateCICountEdgesChan(taskHandle,chan,"",edge,initialCount,countDirection));
DAQmxErrChk (DAQmxSetCICountEdgesTerm(taskHandle, "/Dev2/Ctr0", "/Dev2/10MHzRefClock"));
What type of operation are you trying to perform on counter 1? The strategy for routing signals will change based on this. If you're trying to perform gated counting you can specify the the task similarly as above and use the terminal "/DevN/Ctr0InternalOutput" as before. If you are trying to perform frequency measurement you will need to use the DAQmxGetCIFreqTerm function.
Other channel properties are listed conveniently in the NI-DAQmx C Reference Help found at Start>>Programs>>National Instruments>>NI-DAQ on your start menu. A search for "channel properties list" returns this list.
Please let us know if you have any additional questions.
Thanks-
Tom W
National Instruments