Hi all,
I'm developing an application on a PXI-1000B device in which a DAQ-6259 has to send a trigger signal (in this case, along PXI_Trig0) to a DMM, specifically a PXI-4070. According to another post concerning the 407x series DMMs, they do not reliably trigger on pulses less than 1 µs, and so I've written the following code to try to generate a longer pulsewidth for an analog output task:
// global variables:
TaskHandle DAQ_Task_StimTrigger;
const uInt8 Trig[16] = {0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0}; // desired min trigger width 1 µs
// in main:
DAQmxCreateTask("T_di_STr",&DAQ_Task_StimTrigger);
DAQmxCreateDOChan(DAQ_Task_StimTrigger, "DAQ/port2/line6", "",DAQmx_Val_ChanPerLine);
DAQmxConnectTerms ("/DAQ/PFI14","/DAQ/PXI_Trig0", DAQmx_Val_DoNotInvertPolarity); // PFI14 = port2/line6
DAQmxStartTask(DAQ_Task_StimTrigger);
PostDelayedCall (RepeatCallback, 0, 0.01);
void CVICALLBACK RepeatCallback(void *callbackData)
{
ProcessSystemEvents();
if(exitFlag)
{
DAQmxWriteDigitalLines (DAQ_Task_StimTrigger, // handle
16, // samples per channel
FALSE, // auto-start = false
10.0, // timeout
DAQmx_Val_GroupByChannel, // specifies data layout
Trig, // waveform
NULL, // actual number of samples delivered
NULL); // reserved
PostDelayedCall (RepeatCallback, 0, 0.1);
}
}
Now, I threw the output of /port2/line6 on a scope, and there is considerable variation in the actual pulsewidth of the signal produced, from the vicinity of 700 ns to up to 3 µs. Specifically, based on a handful of still frames (N=89), I observed a mean PW of 1.15 µs and a standard deviation of 15% (179 ns).
What might be the source of this variation? Will it adversely affect my ability to trigger using this signal using my DMM? Ideally, I will have different tasks triggering on the rising and falling edges of this trigger, so producing a reproducible signal with constant pulsewidth is important to me. I also am running a continuous analog output task using my DAQ card.
