X series counter triggered pulse generation

[Victor65]

Dear all,

Win7 64-bit, NIDAQmx 9.5.1., PCIe-6353

I am attempting to do very simple things with counters on a X-series board, without success. Can anyone help? Thanks a lot.

(code simplified for the sake of clarity)

1) TTL-triggered single pulse generation
What works:
After task creation, I call
DAQmxCreateCOPulseChanTicks(myTask, "Dev2/ctr2", 0, "/Dev2/100MHzTimebase", DAQmx_Val_Low, 100, 3000, 5000);
DAQmxCfgImplicitTiming(myTask, DAQmx_Val_Finite_Samps, 1);
and I start the task, no problem, one pulse is generated
What I'd like to do is to trigger the pulse repeatedly on PFI1 so I add:
DAQmxCfgDigEdgeStartTrig(myTask, "/Dev2/PFI1", DAQmx_Val_Rising);
DAQmxSetStartTrigRettrigerable(myTask, True);
I put a periodic voltage from 0 to 5V on PFI1. No triggering, the voltage amplitude falls by half. When I replace DAQmx_Val_Rising by DAQmx_Val_Falling, the pulses come out, but back to back and never synchronized with the voltage on PFI1. All function calls are successful. I must be doing something wrong, but what?

2) Buffered pulse generation. I want to use the 100MHz timebase (i.e., 10 ns / tick) to output very short pulses, most of them with a duration of 20 ns when high and 20 ns when low (when repeated, this gives a pulse frequency of 25 MHz). I load the counter with an array of values using DAQmxWriteCtrTicks. NI-DAQmx complains when the interval values in the High and Low tick buffers are equal to 2 (which is what I want, since this is the value needed to get a duration of 20 ns). Is this a limitation of NI-DAQmx, i.e., you cannot have pulse tick counts equal to 2? If this is the case, is there a way to output 25 MHz from a PCIe-6353?

Best regards.




2) TTL-triggered multiple

[WillPwr]

Hello, Victor65!

For your first question, you may find it useful to reference the examples found in:

National Instruments\NI-DAQ\Examples\DAQmx ANSI C\Counter\Generate Pulse

In particular, "Dig Pulse Train Cont-Pause Trig" will illustrate a during-run trigger, while "Dig Pulse Train-Cont-Dig Start" will show how to tigger via a digital signal. Combining these two should get you where you need to go.

For your second question, could you post a screenshot of the error you are getting? this will help us narrow down a solution.

Thanks!

[Victor65]

Hi Will,

Thanks for your suggestions.

It turns out that for reasons best known to the hardware, (1) works now !??? Don't ask me why.

As for (2), looks like I am able to output 25 MHz on the counter output, with
DAQmxCreateCOPulseChanTicks(myTask, "Dev2/ctr2", 0, "/Dev2/100MHzTimebase", DAQmx_Val_Low, 0, 2, 2);

I'm OK now. Beats me why in the case of buffered generation High and Low ticks array values cannot be equal to 2.