OnDemand after Source Clocked give "internal error status -88700"

Question

Hi,
I am using Analog Input and Counter Input simultaneously with a shared internal clock source on the NI PCIe-6363
I'm running on WinXP, with NIDAQmx Driver 9.1.1f0
I start off by doing some OnDemand acquisitions and it all works.
Then I configure the task for Sample Clocked acquisitions and everything works.
Then I try to configure the task back to OnDemand using DAQmxSetSampTimingType, but when I start the task I get "DAQmx Error: An internal error occurred. Status Code : -88700"
If I ignore the error and try to acquire samples, I get a blue screen of death and the PC reboots.
DAQmx Error: An internal error occurred.
Task Name: MyTaskCI
Status Code: -88700
I tried unreserving the task, and setting the sampling timing type back to on demand, with input buffer size to 0 (also tried 1, and 1000, neither worked). I noticed that going to sample clocked mode changed various properties. I tried manually setting the data transfer mechanism back to programmed io, and disabling CI memory mapping but that did not help. Additionally I tried setting the sampling mode to finite, and number of samples per channel to 1 but that didn't help either. I also tried setting the sample clock source back to blank, but that didn't help. I am not sure if there's something else I am missing. I tried reading all the properties I thought might be getting changed by sample clocked mode, and re-applying them - but that didn't work either.
Please find attached a simplified peice of code (adapted from the NIDAQmx ANSI C Example program: ContAcq-IntClk-EveryNSamplesEvent.c) to reproduce the issue.
Your feedback is greatly appreciated.
Thanks,
   hemdanw
   The MathWorks
Attachments:
BufferedAICI.c ‏9 KB

Answer 1

Hi Falk,
Change detection does two things:
Reads digital input channels when a change occurs on a set of digital input lines.
Optionally provides a (non-periodic) trigger or clock for another task, such as digital output, analog input, analog output, or counters.
This secondary functionality is only useful when you want to detect changes on multiple input lines and treat them as if they are the same, or if you want the input lines to be sensitive to both rising and falling edges. Since you only want your digital output task to look at rising edges on a single line, you can use a PFI line instead of using change detection. The cDAQ-9172 supports PFI lines in slots 5 and 6, so move the NI 9421 to slot 5 or 6.
> Suppose I connect a button to the digital input an I want the output to be triggered when I press the button.
Okay, that partially explains what you're trying to do. How many samples do you want to output when the button is pressed?
If you want each button press to output one sample, then run "Write Dig Chan-Ext Clk.vi" with "Physical Channels" set to "cDAQ1Mod1/port0/line0:7" and "Clock Source" set to "/cDAQ1Mod5/PFI0" (with the NI 9421 in slot 5). Every time you press the button, the output will change once, assuming that the button is debounced.
If you want each button press to output a waveform containing many samples, then ideally you would be able to run "Write Dig Chan-Int Clk-Dig Start.vi", but this uses DIO triggering functionality that isn't supported by the cDAQ-9172. To emulate this functionality on the cDAQ-9172, you would need a combination of "Gen Dig Pulse-Finite-Dig Start.vi" and "Write Dig Chan-Ext Clk.vi". Start the DO task first because it will wait for the sample clock.
If the button is not debounced, you may also want to enable digital filtering on PFI0 (or build a debounce circuit). I don't know of a good example showing how to do this. Maybe someone else has an example to recommend?
Brad
Brad Keryan
NI R&D