Auto-Start DAQmx task functionality

[labviewmission]

Hi,

I had a software which was generating time pulses using counter output. The application is using the "DAQmx Write.vi" to write new high time and low time to the counter. The task has not been started and it is using "autostart" Task input wired to be true.

This software was running fine uptil few months back. Recently I am trying to run the software ,all the acquisition would work but the counter part is not working.

The only difference during this time was that I upgraded to the latest MAX version . I am still working with Labview 7.1 but the DAQ drivers are the latest.

When I explicitly start the task the problem gets solved. But I want to know what is acusing this behaviour. Is it the driver problem or something else.

the error I get is this before explicitly starting the task;

"Error -200874 occurred at DAQmx Write (Counter Time 1Chan 1Samp).vi

Possible reason(s):

DAQmx Write is supported for counter output channels only while the task is running.

To use DAQmx Write with the given task, invoke DAQmx Start prior to DAQmx Write.  To specify the low and/or high time while the task is not running, set DAQmx properties instead of invoking DAQmx Write.

Task Name: _unnamedTask<19>"

I hope i made myself clear.

Thanks for any help

[Ed W]

Hi,

The error that you are receiving is accurate, but I’m not sure why it didn’t exist with your previous driver version.  If you try the suggested fixes, as in using the property nodes or just starting the task before changing its parameters, do you still receive the error?

Also, what is the exact driver that you are currently using, and which one were you using before the upgrade?

Ed W.

Applications Engineer

National Instruments

[labviewmission]

Hi Ed,

I am glad you replied. Can you explain me the purpose of using "autostart" functionality in the "DAQmx Write".

It says that it should start automatically if it has not been started already. I am using DAQmx 8.3  and was using the version that came with labview 7.1. I think it was the one released in May2004.

I am not receiving the error after starting the Task explicitly. But I still cannot get why the"DAQmx " automatic start is not working.

Please explain.

Thanks for the help.

Regards

[Ed W]

Hi,

The autostart option is just what you’d expect it to be – it automatically starts the task when the VI is called.  However, I’m not sure of the reasoning behind taking this functionality out of the VI when using a counter output task.

All in all, I would recommend just using the Start task, which you said was working for your program.

Ed W.

Applications Engineer

National Instruments