How do I stream a digital buffer with DAQmx commands on a PCI 6221?

[L7YSE]

I'm affraid I've given-up searching; 1/2 a day in help documents/coding, 1/2 a day online!!! And no obvious solution can I find.

So, sorry for the basic nature of this question, but I'm about to drive over there and bang on your windows! 😛

Ok, I have been following the article in NI-DAQmx C Reference Help

-> Key NI-DAQmx Concepts -> Generic Programming Flows -> Digital Output Flows -> Finite Digital Output.

This seems to cover my requirements; I am trying to write data to a PIC processor, which requires using two logic lines, one to flag a data logic-level, and the other to clock it into the device. No requirement on hardware clocking to get the data synchronised with an outside source, I intend the PCI card/VC++ to clock itself. Done repeatedly, I can send data to configure the PIC from our PCI 6221 card/PC. This all is done in a visual c++ environment using the DAQmx commands.

Initially, I have done this by creating a task, creating a digital output channel, starting a task, writing a byte to a port of the 6221, and then stop/clearing the task -  and then repeating the process (that does one bit). Of course this takes ages, so I want to prep my 'bytes' in a buffer that I can then stream down through the port much faster. I understand this can be done (if not only from the document discribed above)

From the document in the C reference help, the process is as follows:

Create Channels

Config the timing (DAQmxCfgTimingSampClk)

Write Samples (DAQmxWriteDigitalLines)

Start (DAQmxStartTask)

wait for complete (DAQmxWaitUntilTaskDone)

Stop (DAQmxStopTask)

Clear (DAQmxClearTask)

So, in pseudo-code I call in order:

DAQmxErrChk ( DAQmxCreateTask( "", taskhandle ) );

DAQmxErrChk ( DAQmxCreateDOChan( taskhandle, "Dev1/PFI0:7","", DAQmx_Val_ChanForAllLines ) );

DAQmxErrChk ( DAQmxCfgSampClkTiming( taskhandle, NULL, 100, DAQmx_Val_Falling, DAQmx_Val_FiniteSamps, number ) );

DAQmxErrChk ( DAQmxWriteDigitalLines( taskhandle, number, FALSE, 10.0, DAQmx_Val_GroupByChannel, data, &written, NULL ) );

DAQmxErrChk ( DAQmxStartTask( taskhandle ) );

DAQmxErrChk ( DAQmxWaitUntilTaskDone ( taskhandle, 20.0 ) );

DAQmxErrChk ( DAQmxStopTask( taskhandle ) );

DAQmxErrChk ( DAQmxClearTask( taskhandle ) );

The error I recieve is no. -200077:

 "

Requested value is not a supported value for this property.

Property: DAQmx_SampTimingType

Requested Value: DAQmx_Val_SampClk

Task Name: _unnamedTask<0>

Status Code: -200077

"

This error is thrown when the programme gets to DAQmxWriteDigitalLines; so I think it is either this or the preceeding call to DAQmxCfgSampClkTiming that has caused a problem.

To those that know, this is probably a Very simple fault on my part, but I cannot find it.

If anyone can point out my error, I would be very grateful.

Daniel.

[L7YSE]

I seem to have found a way around this, 1 1/2 days in, and it now seems rediculusly simple.

DAQmxErrChk ( DAQmxCreateTask( "", taskhandle ) );

DAQmxErrChk ( DAQmxCreateDOChan( taskhandle, "Dev1/PFI0:7","", DAQmx_Val_ChanForAllLines ) );

DAQmxErrChk ( DAQmxStartTask( taskhandle ) );

for ( i=0; i<number; i++)

     DAQmxErrChk ( DAQmxWriteDigitalLines( taskhandle, number, FALSE, 10.0, DAQmx_Val_GroupByChannel, data[i], &written, NULL ) );

DAQmxErrChk ( DAQmxStopTask( taskhandle ) );

DAQmxErrChk ( DAQmxClearTask( taskhandle ) );

Obviously, this is different to the technique I was trying to use, but it does work.

I would still be interested to know where I was going wrong with the first code, if anyone can help...

Thanks in advance,

Dan

[stilly32]

Hey Dan,

With this call:

DAQmxErrChk ( DAQmxCreateDOChan( taskhandle, "Dev1/PFI0:7","", DAQmx_Val_ChanForAllLines ) );

You're trying to write to the PFI lines, which are part of port 1. Only the 8 lines on port 0 "Dev1/port0" support clocked/correlated DIO, port 1 only supports static/SW timed DIO (which is what you are using) and counter timer opperations. To do buffered output, check out the Cont Write Dig Port-Ext Clk shipping example at:

C:\Documents and Settings\All Users\Documents\National Instruments\NI-DAQ\Examples\DAQmx ANSI C\Digital\Generate Values\Cont Write Dig Port-Ext Clk

when you use this, you'll need to specify an external clock - M-Series DIO does not have its own timing engine so it has to get its clock signal from somewhere else. Most just use an onboard counter to generate a clocking signal, so the Dig-Pulse Train Cont example under counters can be combined with this.

Most of this is covered in the M-Series user manual, though I realize its not exactly lite reading

Hope this gets you started,

Andrew S

Message Edited by stilly32 on 03-26-2008 05:28 PM

[L7YSE]

Thanks for this!

Yes, the "Dev1/PFI0:7" part was the bit I had thought was in error but could not find a solution to; I had tried NULL (which suggests that the onboard clock is used), but got the same error - which from your reply, would make sense due to there not being an onboard clock.

It all makes sense 😉

Thanks for your help.

Dan.