non buffered hardware timed single point acquisition

[kalganian]

Hi, I'm trying to do triggered digital acquisition of a 10 bit bus using the USB NI6251 board using the Microsoft Visual C API. Using the NI provided example:National Instruments\NI-DAQ\Examples\DAQmx ANSI C\Digital\Read Values\Read Dig Port-Ext Clk\This works great except if I try to read from anything except Port 0, i get the error:
DAQmx Error: Measurements: Selected lines do not support buffered operations.Ensure only lines that support buffered operations are being used in the task. If using change detection, the task must be changed to non-buffered hardware timed single point to support these lines.Device: Dev1Physical Channel: port1/line0Task Name: _unnamedTask<0>Status Code: -201062
I guess only Port 0 can be read using the buffered operation. But is there any way to read Port 1 or Port 2 using an external trigger? Using the Visual C API, how do I change the task to a 'non-buffered hardware timed single point'?I'm guessing I need to change the function DAQmxCfgSampClkTiming in the NI example to some other timing function. Thanks,Regards,Kartik

[mallorim]

Hi Kartik,

The reason you are receiving this error is because you are trying to perform a timed operation on a port which does not support this. M-Series DAQ cards like your USB-6251 only support hardware timed digital acquisition on Port 0. This can be seen on page 7 on the <a href="http://www.ni.com/pdf/manuals/371291h.pdf" target="_blank">User Manual</a>. Buffered acquisition, by definition, is hardware timed and therefore why the error message indicates this is not possible on Port 1. Changing the method of acquisition to non buffered hardware timed single point would still return an error due to the timing.

You will not be able to use an external clock with Ports 1 and 2 because no timing circuit is available. Static, or software timing, is possible on these ports, but then your last two lines would not be correlated with the 8 lines in Port 0. I would suggest looking at the USB-6254 or 6259, each of which has 32 lines in their Port 0.

I hope this clears things up,Mallori M