NI-DAQmx: Correlated Digital I/O with NI CompactDAQ and LabVIEW

Correlated Digital IO enables the coupling of buffered digital tasks with the analog, counter/timer, or external clocks. The CompactDAQ 9172 chassi includes the capability of synchronizing digital input and output. The cDAQ-9172 chassi includes two on-board counters that can be used as external signals to correlate digital input and output. This example program illustrates how to perform correlated DIO with a counter output task using the internal clock on the cDAQ-9172.

1. Create a Digital Input Channel,a  Digital Output Channel, and a Counter Output channel to produce a Pulse in terms of Frequency.
2. Call the DAQmx (Sample Clock) VI which sets the sample clock rate for the digital tasks. Additionally, set the sample mode to continuous.
2a.  Call the Get Terminal Name with Device Prefix VI.  This will take a Task and a terminal and create a properly formatted device + terminal name to use as the source of the digital sample clock.  The terminal used is Counter N's Internal Output.  The Match Pattern VI is used to determine which counter was specified.
2b.  Create digital waveform to be outputted to the buffer.
3. Write the waveform to the output buffer.
4. Call the Start VI on the digital tasks.
5. Call the Start VI on the counter task. Use the sequence structure to ensure that both digital tasks are started before the counter task.
6. Read the digital waveform. Additionally, Call Is Task Done to check for errors in the digital output and counter tasks.
7. Call the Clear Task VI to clear each Task.
8. Use the popup dialog box to display an error or warning if any.

Note1:  Make sure to select the internal counters on the cDAQ-9172 by selecting the appropriate I/O filtering name. 

By Default, the DAQmx physical channel control drop down menu will not list internal channels.  To configure the DAQmx physical channel control drop down menu to include internal channels:

Right-click the DAQmx physical channel control in the front panel.
1.  Select I/O Name Filtering
2.  When the Filter Names dialog appears, check the Internal Channels check box.
3.  Click OK and select one of the two counters of the form: cDAQ1/_ctr0

Note2:  Make sure to also verify that your DIO module is in slots 1 through 4 for buffered hardware tasks.

Requirements

Filename: correlated_dio_cdaq.vi

Software Requirements

Application Software: LabVIEW Base Development System 8.0
Language(s): LabVIEW

Hardware Requirements

Hardware Group: CompactDAQ
Hardware Model: NI 9229, NI 9233, NI 9237, NI 9239, NI 9421, NI 9264, NI 9265, NI 9375, NI 9401, NI 9411, NI 9263
Driver: NI-DAQmx 8.3

Reader Comments | Submit a comment »

Look here: http://digital.ni.com/public.nsf/allkb/9D58 153D1B5E5B66862574C8006A30FB
- Aug 9, 2009

Where do I find these vis
Where do I find 'Get Terminal Name with Device Prefix.vi' and Create Digial Vaveform.vi'
- Thatcher Howard, Northrop Grumman. aquaman55_2000@yahoo.com - Aug 7, 2009

They are utility VIs that ship with the examples. See this KB 4PHDCD9G: Where Can I Find Get Terminal Name with Device Prefix VI?
- Jul 6, 2009

Useful, now i just need to know if the Counter output can be triggered externally. The front panel will not open in 8.6.1f1. Workaround: Drop the vi on a block diagram. Open the VIs block diagram (Hold control down and dbl. click on it). Copy the all the content of the block diagram to a new VI. Now it works.
- Simon Viftrup, CIM Industrial Systems A/S. ssv@cim.as - Jun 18, 2009

This VI crashes Labview 8.6.1 when opened.
- Mar 12, 2009

Could someone tell me where i can find these VI: "Get Terminal Name with Device Prefix.vi" and "Create Digital Waveform.vi"
- hanga@savio.it - Jun 23, 2008

correlated_dio_cdaq.vi missing parts
Hi, This example looks useful, but it is missing the files "Get Terminal Name with Device Prefix.vi" and "Create Digital Waveform.vi" Please let me know where I can find them. Thanks.
- Feb 14, 2008