Hello Philip,
Some further clarification of your application would be helpful. Let's first of all make sure that we're on the same page. A spreadsheet file would not be read using Digital I/O functions. You can read from a spreadsheet using File I/O functions and then use the data returned to build a digital waveform that could then be output on a Digital I/O board using the NI-DAQmx driver. The exact implementation for this would be up to you.
If this is what you are trying to do, I would suggest looking in the LabVIEW Example Finder for examples of Digital I/O and File I/O and then combine these to achieve the functionality you want. I hope this information helps.
Best regards,
