Digital input issues with PCI-6733

[Dr.Chandra]

Hopefully this is a simple question.  I have a PCI-6733 connected to a BNC-2110, and I want one of the digital lines to monitor a connection and light a LabView LED when there is a digital high signal.  Simple, right?  The problem is, I can't get any response from the port in either NI-DAQmx or LabView.  If I open MAX and run the test panels, all the lines show a digital high when configured as inputs with nothing connected.  If I switch a line to output, it goes to digital low.  Then, if I give it +5V, it goes to digital high.  Weird, but OK.  If I go to the DAQ Assistant in Labview or create a NI-DAQmx task directly to measure a digital in, the line shows high even if nothing is connected.  I get the same result regardless of what acquisition mode I use.  Inverting the line changes it to low, but then nothing happens if I connect the +5V.  This happens with more than one line, so I don't think the board is malfunctioning.  Also, it will do digital output just fine.  Am I just missing something?

Thanks,
Chandra

[Dennis_Knutson]

An unconnected digital input should be detected as a logic 1. That is the way TTL compatible logic works and the card probably has a pull-up resisitor there anyway. If you ground one of the inputs, what do you see for that pin?

[Dr.Chandra]

When I ground the line, it goes to digital low.  The help file has a diagram that shows a switch with the +5V wired to the digital input and the return to digital ground, and when I wire up a power supply to do that, it works fine.  But if my signal is one pin from a multi-pin connector, how do I ground it?  I apologize for being such a newbie...

[Dennis_Knutson]

Grounding the input of the digital I/O was just to verify that it works. And the example is just to give an external floating supply a gnd reference. When you wire the signal to the digital input, the digital input will detect whether your signal is high or low. As long as your signals are referenced to gnd, everything should be okay.

[Dr.Chandra]

OK, I think I've got it.  I don't have the box that's going to produce the real signals yet, but when I get it in I'll hook it up and see what happens.  Everything is wired up properly in Labview, and it works with an external supply providing the +5V.  Thanks for your help and enthusiasm.