Why are my digital ports always displaying a high state in example vi's and in MAX(red led lights up)?

[newuser]

I'm using Daqpad 1200 parallel port. I tried using NI-DAQ 6.8, 6.9.0, 6.9.1 but all logic seems to be high on all pins whether I configure individual pins or individual ports, however, if I go to measure the pins with my voltmeter, it shows a voltage of zero. But if I touch a digital grd to one of the pins on one port, all leds will turn off. If I touch a 5 volt supply to any of the pins while I have my grd to one of the pins, I don't see any pins lighting up. I opened my terminal block and could not find any shorts. My ports are not inverted but if I do invert them, the pins will turn off. When I first installed labview with the daq 6.8, everything
worked just fine. I then upgraded to 6.9.1 and everything still worked just fine. If I go into the "test panel" of my daq, and select digital i/o, all pins light up, they never used to light up before. If I press the make input button on one of the pins, that pin will be 5 volts. Currently, it will still do just that but all pins just light up. I don't know what the problem is. Can somebody be kind enough to help me out. Hopefully you can email me at mikehan@fastmail.ca since I check my email everyday.

[Geneva L.]

Note that the DAQPad-1200 powers up with the digital lines as high impedance inputs, meaning they should read high initially. The DAQPad-1200 uses the 8255 digital chip, which will reset all ports if a configure function is called. Thus, each time MAX is opened for the Test Panels, the ports will be configured. The ports will even be reconfigured if you change a port from input to output or vice versa. This may be the behavior you are seeing with the lines.

Also, make sure that the lines are set to inputs when touching the 5 Volt or DGND pins to the digital lines. Otherwise, the board may be damaged.

You can find out more about the 8255 digital chip properties by searching the http://www.ni.com/support pages for "8255". There are a number of KnowledgeBase
entries and a Digital Hardware Overview page that discuss these.

Regards,
Geneva L.
Applications Engineer
National Instruments
http://www.ni.com/ask