Small voltage change; parallel port

[MattMW]

Hi,

I am trying to write to the data lines of my computer's parallel port using the Out Port8.vi with Labview 8.6 under Windows XP. However, after writing zero (I enter 0 in the "write data" field of the VI) to all 8 data ports (at address 378, which I verified is the correct address) the voltage only drops from 4.40V to 4.35V when measuring between pins 2 and 18. Similarly, when connecting the aforementioned pins via a 1kOhm resisitor and measuring the voltage across the resisitor, the difference between "on"/"off" is only ~0.05V. The Parallel Port Read and Write Loop.vi also indicates that all 8 data lines are continuously in "on" mode. In the BIOS, I placed the parallel port into PS/2 mode and I also tried the above described measurements in AT mode, with the same outcome. The parallel port shows up in the Measurement and Automation Explorer. I also carried out the measurements with pins 11 & 12 connected to gound, which again resulted in the same outcome, and is also not neccessary acording to NI when using Out Port.vi. If anyone has a suggestion were the problem might be, I would be very happy.

-Matt 

[Justin_E]

Hey Matt,

I have a quick question for ya : What type of hardware are you trying to output from (e.g. PC, PXI Controller, etc.)?

I also have three KnowledgeBase articles that I'd like you to take a look at to verify that 1) your parallel port is working, and 2) you are communicating with the port correctly. 

KnowledgeBase 3B8H2CL6 : How Can I Verify That My Parallel Port is Working?

KnowledgeBase 42BIT2C5 : Using the Parallel Port in LabVIEW

KnowledgeBase 0TL70ATL : Using the Parallel Port as an Input/Output Channel

Try some of the solutions found in these articles and see if you can write to your parallel port.

[MattMW]

Dear Justin,

Thank you for your reply. I am trying to write to the parallel port of my PC that is directly connected to the motherboard. I used the "Parallel Port Additional Data Register Inputs.vi" to check if the port is working. However, the LEDs on the VI always stay in "on" mode when I ground a data line. So it looks like that there is something wrong with the port, which is strange for the computer is new. Thanks for your help.

-Matthias