Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I have a machine which connects to PC with LPT port. And in the program I am selecting port number on which is LPT port connected, something like etc. ( a326 ).

Now I have bought LPT to USB converter. And my program is not doing anything. And windows recognize it as virtual LPT port.

But which port number do I need to put? How to determine my virtual port number?

Thank you

share|improve this question
up vote 1 down vote accepted

Check devmgmt.msc and look under Ports. It should tell you the LPT port number.

From the Wikipedia article, here's the IRQ's and x86 port ranges of the LPT ports. Use the first I/O address in the range correspnding to the desired LPT port, or just try them all (0x378, 0x278, 0x3bc).

LPT1 IRQ 7 0x378-0x37f

LPT2 IRQ 5 0x278-0x27f

LPT3 IRQ 2 0x3bc-0x3bf

If your LPT->USB hardware adds the port as a LPT4 or higher, you'll need to dig further in any available device documentation to find out the address (LPT's over 4 were extremely rare on actual PC's, if they ever did exist...)

Good luck. Sounds like you are using an old DOS program that expects to talk directly to the LPT ports - not sure how the NTVDM under XP/Vista/7 (if that is what you are using) will work in that situation with a LPT->USB converter. You may need an old PC with an actual parallel port to accomplish what you are trying.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.