PC Parallel Port Interfacing Techniques – Part 1

6 October 2006 v1.0

Article: 2 Elec: 3.5 Comp: 3 Mech: 0


As of 2012, the 25 pin parallel port is obsolete. The bellow tutorial is kept for archival purposes only.


In this tutorial I will just introduce the PC Parallel Port and how to identify its address for use in home electronic projects. Mind you the whole process and learning takes time but is fairly easy too! Remember, if you are interested then keep learning and trying new things. Fill me in if you have any questions or suggestions.

The Parallel Port is the most commonly used port for interfacing usual devices like printers and scanners. It’s found commonly on the back of your PC as a D-Type 25 Pin female connector. But did you know it can even be used to make home made projects?

read on…

This port will allow the input of up to 9 bits or the output of 12 bits at any one given time, thus requiring minimal external circuitry to implement many simpler tasks. These outputs can act like switches in some cases or simply to light up LED’s. The inputs on other hand can act like pushbutton inputs to your PC.

Here you can see what the individual pins stand for.


Now for your Printer Parallel Port to work with a printer, it uses internal software to initialize a protocol for smooth communications. We won’t go into the details of this since it has about 5 different modes of communication. All we need to know is how to connect your little lights and switches to your printer port with the most basic mode!

Hardware Properties

Scroll down for the table of Pin Outs Here for clear explanation.

The output of the Parallel Port is normally TTL (Transistor-Transistor Logic) levels. The voltage levels are the easy part. The current you can sink and source varies from port to port. Most Parallel Ports can sink and source around 12mA. However these are just some of the figures taken from Data sheets. They vary quite a bit. So be careful not to overload your Printer Port.

Port Addresses

When the computer is first turned on, BIOS (Basic Input/Output System) will determine the number of ports you have and assign device labels LPT1, LPT2 & LPT3 to them. Usually the address for LPT1 is 378h.

To know your Parallel Port address, do the following:

Go to Start > Control Panel > System > ‘Hardware’ Tab > Click on Device Manager > Look for ‘Ports’ in the device list > Double click on LPT1 > Click on the ‘Resources’ Tab. In that you can see the starting address of I/O Range. That’s your number!

This address called the Base Address which points to a byte is used to send commands to your Port.
Read more on this if you are interested and in due time I will come up with another Tutorial on how to make some projects with this tool!



NOTES: The points below the title mean how Advance a Tutorial is in each field. 1 being easy and 5 being very advance.
*The above picture has been taken from: http://www.lammertbies.nl/ Thanks a lot

Feel free to ask questions or give sugestions!

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6 Responses to PC Parallel Port Interfacing Techniques – Part 1

  1. Yashoda says:

    Hey.. the above info on Parallel port was really gud…. i have made a PC Based Visitor counter using this port n IC 555 in my college for our wrkshop project….but didnt know how to exactly find the address of my port…. n a few other details…
    Any other projects on the same which you know…. I would definitely be interested in knowing em….

  2. admin says:

    Well, you say you did not know how to find the address but you have already made a project :). Well, adress can be found form the Device manager > COM and LPT Ports > Last tab shows the I/O range.

    Other projects arent there as I have stopped because of lack of LPT Ports in newer PC models and Laptops. Shifted to Basic stamp. and will move on to PIC/AVR later. But yea, in the future I might revamp my oooold ACER laptop which got both serial and parallel ports.

  3. Anonymous says:

    nice, i’ll use this notes in my project
    thanks alot

  4. ananymous says:

    can you tell me how to utilise a usb port instead of a parrallel port

  5. Varun says:

    USB port is a completely different ball game! It has a complicated protocol. Better to search the internet for the information.

  6. Pingback: PC Parallel Port Interfacing Techniques – Part 2 | Search for Sirius

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