Back in the old days of DOS programming for the parallel port was pretty easy: it was just a matter of sending to the parallel port I/O address (378h) the value you wanted to be there. On modern versions of Windows, however, this is not possible, because the operating system doesn’t allow direct calls to the PC hardware, including the parallel port.

So, the easiest way to send data to the parallel port is to download a finished program, like Relaistimer. This program is really simple but will allow you to explore all the basic parallel port capabilities.

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Figure 8: RelaisTimer.

On this program you can turn each bit on or off by pressing keys F1 thru F8, if you want to turn all on just click on “X”, if you want to turn all off just click on “O”. You can also turn on or off individual LEDs by click with the mouse on correspondent LED on the LED diagram on the top of the program.

You can also program when each LED will be turned on or off, allowing you to create lighting patterns or use the program as a timer, since it allows you to turn a LED or a group of LEDs on or off at a specific time of the day. Imagine that instead of a LED you have a light or a home appliance: you will be able to make your computer turn it on or off at a specific time even if you are not home. Really awesome, isn’t it?

If you are a programmer and want to write more advanced programs than RelaisTimer, you should go to http://www.logix4u.net/inpout32.htm and read how to allow your favorite programming language (C, Pascal, VB, etc) to write directly to the parallel port.