View Full Version : Keyboards: how do they work?

11-14-2000, 02:26 AM
This is kind of a basic question, but I can't seem to find the answer anywhere.

Basically, I want to build my own input device and plug it into the keyboard port of my PC. To do this, I need to know how the PC and standard keyboard interface with each other. When you press a key, what does the keyboard send to the computer? My keyboard has five pins, so obviously it has to send the ASCII code for the key pressed in a sort of data-stream. Does anybody out there know what the computer sends to and expects to see from the keyboard? If not, do you know where I can find out?

(Student, The Ohio State University)

Paleo Pete
11-14-2000, 08:35 AM
I can't find much in the way of detailed information either, but the PC Guide has a short description Here (http://www.pcguide.com/ref/mbsys/chip/kbctrl.htm)

Search engines turn up zilch...well, except for the myriad sites selling keyboards...

If you had everything...Where would you put it?

Computer Information Links (http://www.geocities.com/paleopete/)

11-14-2000, 11:57 AM
Paleo Pete,
Thank you for such a prompt reply! Yeah, I've tried searching, too, and I came up with the same endless lists of companies selling keyboards. Also, I've read the PC Guide section that you referenced, which was interesting, but not detailed enough. It's frustrating, because I know it's such basic information, and I know it's out there, obviously, if companies are able to make new keyboards. So again, thanks anyway for your help.


Charles Kozierok
11-14-2000, 10:49 PM
(I shouldn't really do this but... I can't resist...)
There's a non-zero chance that the amount of information on keyboards on this site will increase substantially at some point before you unwrap your Christmas presents... not saying more than that... http://www.PCGuide.com/ubb/smile.gif

Charles M. Kozierok
Webslave, The PC Guide (http://www.PCGuide.com)
Comprehensive PC Reference, Troubleshooting, Optimization and Buyer's Guides...
Note: Please reply to my forum postings here on the forums. Thanks.

11-19-2000, 11:00 AM
This might be what you're looking for: http://www.beyondlogic.org/keyboard/keybrd.htm

11-21-2000, 04:22 AM
Your keyboard is a input device so when you are pressing a key you are causing a short in IRQ 2. The CPU then turns to drivers to figure out how to react to the short, after a few math problems you see it on your monitor.

Stay alert, stay alive!

11-22-2000, 12:02 PM
Your link was absolutely what I was looking for. I hope that the info that ixl has alluded to will be along those lines. It is a little "unscientific" in that it is all in paragraph form, but the info is there.
Thank you to all who replied. Today, I am being given an out-of-class microprocessor project in one of my EE classes here at OSU, and I think I will choose to do something related to this. So you see, forums like this one are educational (as if there was any doubt)!
This topic is by no means closed, so if anyone has more in-depth or better organized information, please, post it up! Thanks again.


11-25-2000, 06:35 PM
Wow! Do you mean to imply you are going to try to make some type of device that interfaces with the keyboard port!? Thats bold! That site you were given seems to say it all. The only problem i forsee is being able to create the logic device. I once made a LED clock from scratch. It took quite some work and that was using instructions(it was huge too). If you need some help with the ASM code let me know. I would love to see your progress. Later...

Chad Wilson
C++/ASM Programmer
PC Support Technician