View Full Version : How motherboard detect the keyboard?

02-23-2001, 10:10 AM
When POST ,how does motherboard detect the keyboard?what data does keyboard contoller give the motherboard?

02-23-2001, 10:21 AM
If I didnt know better I would think this was a Homework problem!!! Go to this site to learn about keyboards and KB controllers: http://www.pcguide.com/ref/mbsys/chip/kbctrl.htm

"As hard as a rock & dumb as a brick"...Windows CEMeNT

02-23-2001, 10:47 AM
Know what you mean. The last reference I saw was someone wanting to simulate a keyboard with another device. (Home designed device)

02-24-2001, 07:25 PM
I had studyed the interrelated information on PCGUIGE.COM before I post the topic,but I didn't find what I needed.
I readed a IBM-PC SYSTEM ROM BIOS code yesterday,and find the KEYBOARD
TEST code;but the BIOS code I found is IBM 8088 system's,so I want to know
whether this code is the same with the BIOS KEYBOARD TEST code we use now!

02-25-2001, 05:18 AM
During POST after RAM is verified and counted the bios sends a signal to the keyboard connector on the back of the computer and if a keyboard is plugged in this leads to the keyboard controller. The keyboard controler sends an electrical signal back that says "I am here". The keyboard controller will then check for keys that are sending repeated signals, (stuck keys or you have something sitting on the keyboard) if a stuck key is detected this message is sent back to the bios as a 301 error and a short beep. If bios recieves a "I am here message" and no "error 301 message it will then move to floppy test.

The only messages involved are "I am here" and "I got a stuck key". Bios has a time limit in which it expects the "I am here" message to be sent after a "are you there" message is sent.

Do note that the keyboard controller is in the keyboard not on the motherboard.

Also... anyone ever figure out why bios tells you to hit F1 to proceed after it detects no keyboard? http://www.PCGuide.com/ubb/smile.gif

Paleo Pete
02-25-2001, 06:43 AM
That one always gets me...I wonder who the rocket scientist is that wrote that error message...

The 8088 keyboard and modern (AT) keyboard do not use the same code. Try an XT keyboard on a modern AT or higher computer and you'll get a keyboard error. And probably be asked to press [F1] http://www.PCGuide.com/ubb/biggrin.gif

XT keyboards, if you've never seen one, have 10 Function keys instead of the 12 on AT's, and they are located vertically in 2 rows on the left. A few of the keys on AT keyboards are also not available, it has fewer keys. Some keys are also in different locations.

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02-27-2001, 08:40 AM
To all friends:
Thank you for helping me, I have gotten enough information in this forum.