Original IBM PC (Model 5150) keyboard

[paul.brett]

Hi guys,

Looking for a bit of historical knowledge here. I have acquired an original IBM PC model 5150 with colour display. Seems to be in good order apart from the keyboard, which is missing.

The connector at the back is the old style DIN connector, (pre PS2 and USB here) and although I have several of these keyboards, and even a converter to use newer PS2 keyboards, I only get garbage on the screen when pressing keys. Note, the garbage is consistent, in that pressing a certain key always gives the same (useless) result.

I seem to recall coming across a keyboard a long time ago that had an XT/AT switch on the back. This would indicate that there are differences, and all my keyboards and the converter only support the AT standard.

Questions:

1. Am I right, or just losing the plot? If I have the above suppositions wrong, then it just means the PC is broken, or at least the keyboard scan part of the motherboard ICs.

2. If I am right, is there a simple modification to make an AT keyboard works with an XT (or pre-XT in this case?)

3. Does anybody have any old IBM parts they can donate? (I am missing the second floppy drive too.)

Thanks in advance for all the head scratching.

[mickjjo]

Hi, This site seems to indicate that the keyboard was a bit non-standard :-

http://en.wikipedia.org/wiki/IBM_PC#Keyboard

Or try:-

http://www.clickykeyboards.com/index....main/pageID/5

http://cma.zdnet.com/book/upgraderepair/ch23/ch23.htm

Regards, Mick.

[paul.brett]

Thanks Mick. Following one of your links I found this:

The XT and AT keyboards are NOT compatible. The only way a XT keyboard will work on an AT computer is if you’ve got a motherboard and BIOS which are specifically designed to support both keyboard types.

The keyboards differ in at least the following ways:

1. The XT kb. generates 2 start bits, 8 data bits, make/break
bit, and a stop bit. The AT kb. is 1 start bit, 8 data, 1 parity,
and a stop bit.

2. The XT uses a make/break bit to indicate key up/down. The
AT sends one byte for keydown and two bytes for keyup.

2. The XT keyboard scan codes have different values than
then AT keyboard make/break codes (for corresponding key
locations).

4. The XT keyboard doesn’t accept any of the command strings
accepted by the AT keyboard.

5. The XT keyboard is reset by fiddling the clock and data
lines; the AT keyboard accepts a reset command string.


So that is the first part of my question answered.

Still looking for those offers of spares Full height floppy and an XT keyboard required (preferably IBM badged)

Thanks.

[mickjjo]

Googling throws up a number of US dealers in keyboards and other 5150 parts:-

http://www.abcresellers.bigstep.com/...l?PRID=1229584

http://www.c-reset.com/parts-ug.html

Good luck.

Regards, Mick.

[Dave Moll]

Originally Posted by paul.brett

I am missing the second floppy drive too.

I have some spare 360K floppy drives, but they are half-height so would not look original in your machine. You can always use a blanking plate in the other half of the full-height bay. PM me if you are interested.