• Please review our updated Terms and Rules here

IBM XT keyboard compatible with IBM AT?

robbo007

robbo007

Experienced Member
Joined
Jan 7, 2012
Messages
287
Location
Iberian Peninsula
Hiya all,
I've just purchased off eBay an original IBM XT keyboard and I've connected it to my AT and it just beeps and they keys don't work.

Is the XT keyboard wired differently and not compatible with the AT? I notice the keyboard has a black cable. Different to the colour of the actual keyboard. Could this not be the original cable and hence my problems?

$_57.jpg
 
The original IBM XT keyboard is not compatible with the AT and usually have the black cable, However "some" AT keyboards are both XT - AT compatible. You'll need to try the XT keyboard on an XT machine.
 
To expand on that, they use two different protocols - commonly known as Set 1 and Set 2. Pinout is the same between Set 1 and 2 keyboards, it's just the protocol is completely incompatible.

If you can't get a proper AT keyboard, you can also use a PS/2 to AT adapter and use a PS/2 keyboard. This is also period-correct and fully supported, as the 101-key Model M was originally used on machines such as the AT, before it was actually used on the PS/2 (with a different cable, but the same keyboard internally).
 
Check out geekhack.org and deskthority.net for details on how it works. As is, the XT keyboard won't work on anything other than a PC or PC XT (or clone) as BHTOOFER said; the protocols are totally different. To make it work, you can buy this:
https://www.hagstromelectronics.com/products/ke18xtat.html

I have one that I use on my modern PC and it works great. I asked Hagstrom to put it into a box for me, which they di at no charge. They were great to deal with.
 
romanon said:
I have later XT keyboard, model M and it is XT/AT compatibile

View attachment 24964
Click to expand...
Janeiac said:
Not possible, the XT and the AT used two different protocols that are not compatible with each other. The Model M was made for ATs or PS/2s --same protocol, different connectors. Model M didn't come out until 1985.
Click to expand...
Some members have reported that they have a Model M that auto-switches.

Reference: The thread at [here]. In that thread, see posts #9, #11 and #13.
 
Janeiac said:
Not possible, the XT and the AT used two different protocols that are not compatible with each other. The Model M was made for ATs or PS/2s --same protocol, different connectors.
Click to expand...
It *is* possible. I have one that works with both XTs and ATs. It doesn't have the three lights , it's #1390120.
 
Indeed. I have several keyboards from various manufacturers that will auto-switch--and some that will switch by changing one or two hidden DIP switches.
 
Sure, there were keyboards from various manufacturers with switches but he said Model M-- that's IBM. The protocol is different, so it can't work without a switch. I have the same early Model M without the lights BTW, and also two model F's one for PC/XT and one that works on an AT or later.
 
The IBM Model M keyboard was XT/AT autoswitching as long as the PS/2 Model 25 and 30 computers were in production, which were XT-based 8086 machines. Once those models ended production, by the early '90s, newer Model M keyboards (such as all those made by Lexmark or Maxi-Switch) no longer supported XT mode, and were AT-only.
 
That's interesting, and makes me remember something about the keyboard controllers on the old motherboards. They were set up to translate, or not, the original protocol and it makes me wonder if this is how the switching is accomplished. People do say some Model Ms work in XTs (thanks for the link, I had no idea!) so they must be switched somehow.
 
You must log in or register to reply here.
Back
Top