Old Keyboard Puzzle.
 

I've always believed that the keyboard from a PC/XT class machine couldn't be used on an AT, or vice versa, as they used a different protocol. Some were duel standard and had a switch on — I've got one.

I recently came across an 88-key keyboard that I'd forgotten about.

Now I never had an AT machine. I've obviously used this keyboard on an XT as the + key on the numeric pad has been re-labelled ◄┘, which I used to do by hacking KEYB.COM.

Today I put it on my Pentium 4 via a 5-Pin Din to PS/2 adapter and it worked. The only niggles were the \ key not working, though I managed to get it to with a re-mapping program, and nor does the ALT key. I didn't mess about with that as for all that it's a nice keyboard it doesn't feel any better than the ones I currently have in use.

What's puzzling me is that this keyboard doesn't have an 88/286 switch on so where some made auto-switching?

Re: Old Keyboard Puzzle.
 

From a dim recall of some of the switched keyboards of which you speak, I think that all the switch did was to connect or disconnect one lead of the five-pin plug.

Re: Old Keyboard Puzzle.
 

No. The XT and AT keyboards had essentially the same pinout, 4 signals (+5V, ground, clock, data). I think the original PC (and XT) had a reset signal (from motherboard to keyboard) on the last pin of the DIN plug but I don't think any keyboard used it.

What was different was the serial communication protocol over the clock and data lines. For one thing the AT one was bidirectional (to control the keyboard LEDs). But there were many other differences too.

But I seem to remember too that the AT would send something to the keyboard at power-on. As a result a keyboard could tell what sort of machine it was connected to. And autoswitching keyboards certainly existed.

Re: Old Keyboard Puzzle.
 

Thanks for that.

I must be getting old as I can't remember a thing about when and how I acquired this keyboard.

Re: Old Keyboard Puzzle.
 

Very much in the past now, but I vaguely remember an IBM employee giving me an update on keycodes which (at least then) could be easily accessed hence working directly with the system rather than Windows or MSDos. I presume the keycodes are still the same as they used to be for backward compatibility.

Re: Old Keyboard Puzzle.
 

I'm pretty sure I had (or probably still do) an adapter that came with a keyboard so it could be used with either. I'll see if it's easily accessible and post a photo.

Re: Old Keyboard Puzzle.
 

Most adapters of the day were just between AT and PS/2, same signals with a different connector. As Tony has pointed out, the protocols used by PC and XT are different to the ones used by the AT.

There are adapters around these days that can convert XT to AT, for people wanting to use early keyboards. Going from AT to XT is a different story - I ended up buying a switchable keyboard on eBay with ridiculous shipping from the US to use with my 5150 PC.

Re: Old Keyboard Puzzle.
 

Ah, yes. Sorry it will have been AT to PS/2.

Re: Old Keyboard Puzzle.
 

That definitely looks to be a clone of some of the earlier IBM XT/AT era boards - probably only in layout rather than the actual keyboard mechanicals. Exactly how much automatic compatibility it has inbuilt will depend quite a bit on when it was made and exactly what chipset has been used.

Northgate were one company who made some keyboards with onboard DIP switches which allowed a plethora of options to be configured, one of those in the case of some models included AT/XT modes.

I seem to have started to collect old and/or obscure keyboards at some point without noticing it...so if it winds up looking for a new home at any point I'd certainly be interested.