Re: PC to Apple 2 Keyboard Conversion

[david@uow.edu.au (David Wilson)]

Michael Black <blackm00@Gloria.CAM.ORG> writes:
>This isn't going to be a simple project.  The Apple keyboard just outputs
>ASCII characters in parallel format.  An IBM-compatible keyboard is not
>only serial, and if I remember isn't exactly the same format usually
>seen when sending serial, but it is not ASCII.  Press a key on an IBM
>keyboard, and you will get a serial code that denotes that key, and I
>think a different code is sent when you let go of the key.  The conversion
>to ASCII is done in the IBM.  ON the original and XT, there is a TTL
>shift register, I think it was the 74LS595, that converted the serial
>input to parallel, and then code in ROM does the actual converstion to
>ASCII.  On the AT and later, there is a separate microcomputer to do
>the serial to parallel conversion, and some or all of the conversion to
>ASCII.

The AT keyboard even differs from the PC & XT keyboard. To turn on the
Caps Lock light the PC/AT or 386/486/Pent etc has to send an LED on command
to the keyboard (the older keyboards did it themselves). You could even get
keyboards with an XT/AT switch underneath that could be used on both varieties
of PC.

>But it won't be that simple.  You either have to do the conversion
>externally, most likely by using a dedicated microprocessor, or
>fix the ROM inside the Apple II to do the conversion.  The former
>has been done, there is/was such a unit available for the Radio
>Shack CoCo, while the latter is going to require a lot of work and
>fitting into place.

Yes, I will (when I get the time) knock up a small board to do this.
One chip (PIC uP) and a crystal should do it.
--
David Wilson  School of IT & CS, Uni of Wollongong, Australia