Re: Is this an Apple ][ clone?

[ferdimh@gmx.de]

On 27 Feb., 06:28, et...@FreeNet.Carleton.CA (Michael Black) wrote:
> Mitchell Spector (mitch...@hotmail.com) writes:
> >     There is an small circuit card that plugs into the standard
> > 16-pin keyboard connector and has a DIN-5 connector for
> > the PC/XT keyboard (incidentally, I remember trying a PC
> > keyboard on it, or its keyboard on a real PC--they're definitely
> > not compatible).
>
> I don't know whether it was the same clone, but I was given one that certainly
> was on the same level.  It had an "IBM" keyboard and that little serial
> to parallel board that plugged into where the regular keyboard went.
>
> But, when it wsa given to me, it came with a ROM that could be put back
> in to turn it back into an "IBM" keyboard.
>
> I don't think I ever tried it, and I dont' think I still have it.
>
> But it made sense.  There is very little circuitry in those keyboards,
> despite them being quite a bit fancier than a regular Apple keyboard. Not
> much beyond a CPU and the ROM and a few interface ICs.  Make the effort
> to figure out what's there, write the code to be Apple compatible, and
> it likely was far less work than trying to have serial keyboards
> manufactured from scratch.
>
> That little interface board was simple because all it had to do was
> collect 8 bits of serial, and then output it in parallel, with something
> to indicate to the Apple that the "key had been pressed".
>
> But of course, if the "IBM" keyboard had remained "IBM compatible" that
> board could not be so simple, since the "IBM Keyboard" puts out scan
> codes that can't easily be converted to ASCII and indicate a key up
> by sending a different scan code.
>
> In order for the little converter board to work, it needed to see
> normal ascii at its input.  Hence that converter could be used with
> any keyboard that put out serial ASCII, including a Teletype keyboard
> if the voltage levels were interfaced properly.

The PC/XT keyboard does not transmit serial ASCII. It just sends a
different set of scancodes using a slightly different protocol. The PC/
AT and compatibles have a micro in them to translate the AT scancodes
to XT scancodes.
So even if the keyboard is a real PC/XT keyboard, it can't be replaced
with some sort of ASCII keyboard.
There were keyboards which could be switched between AT and XT mode (I
got one...).

---
Ferdinand