Re: Is this an Apple ][ clone?

[et472@FreeNet.Carleton.CA (Michael Black)]

 (ferdimh@gmx.de) writes:
> 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...).
> 
Reread what I said. 

It was a straight out of the box "IBM" keyboard, with the ROM changed to
make it a serial ASCII keyboard.  It was easy to do, if you took the
time to figure out what was in there, since there wasn't much more than
the actual CPU.  In other words, the "hardware" was actually in software.

It was a neat trick to use the "IBM" keyboard with the Apple II, because
if they'd not changed the code in the keyboard, they'd have had to add
a CPU at the Apple II to do the IBM to ASCII conversion, it was too
different to be done in simple hardware.  But since there was a whole
CPU in the kayboard, change the code in it so the keyboard generates
ASCII in the first place.

Now I may have made a mistake, assuming the modified keyboard used
the usual serial format with start and stop bits.  It may have been
a simpler serial format, but nevertheless ASCII.  If it wasn't expecting
start and stop bits at the little converter board, then that board
wouldn't be useable with just any ASCII serial keyboard.

  Michel