RE: C128 with IEEE interface, some info needed

From: Baltissen, GJPAA (Ruud) <>
Date: Tue, 14 Aug 2012 08:41:07 +0200
Message-ID: <>
Hallo Michael,

> this has already been done in 64er Sonderheft 10 / 1986.

I know, the ISA card I built for my PC was based on this design. But
there was an earlier one in 7 / 1985, just for the C64 and based on the

> There is a patched Kernal for C64 and C128

That I didn't know (anymore), I just thought there was a C128 version
only. Otherwise I probably had chosen to disassemble these versions. And
maybe I still will.

> There is a board is based on a 8255.

Another reason I chose for the 6821 version is that the 6821 looks more
like the 6526. Only during the disassembling I realised I had forgotten
about the Control Register construction. 
But this version came with a BASIC programm that patched the original
Kernal. And by changing it a bit, it enabled you just to incorperate the
IEEE routines. A file compare enabled me to find out what exactly was
changed. The pattern behind the changes was quite simple: the moment the
C64 found out it had to make use of the IEC bus, a JMP replaced some
original routines. The JMP lead to a routine that first checked whether
the use of IEC or IEEE was wanted. If IEC, the replaced code was
executed and then C64 jumped back to the rest of the original routines. 

In this case the new IEEE routines replaced some tape code. And now the
weird thing: nothing was done to disable the use of the tape! And the
IEEE routines themself weren't that good as well: they simply didn't
follow the official IEEE protocol all the time. But at least it gave me
the most wanted information: what parts of the Kernal do I have to

The program only uses the so far unused (AFAIK) zero page address 2.
Here you write the number of the IEEE device. If the number of the
wanted device is the same as the zero page address, the IEEE routines
are executed. Quite simple.
And I'm going to add another mechanism: treat everyting above 11 as
IEEE. CBM-HD can emulate every number from 8 to 31. So I could even
connect a real IEEE drive, if needed.

    / __|__
   / /  |_/     Groetjes, Ruud Baltissen
   \ \__|_\

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