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Re: 6502 CPU Schematics
Henry S. Courbis wrote:
Some time back I had repaired a damaged PCT board. The SWIM (or some
crippled version of one) was damaged. Luckily for me the case of the IC had
popped and I could see part the die. I then took out the Dremel and
decapped the rest of the IC. I'll have to post some pics of what I saw, but
what a rats' nest! At least 4 layers and traces running all over the place.
Of course not knowing what some of the structures are doesn't help matters.
Being a MFM and GCR controller I assume this is some kind of a Micro
Controller, but can't say for sure. What I always found amazing about the
SWIM is a 'standard' MFM Floppy Controller is 68 Pins. The SWIM does BOTH
MFM and GCR and is only 44 pins.
I would expect the IWM and SWIM to both be logical derivatives of the
original Wozniac "algorithmic state machine" used in the Disk ][
Controller. In both cases, the ROM could be expanded to provide
additional data separation algorithms.
Finding a full microcontroller (as opposed to a simple state machine)
would really surprise me.
So my next step I think would be to start with something 'simple' like the
IWM - being the smallest and easiest to test of all the custom ICs for the
Apple II. I will take a look and see if that IC has anything I can identify
and learn from. If I can produce a working copy of that IC then I'll move
on to something larger. The main idea being that now these custom ICs will
be able to be duplicated using modern custom logic in new designs.
Hopefully it will spur people on to create new hardware that once would have
been almost unthinkable due to the major undertaking of emulating some of
the unknown custom logic and then trying to fully debug it.
Start with the Disk ][ Controller diagram and I think you'll be able to
identify everything. Re-implementation in modern programmable logic
should be a breeze, even if "gate-wasteful". ;-)
-michael
AppleCrate: An Apple II "blade server"!
Home page: http://members.aol.com/MJMahon/
"The wastebasket is our most important design
tool--and it's seriously underused."