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From: Cothrell@DOCKMASTER.ARPA
Newsgroups: comp.sys.atari.8bit
Subject: Custom 6502
Message-ID: <870910151738.120389@DOCKMASTER.ARPA>
Date: Thu, 10-Sep-87 11:17:00 EDT
Article-I.D.: DOCKMAST.870910151738.120389
Posted: Thu Sep 10 11:17:00 1987
Date-Received: Sat, 12-Sep-87 09:03:10 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 25

jwt at Atari has written me a note stating that the CPU in the later
Atari computers (everything but the 800/400 I guess) is indeed custom.
The difference seems to be that the custom chip has the ability to
tri-state its 'bus'.  I have asked for clarification of its 'bus', but I
think that he means the address bus (at least) and possibly more.
Apparently the old 800's had the tri-state logic external to the 6502.

Ed Satterthwaite raised the point of the "worthwhileness" of attempting
to replace the cpu in the atari computers.  I agree that most of his
points are logical and reasonable.  That doesn't change my mind, I just
happen to agree with him.  (I am a hacker at heart and sanity has never
been a prerequisite)

I happen to have the 800 schematics which show the tri-state logic (if
you want to call it that...weirdest contraption I ever saw...anyone know
the reasoning behind that design???  I though one used the 650X because
the phased clocks were generated for you!)  and am going to try to make
a "processor module" that will drop into the custom 6502 socket and
properly tri-state things.

wish me luck (I'll probably need it)

Scott Cothrell

Cothrell -at Dockmaster.arpa