wrd@tekigm2.UUCP (Bill Dippert) (08/19/86)
Apparently the so called "6502" used in the Atari's is a custom modified
chip, hence its not using the industry type JDEC number. From Mike at Xerox
comes the following:
Atari 6502c #C014806 standard 6502
pin no. function pin no. function
36 READ/WRITE 36 N.C.
35 /HALT 35 N.C.
34 N.C. 34 READ/WRITE
Therefore one could bend up pins 34 and 36 and do a wire connection to swap
these two pins, but that would still leave you without a /HALT command.
(Presumably the halt command is necessary.) I do not know if the 6502c
chip used by Atari is identical between the original 400/800, the intermediate
XL series and the current XE series. Presumably there have been some improve-
ments but I do not think that they have gone to CMOS. Any comments from
Atari? Does anyone know if the 65802 chip has a halt function? Possibly,
if it did, it could still be used with a 34/36 pin swap out.
--Bill--
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It is rare to find anything unmodified in my household. Half of my
cats don't even have tails. -- Don't flame me, they are Manx breed!
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Any openings for a mechanical/electromechanical engineer/tinkerer???jhs@MITRE-BEDFORD.ARPA (08/23/86)
According to someone at Atari who shall remain nameless, mostly because I can't find the message with his name on it, the 6502 in the XL/XE series is indeed a custom version with internal tri-state buffers and a HALT line. In some of the old 800 series, presumably the ones in which a new ANTIC chip was added or something, there were external tri-state buffers controlled by the HALT line, and a standard 6502. One could drop in a 65802 in that circuit and it should work. Also, the same logic could be used in a XL/XE machine to make a 65802 work. One would just have to make a piggyback board to plug into the 6502 socket (did someone say SOCKET?) and in turn provide the socket for the 68502 and the tri-state drivers and the control logic. The only thing I am a little unclear on (not quite the same as nuclear) is how to halt the 65802. Perhaps the ANTIC knows what it can get away with and all you have to do is (carefully) halt the clock to the 65802 during the HALT signal period. I suspect everything will fall nicely into place, given a piggyback board. -John Sangster jhs@mitre-bedford.arpa