Cothrell@DOCKMASTER.ARPA (09/10/87)
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
Cothrell@DOCKMASTER.ARPA (09/12/87)
I assume that the custom 6502 tri-states its address bus when the Antic puts pin 9 (HALT) low. I think I have further deduced that pin 35 of the 6502 is the trigger for the tri-stating. two questions. am I right so far, and is the data bus also tri-stated? thanx, Scott Cothrell Cothrell at Dockmaster.arpa
conklin@eecae.UUCP (09/12/87)
A couple people have found out (somehow?!) already and since
this question was brought up I might as well mention that I
have already been working on the 200% Turbo XL.
The 6502 in the XL ("Sally") is, as was sumarized, a 6502
with tri-state buffering. When a chip goes tri-state, it
becomes electronically transparent. Antic tri-states the 6502
so that it doesn't react when Antic starts accessing memory.
The 400/800 (and the TRS-80 for that matter) had tri-state
buffers on the board. To lower the chip count on the XL line,
Atari made a custom 6502 that moves those buffers into the
CPU.
We have long known/required a socket that would simply externalize
those buffers so as to make a path for the XL/XEs take a
65802/65C02. ActuallyI don't care what you put in it as long
as it's pin compatible and runs 4 Mhz. This socket is indeed
a possibilty, I've just been too busy messing with the rest of
the timing considerations.
Mathematically computed benchmarks of the Turbo XL show it runs
quite favorably with the IBM PC, Mac, and (suprise!) ST. This
was borne out to some extent with the release of the turbo-
upgrade for the C64.
I have no plans for attempting a 16-bit version of the mod.
Granted the 64 mod is, but I am planning this mod to be along
the lines of the 256/320 XL/XE memory upgrades. Something
that many can make, easily. The memory upgrade is great, and
I strongly reccommend it to anyone who does anything other than
play Pacman.
Please dont ask major techincal details, since I'd like to
make a little money from the efforts on this. By no means do
we intend on letting this mod cost more than $50. If it
gets
that way, then it gets to be PD.
Terry Conklin (and, actually, partner in crime Ken Sumrall)
ihnp4!msudoc!conklin or ARPA: conklin@cps.msu.edu
or we generally carry this discussion on the Club's ATARI
base at (517) 372-3131.
Disclaimer: I bought a Unix machine of my very own. That puts
MIGHTY cross-interests in with this. But if you want results
now, well, get that Kermit65. It's still great!knutsen@aramis.rutgers.edu.UUCP (09/13/87)
In article <2578@eecae.UUCP> conklin@eecae.UUCP (Terry Conklin) writes: > A couple people have found out (somehow?!) already and since > this question was brought up I might as well mention that I > have already been working on the 200% Turbo XL. > Mathematically computed benchmarks of the Turbo XL show it runs > quite favorably with the IBM PC, Mac, and (suprise!) ST. This > was borne out to some extent with the release of the turbo- > upgrade for the C64. > Please dont ask major techincal details, since I'd like to > make a little money from the efforts on this. By no means do > we intend on letting this mod cost more than $50. If it > gets > that way, then it gets to be PD. I still can't believe I'm reading this. You mean to say I'll soon be able to purchase an upgrade that will double the speed of my 800XL? Hot diggedy! Only a few general questions: When? Where? Major caveats of the increased clock speed? (That is, will all software run?) Will there be a hard or software switch to bring the speed down to normal if desired? If this proposal becomes a reality, you will indeed "make a little money" from the efforts. -- Mark K. -- _________________________________ Jersey\\\\\\\\ _____________________________ ARPA: knutsen@rutgers.edu | \\\Atari\\\\\\ | GEnie GE Mail: M.KNUTSEN UUCP: {...}!rutgers.edu!knutsen | \\\\\\Computer | The JACG BBS: (201)298-0161 --------------------------------- \\\\\\\\\Group -----------------------------