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From: oyster@uwmacc.UUCP (Vicious Oyster)
Newsgroups: net.micro.atari
Subject: Re: 16-bit upgrade for the 800XL, 130XE, etc.
Message-ID: <1935@uwmacc.UUCP>
Date: Wed, 29-Jan-86 14:03:13 EST
Article-I.D.: uwmacc.1935
Posted: Wed Jan 29 14:03:13 1986
Date-Received: Sat, 1-Feb-86 03:34:55 EST
References: <8601272322.AA01905@mitre-bedford.ARPA> <860128-070207-1228@Xerox>
Reply-To: oyster@uwmacc.UUCP (Vicious Oyster)
Organization: UWisconsin-Madison Academic Comp Center
Lines: 41

In an article, Fleysher.wbst@XEROX.COM (Dan Fleysher) writes:
>re: dropping a 65816 into your Atari 800XL in place of the 6502, to
>upgrade it to 16 bits:  Note that ANTIC (the screen display chip) is
>also an 8 bitter, so you would have to confine your display RAM to
>within 64K addresses....

>having usable RAM above the display area violates Atari 8-bit software
>architecture, which always puts the display area at the top of available
>RAM - the extra memory would not be usable by most 8 bitter programs
>(but you could make RAM disk(s) out of it).
>
   Unless I'm mistaken, that's merely a convention.  The display memory
can be anywhere (subject of course, to the usual alignment restrictions).

>Also, you'd have to find a place to put the
>additional memory chips without destroying the RF shield - a packaging
>nightmare.

  Granted, a problem; but there are a *lot* of 800XL's out there with 256K
and 512K already. 

>Sounds like an awful lot of work to me, and when you finished up you
>would still not be able to run ST programs because of instruction set
>differences between the 65816 and ANTIC and their ST equivalents.
>Unless you want the experience of tearing apart your 8-bitter and
>learning something, I think you'd be further ahead to buy a new ST.  (Of
>course, those of us who use our 8 bitters for word processing, game
>playing and bulletin-board-calling don't really need 16 bits anyway...)

   I think you missed the point.  The chip would be faster if only you
take into consideration the fact that it could do memory transfers and
arithmetic in 16 bits.  I once attempted to alter the public domain
Small-C compiler to generate 6502 code, and I gave up when I got sick of
all the high-byte/low-byte garbage-- the compiler would have turned out
twice as big and twice as slow.  
   And who wants to run ST programs, anyway? (:-)

 - Joel ({allegra,ihnp4,seismo}!uwvax!uwmacc!oyster)
 
P.S. I'd like to change my "split the group" vote from a no to a yes, just
so the obnoxious amiga/mac/ham-radio cross(and mis)-postings go away.