Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.3 4.3bsd-beta 6/6/85; site sdcc6.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!gamma!epsilon!zeta!sabre!petrus!bellcore!decvax!ittatc!dcdwest!sdcsvax!sdcc3!sdcc6!ix469
From: ix469@sdcc6.UUCP (david smith)
Newsgroups: net.micro.apple,net.micro.68k
Subject: Re: 68000 vs 6502 (!) (65816 <-> 6502 compatibility)
Message-ID: <2255@sdcc6.UUCP>
Date: Mon, 21-Oct-85 22:25:42 EDT
Article-I.D.: sdcc6.2255
Posted: Mon Oct 21 22:25:42 1985
Date-Received: Fri, 25-Oct-85 01:43:11 EDT
References: <151@uvicctr.UUCP> <7100003@prism.UUCP> <596@sftig.UUCP> <2230@sdcc6.UUCP> <216@ius2.cs.cmu.edu.ARPA>
Reply-To: ix469@sdcc6.UUCP (David L. Smith, Super-Genius)
Organization: U.C. San Diego, Academic Computer Center
Lines: 40
Xref: watmath net.micro.apple:2267 net.micro.68k:1257

In article <216@ius2.cs.cmu.edu.ARPA> ralphw@ius2.cs.cmu.edu.ARPA (Ralph Hyre) writes:
>In article <2230@sdcc6.UUCP> ix469@sdcc6.UUCP (david smith{|ix}) writes:
>>The 65816 is indeed pin-compatible with the 6502 and it may be
>>possible to "drop" one into an Apple II without major problems,
>>provided you don't want to address more than 64K.
>
>I thought only the 65802 was pin-compatible.  Has anyone
>actually made this substitution?
>
According to my spec sheet, it is indeed pin-compatible.  The data
bus doubles as the high eight bits of the address bus during the
time that a "normal:-)" 6502 wouldn't be using it.

>>Unfortunately, during the time, the video is busy playing with
>>things.
>
>Apple // display circuitry should be redone anyway, they should
>give up on this color in even or odd column stuff.  As long as
>they keep the entry points for text and graphics routines the same,
>most stuff should run OK.
If you redo the video circuitry, you may as well trash your Apple,
since all you're using at that point is the keyboard, slots and
power supply.  I was thinking of putting a 65816 on a board and
running it at 4Mhz, or faster if possible and using the 6502 as an
i/o processor.  I would like to be able to let the 65816 handle the
video display, because it's got such neat tricks built in, like move
a block of memory, etc, but I can't think of a neat way to do this without
slowing it down to 1Mhz.  Perhaps a wait state while the 65816 was
addressing low memory would do the trick (slowing it to only 2Mhz).  
The disk drives would have to be handled by the 6502 (it would be 
preferable, too!).

==================
David L. Smith
UC Sandy Eggo
{ucbvax, ihnp4}!sdcsvax!sdcc6!ix469

All opinions expressed herein are strictly the products of my
automated posting facility and have no affiliation with myself, my
employers or my cat.