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From: ralphw@ius2.cs.cmu.edu.ARPA (Ralph Hyre)
Newsgroups: net.micro.apple,net.micro.68k
Subject: Re: 68000 vs 6502 (!) (65816 <-> 6502 compatibility)
Message-ID: <216@ius2.cs.cmu.edu.ARPA>
Date: Wed, 16-Oct-85 18:36:26 EDT
Article-I.D.: ius2.216
Posted: Wed Oct 16 18:36:26 1985
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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?

>In order to address the 16 megabytes, Western Design uses the data
>bus as address bus for the half CPU cycle that the data bus is not
>used.  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.

>I believe that the MMU switches the CPU off the data bus during that time.

This seems to imply that Apple was thinking about bypassing the MMU
at some later point to get at a large bank of memory.  Does the recently
accounced Apple memory card have a linear-addressing coprocessor port that
would allow a 65816 to address more than 64K without bank switching?
(The Applied Engineering Ramworks card does, is AE planning to support people
putting in 65816's in their machines by putting an extender socket which would
connect the data bus to the coprocessor port before it gets to the MMU chip on
the //e motherboard?)

If all of this is so, will we see 65816-enhanced Apple // come January? 
(All the sales people tell me is that the next version of the //e
will be the same shade of white as the //c and the Unidisk drive.)
--
				- Ralph
Internet: ralphw@c.cs.cmu.edu (cmu-cs-c.arpa)
Usenet: ralphw@mit-eddie.uucp
Fidonet: Ralph Hyre at Fido #385 Pitt-Bull (or maybe Net 129, node 0)
Snail Mail: don't bother
-- 
				- Ralph
Internet: ralphw@c.cs.cmu.edu (cmu-cs-c.arpa)
Usenet: ralphw@mit-eddie.uucp
Fidonet: Ralph Hyre at Fido #385 Pitt-Bull (or maybe Net 129, node 0)
Snail Mail: don't bother