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From: 33500911@sdcc13.UUCP ({|lit})
Newsgroups: net.micro.apple
Subject: Re: Apple IIC to Apple IIE Bus Convertor
Message-ID: <384@sdcc13.UUCP>
Date: Wed, 4-Dec-85 01:02:16 EST
Article-I.D.: sdcc13.384
Posted: Wed Dec  4 01:02:16 1985
Date-Received: Thu, 9-Jan-86 07:22:26 EST
References: <> <886@nmtvax.UUCP>
Reply-To: 33500911@sdcc13.UUCP (Jimmy the Kid)
Distribution: net
Organization: U.C. San Diego, School of Bartending
Lines: 47

In article <886@nmtvax.UUCP> kenyon@nmtvax.UUCP (Rob Kenyon) writes:

> That could be very difficult to do.  It would really play havoc with
> programs written for the //c as many of the internal locations are moved.
> Things aren't in normal locations as though they were in a slot.
> In a //c, apple knew where everything was going to be (you can't just throw
> in a 3.6M 6502) and it appears that io rom swap space doesn't (on a //
> you can decide which card to look at by telling the others to get out and
> swaping in the ones you want.)  This doesn't appear to happen on a //c.
> (Note that I used the word "appear."  I haven't hacked that hard on a //c, 
> but there is something funky in the roms.)
>

Yes, there is something funny in the //c MMU.  On regular apples,
you must access $CFFF to tell the other cards to stop using the
expansion area ($C800-$CFFF).  After that, you have to access one
of the valid addresses within the ROM of the peripheral card you
want to have switched in.  If you don't access $CFFF (and depending
on how smart your cards are) the old ROM bank is kept in, causing
notable havoc.

The //c does all this bank switching automatically.  If you access
one "card", and then another, the $C800-$CFFF area is switched
automatically.  (You can do this kind of thing when you know that
there is one and only one "card" built in for each function (and you
know exacly where it will be.))

NOT TO MENTION:  More I/O ports and "switches" ($C000-$C0FF) were
added to the //c.  This may still cause MMU problems.

Good luck trying to get the MMU to recognize a 3.6Meg 6502 though.
:-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-)

But seriously,  by the time you hack through all the address
management and I/O problems, you'll have a //e and not a //c. 


--
					  - Jim Hayes
					    UCSD.

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