Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!ccu.umanitoba.ca!umhild11
From: umhild11@ccu.umanitoba.ca (Jeff 'Zar' Hildebrand)
Newsgroups: comp.sys.atari.8bit
Subject: Re: Paging in MAC/65
Message-ID: <1990Nov1.230312.15522@ccu.umanitoba.ca>
Date: 1 Nov 90 23:03:12 GMT
References: <5983@harrier.ukc.ac.uk>
Organization: University of Manitoba, Winnipeg, Canada
Lines: 35

In article <5983@harrier.ukc.ac.uk> dac@ukc.ac.uk (David Clear) writes:
>I've just acquired MAC/65 for my Atari 800XL. I think that it's one of those
>OSS Supercartridges which can be paged in and out at will (even though it's
>plugged into the cartridge port). This is nice as it allows access to the
>RAM from $A000-$BFFF.
>
>Unfortunately I don't know how to use this feature and the manual doesn't
>say anything. I remembered from reading an article in Analog (I think) a
>couple of years back about paging out OSS BASIC and putting some DOS
>files under there as a RAM-disk. It mentioned addresses around $D500 for
>paging the cartridge. The debugger in MAC/65 certainly does not like looking
>at that area of memory.
>
>If anyone really knows how to control this I would really like to know.
>
>Thanks for any help.
>
>Dave.

	There was also an article in 'Insight: Atari' in _Compute!_ magazine
many MANY years ago. As near as I can tell, this is how the bank-switched carts
work:  accessing locations $D500-$D5FF sets the CARCTL line of the cartridge
port. If your cart was not built to use this line, nothing will happen.
However, since Bill Wilkinson(?) said in his article - it is the LOCATIONS that
you access which is important, not the value you store. The only way I can see
this being useful is this: when CARCTL is set, you read the lower 8 bits of the
address line and store them in a buffer. These bits can then be used as upper
address bits.  MAC/65 uses 8k of space, of which the lower 4k is permanent, and
the upper 4k is one of 4 banks => MAC/65 is a 20k cart (which is how they were
explained in Bill's article).  This also explains how Atari can now have 256k
carts (I think FSII is 128k).  Theoritically I think they could be much bigger,
but I suppose the decoding and stuff would take up more space than is available
in a standard sized Atari cart.

Jeff