dac@ukc.ac.uk (David Clear) (11/01/90)
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.
umhild11@ccu.umanitoba.ca (Jeff 'Zar' Hildebrand) (11/02/90)
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