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Glenn 5200 to A8 Conversions, ROM files to burn to EPROM anywhere?


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Not sure. Quickly looking at Qix from Atarimania - it's a 16K program and appears to reside at $6000 - $9FFF which is 8K lower in memory than you'd expect.

5200 can map cartridge ROM from $4000 - $BFFF but the computer can only map it from $8000 - $9FFF (disregarding the small IO hole $D500).

 

What might work is to rearrange things a bit and compress part of the Rom then depack it to Ram.

 

Have the bottom 8K of 16K hold what goes from $8000-$9FFF which in the case of this game is the top part of the Rom.

Have the top 8K of the cart hold a compressed copy of what lives at $6000-$7FFF, plus the usual Init / Run / flags that a cartridge requires.

 

Prerequisite for this would be a machine with minimum 32K Ram. Also, if the game was modified in such a way that the (now) Rom based portion needed to actually be Ram then the game wouldn't work.

 

 

For other games, not sure how they're done. A potential problem is that in the conversion process the game size might bloat to be bigger than the 8 or 16K which it started at.

 

Better option IMO - just put the games onto Atarimax flashcarts as executables. Advantage is you then fit several at least per cartridge and likely no program modifications needed.

Edited by Rybags
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Just checked a few more games (curiosity took over from the need to sleep).

 

It seems to be a common trait - 16K games have mirror images within the 32K window that carts can live in and it seems that some will favour running at the lower address.

Not sure how the mapping works exactly, it probably varies depending on how the cart is wired up, what size it is and whether it's 1 or 2 chips.

 

Star Raiders, 16K Rom has mirrors 8K apart.

$4000-$4FFF, $6000-$6FFF blank (return FF)

$5000-$5FFF and $7000-$7FFF read the same, code seems to execute in high copy.

$8000-$8FFF and $A000-$AFFF read the same, code executes from low copy.

$9000-$9FFF and $B000-$BFFF read the same, block is mostly blank some data at bottom, cart vectors at top.

 

 

As such, this would mean some games when converted would easily run on smaller Ram computers.

So maybe Atari shot themselves in the foot here... they made it hard for the games to be put onto cart if hacked to work on the computer but made it easier for more people to be able to run them if they only had 32 or 40K Ram.

Edited by Rybags
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