Expanding Kirby's Adventure...

[griever]

Game has 4th Mapper and as far as I was told it already has maximum size for that mapper. The question is - is it possible to expand ROM? Maybe change it mapper to mmc5 for example or something.... Will it be hard to make game run on new mapper?

[Bregalad]

You can't expand rom. It's certainly possible to hack the game to run on mapper 5 MMC5, but it would be a lot of work most probably. If you do this then yes it's possible to expand ROM to 1024 KB.

[griever]

I see, but still - maybe not mmc5... Maybe mapper which is the most similar to 4th, I mean maybe mapper which will require less work (has similar switching techniques or something)

[Bregalad]

As far I know, MMC5 is the only mapper to allow for 1024 KB PRG ROM (I don't consider pirate mulicarts as mappers), and still, no commercial game ever usede that much PRG ROM.

[Disch]

(I don't consider pirate mulicarts as mappers)

=P Why not?

Anyway... I'm a little confused. Is it really that MMC3 can't access 1MB? Or is it just that no boards have that much PRG on them? Like... does the MMC3 just not have enough pinouts?

I'm not really very knowledgable when it comes to hardware. I tried making sense of the pinout on kevtris' page, and it looks like it has pins going up to PRG A18... but wouldn't that make the cap 256K? Obviously I'm misunderstanding because games have more than that.

[tepples]

Anyway... I'm a little confused. Is it really that MMC3 can't access 1MB? Or is it just that no boards have that much PRG on them? Like... does the MMC3 just not have enough pinouts?

MMC3 has enough PRG ROM address pins to switch 64 banks, each of 8 KiB.

I'm not really very knowledgable when it comes to hardware. I tried making sense of the pinout on kevtris' page, and it looks like it has pins going up to PRG A18... but wouldn't that make the cap 256K?

There are a total of 19 pins, numbered A0, A1, A2, ..., A18, going into the PRG ROM's address bus. A0 through A12 come from the NES PRG bus, and A13 through A18 come from the MMC3. If you have 19 address pins and 8 data pins, you can address 2^19 octets = 512 KiB.

[Bregalad]

I guess it would be possible to adress more ROM by using other pins, such as the CHR ROM upper adress, in order to get 1024 KB of PRG ROM split into two big chunks of 512 kb, but then CHRROM would be restricted to 128 KB, and this wouldn't be emulatable unless an emulator was written espeically for this.

[Disch]

Oh duh

Yeah A18 is actually the 19th pin so it would be 2^19. For some reason I was thinking 2^18

[griever]

returning to subject: how 'bout Mapper 52? - Disch said

Yet another MMC3 multicart.

- well I just thought to expand rom, set $6000 to 0 on reset and powerup, and then change blocks(just like extra bank changes) right inside game's routines for romhack's purposes... Is it at all real?

[tepples]

$6000 is within battery-backed SRAM. If you are going to use it to implement a mapper, like that mapper with CHR ROM that shares BNROM's iNES number, you'll have to make sure that the code does not rely on the contents of $6000 being preserved over bank switches or over power cycles. You'll also have to duplicate the fixed banks (last 16 KiB) in both the bottom and top half of the ROM so that interrupt handlers jump to somewhere sane.