Max Rom size for coding

By norakomi

Paragon (1125)

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02-02-2022, 10:39

Quick question.

Is it possible to code a Rom game that is bigger than 2MB ?
Are there fysical cartridges out there that are bigger ?

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By Grauw

Ascended (10618)

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02-02-2022, 10:48

For ASCII8 and the Konami mappers the ROM size limit is 2 MB because there are 256 banks of 8K.

256 * 8K = 2048K

You can use the ASCII16 mapper which has 16K banks to have a size up to 4 MB.

256 * 16K = 4096K

By konamiman

Paragon (1176)

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02-02-2022, 10:50

...and you could always come up with a custom mapper, e.g. one that somehow uses two bytes for specifying the ROM page number (by writing to two addresses, or by writing the two bytes to the same address in sequence) to have virtually unlimited ROM size. That wouldn't be very emulator-friendly, though. Smile

By Pencioner

Scribe (1507)

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02-02-2022, 13:14

konamiman wrote:

That wouldn't be very emulator-friendly, though. Smile

and not modern multifuctional devices friendly either Big smile

By norakomi

Paragon (1125)

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02-02-2022, 16:45

Thanks !

And as far as physical and digital release of a 4MB game?

Physical: I didn't find anyone who produces 4MB roms. Are they out there ?
Digital: Do people have a preference for a game released digitally, choosing between a 2MB ASCII8 or 4MB ASCII16 ?

I suppose many people wanna flash such a digital release on their Flashable cartridges to play on the real hardware.
Do people mostly own 2MB flashable cartridges, or are there also many 4MB flashable cartridges sold and used ?

By Grauw

Ascended (10618)

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02-02-2022, 16:56

norakomi wrote:

Physical: I didn't find anyone who produces 4MB roms. Are they out there ?

The ASCII16 circuit isn’t very different from ASCII8, so there shouldn’t be any big issues with making a physical release. MegaFlashROM SCC+ SD supports ASCII16, so I would imagine Manuel Pazos can produce them. The Carnivore2 and RBSC multi-mapper also support ASCII16.

norakomi wrote:

Digital: Do people have a preference for a game released digitally, choosing between a 2MB ASCII8 or 4MB ASCII16 ? I suppose many people wanna flash such a digital release on their Flashable cartridges to play on the real hardware. Do people mostly own 2MB flashable cartridges, or are there also many 4MB flashable cartridges sold and used ?

I am not aware of any cartridges that do support 2 MB but not 4 MB. The MegaFlashROM SCC+ SD and Carnivore2 both have 8 MB of FlashROM so they should be able to handle it fine.

Although I do recall old versions of the MFRSCC+SD (like mine) do have a bug with ROMs > 2MB, but honestly I should just send mine in to get it updated (and I also have a Carnivore2 as backup).