HKROM as donor?
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Author:  dude3585 [ Sun Jan 22, 2017 11:41 pm ]
Post subject:  HKROM as donor?

Anyone know if I can use HKROM StarTropics as a donor for games that use a battery?
It says here its a MMC3
The Nintendo MMC3 is a mapper ASIC used in Nintendo's TxROM Game Pak boards. Most common TxROM boards, along with the NES-HKROM board (which uses the Nintendo MMC6) are assigned to iNES Mapper 004.

iNES Mapper 004 and MMC6

The unfortunate conflation of MMC3 and MMC6 into the same iNES mapper can be resolved by the use of an NES 2.0 header, but since the new header is not yet well adopted among emulators or ROM sets, an approach that supports both MMC3 and MMC6 may be desired when an NES 2.0 header is not used.

The MMC6 has a smaller PRG-RAM, and a different register scheme for write protecting it.

Because write protection is generally only used to guard against corruption during power off, many implementations of iNES Mapper 004 simply omit the write protection. Leaving PRG-RAM always write-enabled removes most of the incompatibility between MMC3 and MMC6, and is sufficient to support the popular MMC6 games StarTropics and StarTropics II. These games do not rely on the smaller PRG-RAM size of the MMC6, so the larger 8k RAM addressed by the MMC3 is not a problem.

The less well known game Low G Man is problematic. It used an MMC3 board with no PRG-RAM. Because of a bug in its music code, it relies on open-bus behaviour in the RAM's address range to function correctly. The game does use the MMC3 mechanism to disable RAM, so it may function on an MMC3 board with PRG-RAM, but implementing the MMC3 RAM disable may conflict with the effort to support MMC6 games. Alternatively, NES 2.0 could be used to specify a PRG-RAM size of 0, or the problem can be resolved by patching the Low G Man ROM to work around the conflict: patch.

Some romhacks attempt to increase the available PRG-ROM size beyond the MMC3's hard 512k limit (e.g. Translation of Final Fantasy III). Full 8-bit banking registers could theoretically support up to 2048K PRG-ROM, but very few emulators implement this extension.

Kinda confused with the PRG-RAM. Guessing any MMC3 mapper will work? For example a Super Mario Bros. 3 and sense StarTropics has a battery I could create a Mario Adventure?
Any info or anything before I try anything would be great thanks.

Author:  rainwarrior [ Sun Jan 22, 2017 11:50 pm ]
Post subject:  Re: HKROM as donor?

No. MMC6 differs from MMC3 only in the function of battery backed RAM.

Author:  lidnariq [ Sun Jan 22, 2017 11:51 pm ]
Post subject:  Re: HKROM as donor?

MMC6 is an expensive choice for any MMC3 game without PRG RAM, and almost guaranteed to not work on any MMC3 game with PRG RAM.

Author:  rainwarrior [ Sun Jan 22, 2017 11:55 pm ]
Post subject:  Re: HKROM as donor?

If you want to go the other way though, i.e. use an MMC3 board with battery RAM as a donor to host a ROM of Startropics or Startropics II, you could probably do that if you disconnect the PRG-RAM disable feature? (Opposite of what you're asking, I know.)

Author:  dude3585 [ Mon Jan 23, 2017 1:17 am ]
Post subject:  Re: HKROM as donor?

Thanks. I have a few extra copies of Startropics is why I ask. Curious if I can use them as a donor for more expensive required donor games for Mario 2,3 or Zelda hacks. Dont think there is any unreleased games that are HKROM.

Author:  rainwarrior [ Mon Jan 23, 2017 1:47 am ]
Post subject:  Re: HKROM as donor?

HKROM is only for StarTropics and StarTropics II, as far as I know. ... =NES-HKROM

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