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Add MBC30 mapper #661

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avivace merged 1 commit into from
Jun 3, 2026
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Add MBC30 mapper #661

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9 changes: 9 additions & 0 deletions src/MBC3.md
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Expand Up @@ -92,3 +92,12 @@ Year-10000-Proof, provided that the cartridge gets used at least every

When accessing the RTC Registers, it is recommended to wait 4 µs
(4 M-cycles in Normal Speed Mode) between any separate accesses.


# MBC30

(4 MiB ROM, 64 KiB RAM, timer)

The MBC30 is practically identical to MBC3 in operation, but is capable of addressing twice as much memory for both ROM and RAM.
The only title to be shipped with the MBC30 mapper was _Pocket Monsters: Crystal Version_ in Japan, with the various worldwide versions using MBC3.
Comment on lines +97 to +102

@ISSOtm ISSOtm May 1, 2026

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I've heard from @Rangi42 that it may actually be a MBC3O, possibly “oversized” or something like that. What do you think?

We may nonetheless want to mention the “MBC30” name as a common alias in online documentation.

@CasualPokePlayer CasualPokePlayer May 1, 2026 •
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https://gbhwdb.gekkio.fi/cartridges/CGB-BXTJ-0/gekkio-1.html
https://gbhwdb.gekkio.fi/cartridges/CGB-BXTJ-0/gekkio-2.html

That is a 0, not an O (compare it with the other 0 on the chip, also look at the board's MBC30's 0 and 0's elsewhere on the board).

@Rangi42 Rangi42 May 1, 2026 •
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The "MBC3O" naming was first noticed by @pinobatch: #512 (comment)

Is it really MBC30 with a zero or MBC3O with a letter, meaning "MBC3 Oversize"?

If a letter, that would match a pattern on NES where O designates a variant of another cartridge board designed to take a larger memory. This includes UOROM (UNROM + 2 Mbit ROM instead of 1 Mbit) and SOROM (SNROM + two 64 kbit SRAM instead of one).

I see an "O" in "KOREA", but don't notice any clear difference between it and whichever glyph is in the "MBC3_" name.

@ISSOtm ISSOtm May 1, 2026

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It's plausible that the font renders these two glyphs identically. I (we?) am making a judgement call here, because the “O” terminology seems to make sense, like we ended up taking a stab in the dark with the SM83 naming.

Unless anyone has ties with some Nintendo-working uncle, I think we'll have to stick to a guess.

@quinnyo quinnyo May 1, 2026

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It looks like a zero to me. The only known reference to this part number is what you can see on the PCB and mapper IC. I don't see any evidence for it being a letter 'O'.

It being a zero isn't a guess:
In the photos above, there are three instances of the mapper part number, MBC3~ with ~ being the mystery character. The two boards (gekkio-1, gekkio-2) each feature a mapper IC from a different manufacturer. The PCB silkscreen also includes the part number.

  • Each of these three locations has a ~ character unique to it.
  • The mapper ICs both feature a three digit week of manufacture code, both with a leading zero.
    • The leading zero on the week code matches the ~ in the part number on the same IC.
    • again, the ~ are clearly different between the two chips, but they match the zero etched on the same IC.
  • The PCB silkscreen features multiple instances of unambiguous zeroes.
    • Of particular interest is CR2025, which is a close match for the size of the MBC3~ text. CR2025 is the onboard button cell designation. This is definitely a zero: 20 is the diameter in mm, 25 is the height in tenths of mm.

Markings on ICs other than the mapper should not be considered -- there's no reason to expect the typeface to match across manufacturers, plants, etc.

The NES 'O' thing:

  • This chip first appeared in 2000. I assume the NES 'O' carts are at least ten years older than that?
  • The MBC naming scheme generally doesn't appear to match the NES/Famicom one in any significant way, with either 0/O.


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