Add MBC30 mapper#661
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| # MBC30 | ||
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| (4 MiB ROM, 64 KiB RAM, timer) | ||
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| 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. |
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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.
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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).
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The "MBC3O" naming was first noticed by @pinobatch: #512 (comment)
Is it really
MBC30with a zero orMBC3Owith 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.
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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.
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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 leading zero on the week code matches the
- The PCB silkscreen features multiple instances of unambiguous zeroes.
- Of particular interest is
CR2025, which is a close match for the size of theMBC3~text.CR2025is the onboard button cell designation. This is definitely a zero:20is the diameter in mm,25is the height in tenths of mm.
- Of particular interest is
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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This adds a section to the MBC3 page describing the MBC30 mapper, thus resolves #512.
On balance I think MBC30 is different enough to warrant some isolation -- avoiding complicating the MBC3 documentation -- and similar enough to piggyback on the MBC3 page.
// I started working on this when #637 got closed (which is now open again). I'm making this PR now just because that's what I was heading towards doing, but I'm happy to adapt this or whatever really!