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| [[Category:iNES Mappers|155]]
| | #REDIRECT [[MMC1]] |
| [[iNES Mapper 155]] is assigned to games that require the MMC1A variant of the [[MMC1]]. Unlike MMC1B, MMC1A lacks the WRAM disable bit in bit 4 of the PRG bank register ($E000-$FFFF). Games that use this mapper write values between $10 and $1F to the PRG bank register, write to WRAM at $6000-$7FFF, and require the write to succeed.
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| According to the database shipped with Nestopia 1.4.0, these two Famicom games require this behavior:
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| * Tatakae!! Ramen Man: Sakuretsu Choujin 102 Gei (闘将！！拉麺男 炸裂超人一○二芸) ([http://bootgod.dyndns.org:7777/profile.php?id=3736 NesCartDB])
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| * The Money Game (ザ・マネーゲーム) ([http://bootgod.dyndns.org:7777/profile.php?id=3458 NesCartDB])
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| At first, it was conjectured that this was done as a copy protection mechanism or the programmers just weren't aware that a later MMC1 revision would add a bit for disabling WRAM. Later, it was discovered that MMC1A treats bit 3 of the PRG bank register differently from MMC1B: when bit 4 is true, bit 3 bypasses the fixed bank logic and goes straight to the mapper's PRG ROM A17 output. The explicit use of <code>ora #$10</code> in ''The Money Game'' suggests that this behavior may have been intended to support large WRAM, such that <code>ora #$10</code> on the value to be written to the PRG bank accesses the first 8 KiB and <code>ora #$18</code> the second 8 KiB.
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| The two extant games relying on MMC1A behavior are on [[SxROM|SKROM and SJROM]]. Thus theoretically, this mapper should not have to implement any of the boards that repurpose PRG or CHR pins (SE-, SH-, SN-, SO-, SU-, SX-ROM). In particular, SOROM and SXROM have their own WRAM expansion mechanisms. However, it is probably still wise to pay attention to the caveats listed in [[MMC1]].
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| == External links ==
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| * [https://forums.nesdev.org/viewtopic.php?t=23619 Forum topic "MMC1A fixed bank behavior difference"] with test ROM, January 2022
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