NES games come in cartridges, and inside of those cartridges are various circuits and hardware. Different games use different circuits and hardware, and the configuration and capabilities of such cartridges is commonly called their mapper. Mappers are designed to extend the system and bypass its limitations, such as by adding RAM to the cartridge or even extra sound channels. More commonly though, mappers are designed to allow games larger than 40K to be made.
The term "mapper" arises from the concept of memory mapping: translating memory hardware into the CPU's and PPU's address spaces. A memory map describes which addresses correspond to which physical locations of memory.
Multiple functions can be performed by the hardware and circuitry on a cartridge's printed circuit board:
Most mappers fall into one of two categories: discrete logic, and ASIC based. Some discrete logic mappers are susceptible to bus conflicts. Nintendo uses the term Memory Management Controller (or MMC for short) for its ASIC mappers ("Why Game Paks Never Forget" article in Nintendo Power) (note: it may have originally stood for "Multi Memory Controller", at least according to Japanese), while Konami's ASIC mappers use the name Virtual ROM Controller (or VRC).
Discrete logic mappers are often referred to by the name of a board that they are commonly used in (e.g. "UNROM"). ASIC mappers are named after the ASIC (e.g. "MMC1" or "FME-7"), except in boards that use an ASIC in an unusual way (such as "TQROM", "TLSROM", or "NES-EVENT"). The emulation community generally refers to mappers by a numbering scheme that originated with the iNES emulator (e.g. "mapper 002").
The notation used in Disch's docs describing mappers is explained here.
To allocate a mapper number, you should have A. a hardware implementation or B. an emulator implementation and a sketch of hardware. You should also have a publicly-available dump of an existing commercial cart or most of a homebrew game written.
This is the plane 0 table. These mappers do not require a NES 2.0 header.
Most icons next to mapper numbers refer to publishers. Nintendo-made boards with numerous publishers get the Nintendo icon; Nintendo-made boards dominated by one publisher get that publisher's icon. Other icons refer to status:
Plane 1 (NES 2.0 mappers 256-511)
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Plane 2 (NES 2.0 mappers 512-767)
512 | 513 | 514 | 515 | 516 | 517 | 518 | 519 | 520 | 521 | 522 | 523 | 524 | 525 | 526 | 527 |
528 | 529 | 530 | 531 | 532 | 533 | 534 | 535 | 536 | 537 | 538 | 539 | 540 | 541 | 542 | 543 |
544 | 545 | 546 | 547 | 548 | 549 | 550 | 551 | 552 | 553 | 554 | 555 | 556 | 557 | 558 | |
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Categories: Mappers