Memory management controller
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Multi-memory controllers or memory management controllers (MMC) are different kinds of special chips designed by various video game developers for use in Nintendo Entertainment System (NES) cartridges. These chips extended the capabilities of the original console and made it possible to create NES games with features the original console could not offer.
With the advent of NES emulators, the code written to emulate these chips became known as mappers.
List of MMC chips
Early NES mappers were made of 7400 series discrete logic chips.:29 The UNROM, implemented with two such chips, divided the program space into two 16 KiB banks. The mapper allowed a program to switch one bank while keeping one bank always available. Instead of a dedicated ROM chip to hold graphics data (called CHR by Nintendo), games using UNROM stored graphics data on the program ROM and copied it to a RAM on the cartridge at run time.:29
The MMC1 was Nintendo's first custom mapper integrated circuit to incorporate support for saved games and multi-directional scrolling configurations.:30 The chip comes in at least five different versions: MMC1A, MMC1B1, MMC1B2, MMC1B3 and MMC1C. The differences between the different versions are slight, mostly owing to savegame memory protection behavior. The MMC1 chip allowed for switching of different memory banks. Program ROM could be selected in 16KB or 32KB chunks, and character ROM could be selected in 4KB or 8KB chunks. An unusual feature of this memory controller was that its input was serial, rather than parallel, so 5 sequential writes (with bit shifting) were needed to send a command to the circuit.
The MMC2 is only used in Mike Tyson's Punch-Out!! and the later rerelease which removed Mike Tyson. A single 8KB bank of program ROM could be selected (with the remaining 24KB locked) and character ROM could be selected in two pairs of 4KB banks, which would be automatically switched when the video hardware attempted to load particular graphic tiles from memory, thus allowing a larger amount of graphics to be used on the screen without the need for the game itself to manually switch them.
The MMC3 was Nintendo's most popular MMC chip. It comes in MMC3A, B, and C revisions. The MMC3 added a scanline based IRQ counter to make split screen scrolling easier to perform (mainly to allow the playfield to scroll while the status bar would remain motionless at the top or bottom of the screen), along with two selectable 8KB program ROM banks and two 2KB+four 1KB selectable character ROM banks.
This chip is only used in three games, all of which were released only for the Famicom in Japan, and were developed by Intelligent Systems. Functionally, it is nearly identical to the MMC2, where the only difference is that the MMC4 switches program ROM in 16KB banks instead of 8KB banks and has support for a battery-backed SRAM to save game data.
- Manufacturer: Nintendo
- Games used in: Castlevania III: Dracula's Curse(NA/EU), Just Breed, Metal Slader Glory, Laser Invasion, Uchuu Keibitai SDF, Nobunaga's Ambition II, Nobunaga no Yabou - Sengoku Gunyuu Den, Bandit Kings of Ancient China, Romance of the Three Kingdoms II, Uncharted Waters, Aoki Ookami to Shiroki Mejika - Genchou Hishi, Gemfire, L'Empereur, Ishin no Arashi, Shin 4 Nin Uchi Mahjong - Yakuman Tengoku
The MMC5 was Nintendo's largest mapper. It was also the most expensive, making developers avoid it. Only Koei seemed to use this chip regularly. The chip has 1 KB of extra RAM, extra sound channels (two square waves), supports vertical split screen scrolling, improved graphics capabilities (making 16,384 different tiles available per screen rather than only 256, and allowing each individual 8x8-pixel background tile to have its own color assignment instead of being restricted to one color set per 2x2 tile group), highly configurable program ROM and character ROM bank switching, and a scanline-based IRQ counter.
The MMC6 is similar to the MMC3, with an additional 1 KB of RAM which can be saved with battery backup.
Famicom Disk System
- Manufacturer: Nintendo
- Games used in: Arumana no Kiseki, Ai Senshi Nicol, Bio Miracle Bokutte Upa, Exciting Basket, Falsion, Meikyuu Jiin Dababa, Nazo No Kabe, Risa no Yousei Densetsu, Relics - Ankoku Yousai, Big Challenge! Dogfight Spirit, Famicom Tantei Club Part II, Link no Bouken, Metroid (Japanese Version), Nazo no Murasame Jō, Palthena no Kagami (FDS version of Kid Icarus), Pro Wrestling, Shin Onigashima, Vs. Excitebike FDS, Yuuyuuki, Zelda no Densetsu, KikiKaiKai, etc.
The Famicom Disk System's ASIC was an extended chip, which supported a single 6-bit sound channel of wavetable-synthesis with a built in frequency modulator (Not to be confused with Yamaha OPL/OPN chips).
The A*ROM mapper, named after the AMROM, ANROM, and AOROM cartridge boards that use it, was developed by Chris Stamper of Rare Ltd., and manufactured by Nintendo. It is found in games developed by Rare for Nintendo, Tradewest, GameTek, Acclaim, and Milton Bradley. It uses 32 KB ROM switch and a CHR RAM. Unlike other chips, it uses one screen mirroring.
As only first-party hardware was allowed in North America and Europe, these third party chips were supposed to be used only in Japan. However, recently some of them had been found in a few North American cartridges as well.
- Manufacturer: Konami
- Games used in: Contra (Japan), Tiny Toon Adventures (Japan), Akumajō Special: Boku Dracula-kun
The VRC2 is a chip from Konami that allows program ROM to be switched in 8KB banks, and character ROM to be switched in 1KB banks. This mapper had two known revisions: VRC2a and VRC2b.
The VRC6 (Virtual Rom Controller) was an advanced MMC chip from Konami, supporting bank switching for both program code and graphics as well as a CPU cycle–based IRQ counter, which can also act as a scanline counter. The chip also contained support for 3 extra sound channels (two square waves of 8 duty cycles each and one sawtooth wave). It was used in Akumajō Densetsu (the Japanese version of Castlevania III: Dracula's Curse), while the western version used the MMC5 from Nintendo. Since the Nintendo Entertainment System did not allow cartridges to add additional sound channels, the soundtrack on the western versions could only access the original five sound channels built into the NES and had to be reworked to follow those specifications.
The VRC7 was a very advanced MMC chip from Konami, not only supporting bank switching and IRQ counting equivalent to the VRC6 but also containing a YM2413 derivative providing 6 channels of FM Synthesis audio. This advanced audio was used only in the Famicom game Lagrange Point; while the Japanese version of Tiny Toon Adventures 2 also used the VRC7, it did not make use of the extended audio.
- Manufacturer: Namco
- Games used in: Erika to Satoru no Yumebouken, Final Lap, King of Kings, Mappy Kids, Megami Tensei II, Namco Classic II, Sangokushi, Sangokushi 2, Youkai Douchuuki, Rolling Thunder(JP)
The NAMCO106 was only used in games exclusive to Japan. Its capabilities were comparable to Nintendo's MMC3. A variant of this mapper, the NAMCO163 contained extra sound hardware that plays 4-bit wave samples. It supports 1 to 8 extra sound channels, but aliasing increases with the number of active channels.
The FME-7 was a memory mapping circuit developed by Sunsoft for use in NES and Famicom cartridges. It allows the program ROM to be switched in 8KB banks and the character ROM to be switched in 1KB banks. It also contains hardware allowing the cartridge to generate IRQ signals after a specified number of CPU clock cycles, thus enabling split-screen effects with minimal use of processing power. A special version of this mapper, labeled as "SUNSOFT 5B" rather than "FME-7", contains a version of the widely used Yamaha YM2149. This sound generation hardware was used on only one Famicom title: Gimmick!
- Manufacturer: Sunsoft
Some individual and unlicensed developers made custom mappers for the NES, most of which simply expanded the available memory.
228 was a simple bank switching mapper developed for use in the notoriously poor-quality games Action 52 and Cheetahmen II. It does not have a nametable control bit. In the Action 52 multicart, it also contains a small 16-bit register area that contains the old menu selection when exiting a game.
- "Why Game Paks Never Forget" from Nintendo Power No. 20 Mar/Apr 1991, pp. 28–31.
- UxROM from NESdevWiki Retrieved on 2009-11-21.
- MMC1 from NESdevWiki Retrieved on 2009-11-21.
- Nintendo MMC2 from NESdevWiki
- Nintendo MMC3 from NESdevWiki
- Nintendo MMC4 from NESdevWiki
- Nintendo MMC5 from NESdevWiki
- Nintendo MMC6 from NESdevWiki
- List of NES games with publisher and board
- AOROM – NESdevWiki
- Konami VRC2 from NESdevWiki
- Konami VRC7 from NESdevWiki