The NES programmers had limited resources available to them. It makes one appreciate the effort that went into simply creating Donkey Kong Jr.
Design 6502 (capabilities
|CPU Memory:||2 Kilobytes|
|Graphic work RAM:||2 Kilobytes|
Inside a Cartridge:
A NES ROM occupies only a small
fraction of the actual cartridge volume that is available. It
bears a complete set of 72 connector pins through which it
interfaces with the NES. The PRG and CHR ROM chips are the 2
largest components mounted on it. If you can program a computer
then you might understand the distinction between these 2 as the
PRoGram and the CHaRacter ROMs. Think of them as code and data
segments for the assembly language representations of the games--
because that's exactly what they are. The code, the 6502 machine
language instructions, are in the PRG ROM and the graphical data
is in the CHR ROM, if there is one. Sometimes, there is no CHR
ROM and all the graphical data is stored along with the code in
the PRG ROM.
The brain of an NES is a
Motorola 6502 which can physically address 16 bits of memory, or
64 Kilobytes. When the NES first came out in the mid-1980s, this
relatively small amount of memory was adequate. But games evolved
and game developers eventually wanted to do more complex things.
They wanted to make games with more area and depth as well as be
able to save a player's progress so the player didn't have to
finish the game in one sitting.
This is where devices called memory mappers came on the scene. The earlier NES cartridges had 1-32KB PRG bank and 1-8KB CHR bank. The memory mappers performed something called a bank switch to swap banks of memory in and out of a the 6502's limited address space. As it turns out, when Nintendo designed their Gameboy, based on another 8-bit processor, the Zilog Z80, they learned a lesson from the NES and built bank switching capabilities into the Gameboy's hardware.
This is a up-to-date list of known mappers for the NES. Previously there were only 5 we knew about, which are the ones mentioned in Nintendo Power. Thanks to the developer of BioNES for this information.
|0||¤Ê¤·||Super Mario Brothers|
|1||Nintendo MMC1||Dragon Warrior 4|
|4||Nintendo MMC3||Kirby's Adventure|
|5||Nintendo MMC5||Castlevania 3, Uncharted Waters|
|7||74HC161/32||Wizards and Warriors, Battle Toads|
|9||Nintendo MMC2||Mike Tyson's Punch-out|
|10||Nintendo MMC4||Fire Emblem|
|11||Color Dreams||Baby Boomer|
|16||Bandai||Dragon Ball Z series|
|18||Jaleco SS8806||Moero!! ProYakyu'90|
|23||Konami VRC2/4-B||Castlevania Special(J)|
|24||Konami VRC2/4-C||Gradius 2|
|25||Konami VRC6-A||Castlevania 3(J)|
|26||Konami VRC6-B||Esper Dream 2|
|32||iREM G-101||Image Fight(J)|
|33||Taito TC190/TC035||Power Blazer(J)|
|66||74HC161/32||Drgaon Ball, Doraemon|
|67||Sunsoft 3||Fantasy Zone 2|
|68||Sunsoft 4||After Burner|
|69||Sunsoft 5||Batman 2: Return of the Joker|
Moero!! Junior Basket
|80||Taito X1-005||Demon Sword (J)|
|82||Taito X1-17||Kyukyoku Harikiri Stadium|
|85||Konami VRC7||Lagrange Point|
|87||74HC161/32||TwinBee, City Connection(J)|
For more info, check out Marat's Documentation.
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