MBC GB
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Dieser Artikel befasst sich mit den Memory Bank Controllern des Gameboys. Es handelt sich hierbei um einen Auszug aus der "gbspec.txt".
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Hierbei handelt es sich um ein 32kB (256kb) ROM, das von 0000h bis 7FFFh gemappt ist.
MBC1 (Memory Bank Controller 1)
MBC1 has two different maximum memory modes: 16Mbit ROM/8KByte RAM or 4Mbit ROM/32KByte RAM.
The MBC1 defaults to 16Mbit ROM/8KByte RAM mode on power up. Writing a value (XXXXXXXS - X = Don't care, S = Memory model select) into 6000-7FFF area will select the memory model to use. S = 0 selects 16/8 mode. S = 1 selects 4/32 mode.
Writing a value (XXXBBBBB - X = Don't cares, B = bank select bits) into 2000-3FFF area will select an appropriate ROM bank at 4000-7FFF. Values of 0 and 1 do the same thing and point to ROM bank 1. Rom bank 0 is not accessible from 4000-7FFF and can only be read from 0000-3FFF.
If memory model is set to 4/32: Writing a value (XXXXXXBB - X = Don't care, B = bank select bits) into 4000-5FFF area will select an appropriate RAM bank at A000-C000. Before you can read or write to a RAM bank you have to enable it by writing a XXXX1010 into 0000-1FFF area*. To disable RAM bank operations write any value but XXXX1010 into 0000-1FFF area. Disabling a RAM bank probably protects that bank from false writes during power down of the GameBoy. (NOTE: Nintendo suggests values $0A to enable and $00 to disable RAM bank!!)
If memory model is set to 16/8 mode: Writing a value (XXXXXXBB - X = Don't care, B = bank select bits) into 4000-5FFF area will set the two most significant ROM address lines.
* NOTE: The Super Smart Card doesn't require this operation because it's RAM bank is ALWAYS enabled. Include this operation anyway to allow your code to work with both.
MBC2 (Memory Bank Controller 2)
This memory controller works much like the MBC1 controller with the following exceptions:
MBC2 will work with ROM sizes up to 2Mbit.
Writing a value (XXXXBBBB - X = Don't cares, B = bank select bits) into 2100-21FF area will select an appropriate ROM bank at 4000-7FFF.
RAM switching is not provided. Unlike the MBC1 which uses external RAM, MBC2 has 512 x 4 bits of RAM which is in the controller itself. It still requires an external battery to save data during power-off though.
The least significant bit of the upper address byte must be zero to enable/disable cart RAM. For example the following addresses can be used to enable/disable cart RAM: 0000-00FF, 0200-02FF, 0400-04FF, ..., 1E00-1EFF. The suggested address range to use for MBC2 ram enable/disable is 0000-00FF.
The least significant bit of the upper address byte must be one to select a ROM bank. For example the following addresses can be used to select a ROM bank: 2100-21FF, 2300-23FF, 2500-25FF, ..., 3F00-3FFF. The suggested address range to use for MBC2 rom bank selection is 2100-21FF.
MBC3 (Memory Bank Controller 3)
Dieser Controller stimmt weitestgehend mit dem MBC1 überein. Der Unterschied besteht darin, dass man auf alle 16 Mbits zugreifen kann, ohne dass man in den 4000h-5FFFh Bereich schreiben muss. Um die Rombank in 4000h-7FFFh zu wählen, muss man ein Byte (XBBBBBBB - X = ohne Bedeutung, B = Bank-Wahl-Bits) nach 2000h-3FFFh schreiben.
Zudem hat dieser MBC ein eingebaute, batterie-betriebene Real Time Clock (RTC), die man in keinem anderen MBC findet. Manche MBC3 Cartridges unterstützen die RTC (wie z. B. Harvest Moon/jap. Version), es gibt jedoch auch einige, die sie nicht unterstützen (wie z. B. WarioLand II).
MBC5 (Memory Bank Controller 5)
This controller is the first MBC that is guaranteed to run in GameBoy Color double-speed mode but it appears the other MBC's run fine in GBC double-speed mode as well.
It is similar to the MBC3 (but no RTC) but can access up to 64mbits of ROM and up to 1mbit of RAM. The lower 8 bits of the 9-bit rom bank select is written to the 2000-2FFF area while the upper bit is written to the least significant bit of the 3000-3FFF area.
Writing a value (XXXXBBBB - X = Don't care, B = bank select bits) into 4000-5FFF area will select an appropriate RAM bank at A000-BFFF if the cart contains RAM. Ram sizes are 64kbit,256kbit, & 1mbit.
Also, this is the first MBC that allows rom bank 0 to appear in the 4000-7FFF range by writing $000 to the rom bank select.
Rumble Carts
Rumble carts use an MBC5 memory bank controller. Rumble carts can only have up to 256kbits of RAM. The highest RAM address line that allows 1mbit of RAM on MBC5 non-rumble carts is used as the motor on/off for the rumble cart.
Writing a value (XXXXMBBB - X = Don't care, M = motor, B = bank select bits) into 4000-5FFF area will select an appropriate RAM bank at A000-BFFF if the cart contains RAM. RAM sizes are 64kbit or 256kbits. To turn the rumble motor on set M = 1, M = 0 turns it off.
HuC1 (Memory Bank / Infrared Controller)
Dieser Controller, der von Hudson Soft hergestellt wurde, scheint dem MBC1 ziemlich ähnlich zu sein. Es gibt jedoch einen Hauptunterschied, der darin besteht, dass der HuC1 eine Infrarot Schnittstelle besitzt.
Die japanische Cartridge "Fighting Phoenix" (Interner Name: SUPER B DAMAN) ist z.B. mit einem HuC1 ausgestattet.
Bung Carts
The flash carts sold by Bung (http://www.bung.com.hk) on power up appear like an MBC5 cart except that writing $00 to the bank select register selects rom bank 1 instead of rom bank 0. Writing values to 3000-3FFF area does nothing.
Writing values (XXXXXXXS - X = Don't care, S = Select) to 6000-7FFF area selects MBC1 16/8 mode if S=0 except that writes to 3000-3FFF area still do nothing. If S=1 then MBC5 mode is selected. (S=1 by default on power up.)
Cart locations A000 & A100 act as special write only hardware control registers if a value of $c0 is written to 0000-1FFF area. These hardware control registers are used for setting up cart hardware for different games when the Bung cart is used as a Multicart for holding several different games.
