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Where are the memory bank controllers on the Gameboy?
As the gameboys 16 bit address bus offers only limited space for ROM and RAM addressing, many games are using Memory Bank Controllers (MBCs) to expand the available address space by bank switching. These MBC chips are located in the game cartridge (ie. not in the gameboy itself).
What’s the ROM bank number on a Gameboy?
Any attempt to address these ROM Banks will select Bank 21h, 41h, and 61h instead. This 2bit register can be used to select a RAM Bank in range from 00-03h, or to specify the upper two bits (Bit 5-6) of the ROM Bank number, depending on the current ROM/RAM Mode.
How does ROM and RAM bank switching work?
ROM and RAM bank switching is controlled by a memory bank controller present on the cartridge. By writing values to areas of read-only memory, a game or program is able to specify which ROM banks to access when read operations are performed. The simplest cartridges simply contained ROM and had only had 32 KBytes of space.
How many ROM banks can be used in MBC1?
The program may freely switch between both modes, the only limitiation is that only RAM Bank 00h can be used during Mode 0, and only ROM Banks 00-1Fh can be used during Mode 1. Same as for MBC1. Same as for MBC1, but only a total of 16 ROM banks is supported.
How does the memory bank work on a MBC1?
On an MBC1, there are two modes: 16Mb ROM/8KB RAM and 4Mb ROM/32KB RAM. The game is able to switch between the modes on the fly, allowing a game to access extended ROM banks during normal operation and switch to RAM mode temporarily when data needs to be read.
Which is the first MBC chip for the Gameboy?
Click here to go to this section of Pan Docs in the new location: https://gbdev.io/pandocs/#mbc1 This is the first MBC chip for the gameboy. Any newer MBC chips are working similiar, so that is relative easy to upgrade a program from one MBC chip to another – or even to make it compatible to several different types of MBCs.
How much memory does a Gameboy cartridge have?
It is mapped directly to $0000-$7FFF . There was no MBC on these types of cartridges because the entire game would be able to fit on the cartridge. This types of cartridge could also contain up to 8KB of RAM, mapped to $A000-$BFFF, though it would require an MBC-like circuit to work.
What’s the first byte of memory on a Gameboy?
When the GameBoy powers up, program execution starts at $0100, which almost always has a jump to $0150 (jp $0150), the first byte of free space. So really, $0150 will be the start of your programs.