Pinout Explanations

This page will explain the basics for the MBC1, MBC3, and MBC5 cartridge requirements. Follow along with the schematics for each board:

MBC1

MBC3

MBC5

MBC1 Cartridge

• Pin 1 and pin 32 are VCC and GND, respectively.
• Pin 2 is the CLK or PHI pin. These are not used on the MBC1 cartridge.
• Pin 3 is the /WR pin, pin 4 is the /RD pin, pin 5 is the /CS pin. These signals partially determine when data is read from the ROM or when data is read/written to the RAM.
• Pins 6 through 21 are the address pins A0 through A15.
• Pins 22 through 29 are the data pins D0 through D7.
• Pin 30 is the /RST (or reset) pin. When this pin is low, the Game Boy will cease operation.
• Pin 31 is a generally unused pin in Game Boy cartridges, but on custom boards it can be connected to the EEPROM's /WE pin for compatibility with the GBxCART RW.

MBC1 - Memory Bank Controller

The MBC1 is a pretty simplistic memory mapping chip. I won't go into detail how it operates, because you can find sufficient explanations from Tauwasser's website, among others. A high level explanation is that it is used to expand the addressable memory of a Game Boy cartridge. The RA14-RA18 and AA13-AA14 outputs are used to access higher memory banks on the ROM and RAM chips. It also has ROM and RAM chip select outputs to control data access on the ROM and RAM chips, though only the RAM /CS output is commonly used.

ROM and RAM

The connections to the address and data pins here are mostly self-explanatory. However, the upper address pins are controlled by the MBC1.

• A14 through A18 on the ROM chip are controlled by the RA14 to RA18 outputs from the MBC1.
• A19 and A20 on the ROM, and A13 and A14 on the RAM, are both controlled by the MBC1's output pins 6 and 7 - but you can only select one set of pins, not both!
  • This means you can use the MBC1 for games with 512 KB (4 Mbit) of ROM space and 256 Kbit of RAM space, or 2 MB (16 Mbit) of ROM space and 64 Kbit of RAM space.

Other pins include:

• The ROM's /CE pin is controlled by the A15 address pin and the /OE pin is controlled by the /RD pin on the cart edge (pin 4).
• The ROM's /WE pin, which was not on original cartridges, is normally connected to either the /WR cart edge pin or cart edge pin 31 for programming with a cart flasher.
• The RAM's /OE pin is connected to the /RD pin on the cart edge (pin 4).
• The RAM's /WE pin is connected to /WR on the cart edge (pin 3).
• The RAM's /CE pin can be explained by viewing the Battery Management page.

MBC3 Cartridge

• Pin 1 and pin 32 are VCC and GND, respectively.
• Pin 2 is the CLK or PHI pin, which is solely connected to the CLK pin on the MBC3 chip.
• Pin 3 is the /WR pin and pin 4 is the /RD pin. These signals partially determine when data is read from the ROM or when data is read/written to the RAM.
• Pin 5 is the /CS pin, which is unused on MBC3 carts.
• Pins 6 through 21 are the address pins A0 through A15.
• Pins 22 through 29 are the data pins D0 through D7.
• Pin 30 is the /RST (or reset) pin. When this pin is low, the Game Boy will cease operation.
• Pin 31 is a generally unused pin in Game Boy cartridges, but on custom boards it can be connected to the EEPROM's /WE pin for compatibility with the GBxCART RW.

MBC3 - Memory Bank Controller

The MBC3 is a memory mapping chip, used to expand the addressable memory space of a Game Boy cartridge. The RA14-RA20 and AA13-AA14 outputs are used to access higher memory banks on the ROM and RAM chips. It also has a positive and negative RAM chip select output to control data access on the RAM, though only the RAM /CS output is commonly used. The main upgrade over the MBC1 other than addressable memory space is the addition of a real time clock, or RTC, for time-based games like Pokemon GSC and Mary Kate and Ashley's Pocket Planner. The downside to the RTC is that it greatly increases the current draw of the MBC3 when operating on battery power, which is why your older Pokemon Red might still be holding a save, while your Pokemon Silver died a decade ago.

ROM and RAM

The connections to the address and data pins here are mostly self-explanatory. However, the upper address pins on the ROM and RAM chips are controlled, or "banked", by the MBC3.

• A14 through A20 on the ROM chip are controlled by the RA14 to RA20 outputs from the MBC3.
• A13 and A14 on the RAM chip are controlled by the AA13 and AA14 outputs from the MBC3.

Other pins include:

• The ROM's /CE pin is controlled by the A15 address pin and the /OE pin is controlled by the /RD pin on the cart edge (pin 4).
• The ROM's /WE pin, which was not on original cartridges, is normally connected to either the /WR cart edge pin or cart edge pin 31 for programming with a cart flasher.
• The RAM's /OE pin is connected to the /RD pin on the cart edge (pin 4).
• The RAM's /WE pin is connected to /WR on the cart edge (pin 3).
• The RAM's /CE pin can be explained by viewing the Battery Management page.

MBC5 Cartridge

• Pin 1 and pin 32 are VCC and GND, respectively.
• Pin 2 is the CLK or PHI pin. This is not used on the MBC5 cartridge.
• Pin 3 is the /WR pin, pin 4 is the /RD pin, pin 5 is the /CS pin. These signals partially determine when data is read from the ROM or when data is read/written to the RAM.
• Pins 6 through 21 are the address pins A0 through A15.
• Pins 22 through 29 are the data pins D0 through D7.
• Pin 30 is the /RST (or reset) pin. When this pin is low, the Game Boy will cease operation.
• Pin 31 is a generally unused pin in Game Boy cartridges, but on custom boards it can be connected to the EEPROM's /WE pin for compatibility with the GBxCART RW.

MBC5 - Memory Bank Controller

The MBC5 is one of the most popular mappers for Game Boy Color cartridges, and greatly expands the accessible space of a Game Boy cartridge. I won't go into detail how it operates, because you can find sufficient explanations on memory mappers elsewhere, and it doesn't have any extraneous features like MBC3's real-time clock. It's a pretty straightforward device by just looking at the pinout. A high level explanation is that it is used to expand the addressable memory of a Game Boy cartridge. The RA14-RA22 and AA13-AA16 outputs are used to access higher memory banks on the ROM and RAM chips.

ROM and RAM

The connections to the address and data pins here are mostly self-explanatory. However, the upper address pins are controlled by the MBC5.

• A14 through A21 on the ROM chip are controlled by the RA14 to RA21 outputs from the MBC5. On my carts, the RA22 output doesn't go anywhere. This would be used for expanding the ROM space from 4 MB (32 Mbit) to the max size of 8 MB (64 Mbit), but barely any games use this much space. The only board I could find that actually supports it is DMG-A15-10.
• A13 to A16 on the SRAM chip are controlled by the AA13 to AA16 outputs from the MBC5. This means you can address up to a whole 1 Mbit of RAM! The max SRAM size wasn't used on too many games.

Other pins include:

• The ROM's /CE pin is controlled by the A15 address pin and the /OE pin is controlled by the /RD pin on the cart edge (pin 4).
• The ROM's /WE pin, which was not on original cartridges, is normally connected to either the /WR cart edge pin or cart edge pin 31 for programming with a cart flasher.
• The RAM's /OE pin is connected to the /RD pin on the cart edge (pin 4).
• The RAM's /WE pin is connected to /WR on the cart edge (pin 3).
• The RAM's /CE pin can be explained by viewing the Battery Management page.

Resources

• Jeff Frohwein's GameBoy Tech Page
• Game Boy Hardware Database
• Nintendo Gameboy Game List
• Gekkio's Game Boy Schematic Resources