Mega Memory Card (Game Boy)

The Mega Memory Card is a third-party Game Boy accessory which allows you to back up the SRAM save data from a game cartridge into the Mega Memory's internal flash memory. The cartridge has an upside-down cartridge slot to connect the cartridge you want to back up memory from, similar to GameShark and other Game Boy cheat devices. The device has a switch which allows you to bypass the Mega Memory software and run the game on the cartridge in the second slot.

The device comes in two different styles: a yellow, semi-transparent cartridge; and a black, glittery cartridge which was sold in French-language packaging.

One peculiar aspect of the device is that it uses a trick to switch the cartridge base memory area during the boot process to display a custom logo in the startup animation, instead of the usual Nintendo logo.

Factory Test Screen
Hold Select + Start + B + A while the cartridge is booting. The test screen attempts to query the internal flash chip for its ID, as well as enumerate the SRAM banks in the secondary cartridge. The correct value is, which corresponds to the SST 28SF040 EEPROM/flash memory in the cartridge. If the debug screen is executed in an emulator, the result will likely be, which corresponds to the first two bytes in the program ROM.

Mushroom/Kingpin
The Mega Memory uses the 16-byte string "Mushroom/Kingpin" ( in the ROM) as a test string to determine whether there is writable SRAM present in the secondary cartridge. It is unknown whether this is a purely random choice of words or a reference to something, such as a greeting to a member of a scene group. This string appears to not be accessed anywhere else in the ROM.