GB Memory

GB Memory is the Game Boy counterpart to the SFC Memory, which allowed customers to buy games cheaper by writing them onto their carts at NP Memory Kiosks. Exclusive NP games were also released such as Balloon Fight GB, which offers game progress saving and additional features.

Super Game Boy
The GB Memory is Super Game Boy compatible, allowing Games that have enhancements to fully work; loading a game using a Super Game Boy will hard JUMP to the selected game. A single invalid song SOUND command is loaded before the JUMP takes place.

MLT_REQ
Located at is a set of two init MLT_REQ commands which is used to request joypad reads from the second SNES controller, since a normal Game Boy unit would not have the additional joypad registers telling the game that it is running on a Super Game Boy allowing additional packet commands to be invoked. Can also be used for multiplayer games up to four players requiring a SNES multitap accesory.

MASK_EN
A border might have been planned early on, though the commands are loaded right before the DATA_SND commands are sent where  is the last command. It is unknown why the commands were implemented since they are not needed if you are simply sending SNES WRAM bank destinations.

JUMP
Used to set the SNES Prgram Counter to a specified address. Alternatively, the command can be used to set a new address for the SNES NMI handler, the NMI handler remains unchanged if all bytes 4-6 are zero. Examples of JUMP can be seen in Nekketsu! Beach Volley dayo Kunio-kun and Space Invaders (Super Game Boy) allowing custom code to load into the Super Game Boy's WRAM banks and executed.

SOUND
A single SOUND command is called directly before the JUMP command. This command sets the internal system BGM to preparing the APU for a transition vector for the new SHCV code allowing the program to take direct control of the APU. If a BGM is already in progress, setting the flag will stop all system sounds. There is a glitch that if a BGM flag is set before the program changes, the Super Game Boy BIOS will hang. The custom program sent can workaround this by using additional DATA_SND commands or using a custom NMI handler, as is done by Space Invaders.

DATA_SND
Located at is a list of DATA_SND packets. Since the game select menu on the cart takes up one block, Nintendo probably wanted to reserve as much space as possible for the games, so unnecessary enhancements were cut.

The second listing sets the NMI to reset the Super Game BIOS to the selected ROM bank (game) in the GB Memory BIOS. This listing is also used for sending banks in preparation for the SOU_TRN command.

A third listing is loaded upon bootup, located at. This listing directs the Super Game Boy BIOS to reset when the JUMP command is called setting the NMI counter, causing the reset to the selected ROM bank (game).