Hardware What were to happen if you forced a Game Boy Color game to boot in GBA mode on a Game Boy Advance?

[supernintendo128]

We know that the Game Boy Advance has two modes of operation: GBA mode for regular games, and GBC mode for Game Boy and Game Boy Color games. A physical switch in the cartridge slot can activate GBC mode when pressed down. My question is what happens if you were to force a Game Boy Color game to boot in GBA mode by maybe cutting a channel on the edges of a cartridge to bypass the GBC switch on a GBA? Inversely, what if you were to plug a GBA game into a GBC?

 

[Roamin64]

Well for one the carts use different voltages. GB/GBC operate at 5v and GBA cartridges work at 3.3v. Sending 5v to a 3.3v chip could potentially damage the cart. It would most likely not do anything. The GBA would try to boot and then nothing, much like if you power it up with no cartridge inserted.

 

[veikkos]

GBA has two processors; one ARM for GBA games and Z80 for GB/GBC. So the console would try to use the ARM CPU to run different code which is not compatible.

In addition to that the console would probably try to use 3.3v to power the cart instead of correct 5v and I guess the cart interface has some differences so most likely the CPU wouldn't be able to read anything from the cart. So not much would happen.

Other way around, forcing GBA game to GBC. The console would supply too high voltage (5v instead of 3.3v) which might damage the cart as mentioned above. Again the Z80 CPU wouldn't be compatible with the ARM code in the cart so even if the console would be able to read code from the cart it wouldn't work at all.