Programming for the Gameboy/Memory and memory-mapped register layout

Special registers ($FF00 - $FF4B )

P1 (Joypad Register)
Address $FF00
Description Used to read back the device's button inputs, i.e. if A button is held
Bit 0 P10 in port
Bit 1 P11 in port
Bit 2 P12 in port
Bit 3 P13 in port
Bit 4 P14 out port
Bit 5 P15 out port
Bit 6-7 Unused