Part 09 Joypad

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Part 09 - Joypad

The joypad is one of the simplest pieces of the Gameboy. It uses one address (0xFF00). A game will write to this address and cleart bit 4 or bit 5 to select direction buttons or input buttons repectively. The bottom 4 bits indicate which buttons are pressed or not.

Bit 7 - Not used
Bit 6 - Not used
Bit 5 - P15 Select Button Keys      (0=Select)
Bit 4 - P14 Select Direction Keys   (0=Select)
Bit 3 - P13 Input Down  or Start    (0=Pressed) (Read Only)
Bit 2 - P12 Input Up    or Select   (0=Pressed) (Read Only)
Bit 1 - P11 Input Left  or Button B (0=Pressed) (Read Only)
Bit 0 - P10 Input Right or Button A (0=Pressed) (Read Only)