The Game Gear has three face buttons: buttons 1 and 2 as in the Master System, and additionally a Start button.

When running in Game Gear mode, the Start button state may be read by inputting from port $00; bit 7 reflects its state, with active-low logic (1 = not pressed, 0 = pressed).

When in Master System mode, the Start button acts identically to the Pause button.

Example code

    in     a,($00)
    cpl                    ; invert logic so 1 = pressed
    and    %10000000
    ret                    ; result in a (non-zero if pressed)

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