Int 10h, 12h /BL=35h    Display Switch Interface                    MCGA, VGA

    Switches between two video adapters which may otherwise have
    address conflicts (PS/2).

        Entry   AH    = 12h
                AL    = 0   Initial adapter off
                        1   Initial system board video on
                        2   Switch off active video
                        3   Switch on inactive video
                BL    = 35h
                ES:DX = Pointer to 128-byte save buffer (if AL = 0 or 1)

        Return  AL = 12h   If function supported
                Buffer updated (if AL = 0 or 1)