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Int 15h, C3h            Programmable Option Select (POS)                 PS/2

    Interface to the Programmable Option Select (POS) of the Micro
    Channel.

    ------------------------------------------------------------------
    Get Base POS Address

        Entry   AX = C400h

        Return  For PCjr and PC:
                   AH = 80h, CF = 1
                For PC XT, AT, XT 286, Convertible, PS/2 30:
                   AH = 86h, CF = 1
                For All Others:
                   CF = 0  Operation successful
                           AL = 0
                           DX = Base POS register address
                   CF = 1  Operation unsuccessful

    ------------------------------------------------------------------
    Enable Slot for Setup

        Entry   AX = C401h

        Return  For PCjr and PC:
                   AH = 80h, CF = 1
                For PC XT, AT, XT 286, Convertible, PS/2 30:
                   AH = 86h, CF = 1
                For All Others:
                   CF = 0  Operation successful
                           AL = 1
                           DX = Slot number
                   CF = 1  Operation unsuccessful

    ------------------------------------------------------------------
    Adapter Enable

        Entry   AX = C402h

        Return  For PCjr and PC:
                   AH = 80h, CF = 1
                For PC XT, AT, XT 286, Convertible, PS/2 30:
                   AH = 86h, CF = 1
                For All Others:
                   CF = 0  Operation successful
                           AL = 2
                   CF = 1  Operation unsuccessful

    ------------------------------------------------------------------

    This service provides a consistent interface to the Programmable
    Option Select of the Micro Channel (MCA) in PS/2 models 50, 60,
    70, and 80.

    It is a special feature of the Micro Channel that you can now set
    in software information that required dip switches before. For
    example, you can enable or disable options in MCA slots. This
    service allows you to take advantage of this new capability.