INT 33h,  03h (3)        Get Mouse Position and Button Status

    Returns the state of the mouse buttons and the coordinates of the cursor

       On entry:      AX         03h

       Returns:       BX         Button Status
                      CX         Horizontal Position
                      DX         VerticalPosition

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    Function 3 returne the state of the left and right mouse buttons and the
    horizontal and vertical coordinates of the cursor.

    The button state is a single integer value. Bit 0 represents the left
    button; bit 1 represents the right button. Theese bits are 1 if the
    corresponding button is down, and 0 if it is up.

    The cursor coordinates are allways within the range of minimum and
    maximum values for the virtual screen.