VGA Attribute Controller Registers

         Each register for the attribute controller has two
         addresses. Address 3C0 is the write address and
         address 3C1 is the read address. The individual data
         registers are selected by writing their index to the
         Address register.

         3C0          Address Register
         3C0, 00-0F   Palette register
         3C0, 10      Attribute Mode Control
         3C0, 11      Overscan Color
         3C0, 12      Color Plane Enable
         3C0, 13      Horizontal PEL Panning
         3C0, 14      Color Select