Color compare          index 02h  GRAPH

Layout  b3-b0  CC   Color compare register

        The value in this register represents a four-bit color. This
        color value will be compared to eight neighboring horizontal
        pixels when read mode #1 is selected. The result of this
        comparison will be returned to the host processor through a
        MOV instruction. Not all four display planes need to take an
        active part in the comparison. The Color don't care register
        determines which planes should be considered in the
        comparison. This read mode is contrasted to read mode #0, in
        which the MOV instruction would return the actual data located
        in the eight pixels of the selected display plane.