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        Port 3C5, 03  -  Character Map Register

        In alphanumeric modes, bit 3 of the attribute byte normaly
        defines the foregound intensity. This bit can be redefined as a
        switch between character sets allowing 512 displayable characters.
        To enable this feature:

          1. Set the extended memory bit in the Memory Mode register
             (3C5, 04) to 1.
          2. Select different values for character map A and character
             map B.

        The BIOS supports this feature.


                11xx xxxx  Reserved
                xx1x 11xx  Character map A select
                             These bits select the location of the
                             character map A. Map A is the area of map 2
                             containing the characters

                             Bits  Map    Table Location  
                             000:  0      1st 8Kb of Map 2
                             001:  1      3rd 8Kb of Map 2
                             010:  2      5th 8Kb of Map 2
                             011:  3      7th 8Kb of Map 2
                             100:  4      2nd 8Kb of Map 2
                             101:  5      4th 8Kb of Map 2
                             110:  6      6th 8Kb of Map 2
                             111:  7      8th 8Kb of Map 2
                xxx1 xx11  Character map B select
                             These bits select the location of the
                             character map B. Map B is the area of map 2
                             containing the characters

                             Bits  Map    Table Location  
                             000:  0      1st 8Kb of Map 2
                             001:  1      3rd 8Kb of Map 2
                             010:  2      5th 8Kb of Map 2
                             011:  3      7th 8Kb of Map 2
                             100:  4      2nd 8Kb of Map 2
                             101:  5      4th 8Kb of Map 2
                             110:  6      6th 8Kb of Map 2
                             111:  7      8th 8Kb of Map 2