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         RAM Loadable Character Generator

         The character generator is RAM loadable and can support
         characters up to 32 scan lines high. Three character font are
         stored in BIOS, and one is automatically loaded when an
         alphanumeric mode is selected. The Character Map Select register
         can be programmed to redefine the function of bit 3 of the
         attribute byte to character-font switch. This allows the user to
         select between any two character sets residing in map 2, and
         effectively gives the user access to 512 characters instead of
         256. Character fonts can be loaded offline, and up to eight
         fonts can be loaded at any one time.

         The structure of the character fonts is described in the
         following figure. The character generator is in map 2 and must
         be protected using the map mask function.

                                     Map 2
          +0Kb +-------------------------------------------+
               |---+---+---+---+---+---+---+---+---+---+---|   Font 0
          +8Kb |-------------------------------------------|
               |-+---+---+---+---+---+---+---+---+---+---+-|   Font 4
               |-------------------------------------------|
          +16Kb|-------------------------------------------|
               |---+---+---+---+---+---+---+---+---+---+---|   Font 1
               |-------------------------------------------|
               |-+---+---+---+---+---+---+---+---+---+---+-|   Font 5
               |-------------------------------------------|
          +32Kb|-------------------------------------------|
               |---+---+---+---+---+---+---+---+---+---+---|   Font 2
               |-------------------------------------------|
               |-+---+---+---+---+---+---+---+---+---+---+-|   Font 6
               |-------------------------------------------|
          +48Kb|-------------------------------------------|
               |---+---+---+---+---+---+---+---+---+---+---|   Font 3
               |-------------------------------------------|
               |-+---+---+---+---+---+---+---+---+---+---+-|   Font 7
          +64Kb+-------------------------------------------+


          The following figure illustrates the structure of each
          character pattern. If the CRT controller is programmed to
          generate 16 row scans, the 16 bytes must be filled in for
          each character in the font. The example below assumes eight
          row scans per character.

          Address                  Byte Image                    Data
                        80h 40h 20h 10h 08h 04h 02h 01h              

          CC*32 + 0                 XXX XXX                       18h
                  1             XXX XXX XXX XXX                   3Eh
                  2         XXX XXX         XXX XXX               66h
                  3         XXX XXX         XXX XXX               66h
                  4         XXX XXX XXX XXX XXX XXX               7Eh
                  5         XXX XXX         XXX XXX               66h
                  6         XXX XXX         XXX XXX               66h
                  7         XXX XXX         XXX XXX               66h

          CC equals the value of the character of the character code.
          For example 41h equals an ASCII "A".