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Int 10h, 11h            Character Generator

    General description

    Subservices 00h, 01h, and 02h perform a mode set, completely
    altering the video state but not clearing the display buffer.

    Subservices 10h, 11h, and 12h are the same as 00h, 01h, and 02h,
    respectively, except for the following differences:

        *  Subservices 10h, 11h, and 12h rely on page 0 as being
           the active page
        *  The number of bytes per character is recalculated
        *  The number of rows is recalculated
        *  The length of the regeneration buffer is recalculated
        *  Five cursor control (CRTC) registers are reprogrammed

    Subservices 10h-23h should only be called immediately after a mode
    set.

    Subservice 03h (Set the block specifier) lets you display two
    character sets at the same time, each from one block of 256
    characters, thus allowing for a 512-character set. When a
    512-character set is used, it is recommended that you set the
    color planes with 8 consistent colors by executing Service 10h,
    Subservice 00h (AX=1000h) and setting BX = 0712h.

    Each increment of 64K EGA/VGA memory allows another font block to
    be used. The default of 64K allows one font block, whereas an
    EGA/MCGA memory of 256K allows up to four font block. Each block
    holds definitions for 256 characters. The VGA allows up to 8 font
    blocks.

    When defining the character set in graphics modes, a full set of
    256 characters must be supplied (compare this with character-set
    definitions in the text modes, where any number of characters--up
    to 256 per block--may be loaded).

    Subservice 21h will load 256 character definitions. Video modes 4,
    5, and 6 use only the first 128 characters. All other modes use
    all 256 characters.