INT 1Fh (31)             Video graphics Character Extensions

        When operating in the graphics modes of the CGA Monitor Adaptor
        the read/write character interface will form the character from
        the ASCII code point, using a set of dot patterns. The dot patterns
        for the first 128 code points are contained in ROM. To access the
        second 128 code points, this vector must be established to point
        at a table of up to 1 K bytes, where each code point is represented
        by eight bytes of graphic information. At Power-on, this vector is
        initialized to 0000:0., and is is the responsibility of the user to
        change this vector if if the additional code points are required.
        (e.g. using Grafchars.com)