INT 18 - NEC PC-9800 series - VIDEO
        AH = function
            0Ah set video mode
            0Bh get video mode
            0Ch start text screen display
            0Dh end text screen display
            0Eh set single display area
            0Fh set multiple display area
            10h set cursor shape
            11h display cursor
            12h terminate cursor
            13h set cursor position
            14h read font patter
            16h initialize text video RAM
            1Ah define user character
        ???
Return: ???
Notes:  details are not available at this time
        text video RAM is located at segments A000h (characters) and A200h
          (attributes)