Int 10h, 12h /BL=30h    Select Scan Lines for Text Modes                  VGA

    Selects number of scan lines for text video modes, to be used on
    the next video mode set.

        Entry   AH = 12h
                AL = 0   200 scan lines (invalid for mode 07h)
                     1   350 scan lines
                     2   400 scan lines
                BL = 30h

        Return  AL = 12h   If function supported