INT 10 - VIDEO - ALTERNATE FUNCTION SELECT (VGA, MCGA) - GRAY-SCALE SUMMING
AH = 12h
BL = 33h
AL = 00h enable gray scale summing
01h disable gray scale summing
Return: AL = 12h if function supported
SeeAlso: AX=BF06h

See also: 10101B

1012 - VIDEO - ALTERNATE FUNCTION SELECT (VGA, MCGA) - GRAY-SCALE SUMMING