INT 10 - VIDEO - ALTERNATE FUNCTION SELECT (PS,EGA,VGA,MCGA) - ALTERNATE PRTSC
AH = 12h
BL = 20h  select alternate print screen routine
Notes:  installs a PrtSc routine from the video card's BIOS to replace the
default PrtSc handler from the ROM BIOS, which usually does not
understand screen heights other than 25 lines
some adapters disable print-screen instead of enhancing it

See also: 05

1012 - VIDEO - ALTERNATE FUNCTION SELECT (PS,EGA,VGA,MCGA) - ALTERNATE PRTSC