Int 10 Fn 4F15  - Vesa Vbe/dc (display Data Channel) - Read Vdif           [V]

   AX = 4F15h
   BL = 02h
   ???

Return: AL = 4Fh if function supported
       AH = status
       00h successful
           ???
       01h failed

See Also: AX=4F15h/BL=00h,AX=4F15h/BL=01h