Int 10 Fn 12  - Cirrus Logic BIOS - Set Monitor Type                       [V]

   AH = 12h
   BL = A4h
   AL bits 3-0 = maximum vertical resolution
       (0 = 480 scanlines, 1 = 600, 2 = 768, 3 = 1024, other reserved)
   AL bits 7-4 = vertical refresh at 640x480
       (0 = 60Hz, 1 = 72Hz, other reserved)
   BH bits 3-0 = vertical refresh at 800x600
       (0 = 56Hz, 1 = 60Hz, 2 = 72Hz, other reserved)
   BH bits 7-4 = vertical refresh at 1024x768
       (0=87Hz-int, 1=60Hz, 2=70Hz, 3=72Hz, 4=76Hz, other reserved)
   CH bits 4-7 = vertical refresh at 1280x1024
       (0=87Hz-int, 1=60Hz, 2=70Hz, other reserved)

See Also: AH=12h/BL=9Ah,AH=12h/BL=A3h