Int 10 Fn A004  - Ati Mach64 Bios - ???                                    [-]

   AX = A004h
   BX = video mode??? (0000-00FFh)
   DX = ??? (sent to some port [66ECh???] one bit at a time, high to low)
   ???

Return: AH = status
       00h successful
       01h failed
   ???

See Also: AX=A000h,AX=A002h