Int 10 Fn BF12  - Video - Compaq Extensions - New Active Monitor           [b]

   AX = BF12h
   BH reserved
   BL = function mask (see #0147)

Return: CF clear

Notes: this function is a NOP if the VGA subsystem is inactive or the current
     Display Combination Code is 10h or higher
   supported by at least the QVision board and the LTE Lite and ProSignia
     ROM BIOSes

See Also: AX=BF01h,AX=BF02h,#0657

Bitfields for function mask:
Bit(s) Description (Table 0147)
 7 command mode
   if set, bits 1 and 0 make the monitor active when set
   if clear, bits 1 and 0 toggle the monitor's state when set
 6-2   reserved
 1 internal monitor
 0 external monitor