INT 10H 1aH: Set or Query Display Combination Code

                                                          Compatibility: VGA 
 Expects: AH    1aH
          AL    Subfn: 00H= Query current display combination
                       01H= Select DCC (activate a different display)
          BX                BL=ID of active display;
                            BH=ID of inactive display
 Returns: AL    1aH (if this fn is supported)
          BL    ID of active display
          BH    ID of inactive display
    Info: This returns or updates the DCC byte at 0040:008a.

          When AL=00H, the current DCC code is returned in BX.
          When AL=01H, the BIOS examines the DCC table to see if the
          specified combination is valid, and then deactivates the video
          subsystem identified in BH and activates that in BL.

          The following display ID codes are recognized

           00H no display   (BH=00H if only one display is installed)
           01H MDPA on monochrome screen
           02H CGA color                  07H VGA analog monochrome
           04H EGA color                  08H VGA analog color
           05H EGA monochrome             0bH Model 30 analog monochrome
           06H PGC color                  0cH Model 30  analog color

   Notes: DCC handling is mainly a feature of PS/2 hardware; it was
          designed as a means to disable the VGA controller on the PS/2's
          motherboard in order to take advantage of future improvements in
          video technology.

          Not many VGA BIOSes provide full support of display combination
          switching, though most support subfn AL=00H to indicate type 08H
          in BL.

See Also: INT 10H: Video Services
          EGA/VGA Data Areas