INT 10H 12H BL=35H: Switch PS/2 Displays

                                                          Compatibility: VGA 
 Expects: AH    12H
          BL    00H
          AL    subfn: 00H = prepare for adapter switching off
                             ES:DX => 128-byte buffer to hold state data
                       01H = prepare for system board video switching off
                       02H = switch off active video
                             ES:DX => 128-byte buffer to hold state data
                       03H = switch on active display
                             ES:DX => 128-byte buffer containing saved data
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 Returns: AH    12H if a valid value was passed in AL
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    Info: ON PS/2 systems, this provides a means to switch between the
          built-in VGA (on the motherboard) and another, incompatible
          display system.

See Also: INT 10H 12H (EGA/VGA Special Functions/Alternate Select)
          INT 10H: Video Services
          EGA/VGA Data Areas
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