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INT 10h,  12h (18)       Alternate Select                                 EGA

    Returns information on the Enhanced Display Adapter (EGA) and allows
    the selection of an alternative EGA Print Screen routine.

       On entry:      AH       12h
                      BL       Subservice
                               10h - Return EGA information
                               20h - Select alternative EGA Print Screen
                                     routine
                             VGA Only:
                               30h - Set number of scan lines
                                     0-200, 0-350, 2-400
                                     Activates after mode change
                               31h - AX = 0/1 -> allow/prevent palette load
                                                 with new mode
                               32h - AL = 0/1 -> Video On/Off
                               33h - AL = 0/1 -> Gray scale summing On/Off
                               34h - AL = 0/1 -> Scale cursor to font On/Off
                               35h - Switch betwen adapter and motherboard
                                     video
                                     AL = 0 adapter off, es:dx save state
                                        = 1 motherboard on
                                        = 2 active video off, es:dx save..
                                        = 3 inactive video on, es:dx ..
                               36h - Turn Screen On / Off
                                     AL = 0/1 -> Screen On/Off

       Returns:       (for Subservice 10h only):
                      BH       Display mode in effect
                               00h    Color mode (3Dxh address range)
                               01h    Monochrome mode (3Bxh address range)
                      BL       EGA memory
                               00h    64K
                               01h    128K
                               02h    192K
                               03h    256K
                      CH       Adapter bits
                      CL       Switch setting

  --------------------------------------------------------------------------

       Notes:         The value returned in CL (Switch setting) represents
                      the DIP switch settings on the EGA. The Adapter bits
                      (CH) is defined as follows:

                              Adapter bits (CH)

                          7 6 5 4 3 2 1 0
                          x x x x . . . .       Unused
                          . . . . x x . .       Reserved
                          . . , . . . x .       FEAT1 (pin 17)
                          . . . . . . . x       FEAT0 (pin 19)

                      To print the screen contents when the number of rows
                      changes, use Subservice 20h (Set Alternative Print
                      Screen) to install a Print Screen routine that will
                      work correctly with the row change.