INT 10H 12H BL=20H: Select Alternate Print Screen Handler

                                                      Compatibility: EGA VGA 
 Expects: AH    12H
          BL    20H
 Returns: (none)
    Info: This redirects the INT 05H (print screen) vector to a handler
          within the EGA/VGA ROM-BIOS.

          On older PCs, XTs, and ATs, the default ROM-BIOS print-screen
          handler stops printing after 25 lines.  The EGA/VGA handler
          correctly prints the number of lines specified in the byte at
          0040:0084 in the BIOS Data Area.

   Notes: Most EGAs and VGAs set this automatically.  However, it is good
          practice to use this fn whenever you change the number of video
          lines that are displayed in text mode.

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