INT 05h           Print Screen

    Prints the current screen contents to the first parallel printer
    (LPT1).

    This interrupt can be called from within a program as well as by means
    of the Shift-PrtSc key combination. The service returns no register
    values but sets a status code at memory location 0000:0500h. The
    possible values of this status code, and their meanings, are as
    follows:

         00h          Print Screen not called, or operation completed

         01h          Print Screen currently in progress

         FFh          Error encountered during most recent Print Screen

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       Notes:         The cursor position is saved before the Print Screen
                      is executed and restored upon completion of the
                      Print Screen.

                      The Print Screen service runs with interrupts
                      enabled.

                      While a Print Screen is in progress, additional
                      Print Screen requests are ignored.

                      The DOS GRAPHICS program replaces the normal INT 05h
                      handler and installs a handler that will print
                      graphic displays.