Int 15h, 85h            System Request Pressed                           many

    Provides an interface for special processing of the Sys Req key.

        Entry   AH = 85h
                AL = Subservice
                     | 00h - System Request key Make (pressed)
                     | 01h - System Request key Break (released)

        Return  CF Set if service not supported, else cleared

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    By default, this service does nothing but clear the Carry Flag. It
    is up to the operating system or user to provide a handler to
    process the Sys Req key. This service is called by Int 09h
    (Keyboard) after the Sys Req key has been pressed ("made") or
    released ("broken").

    The PC, PCjr, and the XT dated 11/08/82 do not support this
    service.