INT 15H 85H: SysReq Key

                                                                        [AT]
 Expects: AH    85H
          AL    00H = key make (pressed down)
                01H = key break (released)
          CF    NC (0)
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 Returns: AX    0085H
          CF    NC (0) if no error; CY (1) if invalid value in AL on entry
          ──────────────────────────────────────────────────────────────────
    Info: Called by INT 01H upon press and release of the SysReq key.

          A multitasking operating system might intercept this fn in order
          to monitor user-requests to switch tasks.

          When unintercepted, the BIOS simply sets AH to 0 and clears CF.

See Also: INT 15H (extended AT services)
          BIOS Data Area
          ROM-BIOS Functions
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