INT 15h, C3h (195)         Enable/disable Watchdog Time-Out       PS/2

               On entry:          AH    C3h
                                  AL    00h . Disable watchdog time-out
                                        01h . Enable watchdog time-out
                                            BX = Watchdog timer count (1-255)

               Returns:       For PCjr and PC:
                                  AH = 80h, CF = 1
                              For PC XT, AT, XT 286, Convertible, PS/2 30:
                                  AH = 86h, CF = 1
                              For All Others:
                                  CF = 0 . Operation successful
                                     = 1 . Operation unsuccessful

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     The watchdog time-out is specifically inteded for use in operating
     system software, and is rarely of use in application programs.
     However, you can enable or disable the watchdog time-out with this
     service.