Int 15h, C3h            Enable/disable Watchdog Time-Out                 PS/2

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

        Return  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.