IEI Technology JUKI-6770 User Manual

IEI Technology JUKI-6770 User Manual Manual pdf 49 page image

48Appendix A. WatchDog TimerThe WatchDog Timer is provided to ensure that standalonesystems can always recover from catastrophic conditions thatcause the CPU to crash. This condition may have occurred byexternal EMI or a software bug. When the CPU stops workingcorrectly, hardware on the board will either perform a hardwarereset (cold boot) or a Non-Maskable Interrupt (NMI) to bring thesystem back to a known state.A BIOS function call (INT 15H) is used to control the WatchDogTimer:INT 15H:AH – 6FHSub-function:AL – 2 : Set the Watchdog Timer’s periodBL : Time-out value(Its unit--second or minute, isdependent on the item “WatchDog Timer unitselect” in CMOS setup).You have to call sub-function 2 to set the time -out period ofWatchdog Timer first. If the time -out value is not zero, theWatchdog Timer will start counting down. While the timer valuereaches zero, the system will reset. To ensure that this resetcondition does not occur, the WatchDog Timer must beperiodically refreshed by calling sub-function 2. However theWatchdog timer will be disabled if you set the time -out value tobe zero.A tolerance of at least 10% must be maintained to avoidunknown routines within the operating system (DOS), suchas disk I/O that can be very time-consuming.