IEI Technology ICPMB-8650, Manual

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Appendix A. Watchdog Timer
The Watchdog Timer is provided to ensure that standalone systems can
always recover from catastrophic conditions that cause the CPU to
crash. This condition may have occurred by external EMI or a software
bug. When the CPU stops working correctly, hardware on the board will
either perform a hardware reset (cold boot) or a Non-Maskable Interrupt
(NMI) to bring the system back to a known state.
A BIOS function call (INT 15H) is used to control the Watchdog Timer:
INT 15H :
AH – 6FH
Sub-function:
AL – 2 : Set the Watchdog Timer’s period
BL : Time-out value(Its unit--second or minute, is
dependent on the item “Watchdog Timer unit
select” in CMOS setup).
You have to call sub-function 2 to set the time-out period of Watchdog
Timer first. If the time-out value is not zero, the Watchdog Timer will start
counting down. While the timer value reaches zero, the system will reset.
To ensure that this reset condition does not occur, the Watchdog Timer
must be periodically refreshed by calling sub-function 2. However the
Watchdog timer will be disabled if you set the time-out value to be zero.
A tolerance of at least 10% must be maintained to avoid unknown
routines within the operating system (DOS), such as disk I/O that
can be very time-consuming.
Note: when exiting a program it is necessary to disable the Watchdog
Timer, otherwise the system will reset.