ICP DAS USA SAGP-845EV Manuel D’Utilisation

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). 

 
The sub-function 2 needs to be called to set the time-out period 
of Watchdog Timer first. If the time-out value is not zero, the 
Watchdog Timer will start to count 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 the user set the time-out value 
to 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.