User Manual

AFL2-W10A-N28 Panel PC
Page 183
NOTE:
The following discussi on applies to DOS. Conta ct IEI support or visit the IEI
website for drivers for other operatin g systems.
The Watchdog Timer is a hard ware-based timer that at tempts to restart the syste m when it
stops working. The system may stop working because of external EMI or software bugs.
The Watchdog Timer ensures that standalone systems like ATMs will automatically
attempt to restart in the case of system problems.
A BIOS function call (INT 15H) is used to control the Watchdog Timer.
INT 15H:
AH – 6FH Sub-function:
AL – 2: Sets the Watchdog Timer’s period.
BL: Time-out value (Its unit-second is dependent on the item “Watchdog
Timer unit select” in CMOS setup).
Table D-1: AH-6FH Sub-function
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 starts counting down . When the timer value reaches ze ro,
the system resets. To ensure that this reset condition does not occur, calling sub-function
2 must periodically refresh the Watchdog Timer. However, the watchdog timer is disabled
if the time-out value is set to zero.
A tolerance of at least 10% must be maintained to avoid unknown routines within the
operating system (DOS), such as di sk I/O that can be very time-consuming.