AFL3-12C-ULT3 Panel PCPage 119NOTE:The following discussion applies to DOS. Contact IEI support or visit the IEIwebsite for drivers for other operating systems.The Watchdog Timer is a hardware-based timer that attempts to restart the system when itstops working. The system may stop working because of external EMI or software bugs.The Watchdog Timer ensures that standalone systems like ATMs will automaticallyattempt 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 “WatchdogTimer unit select” in CMOS setup).Table D-1: AH-6FH Sub-functionCall sub-function 2 to set the time-out period of Watchdog Timer first. If the time-out valueis not zero, the Watchdog Timer starts counting down. When the timer value reaches zero,the system resets. To ensure that this reset condition does not occur, calling sub-function2 must periodically refresh the Watchdog Timer. However, the watchdog timer is disabledif the time-out value is set to zero.A tolerance of at least 10% must be maintained to avoid unknown routines within theoperating system (DOS), such as disk I/O that can be very time-consuming.
