D WATCHDOG TIMER. IEI Technology POC-W24C-ULT3

POC-W24C-ULT3 FHD Medical Panel PC

Appendix

D

D

Watchdog Timer

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POC-W24C-ULT3 FHD Medical Panel PC

NOTE:

The following discussion applies to DOS. Contact IEI support or visit the IEI website for drivers for other operating systems.

The Watchdog Timer is a hardware-based timer that attempts to restart the system 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 zero, 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 disk I/O that can be very time-consuming.

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NOTE:

The Watchdog Timer is activated through software. The software application that activates the Watchdog Timer must also deactivate it when closed. If the Watchdog Timer is not deactivated, the system will automatically restart after the Timer has finished its countdown.

EXAMPLE PROGRAM:

; INITIAL TIMER PERIOD COUNTER

;

W_LOOP:

;

MOV AX, 6F02H ;setting the time-out value

MOV BL, 30 ;time-out value is 48 seconds

INT 15H

;

; ADD THE APPLICATION PROGRAM HERE

;

CMP EXIT_AP, 1 ;is the application over?

JNE W_LOOP ;No, restart the application

MOV AX, 6F02H ;disable Watchdog Timer

MOV BL, 0 ;

INT 15H

;

; EXIT ;

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