Chapter 16
Watchdog Timer
Kontron User's Guide PC/104-520
31
16.
Watchdog Timer
The watchdog timer (WDT) is integrated in the Winbond W83977F controller of the PC/104-520 and can
issue a reset to the system. The watchdog timer circuit has to be triggered within a specified time by the
application software. If the watchdog timer is not triggered because proper software execution fails or a
hardware malfunction occurs, it resets the system.
16.1
Programming
16.1.1
Initialization
You can initialize the watchdog timer from the application software (sourcecode on request) or BIOS setup.
Setup option uses a fixed timeout period of 32 seconds.
Likewise a JIDA call (INT 15h) is available. Register values:
AX
=
0E000h
BX = 0h
Watchdog off / BX = 1h
timeout 1 sec. / BX = 2h
2 sec. / BX = 3h
4 sec.
BX = 4h
8 sec. / BX = 5h
16 sec. / BX = 6h
32 sec.
CX = 0h
DX = 0h
16.1.2
Trigger
The watchdog needs to be triggered out of the application software within a specified timeout period. You
can only do this in the application software by using low-level programming.
Likewise a JIDA call (INT 15h) is available. Register values:
AX
=
0E001h
BX = CX = DX = 0h
16.1.3
Utility SC520Wdt
SC520Wdt is a program to activate, deactivate and trigger the watchdog. Syntax:
SC520Wdt
[options]
/A
Enable
Watchdog
/D
Disable
Watchdog
/R
Trigger
Watchdog
