3-10
System Installation
Watchdog Timer Programming
There are two methods of activating the Watchdog Timer (WDT) function. One
way is to utilize the hardware jumper settings and program it using a software
command. After this feature is enabled, a system reset will be generated unless a
user created application triggers the timer periodically within the time-out period.
This allows the system to restart in case any abnormal condition is found. Another
way is to program the super I/O W83977ATF chip to start the WDT time-out
counting.
ICS Advent recommends using the first approach
. The second
approach is comparatively difficult and complicated. In addition, you may also
connect the WDT output to the NMI input by setting jumper JP6 to generate an
NMI event.
The WDT comes with eight possible ranges of time intervals from 500 ms to 64
seconds, which can be adjusted by setting jumper positions. The two port WDT can
be enabled and programmed by reading I/O port 0533H or 0543H to issue a trigger
continuously, and disabled by reading I/O port 0033H or 0343H. A 30% tolerance
timer limit must be considered for the WDT function. For instance, if the time-out
interval is set to 1 second, the WDT trigger command must be issued within
700ms.
The example below provides a reference algorithm for WDT programming via
I/O port 0533H and 0033H:
Enable WDT
Re-trigger WDT
MOV
DX, 0533H
MOV
DX, 0533H
IN
AL, DX
IN
AL, DX
Disable WDT
MOV
DX, 0033H
IN
AL, DX
