3301770
NOTE:
The following discussion applies to DOS environment. It is recommended
you contact GAI support or visit our website for specific drivers for more
sophisticated operating systems, e.g., Windows and Linux.
The Watchdog Timer is a device to ensure that standalone systems can always recover from
catastrophic conditions that cause the CPU to crash. This condition may have occurred by EMI
or a software bug. When the CPU stops working normally, hardware on the board will perform
hardware reset (cold boot) to bring the system back to a known state.
Three I/O ports control the Watchdog Timer:
443 Write Set Watchdog time period
443 (hex) Read Enable the refresh to the Watchdog Timer
043/843 (hex) Read Disable the Watchdog Timer
Table -1 I/O Ports to Watchdog Timer
Prior to enable the Watchdog Timer, users have to define the Timer first. The output data is a
value of time interval and the range of the value is from 01 (hex) to FF (hex) and the range for time
interval ranges from 1 second to 255 seconds.
DATA TIME INTERVAL
01 1 sec
02 2 sec
03 3 sec
04 4 sec
- - - - - -
FF 255 sec
Table -2 Watchdog Timer Output Data
This will enable and activate the countdown timer which eventually time out and reset the CPU to
ensure that this reset condition does not occur; the Watchdog Timer must be periodically
refreshed by reading the same I/O port 043/843H and 443H. This must be done within the time
A-2
