User`s guide

54 • Appendix B
B
WatchDog Timer Programming
Guide
The Watchdog Timer (WDT) can monitor the system’s status. Once a value is
given to the WDT, the timer will begin to count down. If the system idles or
hangs, the system will reboot itself when the timer times out.
The Watch Dog timer includes an 8-bit timer clocked by a 1-minute internal
clock that is derived from the battery-backed 32.768KHz crystal clock
generator. The timer is loaded with the WATCHDOG Time-Out data value
written in the WDTO register and counts down to zero. This 8-bit data enables
time-out values between 1 to 255 minutes to be programmed (00h is an
invalid data value)
Following events can trigger the WATCHDOG by reloading the timer:
• Keyboard interrupt
• Mouse interrupt
• Serial Port 1 interrupt.
• Serial Port 2 interrupt.
• Software writing to control register
All control registers are accessed through the following I/O ports.
I/O mapped Port
Index port Data Port
2EH 2FH