CHAPTER 7 - Chapter 7 Watch-Dog-Timer (WDT) Setting
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Chapter 7 Watch-Dog-Timer (WDT) Setting
The watchdog timer serves as a safeguard against possible system lock-up in your industrial
computer system. In most industrial environments, there are heavy equipment, generators,
high-voltage power lines, or power drops that have adverse effects on your computer system.
For instance, when a power drop occurs, it could cause the CPU to come to a halt state or enter
into an infinite loop, resulting in a system lock-up.
With the watchdog timer enabled, a RESET can be automatically generated unless the CPU
periodically triggers the timer within the time-out interval. That is, while the system gets
hung up, the running program can’t trigger the timer periodically. The timer will generate a
reset signal to reboot the system. This feature allows a running program to restart in an
orderly way when a power glitch or any abnormal condition occurs.
The watchdog timer comes with 255-level time-out interval, 1 to 255 seconds per interval,
which can be adjusted by software setting. There is a tolerance of 2 second for this time-out
interval. For example, if the time-out interval has been set to 32 seconds, your program should
trigger the watchdog timer before 28 seconds are escaped. Otherwise, after 28-32 seconds are
escaped, the system will automatically reboot. To keep the system running normally, your
program should trigger the watchdog timer every 28 seconds.
(1)Start WDT – (before 28 seconds) – (2)Stop WDT + (3)Start WDT – (1)(2)(3)Repeat
The I/O port is defined at address 2e/2fh. You can trigger/enable disable the timer by writing
port2e/2fh.