Contec SEH-9450-LAS - Manual (Page 38)

6. Watch-Dog-Timer (WDT) Setting
SEH-9450-LAS
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6. Watch-Dog-Timer (WDT) Setting
Introduction
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 - 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.
The I/O port is defined at address 2e/2fH. You can trigger/enable disable the timer by writing
port2e/2fH.
Here is an example for flow chart and programming how to use the watch-dog-timer.
(1) Example flow chart
WDT
Restart?
END
START
No
WDT Stop
WDT Initial
WDT Start
Yes
If it passes over the time,
"System Reset" will occur.
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