Table of Contents
Advertisement
6. Appendix
Watch-Dog-Timer
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.
The application software created by user with the watchdog timer enabled, a RESET automatically
generated unless the software periodically triggers the timer within the setting 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. To maintain the
normal system operation, trigger the timer periodically by the user-created program in consideration of
the tolerance.
Ex.) If the time-out interval is set to 30 seconds, the user-created program must retrigger the watchdog
timer before 28 seconds will have elapsed in consideration of the tolerance. If the program failed to
retrigger the timer (if 28 - 32 seconds have elapsed), the system will automatically reboot.
The I/O port is defined at address 2e/2fH. You can trigger/enable disable the timer by writing address
2e/2fH.
Here is an example for flow chart and programming how to use the watch-dog-timer.
(1) Example flow chart
START
WDT Initial
}
WDT Start
WDT Stop
Yes
WDT
When performing the re-start of WDT, it repeats [WDT Start] and [WDT Stop].
Restart?
No
END
*
It is also possible not to perform [WDT Stop] instead of performing [WDT Stop] to [WDT Start], but to perform
[WDT Start] continuously at the time of a re-start.
76
If [WDT Stop] is not performed within the limit time set up
by [WDT Start], system reset occurs.
BX-955Sx Series User's manual
Advertisement
Table of Contents
