Contec BX-956SD-DC 781724, Руководство пользователя

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6. Appendix
72
BX-956S User’s manual
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.
With this function, running programs can be restarted in the usual way even if an abnormal state occurs.
The software can be configured using 255 levels (1 to 255 seconds) of timeout intervals for the watchdog
timer. There is also a 2-second tolerance for timeout intervals. To maintain normal system operation,
trigger the watchdog timer again using a user-written program with the tolerance in mind.
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
* 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.
(2) Example programming
The following example is written in Intel8086 assembly language.
;===============
;<WDT Initial>
;===============
;-------------------------------------------
;Enter the extended function mode
WDT
Restart?
END
START
No
WDT Stop
WDT Initial
WDT Start
Yes
If [WDT Stop] is not performed within the limit time set up
by [WDT Start], system reset occurs.
}
When performing the re-start of WDT, it repeats [WDT Start] and [WDT Stop].