Contec bx200 SERIES, User Manual

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6. Appendix
BX-2x0-DCxxxx, BX-2x0D-DCxxxx User’s manual
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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.
You can select from the four options below for actions taken after a timeout.
- Reset signal output
- Shutdown (Windows used)
- PO0, L output
- PO0, H output
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 65535-level time-out interval, 1 - 65535 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.
CONTEC’s Web site [IPC-SLIB-01], which is bundled with this product, contains a sample program for
the watchdog timer. To view the sample program for the watchdog timer, decompress
“HWMandRTCut.zip”, which is found under \RasUtility\Samples\Module.
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.