ICP Electronics NOVA-3710, Руководство пользователя

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NOVA-3710/3710SV Socket 370 Celeron
TM
& Pentium III
®
Multimedia & Dual VGA , Ethernet Embedded Board
71
Appendix A. Watch-Dog Timer
The Watchdog Timer is a device ensures the standalone systems can
always recover from abnormal conditions that cause the system to crash.
These conditions may result from an external EMI or a software bug.
When the system stops working, hardware on the board will perform
hardware reset (cold boot) to bring the system back to a known state.
Three I/O ports control the operation of Watch-Dog Timer.
440 (hex) Write
Set Watchdog Time period
Enable the refresh the Watchdog Timer.
440 (hex) Write Disable the Watch-Dog Timer.
Prior to enable the Watch-Dog Timer, user has to set the time-out period.
The resolution of the timer is 1 minute and the range of the timer is from 1
min to 255 min. You need to send the time-out value to the I/O port –
440H, and then enable it by write data from the same I/O port –
440H( value is 01h-ffh ). This will activate the timer that will eventually time
out and reset the CPU board. To ensure that this reset condition won’t
occur, the Watch-Dog Timer must be periodically refreshed by write the
same I/O port 440H( the same value is 01h-ffh ). This must be done within
the time-out period, please refer to the example program. Finally, we
have to disable the Watch-Dog timer by write the I/O port -- 440H ( value
is 0h ). Otherwise the system could reset unconditionally.
• Watch-Dog Timer Type Setting By RESET
• Write port 440 : WDT Enable & Time-out Period
PERIOD Value
1 – 255 min. 01 – FF