ICP Electronics ROCKY - 058HV, Руководство пользователя

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Appendix A. Watch-Dog Timer
The WatchDog Timer is provided to ensure that standalone
systems can always recover from catastrophic conditions that
cause the CPU to crash. This condition may have occurred by
external EMI or a software bug. When the CPU stops working
correctly, hardware on the board will perform a hardware reset
(cold boot) to bring the system back to a known state.
The Watch-Dog Timer is controlled by three I/O ports.
443 Write Set Watch-Dog Time period
443
(hex)
Read Enable the refresh the Watch-Dog
Timer.
843
(hex)
Read Disable the Watch-Dog Timer.
To enable the Watch-Dog Timer, user has to define Timer before
enable the Watch-dog Timer function. The output data is a value
of time interval and the range of the value is from 01(hex) to
FF(hex) and time interval 1 sec to 255 sec.
Data Time Interval
01 1 sec
02 2 sec
03 3 sec
04 4 sec
.
.
. .
.
.
FF 255 sec
This will enable and activate the countdown timer which will
eventually time out and reset the CPU to ensure that this reset
condition does not occur, the Watch-Dog Timer must be
periodically refreshed by reading the same I/O port 843H and
443H. This must be done within the time out period that is
selected by software, please refer to the example program.