Appendix D: Modbus Application Notes
ET-7000 AIO User Manual, Apr. 2009, V1.04, EMH-011-104----------136
Appendix D: Modbus Application Notes
Dual Watchdog
Dual Watchdog consists of Module Watchdog and Host Watchdog.
The Module Watchdog is a built-in hardware circuit that will reset the CPU module if a failure
occurs in either the hardware or the software. If the application does not refresh the watchdog
timer within 0.8 seconds, the watchdog circuit will initiate a reset of the CPU.
The Host Watchdog is a software function that can be used to monitor the operating status
of the host. Its purpose is to prevent network communication problems or a host failure. If the
Watchdog timeout interval expires, the module will return all outputs to a predefined Safe
value (Refer to the Safe Value application note), which can prevent the controlled target from
unexpected situation.
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