ICP DAS USA PET-7060, User Manual

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Appendix D: Modbus Application Notes
PET-7000 DIO User Manual, May 2009, V1.00, EMH-013-10----------
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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.
AO address 40257 of the ET-7000 series Modbus register is the
address of the Host Watchdog timer, and will be stored into EEPROM. The WDT function