Mitsubishi Electric FR-S520E Series Instruction Manual page 163

Communication parameters
CAUTION
Always set the communication check time interval before starting
operation to prevent hazardous conditions.
Data communication is not started automatically but is made only once
when the computer provides a communication request. If communication
is disabled during operation due to signal cable breakage etc., the inverter
cannot be stopped. When the communication check time interval has
elapsed, the inverter will come to an alarm stop (OPT).
The inverter can be coasted to a stop by switching on its RES signal or by
switching power off.
If communication is broken due to signal cable breakage, computer fault
etc., the inverter does not detect such a fault. This should be fully noted.
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