Mitsubishi FR - S500 Instruction Manual page 134

When the inverter's permissible communication time interval is not set,
interlocks are provided to disable operation to prevent hazardous conditions.
Always set the communication check time interval before starting operation.
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.
CAUTION
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