Mitsubishi Electric MELSEC iQ-R Series User Manual page 5

[Design Precautions]
WARNING
● Especially, when a remote programmable controller is controlled by an external device, immediate
action cannot be taken if a problem occurs in the programmable controller due to a communication
failure. To prevent this, configure an interlock circuit in the program, and determine corrective actions
to be taken between the external device and CPU module in case of a communication failure.
● Do not write any data to the "system area" and "write-protect area" of the buffer memory in the
module. Also, do not use any "use prohibited" signals as an output signal from the CPU module to
each module. Doing so may cause malfunction of the programmable controller system. For the
"system area", "write-protect area", and the "use prohibited" signals, refer to the user's manual for the
module used. For areas used for safety communications, they are protected from being written by
users, and thus safety communications failure caused by data writing does not occur.
● If a communication cable is disconnected, the network may be unstable, resulting in a communication
failure of multiple nodes. Configure an interlock circuit in the program to ensure that the entire system
will always operate safely even if communications fail. Incorrect output or malfunction due to a
communication failure may result in an accident. When safety communications are used, an interlock
by the safety station interlock function protects the system from an incorrect output or malfunction.
● If a communication failure occurs on a DeviceNet network, faulty nodes will behave as (1) and (2)
below. Configure an interlock circuit in the program using the communication status information of
slave nodes and provide a safety mechanism external to the slave node to ensure that the entire
system will operate safely.
(1) The master node (RJ71DN91) holds input data which had been received from slave nodes before
the communication failure occurred.
(2) Whether output signals of a slave node are turned off or held is determined by the specifications
of slave nodes or the parameter settings of the master node. When the RJ71DN91 is used as a
slave node, it holds input data that had been received from the master node before the
communication failure occurred.
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