Mitsubishi Electric MELSEC iQ-RJ71EN71 User Manual page 233

Communications using the fixed buffer
■Receive processing by the standby system
If data is sent to the standby system Ethernet-equipped module, data reception processing will not be performed because the
module reads and discards the received data.
■Receive processing with interrupt program
If system switching occurs before execution with the interrupt program, and the control system is switched to the standby
system, the interrupt factor will not be transferred to the other system. The interrupt factor will be retained on the own system.
Therefore, if system switching occurs again and the own system becomes the control system, the interrupt program will be
executed by the retained interrupt factor.
■When data is sent from an external device
The data sending method will differ according to whether the communication method and the control system IP address are
usable.
Communication method
Fixed Buffer (Procedure Exist)
Fixed Buffer (No Procedure)
When performing the resend processing when system switching occurs, pay attention to the following.
• When communicating while synchronizing send and receive, system switching may occur in the middle of
communication, and systems may be switched in a state where send and receive are not synchronized
together. When system switching occurs, out of safety considerations, restart communication after
initialization of synchronization.
• When using dedicated instructions, note that the completion of the execution of a write instruction needs to
be executed is difficult to judge, and that the same instruction needs to be executed again. Note, however,
that the same instruction may be executed twice.
Availability of control system
IP address
Not Use
Use

Send method
When system switching occurs because of a response timeout to the
Ethernet-equipped module, send by changing the connection destination to
the other system.
When system switching occurs because of a response timeout to the
Ethernet-equipped module, open a new control system.
Also, check whether the Ethernet-equipped module is alive from the external
device side.
System switching timing cannot be ascertained because of no setting for the
response timeout. Send data to the Ethernet-equipped modules of both
systems.
1.17 Redundant System Function
1
1 FUNCTIONS
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