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PPENDICES
(3) Automatic switching of communication route
If a communication error occurs during access to the Redundant CPU connected
to MELSECNET/H, Ethernet or CC-Link IE Controller Network in Control system
specification, the communication route is automatically switched to continue
access to the control system.
Hereinafter, this automatic switching of the communication route is referred to as
route switching.
The following describes the route switching conditions, how to check for route
switching occurrence, and examples of access by route switching.
(a) Route switching conditions
When access is being made under the following conditions, access to the
Redundant CPU is continued by route switching if a communication error
occurs.
Conditions for continued access
Operation mode Backup mode, Separate mode
Target system Control system
However, if a tracking error*1 had already occurred at a start of
communication, access to the control system is not continued by route
switching even if tracking is recovered after that.
*1: Includes the status in which either Redundant CPU is powered off or
reset.
(b) How to check for route switching occurrence and examples of
access by route switching
1) How to check whether route switching occurred or not
When communication is being made in Target system, whether
communication is continued by route switching due to communication
error can be estimated.
<Special relay and special registers to be monitored and estimated possibility of route switching>
SM1600*1 SD1590*2 SD1690*2 Possibility of route switching Reference
OFF Either one is other than 0
Since a system switching request from the network module was
detected, route switching may have been executed.
2) Fig. 1
ON 0 0
Since an other system fault occurred, route switching may have
been executed.
2) Fig. 2
ON Either one is other than 0
Since an other system fault occurred or a system switching
request from the network module was detected, route switching
may have been executed.
2) Fig. 2
2) Fig. 1
*1: Even if SM1600 is ON, route switching does not occur when the
CPU is not accessed via the tracking cable.
*2: When using SM1600, SD1590 and SD1690 to estimate whether
route switching has occurred or not for the Redundant CPU
connected to Ethernet, check the following items in the redundant
setting of the network parameter dialog box of GX Developer.
• Issue a system switching request at disconnection detection.
• Issue a system switching request at communication error.
Check the following based on the statuses of the above special relay
and special registers, and remove the error cause.
• Check the Redundant CPU for an error.
• Check the tracking cable status and whether the tracking cable is
correctly connected.
• Check the relevant network module for an error and the network
where the relevant network module is connected for an error.