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5.3 The System Switching Function
5.3.6 System Switching Precautions
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(3) Enabling System Switching During Online Program Change
System switching is disabled during online program change.
In order to prevent system switching during online program change, the redundant
system disables the redundant CPU module from performing system switching prior
to online program change, and enables it to perform system switching upon
completion of online program change.
If the communication is interrupted between the redundant CPU module and
GX Developer due to cable disconnection or other reason during online program
change, the redundant system CPU module cannot complete the online program
change and may remain to be disabled from performing system switching.
As long as the redundant CPU module is in this status, either of manual system
switching or system switching by network module system switching request cannot be
performed.
In this case, enable the system switching by performing the following operation, in
order to enable the manual system switching or system switching by network module
system switching request.
• Turn on the control system CPU module special relay "Disable prohibition of
system switching during Online program change" (SM1709).
• Perform online program change again to complete it.