Siemens SIMATIC PCS 7 CPU 410-5H System Manual page 155

Special features
● Keep changes to a manageable extent. We recommend that you modify only one DP
master and/or a few DP slaves (e.g., no more than 5) per reconfiguration run.
● When using an IM 153-2, active bus modules can only be plugged in if the power supply
is off.
Note
When using redundant I/O that you have implemented as one-sided I/O at the user level
(see section Other options for connecting redundant I/Os (Page 294)), you must take the
following into consideration:
Due to the link-up and update process carried out after a system modification, the I/O
data of the previous master CPU may be temporarily deleted from the process image
until all (changed) I/Os of the "new" master CPU are written to the process image.
During the first update of the process image after a system modification, you may
(incorrectly) have the impression that the redundant I/O has failed completely or that a
redundant I/O exists. So correct evaluation of the redundancy status is not possible until
the process image has been fully updated.
This does not apply for modules that have been enabled for redundant operation (see
section Connecting redundant I/O to the PROFIBUS DP interface (Page 76)).
Preparations
To minimize the time during which the fault-tolerant system has to run in single operation,
note the following before making the hardware change:
Modules which are plugged but not configured yet do not have any unwanted influence on
the process.
CPU 410-5H Process Automation
System Manual, 09/2014, A5E31622160-AB
System modifications during redundant operation
10.2 Possible hardware modifications
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