Siemens SIMATIC S7-400H System Manual page 203

Special features
● Keep changes to a manageable extent. We recommend that you modify only one DP
● When using an IM 153-2, active bus modules can only be plugged in if the power supply
Preparations
To minimize the time during which the fault-tolerant system has to run in single mode, you
should perform the following steps before making the hardware change:
● Check whether the CPUs provide sufficient memory capacity for the new configuration
● Always ensure that plugged modules which are not configured yet do not have any
Procedure
Follow the steps below for any system change during operation:
1. Make the changes in HW Config.
2. Download the changed engineering to the CPU in STOP.
3. Make the system change as described in the following sections.
4. Do not save the modified project engineering until the modification has been completed
S7-400H
System Manual, 09/2007, A5E00267695-03
master and/or a few DP slaves (e.g. no more than 5) per reconfiguration run.
is off.
NOTICE
Remember the following 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 151)):
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 phenomenon does not occur with modules that have been enabled for redundant
operation (see section Connecting redundant I/Os (Page 127)).
data and user program. If necessary, first expand the memory configuration (see section
Changing the CPU memory configuration (Page 239)).
unwanted influence on the process.
successfully.
System modifications in operation
14.2 Possible hardware modifications
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