Siemens SIMATIC S7-400H System Manual page 100

Link-up and update
9.3 Link-up and update
For information on the required steps, based on the scenarios described above (alteration of
the hardware configuration, or of the type of memory for load memory), refer to section Failure
and replacement of components during operation (Page 185).
Note
Event though you may not have modified the hardware configuration or the type of load
memory on the standby CPU, a master/standby changeover is carried out and the previous
master CPU changes to STOP.
Switch to CPU with expanded memory configuration
You may have expanded the load memory on the standby CPU. The memory media for
storing load memory must be identical, i.e. either RAM cards or FLASH cards. If you
expanded with FLASH cards, their contents must be identical.
During the link-up, the system transfers the user program blocks (OBs, FCs, FBs, DBs, SDBs)
from load memory and work memory of the master to the standby CPU. Exception: If the load
memory modules are FLASH cards, the system only transfers the blocks from work memory.
For information on changing the type of memory module or on load memory expansions,
refer to section Changing the CPU memory configuration (Page 239).
NOTICE
Assuming you have changed the load memory type or modified the operating system on
the standby CPU, this CPU does change to RUN, but returns to STOP and entry to the
diagnostic buffer.
If you have not expanded load memory on the standby CPU, this CPU does not change to
RUN, but returns to STOP and writes an entry to the diagnostic buffer.
The system does not perform a master/standby changeover, and the previous master CPU
remains in RUN.
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System Manual, 09/2007, A5E00267695-03
S7-400H