Siemens SIMATIC S7-400H System Manual page 330

System modifications during operation
17.8 Changing the CPU memory configuration
Procedure
Proceed as follows in the specified sequence:
Step What to do?
1 Switch the reserve CPU to STOP using the
programming device.
2 Replace the memory card in the CPU with a card
which has the required (higher) capacity.
3 Reset the reserve CPU using the programming
device.
4 Start the reserve CPU with the menu command "PLC
> Mode > Switch to CPU ... with expanded memory
configuration".
5 Turn off power to the second CPU.
6 Modify the memory configuration of the second CPU
as you did in steps 2 to 3 for the first CPU.
7 Start the second CPU with the menu command "PLC
> Mode > Switch to CPU ... with expanded memory
configuration".
330
How does the system react?
The system is now operating in single mode.
Reserve CPU requests memory reset.
–
The reserve CPU links up, is updated and

becomes the master.
Previous master CPU changes to STOP.

System operates in single mode.

The subsystem is disabled.
–
The second CPU is linked up and updated.

The system is now operating again in redundant

system mode.
System Manual, 03/2012, A5E00267695-11
S7-400H