S7-300, CPU 31xC and CPU 31x: Installation 
Operating Instructions, Edition 08/2004, A5E00105492-05 
9-1 
Maintenance 
9
9.1  Overview 
S7-300 is a maintenance-free automation system. 
Thus, maintenance is considered 
•  The backup of the operating system on a Micro Memory Card (MMC) 
•  The update of operating system from MMC 
•  Firmware update 
•  Backup of project data to a Micro Memory Card (MMC) 
•  Replacement of modules 
•  Replacement of fuses in digital output modules 
•  Replacement of digital output module AC 120/230 V. 
9.2  Backup of firmware to Micro Memory Card (MMC) 
In which situations should I back up the firmware? 
In some cases, we recommend that you back up your CPU firmware: 
For example, you might want to replace the CPU in your system with a CPU from store. In 
this case, you should make sure that the shelf CPU has the same firmware that is used in 
the plant. 
We also recommend that you create a back-up copy of the firmware for emergency 
situations.