Siemens Simatic S7-300 CPU 31xC and CPU 31x S7-300 - Manual (Page 71)

Memory concept
4.1 Memory areas and retentivity
CPU 31xC and CPU 31x, Technical data
Manual, Edition 08/2004, A5E00105475-05
4-9
4.1.5 Properties of the Micro Memory Card (MMC)
The MMC as memory module for the CPU
The memory module used on your CPU is a SIMATIC Micro Memory Card (MMC.) You can
use MMCs as load memory or as a portable storage medium.
Note
The CPU requires the MMC for operation.
Data stored on the MMC:
•
User programs (all blocks)
• Archives and recipes
• Configuration data (STEP 7 projects)
• Data for operating system update and backup
Note
You can either store user and configuration data or the operating system on the MMC.
Properties of an MMC
The MMC ensures maintenance-free and retentive operation of these CPUs.
Caution
Data on a SIMATIC Micro Memory Card can be corrupted if you remove the card while it is
being accessed by a write operation. In this case, you may have to delete the MMC on your
PG, or format the card in the CPU. Never remove an MMC in RUN mode. Always remove it
when power is off, or when the CPU is in STOP state, and when the PG is not a writing to
the card. When the CPU is in STOP mode and you cannot not determine whether or not a
PG is writing to the card (e.g. load/delete block), disconnect the communication lines.