Siemens SIMATIC S7-300 Manual page 54

Memory concept
6.1 Memory areas and retentive address areas
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.
MMC copy protection
Your MMC has an internal serial number that provides copy protection at user level. You can
read this serial number from the SSL partial list 011C
You can then program a STOP command, for example, in a copy-protected block if the
expected and actual serial numbers of your MCC do not tally.
Reference
Further information
• can be found in the
• in the
Useful life of an MMC
The useful life of an MMC is determined in particular by the following factors:
• The number of delete or programming operations,
• external influences such as the ambient temperature.
At ambient temperatures up to 60 °C, a maximum of 100,000 delete/write operations can be
performed on an MMC.
Caution
in order to prevent data losses, do not exceed this maximum of delete/write operations.
6-8
SSL partial list in the instruction list,
System and Standard Functions
index 8 using SFC 51 "RDSYSST."
H
or
manual.
S7-300 CPU Data: CPU 315T-2 DP
Manual, 12/2005, A5E00427933-02