The service life of an MMC depends mainly on the number of delete and programming procedures.
The memory blocks of the MMC memory permit at least 100,000 write/delete operations. This refers to the operations with STEP 7 and data block backups upon power OFF and with SFC 84. In particular, therefore, SFC 84 should only be called at corresponding time intervals (e.g. hourly, daily ...).
If there is an MMC defect during saving, then the relevant application (e.g. load block, SFC) issues a negative acknowledgment or RET_VAL. This indicates that the routine has not been executed.
A resources or memory error is then recorded in the diagnostics buffer of the CPU.
The MMCs are also used with the C7 complete devices C7-613/635/636.
More information on this topic is available in the device manual "CPU 31xC and CPU 31x, Technical Data", in the chapter entitled "Properties of the SIMATIC Micro Memory Card". The manual is available in Entry ID: 12996906 .