Specifications

CPU Memory: Data Types and Addressing Modes
5-21
S7-200 Programmable Controller System Manual
C79000-G7076-C233-01
Limiting the Number of Programmed Saves to EEPROM
Since the number of save operations to the EEPROM is limited (100,000 minimum,
and 1,000,000 typical), you should ensure that only necessary values are saved.
Otherwise, the EEPROM can be worn out and the CPU can fail. Typically, you
perform save operations at the occurrence of specific events that occur rather
infrequently.
For example, if the scan time of the S7-200 is 50 ms and a value was saved once
per scan, the EEPROM would last a minimum of 5,000 seconds, which is less than
an hour and a half. On the other hand, if a value were saved once an hour, the
EEPROM would last a minimum of 11 years.