EEPROM 6ES5374-1FH21 is

A new generation of memory cards in 5 V only technology is now available for SIMATIC S5. This means
that both the reading and the writing voltage is 5 V. In the case of products that access both reading and
writing (e.g. IM 308 C), the use of the new generation flash memory cards is tied to a particular revision
level of these product:                                                                      
                                                                            
Item:               ! Catalog No.:    ! Revision level:                     
--------------------+-----------------+--------------------------           
  IM 308 C        !                       ! From rev. level 3 onward