Siemens S7-1500 Function Manual page 34

Impacts of software changes on data blocks without memory reserve
If you are not using memory reserve, you can load the following software changes without
this reinitializing the actual values of DB tags that have already been loaded:
● Change of start value
● Comment change
Impacts of software changes on data blocks with memory reserve
If you are using the memory reserve for data blocks ("Optimized block access" attribute and
"Enable download without reinitialization for retentive tags" button selected), you can load
the following software changes. The actual values of previously downloaded DB tags are not
reinitialized by this.
● Change of start value
● Comment change
● Addition of new tags
If the button "Enable download without reinitialization for retentive tags" is deactivated, then
all actual values of the data block are reinitialized on the next loading of the following
software changes:
● Name change
● Data type change
● Retentivity change
● Deletion of tags
● Changes to the memory reserve settings
Reference
You can find additional information on setting and activating the memory reserve and on
downloading block changes in the STEP 7 online help under "Programming a PLC >
Compiling and downloading PLC programs > Downloading blocks for S7-1200/1500 >
Loading block extensions without reinitialization".
Structure and Use of the CPU Memory
Function Manual, 10/2018, A5E03461664-AC
Memory areas and retentive memory
2.5 Memory behavior when loading software changes
33