Technical data

Memory areas and retentive memory
2.4 Memory behavior when loading software changes
Structure and Use of the CPU Memory
Function Manual, 01/2013, A5E03461664-01
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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 tags that have already been loaded:
● Start value change
● Comment change
When loading the following software changes, all actual values of the data block will be
reinitialized:
● Name change
● Data type change
● Retentivity change
● Addition of new tags
● Deletion of tags
Memory reserve of data blocks
Each function block or data block with the "Optimized block access" attribute activated
contains, by default, a memory reserve which you can use for subsequent interface changes.
The memory reserve is initially not used. When you have compiled and loaded the block,
and then observe that you want to reload interface changes, activate the memory reserve.
All tags that you subsequently declare will be placed in the memory reserve. During the next
load, the new tags are then initialized to their start values. Tags which have already been
loaded are not reinitialized.
The setting for memory reserve can be found in STEP 7 in the data block properties under
"Download without reinitialization".
Reference
You can find additional information on setting and activating the memory reserve, and on
loading block changes, in the online help for STEP 7 under "PLC programming > Create
user program > Compile and download blocks > Download blocks > Download block
extensions without reinitialization".