Memory Behavior When Loading Software Changes - Siemens S7-1500 Function Manual

Memory areas and retentive memory

2.5 Memory behavior when loading software changes

2.5 Memory behavior when loading software changes
Introduction
You can download software changes in STOP and RUN without affecting the actual values
of previously loaded tags.
You load changes to the software in STEP 7 (in the project tree and with selected PLC
station) under "Download to device > Software (only changes)".
Note
Redundant system S7-1500R/H
The CPUs of the redundant system S7-1500R/H permit the downloading of software
changes only in the STOP or RUN-Solo system state.
Impact of software changes on PLC tags
You can load the following software changes without affecting the actual values of PLC tags
that have already been loaded:
● Name change
● Comment change
● Addition of new tags
● Deletion of tags
● Change of retentivity settings for Retentive memory areas (Page 26)
The actual values are affected by loading the following software changes:
● Data type change
● Address change
Memory reserve of global DBs and instance DBs
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 of the memory reserve can be found in STEP 7 under the data block properties
in the "Download without reinitialization" category.
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Structure and Use of the CPU Memory
Function Manual, 10/2018, A5E03461664-AC