Siemens S7-1500 Function Manual page 36

Example:
A STEP 7 program contains an organization block (OB), 20 functions (FC) and a data block
(DB). The OB calls the 20 FCs. All the FCs access the DB. If you change the program code
in one of the FCs, the following load procedure only contains the changed FC. If you change
the data type of a tag in the DB, however, the following load procedure then contains all the
FCs and the DB.
The following figure shows the objects in the load procedure in a preview.
Figure 2-8
Structure and Use of the CPU Memory
Function Manual, 10/2018, A5E03461664-AC
2.6 Memory requirements for downloading software changes
Preview for loading
Memory areas and retentive memory
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