Technical data

Appendix
27.2 Memory Areas of S7 CPUs
Programming with STEP 7
572 Manual, 05/2010, A5E02789666-01
27.2.2 Load Memory and Work Memory
When you download the user program from the programming device to the CPU, only the logic and
data blocks are loaded in the load and work memory of the CPU.
The symbolic address assignment (symbol table) and the block comments remain on the
programming device.
Dividing Up the User Program
To ensure fast execution of the user program and to avoid unnecessary load on the work memory
that cannot be expanded, only the parts of the blocks relevant for program execution are loaded in
the work memory.
Parts of blocks that are not required for executing the program (for example, block headers) remain
in the load memory.
The following figure shows a program being loaded in the CPU memory.
Note
Data blocks that are created in the user program with the help of system functions (for example,
SFC22 CREAT_DB) are saved entirely in the work memory by the CPU.
Some CPUs have separately managed areas for code and data in the work memory. The size and
assignment of these areas is shown in the "Memory" tab of the Module Information for these CPUs.