Technical data

Appendix
27.2 Memory Areas of S7 CPUs
Programming with STEP 7
Manual, 05/2010, A5E02789666-01 573
Identifying Data Blocks as "Not Relevant for Execution"
Data blocks that were programmed in a source file as part of an STL program can be identified as
"Not Relevant for Execution" (keyword UNLINKED). This means that when they are downloaded to
the CPU, the DBs are stored only in the load memory. The content of such blocks can, if
necessary, be copied to the work memory using SFC20 BLKMOV.
This technique saves space in the work memory. The expandable load memory is then used as a
buffer (for example, for formulas for a mixture: only the formula for the next batch is loaded in the
work memory).
Load Memory Structure
The load memory can be expanded using memory cards. Refer to your "S7-300 Programmable
Controller, Hardware and Installation Manual" and your "S7-400, M7-400 Programmable
Controllers Module Specifications Reference Manual" for the maximum size of the load memory.
The load memory can also have an integrated EPROM part as well as an integrated RAM part in
S7-300 CPUs. Areas in data blocks can be declared as retentive by assigning parameters in STEP
7 (see Retentive Memory Areas on S7-300 CPUs).
In S7-400 CPUs, it is imperative that you use a memory card (RAM or EPROM) to expand the load
memory. The integrated load memory is a RAM memory and is mainly used to reload and correct
blocks. With several S7-400 CPUs, additional work memory can also be plugged in.
Load Memory Behavior in RAM and EPROM Areas
Depending on whether you select a RAM or an EPROM memory card to expand the load memory,
the load memory may react differently during downloading, reloading, or memory reset.
The following table shows the various loading methods:
Memory Type Method of Loading Type of Loading
Downloading and deleting individual blocks PG-CPU connection
Downloading and deleting an entire S7 program PG-CPU connection
RAM
Reloading individual blocks PG-CPU connection
Integrated (S7-300 only)
or plug-in EPROM
Downloading entire S7 programs PG-CPU connection
Plug-in EPROM Downloading entire S7 programs Uploading the EPROM to the PG
and inserting the memory card in
the CPU
Downloading the EPROM to the
CPU
Programs stored in RAM are lost when you reset the CPU memory (MRES) or if you remove the
CPU or RAM memory card.
Programs saved on EPROM memory cards are not erased by a CPU memory reset and are
retained even without battery backup (transport, backup copies).