Storage Concept and Startup Types
8.1 Overview of the memory concept of S7-400 CPUs
S7-400 Automation System, CPU Specifications
Manual, 10/2006, 6ES7498-8AA04-8BA0
8-3
● System memory of the CPU also makes temporary memory available (local data stack,
diagnostic buffer and communication resources) that is assigned to the program for the
temporary data of a called block. These data are only valid as long as the block is active.
By changing the default values for the process image, local data, diagnostic buffer and
communication resources (see object properties of the CPU in HW Config), you can
influence the work memory available to the runtime-relevant blocks.
Notice
Please note the following if you expand the process image of a CPU. Make sure that you
configure the modules that can only be operated above the process image in such a way
that they are also positioned above the expanded process image. This applies, in
particular, to IP and WF modules that you operate in the S5 adapter casing in an S7-400.
Flexible Memory Capacity
● Work memory:
The capacity of the work memory is determined by selecting the appropriate CPU from
the graded range of CPUs.
● Load memory:
The integrated load memory is sufficient for small and medium-sized programs.
The load memory can be increased for larger programs by inserting the RAM memory
card.
Flash memory cards are also available to ensure that programs are retained in the event
of a power failure even without a backup battery. Flash memory cards can also be used
(more than 4 MB, at CPUs with FW Version 5.0 more than 8 MB) to send and run
operating system updates.
Backup
● The backup battery provides backup power for the integrated and external part of the
load memory, the data section of the working memory and the code section.
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