Memory concept
10.1 Overview of the memory concept of S7-400H CPUs
S7-400H
System Manual, 03/2012, A5E00267695-11
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Basis for Calculating the Required Working Memory
To ensure that you do not exceed the available amount of working memory on the CPU, you
must take into consideration the following memory requirements when assigning parameters:
Table 10- 1 Memory requirements
Parameter Required working memory In code/data memory
Size of the process image
(inputs)
20 bytes per byte in the process image of inputs Code memory
Size of the process image
(outputs)
20 bytes per byte in the process image of inputs Code memory
Communication resources
(communication jobs)
72 bytes per communication job Code memory
Size of the diagnostics buffer 32 bytes per entry in the diagnostics buffer Code memory
Quantity of local data 1 byte per byte of local data Data memory
Flexible memory space
● 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 (8 MB or more) are
also suitable for sending and carrying out 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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