Siemens Simatic S7-300 Specifications download pdf (Page 46)

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S7-300 Automation System CPU Specifications: CPU 31xC and CPU 31x

4-2 A5E00105475-03

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The user program can only be downloaded and thus the CPU can only be used if

the MMC is inserted.

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The RAM is integrated in the CPU and cannot be extended. Its only purpose is

processing of code and user program data. Programs only run in RAM and system

memory.

The RAM of &38[&and'3is always retentive.

For &38'3,256 Kbytes of RAM can be used for retentive data blocks. The

remainder of the RAM can only be used for code blocks and non-retentive data

blocks.

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The RAM system memory is integrated in the CPU and cannot be expanded.

It contains

• the address areas for memory bits, timers and counters

• the process image of the I/Os

• local data

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Your CPU is equipped with retentive memory . Retentive memory is provided by

the MMC and CPU. Data is kept in retentive memory across POWER OFF and

restart (warm start).

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Your program in the load memory is always retentive; It is saved upon loading on

the MMC to protect against network failure and resets.

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Siemens Simatic S7-300 Specifications Page 46