Siemens S7-300 appendix Retentive behavior of a DB for CPUs with firmware =, Run-Stop

Memory concept

4.1 Memory areas and retentivity

Retentive behavior of a DB for CPUs with firmware >= V2.1.0

For these CPUs you can specify in STEP 7 (beginning with version 5.2 + SP 1), or at SFC 82 CREA_DBL (parameter ATTRIB -> NON_RETAIN bit), whether a DB at POWER ON/OFF or

RUN-STOP

•keeps the actual values (retentive DB), or

•accepts the initial values from load memory (non-retentive DB)

Table 4-3	Retentive behavior of DBs for CPUs with firmware >= V2.1.0
At POWER ON/OFF or restart (warm start) of the CPU, the DB should
receive the initial values		retain the actual values (retentive DB)
(non-retentive DB)
Background:		Background:
At POWER ON/OFF and restart (STOP-		At POWER OFF/ON and restart (STOP-RUN) of the
RUN) of the CPU, the actual values of the		CPU, the actual values of the DB are retained.
DB are non-retentive. The DB receives the
start values from load memory.
Requirement in STEP 7:		Requirement in STEP 7:
• The "Non-retain" check box must be set		• The "Non-retain" check box must be reset in the
in the block properties of the DB, or		block properties of the DB or
• a non-retentive DB was generated with		• a retentive DB was generated with SFC 82.
SFC 82 "CREA_DBL" and the
corresponding block attribute (ATTRIB -
> NON_RETAIN bit.)

Note

Note that only 256 KB of RAM can be used for retentive data blocks on a CPU 317. The remainder of the RAM is used by code blocks and non-retentive data blocks.

4-4	CPU 31xC and CPU 31x, Technical data
	Manual, Edition 08/2004, A5E00105475-05