Siemens SIMATIC S7-300 CPU Data: CPU 315-T-2 DP User Manual

Memory concept
6.4 Measured value log files
Measured value logging:
• Before the data volume can exceed work memory capacity, you should call
SFC 84 "WRIT_DBL" in the user program to swap measured values from the DB to load
memory.
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Figure 6-5 Handling measured value log files
• You can call SFC 82 "CREA_DBL" in the user program to generate new (additional) static
DBs in load memory which do not require RAM space.
The data written to load memory are portable and retentive on CPU memory reset.
Note
SFC 82 is terminated and an error message is generated if a DB already exists under the
same number in load memory and/or RAM.
Evaluation of measured values:
• Measured value DBs saved to load memory can be uploaded and evaluated by other
communication partners (PG, PC, for example).
Note
The active system functions SFC 82 to 84 (current access to the MMC) have a distinct
influence on PG functions (block status, variable status, load block, upload, open, for
example).
This typically reduces performance (compared to passive system functions) by the factor
10.
With the
Technology CPU, you can also generate non-retentive DBs using SFC 82
(parameter ATTRIB -> NON_RETAIN bit.)
in order to prevent data losses, do not exceed this maximum of delete/write operations. Also
refer to the SIMATIC Micro Memory Card (MMC) section in the "Structure and
Communication Functions of a CPU 31xC" chapter.
S7-300 CPU Data: CPU 315T-2 DP
6-16 Manual, 12/2005, A5E00427933-02

Siemens SIMATIC S7-300 CPU Data: CPU 315-T-2 DP Specifications

General

Brand	Siemens
Model	SIMATIC S7-300 CPU Data: CPU 315-T-2 DP
Category	Control Unit
Language	English