Siemens S7-300 appendix Measured value log files, Measured values, Working memory

Memory concept 4.2 Memory functions

4.2.6Measured value log files

Introduction

Measured values are generated when the CPU executes the user program. These values are to be logged and analyzed.

Processing sequence

Acquisition of measured values:

•The CPU writes all measured values to a DB (for alternating backup mode in several DBs) which is located in RAM.

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. The figure below shows how to handle measured value log files:

Loading memory

(MMC)

Measured values 1

Measured values 2

:

SFC 82 CREA_DBL

SFC 84 WRIT_DBL

Working memory

(CPU)

Current measured values

Measured values n

•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.

Reference

For detailed information on SFC 82, refer to the System Software for S7-300/400, System and Standard Functions Reference Manual, or directly to the STEP 7 Online Help.

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.

CPU 31xC and CPU 31x, Technical data	4-17
Manual, Edition 08/2004, A5E00105475-05