Memory concept
4.2 Memory functions
CPU 31xC and CPU 31x, Technical Data
4-16 Manual, 01/2006 Edition, A5E00105475-06
4.2.6 Measured 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:
00&
6)&&5($B'%/
6)&:5,7B'%/
&38
:RUNLQJPHPRU\
&XUUHQWPHDVXUHG
YDOXHV
/RDGLQJPHPRU\
0HDVXUHGYDOXHV
0HDVXUHGYDOXHV
0HDVXUHGYDOXHVQ
• 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.
The data written to load memory are portable and retentive on CPU memory reset.
Evaluation of measured values:
• Measured value DBs saved to load memory can be uploaded and evaluated by other
communication partners (PG, PC, for example).
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