Siemens Simatic S7-300 CPU 31xC and CPU 31x S7-300 - Manual (Page 77)

Memory concept
4.2 Memory functions
CPU 31xC and CPU 31x, Technical data
Manual, Edition 08/2004, A5E00105475-05
4-15
4.2.5 Recipes
Introduction
A recipe represents a collection of user data. You can implement a simple recipe concept
using static DBs. In this case, the recipes should have the same structure (length). One DB
should exist per recipe.
Processing sequence
Recipe is written to load memory:
•
The various data records of recipes are created as static DBs in STEP 7 and then
downloaded to the CPU. Therefore, recipes only use load memory, rather than RAM.
Working with recipe data:
•
SFC83 "READ_DBL" is called in the user program to copy the data record of a current
recipe from the DB in load memory to a static DB that is located in work memory. As a
result, the RAM only has to accommodate the data of one record. The user program can
now access data of the current recipe. The figure below shows how to handle recipe
data:
Loading memory
:
Current
recipe
Recipe 1
Recipe 2
Recipe n
Working memory
(MMC)
(CPU)
SFC 83 READ_DBL
SFC 84 WRIT_DBL
Saving a modified recipe:
•
The data of new or modified recipe data records generated during program execution can
be written to load memory. To do this, call SFC 84 "WRIT_DBL" in the user program.
These data written to load memory are portable and also retentive on memory reset. You
can backup modified records (recipes) by uploading and saving these in a single block to
the PG/PC.
Note
Active system functions SFC82 to 84 (active access to the MMC) have a distinct
influence on PG functions (for example, block status, variable status, download block,
upload, open). This typically reduces performance (compared to passive system
functions) by the factor 10.