Siemens Simatic S7-300 CPU 31xC and CPU 31x S7-300 - Manual (Page 73)

Memory concept
4.2 Memory functions
CPU 31xC and CPU 31x, Technical data
Manual, Edition 08/2004, A5E00105475-05
4-11
4.2 Memory functions
4.2.1 General: Memory functions
Memory functions
Memory functions are used to generate, modify or delete entire user programs or specific
blocks. You can also ensure that your project data are retained by archiving these. If there
is... You created a new user program, use a PG/ PC to download the complete program to
MMC.
4.2.2 Loading user program from Micro Memory Card (MMC) to the CPU
User program download
All user program data are downloaded from your PG/PC to the CPU via MMC. The previous
content of the MMC is deleted in the process. Blocks use the load memory area as specified
under "Load memory requirements" in "General block properties".
The figure shows the load and work memory of the CPU
Loading memory Working memory Stored on
hard disk
Code modules
Data modules
Comments
Symbols
Code modules
Data modules
Process-relevant
parts of the code
and data modules *
MMC
PG
CPU
* If not alI of the work memory area is retentive, its retentive area is indicated in the STEP 7
module status as retentive memory (same as on CPU 317). You cannot run the program
until all the blocks are downloaded.