Examples/applications
6.8 Determing the memory requirement in the SIMATIC
FC 45
6-20
Function manual, Release 03/2006 , J31069-D0167-U001-A2-7618
6.8
6.8
Determing the memory requirement in the SIMATIC
The memory resources used in SIMATIC S7 by a MOBY application should normally not
reach the system limits on the PLC. However, if the following conditions occur
simultaneously, the memory requirement must be considered:
•
SIMATIC S7 with small memory configuration
•
Many MOBY channels (write/read devices) are processed in one S7.
•
Processing of large volumes of data on each MOBY channel
The following example shows a configuration for the memory required by FC 45 in an S7.
Twenty write/read devices with 1KB of MDS data each are to be processed:
Memory Requirements [KB]
per channel
Total
FC 45 (needed once)
Parameter data block (UDT 10)
Command data block (UDT 20)
DB for MDS data
–
0.3
0.01
1
~7
6
0.2
20
Total
1.31
33.2
In this configuration, a SIMATIC CPU with only 48 KB memory can reach the memory limits
quickly if further programs are also running.
