Why does offline information vary in part substantially from
information in the online mode of the module?
In STEP 7 let object properties of the block folder show you the
required memory of code and data memory.
Fig. 1: Properties of Block Folder Offline
When loading the program into CPU, the values of the online mode
of the module vary in part substantially from those calculated in
the offline view of STEP 7.
The offline view only shows static information of the (user)
module, not system data information of the block (SDB). In this
view, the dynamically used system ressources of the user data
blocks as well as the dynamic system ressources of the alarm blocks
are unavailable as well.
Fig. 2: Module Information - ONLINE
The size of the load memory is the sum of
the block size (offline view) plus the sum of SDBs (these are shown
in the SDB folder).
The work memory code is different before and after the first
Prior to the first start-up the code requirement of work memory is
the sum of:
code requirement of blocks
+ code requirement of communication blocks
+ code requirement of PAE
+ code requirement of PAA
+ code requirement of diagnostics buffer
After the first start-up, the requirement of communication data is
The work memory requirement of data is independent of the first
start-up. This is determined by the dynamics of the user program
and is the sum of:
data requirement of blocks (offline view)
+requirement of system data
+user blocks created by SFC
+local data requirement (configuration)
The catalogue specifications of available code and data memory
always refer to default settings of the CPU within the Hardware
Configuration. E. g. , if process imaging is expanded within CPU
Properties, this will draw on free work memory of code. Same
applies to the maximum number of communication batches and to the
number of messages in the diagnostics buffer.
Fig. 3: Details on Work Memory of Code
The following table states the additional memory requirement in
the work memory of code for expanding the ressources:
||Additional need in
work memory code|
|per additional byte of PAE/ PAA
|per additional communications
|per additional message in the
Table 1: Additional Memory Requirement in the Code Memory
Similar applies to the memory requirements of data in the work
memory. In addition system data, local data and data blocks created
by SFC are stored here.