Siemens SIMATIC PCS 7 Configuration Manual page 168

Configuring AS functions
8.2 Creating process tags
The default settings are:
● DB: 1 to 60
● FC: 60 to 700
Installed blocks for each sequence group or OB
The default limit of 50 blocks is sufficient for typical configuration cases.
The monitoring is performed for:
● Blocks per sequence group (GROUP FC) or
● Blocks per TASK FC + sequence groups per TASK FC + SFCs per TASK FC
With the default setting of 50 blocks per sequence group or OB, a warning is triggered if more
than 50 sequence groups (CFCs) are configured.
Too many blocks per OB without using sequence groups can cause the SCL Compiler to abort,
as the compiler can only create a maximum of one 64 KB FC per OB.
The warning limit exists so that the 64 KB limit is not exceeded. You can set the warning limit
individually (1 – 32767), for example, after empirical determination. To determine the warning
limit empirically, the program must be compiled at regular intervals during the configuration.
Then you can check in the block folder of the program whether a block (Task FC) is
approaching the maximum allowable size of 64 KB. If the block size is close to this limit, the
warning limit is set too high. If the block size is well below the limit of 64 KB, the warning limit
can be increased.
If a block is close to the limit of 64 KB, you can reduce the block size by inserting new sequence
groups or by moving blocks/sequence groups to a different cyclic interrupt.
You can find additional information on this topic in the FAQ "Why does the error message
"Maximum length of code area reached (max. 64 KB)" or "Insufficient main memory" appear
when the CFC charts are compiled?"
771569).
Generate image of downloaded program for comparison
As of the PCS 7 V7.0, the "Generate image of downloaded program for comparison" option is
available. This can prove useful or necessary as of a certain configuration phase
(commissioning, production).
If the option is activated, this allows you to subsequently view details of the changes to be
downloaded; The "Show Changes" button is available for this purpose in the "Download" dialog
window. The VXM tool (Version Cross Manager, including license) must be available.
Note
The VXM process image is not updated during selective downloading of charts. An update is
complete if all changed charts have been downloaded.
168
(https://support.industry.siemens.com/cs/ww/en/view/
Compendium Part A - Configuration Guidelines (V8.2)
Configuration Manual, 08/2016, A5E38166869-AA