Defining The Program Structure - Siemens SIMATIC S7 F Manual

Programming
5.2.3

Defining the Program Structure

Rules for the Program Structure
You must comply with the following rules when you design a user program for the
S7 F/FH Systems:
•
You can combine standard and Safety Program sections within a CPU.
•
Multiple charts with fail-safe blocks are permissible for each priority class (task
or OB).
•
Run-time groups with fail-safe blocks can only be assigned to OB3x cyclic
interrupts (OB 30 to OB 38).
•
It is recommended to place all the blocks in a chart, with the exception of the
module driver, in the same run-time group whenever possible. A run-time
group can, however, contain blocks from several charts.
•
A chart may contain both F-blocks and standard blocks, as long as the F-
blocks are in separate run-time groups from the standard blocks, and as long
as the charts are not compiled as block types.
•
You can only access the F-I/Os in the Safety Program via the F channel
drivers, which make the process signals available in the safe data format.
•
As of about 1000 blocks, you have to distribute the Safety Program to several
F-run-time groups; otherwise, it can't be compiled.
•
110 Run-time groups maximum.
Specifications for the Safety Program
When you design a user program for the S7 F/FH Systems, you must also make
the following decisions in addition to what is required for a standard system:
•
Which sections of the user program have to be fail-safe?
You must create separate CFC charts and run-time groups for these sections
of the user program.
•
Which OB3x cyclic interrupts do the fail-safe sections of the user program have
to be assigned to? With which priorities and cycle times?
You must configure these OBs for the CPU.
Note
You can improve the performance by removing the non-safety-related functions
from the Safety Program section and leaving them in the standard program
section. This particularly includes functions such as reporting, monitoring etc.
When distributing functions between the standard and fail-safe section of the
program, note that it is easier to change the standard section of the program and
download it to the CPU. Changes to the standard section do not normally require
acceptance.
Fail-Safe Systems
A5E00085588-03
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