Siemens SIMATIC S7 F, Manual

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Safety Mechanisms
Fail-Safe Systems
3-10
A5E00085588-03
3.9.1 Communication Between the Safety Program and the Standard
User Program
The standard and Safety Programs use different data formats. Special conversion
blocks must therefore be used for the data exchange.
F-CPU
Standard program
Safety Program
Non-safety-related
From To Block Safety-
Related
Safety Program Standard program F_Fdata type_data type No
Standard program Safety Program F_data type_Fdata type No
The following data types are supported: BOOL, REAL, INT and TIME.
Parameters are passed as safety-related F-data types in the Safety Program. If the
standard user program has to process data from the Safety Program, for
monitoring purposes, for example, then a block for the conversion of data (F_Fdata
type_data type) must be inserted in CFC to convert the F-data types to standard
data types.
These blocks can be found in the Failsafe Blocks, User Blocks library.
The F_Fdata type_data type blocks must be called in the standard user program
(CFC chart, standard run-time group).
If data from the standard user program has to be processed in the Safety Program,
safety-related F-data types must be created from the standard data types using
F_data type_Fdata type blocks for data conversion and, if necessary, then
subjected to a plausibility check programmed using fail-safe blocks. The F_data
type_Fdata type data conversion blocks must only be used in the Safety Program
(CFC chart, F-run-time group).
See Also
Programming Communication Between F User Programs and Standard User
Programs