Siemens SIMATIC S7 F, Manual

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Fail-Safe Blocks
Fail-Safe Systems
8-2
A5E00085588-03
8.1.2 F-Data Types
Special F-data types in a safety data format are used for fail-safe block I/Os. The
safety data format is used to expose data and address corruptions.
The F-data types are programmed as structures and appear in the CFC chart with
the prefix "ST". The structures always consist of three components, of which the
first component, DATA, determines the data type. The PAR_ID and COMPLEM
components are included for safety reasons and are automatically assigned values
at compilation of the CFC chart.
For example, in the structure of the F_BOOL data type, DATA is of the type BOOL:
F_BOOL:
STRUCT
DATA BOOL
PAR_ID WORD
COMPLEM WORD
END_STRUCT
Note
Only I/Os with the same F-data type can be interconnected.
!
Safety Note – Do Not Change PAR_ID and COMPLEM parameters
You must not change the PAR_ID and COMPLEM components after the Safety
Program has been compiled since this might result in serious errors remaining
undetected. If errors are detected in the safety data format during execution of the
Safety Program, the Safety Program will be disabled and may require the Safety
Program to be recompiled and downloaded to the CPU.
Possible Data Types
The data types F_REAL and F_BOOL are possible for calculations.
If the F blocks have parameters with the data types F_INT, F_DINT, F_BYTE,
F_WORD, F_DWORD and F_TIME, these parameters can only be assigned
constants. You can use F_FR_FI to convert to F_INT.
Note
Output parameters of the types F_TIME and F_INT can be converted by
conversion blocks into the associated elementary data types for further processing
in the standard program. Conversely, elementary data types of the types TIME and
INT can be converted into F data types and processed further in the Safety
Program with the appropriate plausibility check.