Siemens SINUMERIK MC Commissioning Manual page 66

Safety program of the F-PLC
3.5 Restrictions in the programming languages FBD/LAD
Operand area
● F-DB
● DB
Temporary local data
File type conversion
Just as with the standard user program, there are two possibilities for file type conversion in the
safety program.
● Implicit conversion
The implicit conversion is executed as in the standard user program with the following
restrictions: The bit length of the source data type has to match the bit length of the
destination data type.
● Explicit conversion
You use an explicit conversion instruction before the actual instruction is carried out.
Slice access
Slice access is not possible in the safety program.
Non-permitted operand areas
Access via units other than those listed in the table above is not permitted. The same applies
to access to operand areas not listed, in particular:
● Data blocks that were automatically added
Exception: certain variables in the F-I/O DB and in the F-runtime group information DB
● I/O area: Inputs
● I/O area: Outputs
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Description
Data blocks store information for the program. They can either be de‐
fined as global data blocks such that all F-FBs, F-FCs, or main safety
blocks can access them or assigned to a particular F-FB or main safety
block (instance DB). A tag of a shared DB can only be accessed from
one F-runtime group, and an instance DB only from the F-runtime group
in which the corresponding F-FB/instruction is called.
This area is used for data exchange with the standard user program.
In addition, read access requires a process-specific validity check.
For a tag of a DB, either read access or write access is possible in the
safety program.
Transfer to IN_OUT parameters of an F-FB or F-FC is therefore not valid
either.
Please note that the tags of a DB can only be used for transferring data
between the standard user program and the safety program; DBs must
not be used as a buffer for F-data
This memory area holds the temporary tags of a block (or F‑block) while
the (F-) block is being executed. The local data stack also provides
memory for transferring block parameters and for saving intermediate
results.
Commissioning Manual, 02/2020, A5E46305916B AB
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Safety Integrated (with SINAMICS S120)