Creating Fail-Safe Block Types; F-Blocks Outputs' Always Use The Preset Initial Values - Siemens SIMATIC S7 F Manual

Programming
5.4.5

Creating Fail-Safe Block Types

You can create a fail-safe block type that can be reused in other safety programs
from the CFC chart of a safety program.
Rules for Fail-Safe Block Types
To create a new block type with fail-safe blocks, proceed as you would normally.
The same rules apply as in the standard case, with the following additional points:
•
The new block type must be a function block (FB).
•
The new block type can only contain fail-safe blocks. Standard blocks are not
permissible.
•
The fail-safe blocks that are to be called in the new block type and the F-
Blocks of the entire Safety Program in which the block type is to be used must
come from one and the same library version. Blocks from different versions of
the "Fail-safe Blocks" library are not permitted.
•
The fail-safe blocks must not be used in new block types:
- The system blocks F_S_BO, F_S_R, F_R_BO, F_R_R
- All control blocks
•
Nesting of newly created fail-safe block types is not permitted.
•
An output of an F-Block must not be connected to two chart I/Os.
•
The run sequence is not corrected automatically at compilation. The sequence
defined during creation is retained.
Note
If the run sequence is different to the data flow due to feedback, for example, an
error is reported when the F-Block type is compiled.
•
The chart I/Os of the new block type can be F-data types and standard data
types.
•
You can use the following names for F-Blocks that are called in a block type:
- Numerals only, as specified by CFC
- Alphanumeric names that must always begin with F_.
Safety Note – F-Blocks outputs' always use the preset initial values.
!
When F-block types are created, none of the initial values at outputs of fail-safe
blocks may be changed. CFC will permit them to be changed and will display the
change, but the preset initial values, as specified in the library, are always used.
5-44
Fail-Safe Systems
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