Siemens SIMATIC S7 F Manual page 128

Programming
Changing a Fail-Safe Block Type
Changes to a block type require acceptance.
Modified block types must be entered using the Options > Block Types menu
command. After using a modified block type, you must recompile the safety
program and download it to the CPU. It is not always possible to download the
changes in RUN. In the case of changes to chart I/Os or modified block calls, for
example, it is not possible to download the changes.
Both the rules for the standard case and the rules for Safety Programs apply to the
downloading of changes.
When you use a new version of the Fail-safe Blocks library, you must also
recompile the F-Block type after you have imported the new blocks. In this way,
you ensure that the F-Blocks in the Safety Program all have the same library
version.
F Channel Drivers in F-Block Types
If F channel drivers are used in a block type, the VALUE, ADDR_CODE, CHADDR
I/Os at least must be defined as chart I/Os, because these I/Os have to be
interconnected outside of the F-Block type with the symbolic name of the
associated channel or with the F module driver, or they have to be supplied
automatically.
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Fail-Safe Systems
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