Programming
Fail-Safe Systems
A5E00085588-03
5-49
5.4.8 Changes to the Safety Program in RUN Mode
You can only make changes to the Safety Program during operation (RUN) if
safety mode is deactivated. You have the following options for changing the Safety
Program during operation:
• Change the CFC charts, and compile and download the changes to the CPU.
• Change fail-safe constants (I/Os that are interconnected ) in CFC test mode.
Notes on the Run Sequence During the Downloading of Changes
Time stamps are not taken into account when changes are downloaded. Instead,
all changes detected (i.e. caused by editing operations) are downloaded.
!
Safety Note - Downloading
Downloading the changes is executed in two stages:
• All complete blocks are downloaded first. These are newly placed blocks, new
instance DBs or newly generated FCs (for modified run-time groups or tasks).
These blocks are downloaded in sequence in such a way that called blocks are
available for every phase (i.e. the CPU continues to run). (For example, new
run-time group FCs are only downloaded when newly called blocks in them
have already been downloaded.)
All blocks that are no longer required are deleted during this downloading
phase.
• All changed input or output parameters of blocks are then downloaded. These
changes are downloaded by only writing the parameters that have been
changed (not the whole block) to the CPU. This can take several cyclic
interrupt cycles. The order in which the parameters are written cannot be
predicted. Make sure that parameters are not changed in such a way that
downloading across several cyclic interrupt cycles and/or in a particular order
can result in temporary dangerous states. You can avoid this by separating
control functions (in the standard program) from protection functions (in the
Safety Program) and by making changes to standard and Safety Programs
separately.
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