Programming
Fail-Safe Systems
5-40 A5E00085588-03
5.4.2 Deactivating Safety Mode
The Safety Program usually runs on the CPU in safety mode. In other words, all
the safety mechanisms for fault detection and fault reactions are activated. It is not
possible to change the Safety Program during operation (RUN) when it is in safety
mode. To download changes to the Safety Program in RUN or to change F
constants in CFC test mode, you must deactivate safety mode for the Safety
Program .
!
Safety Note – When Deactivating Safety Mode
Since modifications to the Safety Program can be made in RUN mode when safety
mode is deactivated by downloading the changes, you must observe the following:
• You should deactivate safety mode for test purposes, commissioning, etc.
When safety mode is deactivated, the safety of the system must be ensured by
means of other organizational measures (e.g. monitored operation and manual
safety shutdown).
• When you make changes to the Safety Program in RUN mode with safety mode
deactivated, switchover effects can occur. The information on the downloading
sequence for download changes in the section entitled "Changing the Safety
Program in RUN Mode" will give you an overview of this.
• Wherever possible, the standard program and the Safety Program should only
be changed separately, and the changes downloaded, because otherwise an error
could be downloaded at the same time into the standard program, and the required
protection function in the Safety Program could be destroyed, or switchover effects
could occur in both programs.
• Deactivation of safety mode must be detectable. Logging is necessary, if
possible by recording messages to the OS, or if necessary by means of
organizational measures. It is also recommended that deactivation of safety mode
should be indicated on the OS.
• Safety mode can only be deactivated CPU-wide. In the case of safety-related
CPU-CPU communication, note that the data sent by an F_SENDBO or F_SENDR
with safety mode deactivated and the outputs obtained from must be included in
monitored operation.
Note
If simulation mode is activated, you cannot deactivate safety mode or download
changes.
Prerequisites
• The CPU is in RUN mode (the mode selector is on RUN or RUN-P).
• Safety mode is activated.
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