Entry type: FAQ, Entry ID: 27832833, Entry date: 01/29/2008
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Why does my F system go into STOP at startup?

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Description:
When using S7 Distributed Safety V 5.4 SP1 to V 5.4 SP3, despite correct setting of the monitoring times it still might happen that when the F system starts up, the F CPU goes into STOP. In this case, you find the following entries in the diagnostics buffer:

  • "Cycle time exceeded" or
  • "Error in the safety program: cycle time exceeded".

Note:
With S7 Distributed Safety V 5.4 SP1 the behavior described can only occur when you are using an F CPU that supports "Startup protection in case of inconsistent safety program" (see Product Information for F CPU concerned).

The F CPU's operating mode STOP depends on the following:

  • Number of F peripherals addressed in the safety program.
  • Available time buffer in the value configured for the maximum cycle time of the F runtime group (F monitoring time).
  • Available time buffer in the value configured for the cycle monitoring time (in the "Cycle/Clock marker" tab in the Object Properties of the F CPU).

Remedy:
Execute the steps as in the table below.
 

No. Procedure Note
1 First check whether you have set the monitoring time correctly. Also refer here to the Excel file on response time calculation, s7cotia.xls, Entry ID 25412441.
2 Change to S7 Distributed Safety V 5.4 SP4. Instructions for this are available in the programming and operating manual "S7 Distributed Safety, Configuring and Programming", Edition 10/2007.
3 Generate the safety program with S7 Distributed Safety V 5.4 SP4.  

Keywords:
Safety Integrated, Fail-safe