Entry type: FAQ, Entry ID: 23718479, Entry date: 08/07/2006

Why should you switch the operating mode of the CPU from Test to Process after commissioning the STEP 7 program?

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Difference between Test mode and Process mode (excerpt from the Online Help of STEP 7):

  • In Process mode the debug functions such as Program Status and Monitor/Control Variables are limited so that the permissible cycle increase set is not exceeded. It is not possible to debug with breakpoints or run the program step by step.
  • In Test mode all the debugging functions can be used without any restrictions via PG/PC, which can greatly increase the cycle time. If the CPU is in Test mode, you must make sure that the CPU or the process can "tolerate" great increases in cycle time. In this mode, increases in the CPU cycle times might occur, because the status of statements in programmed cycles is determined each cycle, for example.

For SIMATIC S7-400 CPUs the Process mode is set as the default operating mode (status after slotting the CPU).

Changing from Test mode to Process mode:
In a SIMATIC S7-400 CPU you can set the operating mode in the LAD/STL/FBD editor (see Entry ID: 21336333). You then save the block and load it into the CPU.

Make sure that the breakpoints are deleted again after successful debugging, because otherwise it is not possible to load the blocks concerned into the automation system.