Siemens Industry Online Support
Siemens AG
Entry type: FAQ, Entry ID: 51825007, Entry date: 12/12/2011

How does startup work in an S7-1200?

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The startup mode "Warm restart - operating mode before POWER OFF" is set by default in the device configuration. This prevents the CPU from changing unintentionally to the RUN mode during the commissioning phase when the power returns. An unintentional change to the RUN mode will set the outputs and start any machines to which the outputs are connected. However, with this default setting you need a PG with STEP 7 V10.5, STEP 7 V11 or the S7-1200 Tool (see Entry ID 41737437) to be able to change the CPU from STOP mode to RUN mode. The CPU can change to STOP mode for one of the following reasons:

  • Inserting an SD card
  • Failure of an expansion module
  • Other reasons

If STOP mode occurs, you need software for changing to RUN mode.

We recommend setting the startup mode "Warm restart – RUN". Then, the CPU changes automatically back into RUN mode when power returns. In this way, neither you nor your customers need customer support’s assistance to set the CPU back into RUN mode.

The table below shows the startup modes of the S7-1200 CPU.

Startup mode CPU behavior
No startup CPU remains in STOP mode.
Warm restart – RUN CPU goes into RUN mode when power returns.
Warm restart - operating mode before POWER OFF CPU goes into the same mode as before loss of power.

As from STEP 7 V11 and firmware version V2.0 you have the option of changing operating modes using the web server if activated.
Proceed as follows.

  1. Open the internet browser and start the web server.
  2. Log on as "admin".
  3. Select the "Start page".
  4. Use the "Go to RUN" and "Go to STOP" buttons to change the operating mode accordingly.

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