In the last article I ended after compiling and downloading to the S7 1200.

In this article, I am going online with the CPU, changing the Mode to “RUN” and exploring the status information and general properties of the CPU.

There are so many options, parameters and tabs in the CPU properties, I will only be able to cover a few, but it will give you an overview of what the accessible CPU properties are.

To Go Online with the CPU

To go online with the CPU, right-click on the CPU and select “Go online” as shown below

You can now see the online status of the CPU and components

To Change the CPU to Run Mode

Click on the “RUN” button on the right side of the display. You will be greeted with an “Are you sure you want to change the CPU to RUN Mode?” prompt in which you will click “OK”.

After a transition in a “Startup” Mode, the PLC will move to “RUN” Mode

Note the Status LEDs for a CPU

STOP/RUN Status Indicator

  • On Yellow – Stop Mode
  • On Green – Run Mode
  • Flashing – Startup, Selftest, or firmware update

ERROR Status Indicator

  • Flashing Red – Error with CPU, Memory card, mismatched modules, etc
  • Solid Red – Defective state

MAINT Status Indicator

  • Flashing – Memory Card Inserted

For a complete list of other LEDs and status information see the Siemens System Manual:

 A Few CPU Properties to Explore

  • Communication Load

This is the percentage of overall processing capacity that can be available for communication processes.

The default is 20%. I’ve seen this type of setting need to be modified when doing heavy peer to peer communications or when an HMI system is polling very large numbers of tags.

I really like the “Help” access here. When going through a new system, I found it extremely convenient and helpful to have the help indicators pop up as you click on a parameter.

  • Click the arrow next to “Cycle load due to communication”

  • Now I get a drop down that gives me a little more explanation of the parameter as well as a link to the manuals that further information can be found in. Since I am using an S7-1200, I can click that link and it takes me right to what I am looking for. I really love this feature.

  • Time of Day

Another helpful feature is the ability to set when the CPU will adjust the time for daylight savings. You can set it here and it will compensate at the needed day/time.

  • Web Server

You can enable/disable the web server as shown below as well as apply security settings and other parameter settings.

  • CPU Web Page


I am now able to go online with my S7-1200 CPU, it is in the “RUN” state and I have at least become familiar with CPU general settings and navigation of the settings. .

By taking this time to navigate through the settings, I will at least be familiar with them in case I am looking for a parameter in the future.

Spending time, simply clicking, reading, and looking is a good way to get familiar with a system and the more familiar it becomes, the more it will be second-nature to use it.

Written by Brandon Cooper
Senior Controls Engineer and Freelance Writer

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Brandon Cooper


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