Hllo Arishgolra;

Experience will how you that very often when the wording "Stop caused by SFB20" appears in the diagnostic buffer, the critical messages that originated the CPU stop are in the first or second preceding messages.

In your case, message 14 tells you bout SFB20, whereas message 15 declares you have an issue with I/O access error, which is generally linked with the appearance of the SF LED. It is generated by your program trying to read or write to a Profibus slave that has been declared defective and that causes the BF LED to light up.

There are more buttons that you do not show in your screenshot,  at the bottom of the diagnstic buffer screen, under the Details section. One of them is marked "Save As". Clicking on it wll open an new text file, diagnose.txt, that will contain all the logged messages from the buffer, with a few additional details that we can use to look for the source of your error messages. Please take that text file and attach it to your next post here, that way we can examne it and hopefully help you locate the problem you are facing.

Hope this helps,

Daniel Chartier

Hello Arishgolra;

To start off with, the diagnose.txt fileyou sent us lists 44 events, whereas the buffer shows 120 messages, the numbers should match. Strange discrepancy.

Every one of the 44 entries in your text log is linked to OB 85. For example:

If you look at the screenshot below, you will see the basic description of OB 85, an Organization Block that should be present in your PLC program: the fact that the OB 85 is called by the operating system when specific errors happen (the I/O access error events) but is not found in your problem leads to a CPU STOP,.

The screenshot is taken from the first chapter of the s7-300/400 System and standard Functions manual, which you can locate here:

https://support.industry.siemens.com/cs/ca/en/view/44240604

My suggestion, as a first step to understand the faults you ar ehaving, would be t create an OB 85 block in your program, compile it (without placing any program instructions in it). Then disconnect your slave no. 9 from the network, and remove it from the hardware configuration. Download the new configuration and the program (with the empty OB 85) to the CPU.

Tell us if you are now able to download, and if your LEDs are still lit.

The next step will depend on what the results are from thse tests.

Hope this helps,

Daniel Chartier