I use a 315-2 DP CPU and communicate with a single profibus interface. The connection between CPU and HMI is ethernet where I use a CP 343-1 Lean.

I will add a picture of how it looks.

So my experience with the FB126 is that it can work, but with some devices it has definitely problems.. For example it doesn't work with two PB interfaces on one CPU. I also think that it has problems with an ethernet-CP (CP343). You can forget troubleshooting. This FB was written 20 years ago and was expanded every time so there is also much punk in it which can make problems..

When you want a diagnostic write your own. You can use SFC51 "Read System Status". With this function you can read different System lists from CPU.

Look here:

https://support.industry.siemens.com/cs/#document/19951051?lc=de-CH

Or mark SFC51 in S7 and look at the help.

I hope this can help you..

nice regards

Ok, then i will give it up and continue work on my own solution with FB99 "FB_READ_DR_CTRL".

Thanks :)