you mean this was an unprecise description?
Sorry for misunderstanding, that was precise description, thank you. What I mean is situation when we develop .library from scratch so there is no .project yet using that library.
So after I create and open new library e.g. d:\mynewlib.library and keeping open it, how to actually test/debug with second instance of CodeSys.
Hope now it's more clear. Thank you.
You should debug in the second instance of Codesys:
1. open the library in the project, find the FB and/or methods in the library
2. log into the RPi, download the application, run the application
3. set breakpoints in the FB/methods as you would do with your program.
4. Then you can modify the library in the first instance of Codesys accordingly.
5. Once you make any changes in the first instance, you can update it by clicking the yellow cabinet icon.
6. Then you log out from the RPi and relog into the RPi and download the application, which should use the new library now.