SIL to NonSIL communication
Communication to an application with higher SIL level must go through Diagram. This is explained in manuals and on this forum. No problem.
But, what about from SIL to NonSIL application, is that possible with communication variables directly, or do I need to go through Diagrams even in this direction? The manual does not mention this so I presume it is OK.
When downloading to SoftPLC it accepts communication without Diagrams in both directions, could be a nasty suprise on site :-(
In case of IAC, there are two types of communication according to manual, one is internal IAC and another is external IAC.
In case you are using IAC between same controller, then termed as internal IAC where no external communication is being established. So I guess, your case fals in this category. Please go through the manual 3BSE035982-xxx (Communication Protocol) page 56. For your reference pasted the extract from the manual.
I guess, when you are having a communication between two different physical controllers, the restrictions work as usual (as an external commuication is being set up).
For communication to an application with higher SIL level You don't have to make it in diagram, for this kind of communication You can use control module MMSDef2Real / MMSRead2Real [HI version for SIL 3] (or simmilar from that library, according to Yours needs).
for SIL to NonSil You are able to use communication variables freely (in older versions of 800xA HI You have to use control modules/function blocks).
If on living CPU recieve error message that nonSIL CV [communication from nonSIL to SIL] is not allowed in SIL app check project compiler switches (for SIL1/2 only).
good luck on site :)