TIA Portal Openness C# — Common Foundation

Source: TIA Portal Openness General Functions Manual (03/2026, V21); V21 IntelliSense XML documentation files (PublicAPI\V21\net48*.xml)

V21 modular assembly architecture

V21 splits the API across multiple DLLs instead of a single Siemens.Engineering.dll. Every project needs Siemens.Engineering.Base.dll; add domain DLLs as required. Referencing the wrong DLL (or omitting one) causes TypeLoadException at runtime.

Full mapping: See references/assembly-namespace-map.md for the exhaustive namespace → DLL → domain skill table, cross-assembly warnings, and csproj patterns.

Namespaces by assembly