tia-csharp-common

# 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 V21 > namespace → DLL → domain skill table, cross-assembly warnings, and csproj patterns. ### Namespaces by assembly Only import what is actually used. The list below covers the most commonly needed namespaces. The mapping file summarizes the XML-documented namespaces across all 16 installed V21 PublicAPI DLLs. **Siemens.Engineering.Base.dll** (always required): ```csharp using Siemens.Engineering; // TiaPortal, Project, ExclusiveAccess, Transaction, events, exceptions using Siemens.Engineering.Compiler; // CompilerResult using Siemens.Engineering.Compare; // CompareResult using Siemens.Engineering.Connection; // connection objects between devices using Siemens.Engineering.CrossReference; // cross-reference queries using Siemens.Engineering.Download; // DownloadProvider, DownloadConfiguration using Siemens.Engineering.Download.Configu...