Data types

The TwinCAT 3 type system displays the data types in an editor on four different tabs. The editor is opened by double-clicking on the "Type System" object in the TwinCAT 3 project tree.

The following data types (TMC editor: "Specifications") are displayed on the Data Types tab:

• Alias: these data types are simply synonyms for other data types. For example, a time range (duration) can be defined in a specific project as UINT.
• Struct: these data types are structures of other data types, which in turn can also be structures.
• Enum: these data types describe enumerations.
• Array: these data types are arrays with a defined number of dimensions as well as the respective length.

The interfaces are displayed on the Interfaces tab. This data type describes an interface that can be provided or used by different components such as function blocks or TcCOM modules. An interface consists of methods that have a respective signature.

The Functions tab shows PLC functions and PLC function blocks whose definition was read from in a TMC/TML file.

The Event Classes tab defines event classes that are used for the TwinCAT 3 EventLogger.