Attributes for software elements of the IEC 1131-3 programming languages

Extensions to the IEC DIS 1131-3 standard for programmable controllers are proposed. This standard defines an architecture and several graphical and textual languages for describing applications for programmable controllers. The architecture supports multi-tasking and deterministic behaviour. The languages which are suitable for describing both continuous and sequential aspects of control applications include: Structured Text (ST), a high level textual language; Sequential Function Chart (SFC) for graphically describing sequences in terms of steps and transitions; and Function Block Diagram (FBD), a graphical language for depicting the flow of control signals through software elements known as function blocks. Practical implementations of the standard have shown that software elements as defined by DIS 1131-3, require additional information when used in real industrial systems. This additional information is required by system tools and utilities that interact with the software elements. It is proposed that this information is added by extending the 1131-3 Structured Text (ST) language, to allow attributes to be attached to certain software elements