Which of the following is a programming language used in CompactLogix PLC systems?

Structured Text is indeed a recognized programming language used in CompactLogix PLC systems. It is part of the IEC 61131-3 standard that defines programming languages for programmable logic controllers. Structured Text allows for high-level programming, enabling the use of more complex data structures and control logic compared to other languages specified in this standard, such as Ladder Logic and Function Block Diagram. This makes it particularly useful for sophisticated calculations, algorithm implementation, and handling of complex data processing tasks, which are common in modern automation applications.

The other options mentioned do not serve as programming languages for PLCs. While a Waterfall Flowchart is a project management tool that illustrates a sequential progression through phases of a project, an Excel Macro is a way to automate tasks in Microsoft Excel, not applicable to PLC programming. Similarly, a Data Flow Diagram is used to represent data processing and flow in systems analysis but does not qualify as a programming language.