LD UDFB Guided Learning Q04: – Define Enumeration as Related to a PLC-based State Machine

Automation and Control
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This article is part of a guided learning series on building and analyzing User-Defined Function Blocks (UDFBs).

:pushpin: Canonical Article: Building a User-Defined Function Block (UDFB) Using Siemens TIA Portal
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You are reading: Question 4

Define enumeration and then describe how it assists with the design and maintenance of a state machine.

Answer

In the context of the state machine, enumeration is a mapping of state descriptors to integers. For example, instead of saying we are in state 2 we use a human-readable abstraction called uiStClosed.

The primary article uses constants to simulate the enumerated data types.

The enumerated state variables significantly improve the program’s readability while lowering the cognitive load. Instead of remembering the decimal numbers (e.g. state 4), the programmer and technician can read the English description (e.g. fault state).

:writing_hand: Article by Aaron Dahlen, LCDR USCG (Ret.), Application Engineer at DigiKey