Book Image

Mastering PLC Programming

By : Mason White
Book Image

Mastering PLC Programming

By: Mason White

Overview of this book

Object-oriented programming (OOP) is a new feature of PLC programming that has taken the automation world by storm. This book provides you with the necessary skills to succeed in the modern automation programming environment. The book is designed in a way to take you through advanced topics such as OOP design, SOLID programming, the software development lifecycle (SDLC), library design, HMI development, general software engineering practices, and more. To hone your programming skills, each chapter has a simulated real-world project that’ll enable you to apply the skills you’ve learned. In all, this book not only covers complex PLC programming topics, but it also removes the financial barrier that comes with most books as all examples utilize free software. This means that to follow along, you DO NOT need to purchase any PLC hardware or software. By the end of this PLC book, you will have what it takes to create long-lasting codebases for any modern automation project.
Table of Contents (25 chapters)
1
Part 1 – An Introduction to Advanced PLC Programming
6
Part 2 – Modularity and Objects
10
Part 3 – Software Engineering for PLCs
14
Part 4 – HMIs and Alarms
19
Part 5 – Final Project and Thoughts

Understanding constants

It is often necessary to have an immutable variable. In other words, it is often necessary to declare a variable, assign it a value, and ensure that the value never changes. Possible examples of required constants are as follows:

  • Mathematical constants such as pi
  • Motor speeds that never change
  • Machine part sizes for calculation (things such as gear ratios)

This list is by no means comprehensive, nor will you always need to declare constants for the preceding bullet items. Whether or not you declare a constant is up to you and the application that you’re developing. In short, you will declare a constant when you want to add a level of protection so that a variable’s value never changes.

Declaring a constant is very simple. You can either use the Auto Declare tool and simply check the CONSTANT box, or you can declare one manually with the following syntax:

VAR CONSTANT
      const: INT :...