Part Three: Differences in PLC Programming Languages

You are reading Part 3 of the History of PLCs series. In this series of blogs, we write about the PLC industry. Its challenges. And how to overcome them. Enjoy!

Let’s dive in and review the different approaches

For newbies, we will briefly describe the ways of programming PLC systems. Programming methods are now described by a standard (IEC 61131-3), which most PLC manufacturers follow either with greater or lesser fidelity rates. There are multiple ways to approach this:

  • IL (a low-level assembler-like language)
  • Graphical programming languages such as LD, or ladder logic (these enable the drawing of a logic pattern that resembles an electrical scheme), and FBD (a similar, yet more sophisticated language, which resembles an integrated circuit with an electronics scheme)
  • SFC (also a graphical language, which facilitates the means of sequential programming processes) — and finally . . .
  • Text ST or Structured Text.

IL is the original way to program PLC systems, and it does not bring any major benefits, apart from a questionable contribution to the program's performance.

On the other hand, graphical programming procedures have the advantage of relative simplicity and readability. However, this only applies when we apply them to simple problems. In the case of complex problems, their former advantages turn into mere incomprehensibility and chaos.

SFC solved many problems with the coordination and organization of the PLC program, and was undoubtedly a step in the right direction. Its downside is the graphical representation, which slows down the speed of change implementation.

ST resembles programming languages, as we know them from the IT world, the most. It is a procedural system of programming; an imperative procedural paradigm of programming, which has seen the light of this world since the '60s.

The most significant part of creating a solution with a PLC system does not concern the price of its hardware as much as it concerns the price of its programming. That is why it is crucial to think about the tool you are using. As a programmer, you want to spend as little time as possible with tedious tasks and mundane work.

Part one: Rise of the PLC Systems
Part two: PLCs are Challenged
Part three: Differences in PLC Programming Languages
Part four: What Can Australian Natives Teach Us About Modern PLCs?
Part five: Will Industry 4.0 Save Us?
Part six: PLC Performance Challenges
Part seven: Why Beckhoff PLCs?
Part eight: Connecting PLCs to the .NET Environment

Tags: History of PLCs

Peter Kurhajec
CTO of Inxton

Peter Kurhajec

Hello! I'm the CTO of Inxton! More than a decade ago my pet project turned into a full-time job - INXTON. Now I'm on a mission to bring industrial automation and information technologies together.