⌨ IEC 61131-3 Fundamentals0%
⌨ The Suspiciously Fun PLC Series · Cross-brand

IEC 61131-3:
five languages, one logic.

One international standard defines how almost every PLC is programmed, whatever the brand. IEC 61131-3 gives you five languages for the same job: Ladder (LD), Function Block Diagram (FBD), Structured Text (ST), Sequential Function Chart (SFC) and Instruction List (IL). The 3rd edition deprecated IL and the 4th edition (2025) removed it, but you will still find it in older code. This lesson walks through all five in plain language, with a live example of each.

One logic, five views

🌱 the same motor start/stop appears as rungs, as wired boxes, as a few lines of text and as a step chart, and the PLC runs the same logic whichever view you pick. Choosing a language comes down to who reads it next.

Pick by the job

🎯 LD for boolean interlocks, FBD for signal flow, ST for math and loops, SFC for sequences, IL for legacy. You can even mix several in one project, because the standard lets them call each other.

🌐
Vendor-neutral and accurate. The standard, language and product names (IEC 61131-3, LD, FBD, ST, SFC, IL, PLCopen, Modbus) are kept exact. The logic shown works on any compliant PLC.
No prior PLC experience needed. Every term is defined the first time it appears.