ISA Interchange

Welcome to the official blog of the International Society of Automation (ISA).

All Posts

IEC 6-1131-3

The IEC (International Electrotechnical Commission) 6-1131-3 Standard is a widely recognized international standard for the programming of a PLC.

How many ‘Graphical languages’ are there in the IEC  6-1131-3  ?

a.  2

b.  3

c.  4

d.  5

The correct answer is A.
They are Ladder Diagram (LD) and  Function Block Diagram (FBD).

Ladder Diagram


Function Block Diagram


Programming Languages

1. Graphical

1. Ladder Diagram (LD)

2. Function Block Diagram(FBD)


2. Textual

1. Instruction List (IL)

2. Structured Text (ST)


3. Program Control Flow

1. Sequential Function Charts (SFC)

Sequential Function Charts are considered by many to be a graphical language.

IEC 61131-3 is the third part of the IEC 61131 family. This consists of:

•Part 1: General Overview

•Part 2 Hardware

•Part 3 Programming Languages

•Part 4 User Guidelines

•Part 5 Communication

•Part 7 Fuzzy Logic

• Part 8 Application Guidelines


  • Standard will provide greater uniformity between PLCs
  • Does for the process world what OPC (OLE2) did for the computer world
  • Reuse work
  • Reduce amount of retraining
  • Enables programmers to integrate multiple languages within the same application
  • Does not…–
    Specify physical I/O–
    Memory  address mapping
Mark Weisner
Mark Weisner
Mark Weisner is a technical specialist at ISA.

Related Posts

What Is the Difference Between IT and OT Security?

Information Technology (IT) is defined as hardware, software, and communications technologies that focus ...
Jennifer Infantino Halsey Dec 1, 2020 5:15:00 AM

SAMA and ISA Cybersecurity Expert Steve Mustard in Conversation [Podcast]

Recent attacks on safety systems across multiple industries have proven that cybersecurity is no longer j...
Contributing Author Nov 30, 2020 9:57:19 AM

What No One Tells You About Industrial Automation Marketing (Part 3): Email Marketing

Welcome to part three of this multipart series on marketing for the industrial automation industry. If yo...
Chris Sciulli Nov 27, 2020 5:30:00 AM