PLCopen Guidelines for Object Orientation

The 3rd edition of the IEC 61131-3 standard enables Object Oriented Programming, OOP. With Object Orientation one can make many additional choices in the way the program is structured and decomposed, providing a different look & feel to the users especially across the different systems and platforms, creating different training guidelines and differences in maintenance.

To support the right choices and to add to the training programs, PLCopen started an OOP Guidelines initiative, in order to create a more homogeneous method. This activity helps to understand to make the right choice upfront, and to create consistent programs with long-term support.

PLCopen was already involved in OOP with the definition of PLCopen compliant function block libraries, which included both object orientation and classical programming (procedural). With the specification on communication via OPC UA other OOP aspects come in, and with the security aspects more OOP will arrive at the controller level.
This does not mean that the classical programming will be replaced: due to the upwards compatibility both programming styles can cooperate in parallel and be used in those areas that they serve best.

A kick-off meeting took place earlier this year. And, together with its members, PLCopen is now working on an additional document within the framework of the PLCopen Software Construction Guidelines. This new document is expected to be published in the course of next year.
The existing documents from this activity can be found at our website :

  • Coding Guidelines,
  • PLCopen Compliant Libraries, and
  • Structuring with SFC – do’s & don’ts.