Evolution of IEC 1131 (published in 1992), IEC 61131 represents the most successful effort to standardize industrial control technologies by bringing them back to an international standardization system. For many years, in fact, the control systems market has seen the proliferation of a variety of languages, sub-languages, development and test environments, different for each manufacturer. Result: loss of common methodological basis (in software and hardware) and communication problems between PLCs of different manufacturers. To remedy this situation and to facilitate a meeting point between designers, users and manufacturers of PLCs, the International Electrotechnical Commission (IEC) introduced the 61131 standard in the early 1990s.

IEC 61131-3

The third part of IEC 61131 deals with the programming languages used in industrial controllers. The standard defines text programming languages (instruction list, structured text) and graphics (contact diagram, function block diagram, sequential function diagram). According to the IEC 61131-3 standard, Plc programs consist of a number of software elements, implemented in different languages. Typically, a program consists of a network of functions and function blocks capable of exchanging data. The functions and functional blocks are the basic building blocks, containing a data structure and an algorithm.


SoftPlcs are software emulations of typical Plc functionality. Based on PC type hardware architectures and equipped with real-time operating systems (e.g. Windows CE, Rtai, RTLinux, Qnx), they have the fundamental objective of making the control software-hardware independent. The main fields of applications are those of motion control, machine builders and in test and simulation sessions. SoftPlc implement the IEC 61131-3 standard and its programming languages. Associations such as PLCopen ( promote standards related to programming technology, their reuse and interoperability with other systems: not only the IEC 61131-3 standard, but also libraries for motion control, safety features, XML specifications for interface management.


Straton is one of the most popular platform-independent soft PLCs in the industry completely based on IEC 61131-3 and the programming languages ST, IL, FBD, SFC, LD. Straton is an integrated development tool that supports, among others, protocols for energy (IEC 60870-5-101 and IEC 60870-5-104) and remote control (IEC 61850).

SENECA multifunction controllers (Z-TWS11, Z-TWS4, S6001-RTU, Z-PASS2-S) are developed on a Linux basis to accommodate this development environment.

SENECA controllers are also able to perform RTU/Gateway functions, ModBUS RTU ModBUS TCP conversion, virtual networking via the Internet and point-to-point tunnelling.

They can also act as redundant controllers for plant automation, energy produced control, management of renewable energy plants (biomass, photovoltaic, wind etc.), development of smart grids. Configurable as web server and TCP-IP nodes, they are open to SCADA/EMS/WEB-based supervision platforms.

Ladder Diagram screen in Straton environment