Τhe Function Block Model in Embedded Control and Automation From IEC61131 to IEC61499

The Function Block (FB) model was first standardized by the 1131 standard of the International Electrotechnical Commission (IEC) for programmable controllers. This standard was successfully adopted by the industry but it seems to have several constraints for the development of today’s complex embedded control and automation systems. These constraints are mainly imposed by the procedural programming paradigm and the device centric approach that are adopted by the standard. The IEC to address these constraints proposed the 61499 standard that is an attempt to exploit object-orientation and the application-centric paradigm in the control and automation domain. In this paper, the FB models of 1131 and 61499 are briefly described and several unclear issues related to the programming paradigms adopted, interoperability, composability and execution semantics of these FB models are clarified. The paper focuses on the execution semantics of the 61499 standard since this is one of the most important reasons that the industry has not yet accepted this standard. Key-Words: embedded control and automation systems, IEC 61131; IEC 61499; 1131 Function Block Model; IEC61499 execution environment; execution model semantics; Factory Automation.