AN OPERATIONAL SEMANTICS OF IEC 61499 FUNCTION BLOCKS (PART 2. CYCLIC EXECUTION MODEL) 

Dubinin Viktor Nikolaevich, Candidate of engineering sciences, associate professor, sub-department of computer science, Penza State University (Penza, 40 Krasnaya str.), victor_n_dubinin@yahoo.com 

004.423 : 519.71 

The international standard IEC 61499 in the field of industrial automation introduces a class of the new generation control systems which are characterized as smart reconfigurable distributed component-based ones. This standard supports the design paradigm based on the function blocks (FB). One of the most important FB execution model is the cyclic execution model. The lack of a clearly defined formal semantics for this model can negatively impact on the quality of designed control software, in particular, it may hinder the verification and simulation of automation systems. In this paper a syntactic-semantic model of IEC 61499 function blocks working in accordance with the cyclic execution model is proposed. The complete structure of the model and the functioning of each module are defined. Besides, a formal model of the system configuration and its unfolding algorithm making it possible to understand the rules of FB systems building on resources and devices are considered. For the definition of operational semantics of FB the author uses a formal notation based on modified abstract state machine. At that, the formal model of FB defines both a model's scheme, representing a set of variables and a set of functions for changing variables' values, and the dynamics of the model in the form of rules for changing these functions. The special attention is paid to the functioning of modules of composite FB and dispatcher as well as the interconnection between the modules at the variables level. The dispatcher module determines a start order for the execution of FB and thus mainly defines a FB execution model. A change of the
dispatcher automatically alters the FB execution model, thus this makes it easy to change the FB semantics in general. 

function block, standard IEC 61499, operational semantics, abstract syntax, cyclic execution model, configuration. 

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