PLC PROGRAMMING LANGUAGES: A FORMAL APPROACH Luciano Baresi( + ), Stefania Carmeli( ++ ) 1 , Antonello Monti( ++ ), and Mauro Pezzè( + ) ( + )Dipartimento di Elettronica e Informazione - Politecnico di Milano Piazza L. da Vinci 32, I-20133 Milano, Italy Phone: +39-02-23993400 Fax: +39-02-23993411 E-mail: baresi|pezze@elet.polimi.it ( ++ )Dipartimento di Elettrotecnica - Politecnico di Milano Piazza L. da Vinci 32, I-20133 Milano, Italy Phone: +39-02-23993702 Fax: +39-02-23993703 E-mail: carmeli|anto@etec.polimi.it Abstract This paper introduces describes how to integrate standard editing and code generation functionalities offered by most tools supporting the IEC standard 1131-3 with capabilities for modelling and simulating the plant and its interactions with the digital controller. The 1131-3 notations (in particular Functional Block Diagrams) are complemented with differential equations that describe the behaviour of the plant and with an underlying formal model, which supports the analysis of functional and timing properties. Introduction Standards play a key role in industrial development. They enhance compatibility, openness and interoperability among different products, increase the confidence level of users and certification agencies, and promote the development of tools and methodologies by freezing notations, methods and techniques. The IEC standard 1131-3 [5] defines a set of notations and methods for developing control systems. It is now adopted by many manufacturers and is increasingly supported by tools. Most existing tools support editing of the IEC 1131-3 notations and code generation, but provide little support to simulation and analysis of early specifications. In this paper, we describe how to complement the main editing and code generation functionalities offered by most tools supporting the IEC standard 1131-3 with capabilities for modelling and simulating the plant and its interactions with the digital controller. Suitable simulation and analysis of the early specifications of the digital controller integrated with the plant can identify functional and timing errors that would be difficult to identify in and expensive to remove from the final system. In this paper, the 1131-3 notations (in particular Functional Block Diagrams) are complemented with differential equations that describe the behaviour of the plant and an underlying formal model, which supports the analysis of functional and timing properties. The paper introduces the approach and describes the industrial experience within the ESPRIT project INFORMA 2 . 1 Luciano Baresi and Stefania Carmeli are partially supported by Ansaldo Sistemi Industriali S.p.A., viale Sarca 336 - 20126 Milano (Italy) 2 The work presented in this paper has been partially funded by European Community under ESPRIT Project INFORMA (EP23163). The consortium comprises IFAD (Denmark),