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Vol: 4(4) No: 1 / March 1994 Communication Protocol for Interconnection Dan Buzuloiu Institutul de Cercetari în Informatica, Miciurin nr. 8-10, 71316 Bucuresti, Romania Dumitru Popescu Facultatea de Automatica si Calculatoare Institutul Politehnic Bucuresti, Splaiul Independentei nr. 106, Bucuresti, Romania Keywords: communication protocols, PLC, CNC Abstract A protocol for field level interconnection is used to connect the process interface level (process I/O) and the first level of automation devices. The protocol described in the paper was designed for fast means of communications between PCs and simple, low memory PLCs and CNCs. It follows the OSI architecture, implementing layers 1,2 and 7 of this model. Layer 1 is implemented by RS 232, RS 422 or RS 485 standards. A short discussion about connection between - communicating devices using these standards is made. Layer 2 implements a master- s1ave medium access strategy, as being simpler than other strategies (e.g. token passing) and adding a smaller overhead. Service definition and protocol for layer 2 are given. Layer 7 service primitives implement functions useful in process automation. These primitives are using four object types: variable, domain, program, event. Detailed protocol description is given. Service primitives are implemented as C procedures, for their use in embedded C programs, as well as MEX programs, for their use directly in MATLAB. Further protocol extension is foreseen. In this purpose, an extended protocol structure is given, as well as an algorithm for CRC computing. References [1] Cole, D. Gerald, Implementing OSI Networks (John Wiley, 1990) [2] d’Amson, C, Pell, A, Understanding OSI Networks (Prentice Hall, 1993) [3] Mullender, S., Distributed Systems (Addison Wesley, 1989) [4] Nutt, G., Open Systems (Prentice Hall, 1992) [5] Olsson, G., Piani, G., Computer Systems for Automation and control (Prentice Hall, 1992) [6] Tannenbaum, AS., Computer Networks (Prentice Hall, 1992) [7] Pimentel, J., Communikation Networks for Manufocturing (Prentice Hall, 1991) [8] Buzuloiu, D, Reţle de calculatoare in CIME, in: Revista de informatică şi automatică vol. IV, 1993 [9] Comanescu, N., Jitaru, N., Domide, A., Buzuloiu, D., Centru de transfer tehnologic în CIME – Raport de cercetare ICI, 1993 |