Real-time clock synchronisation over a CAN-based fieldbus

• Main Author: Dimyati, K.
• Published: Swansea University 1996
• Subjects: 004.33
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636447

The steady increase in the use of automation systems in industries such as manufacturing and transportation has created the need for low-cost, robust, real-time communication systems. Various standard communication proposals, such as those based on the MAP and fieldbus initiatives, have been developed to address this need. An important and essential feature of any such real-time communication systems is, it is suggested here, support for clock synchronisation. The need for this arises from the fact that all the data that is read by a real-world controlling process, and then used by a particular node associated with that process, will necessarily be related to the temporal characteristics of the process under control. The Controller Area Network (CAN) fieldbus, initially developed for use in the automotive industry, is finding increased use in the more general industrial automation field, because of its simplicity, robustness and low cost. CAN, however, does not offer direct facilities to support real-time clock synchronisation between the interconnected nodes. Thus, the aim of the work presented in this thesis is to develop techniques that will allow real-time clock synchronisation over the CAN protocol. The solution, which is realised as a hardware-assisted software system, will allow CAN to support truly real-time communication over an existing, commercial system. In this thesis, a study of other possible protocols has been made, leading to the conclusion that CAN is industrially important for use in truly real-time applications. The need for clock synchronisation is reviewed, and possible solutions are surveyed. A hybrid scheme is suggested as being the most promising solution to the problems investigated, in that it balances the performance and cost criteria. Before proceeding to an actual hardware/software design of such a solution, the system was modelled, simulated and analysed. This provided a deep insight into the protocol, helped to resolve many vague manufacturer's specifications, and showed that the proposed solution is viable - especially in terms of the traffic loading introduced. A fully operational 4-layer PCB version of the proposed solution was then developed, and the excellent results achieved are reported here. Based on this, suggestions for full commercialisation have been derived.