A hard real-time bus arbitration protocol based on EIA-709

Field area networks (fieldbus) are used in a wide area of applications. A lot of different protocols satisfy the needs of the manifold demands of these applications. In process automation, hard real-time requirements make it difficult to use flexible, well established OSI fieldbus systems like e.g. LonWorks (standardized as ANSI/EIA-709) which is now mainly used for home and building automation. Companies developing LonWorks products are starting to evaluate the possibilities of using the same technology for high-speed and real-time applications in order to avoid the overhead of several different communication protocols. This paper describes the development and implementation of a hard real-time bus arbitration scheme for the high-speed network controller "L-Chip", which processes the lower three layers of the EIA-709 protocol. It is shown that the approach presented herein combines optimized bandwidth utilization, fault tolerance and compatibility to existing implementations with the adherence to hard deadlines.