An improved CAN fieldbus for industrial applications

The controller area network (CAN) was originally developed to support cheap and rather simple automotive applications. However, because of its performance and low cost, it is also being considered in automated manufacturing and process control environments to interconnect intelligent devices, such as modern sensors and actuators. Unfortunately, CAN, in its current form, is not able to either share out the system bandwidth among the different devices fairly or to grant an upper bound on the transmission times experienced by the nodes connected to the communication medium as it happens, for instance, in the token-based networks. In this paper, two slight modifications of the basic CAN protocol are presented that satisfy the above-mentioned requirements at the expense of a very small degradation of the system's performance. Both these solutions exhibit a high degree of compatibility with those devices which have already been designed for the conventional CAN fieldbus. Besides introducing the new mechanisms, this paper also presents some performance figures obtained using a specially developed software simulator, while the behavior of the new mechanisms is compared to the traditional CAN systems, in order to see how effective they are.