Layering Design Research Of Remote Monitored System Based On CAN FieldBus

Controller Area Network (CAN) is a high safety serial communication protocol which today is very popular in industrial environments because of its supporting real-time and distributed control. Among the different device level networks available today, CAN is surely one of the most appealing solutions, because it is clearly defined, stable, and well established, and, what is more, many of products exist on the market based on that communication technology. But the bits to bits arbitration of the CAN protocol defines a static priority to messages exchanged. Due to the fact of the lack of timing information for non periodic data transmission, it is impossible to find a static manner to attribute CAN identifiers to exchanged objects so that applications periods limit can be always be satisfied. When one or many network stations (nodes) send data using the same identifier, at some point, data will differ and generate error. All stations will then back off and retransmit restarting the whole process. In this case, retransmission can lockup the network. The computation-time delay in the feedback controller of a real-time control system may cause failure to update the control inputs during one or more sampling periods. If this delay exceeds a certain limit called hard deadline, the necessary conditions for system stability are violated. In such a case a dynamic failure is said to occur to the system.In this study, the software for control and management is designed based on CANOpen protocol. The master computer communicates with all other nodes in CAN network by the intelligent interface for management and control between the computer enhanced parallel port and CAN field bus to fulfill the functions of diagnosis, disposal, storage and communication. Especially, we derive the hard deadline using dynamic layout theory for such system – the feedback delay is assumed to result only from computation-time delay because other delay elements can be readily dealt with. The paper proposes a bandwidth allocation algorithm not only satisfies the performance requirements of motor control system, but also consider the delay limit of the non-real-time system. In addition, it maximizes the utilization of the bandwidth of the network medium by fully utilizing the residual bandwidth through non-real-time data are transmitted.