Research Of Measuring And Controling Network Transport Protocol Based On The CAN Bus

With the development of industrial control systems to network direction, real-time communication is becoming increasingly important among the network instruments, even between the network instrument and the controller. Therefore, a suitable network transmission protocol should be formulated. This issue does a research on CAN-bus transport protocol in the realization based on CAN communication, by building a multi-channel data acquisition circuit. And try to solve the problem on bus competition and bus congestion existing at the multi-master communication. So the topic of this issue is mainly divided into two parts:one part is research of the CAN-bus transport protocol and another part is designing multi-channel data acquisition circuit.The designing principle of CAN-bus transport protocol is using simply, being universal, equipment can be increased and the software can be upgraded. And it must be satisfied to the basic demands of CAN communication. This transport protocol formulated parameter registers by using theory of Modbus communication protocol and applied designing ways of classifying function and parameter registers that referenced Hart communication protocol. Priority of message types and priority of sending nodes are combined in the protocol and the identifier will be divided into the frame type, MAC ID and the frame code, in order to deal with the arbitration problem when multi-master communication occurred. Content of the protocol will be reflected by the identifier and data field.4bytes of data field will be used for data transmission and the other4bytes used for the protocol. To visit a data among network nodes by visiting the parameter registers. The protocol made regulations in detail on the specific frame format, the distribution method of identifier and data field and communication patterns.The multi-channel data acquisition circuit is responsive to designing idea of SOC and contains three modules, including the main controller, the CAN communication module and the ADC module. The entire circuit is divided into the motherboard and the sampling board. The motherboard is responsible for processing the measurement data and the realization of CAN network communication. And the sampling board is responsible for analog quantity sampling of multi-channel. The main controller is a8-bit SOC MCU C8051F500, which is usually launched in a vehicle. The CAN communication will be achieved by the CAN controller embedded in C8051F500and the CAN interface chip CTM1050.ADC module used a highly integrated chip ADS1248who greatly reduced the complexity of the signal sampling, multi-channel choice and signal amplification circuit and increased reliability of system at the same time.