Designs Of CAN And BACnet Interactive Gateway For Intelligent Building

As an open international standard of building automation, BACnet standard is supported by most intelligent building facilities manufacturers. MS/TP is a proprietary protocol of BACnet standard, which has been widely used as bottom protocol of building automation net because of its high performance price ratio. However, MS/TP protocol uses EIA-485 as physical layer, and uses token mechanism as the access control of transmission medium. As a result, the MS/TP is incompetent to some high real-time facilities and events. CANbus has the Multi-Master working mode, and divides nodes into different priority levels. Meanwhile CAN adopts non-destructive arbitration bus technology, so it can meet the demand for real-time. Therefore, it is necessary that CAN with CSMA/CD faction can be applied in intelligent building automation system.The communication network is designed with PIC chip and MS/TP protocol of BACnet standard for the characters of intelligent building and the communication standard demanded by building automation facilities. The bottom communication network of CAN bus is designed for high real-time facilities. The interactive gateways of two networks are designed and tested.First, the basic content of BACnet standard is introduced and BACnet node module is designed based on MS/TP protocol. Software is designed based on PIC24 series chips. The physical layer, data link layer, network layer, application layer of BACnet is realized.Second, CAN bus is studied by adopting MCP2515, MCP2551 as controller and transceiver. Meanwhile, CAN bus is described in detail on the basis of MCP2515. According to several normative CAN application layer protocols, a more practical CAN application layer protocol is developed, which not only keeps the inherent reliability and high effectiveness of CAN bus, but also simplifies the system structure.Third, the gateway BACnet protocol_CANbus is designed by analyzing the whole system. The gateway hardware consists of the bottom RS-485 circuit based on MS/TP protocol of BACnet standard and the circuit which communicates with main microcontroller through SPI. Based on PIC24 series mcu, embedded real-time operation system is designed, which the gateway's function is realized on the basis of BACnet protocol and CAN application layer. A high-accuracy design method is proposed based on PIC 18,24 series mcu for real-time clock.At last, BACnet node is tested by VTS software developed by BTL and CAN node is tested by CAN232 interface card and ZLGCANTest software. The feasibility stability and efficiency of the CAN bus is proved through the test of PC software designed for the gateway system.