CAN bus in the central air-conditioning control system

Abstract: The CAN bus based on the central air-conditioning control system, and system design programs and software and hardware design are analyzed and discussed. The system can achieve high-precision temperature and humidity control.

Central Air Conditioning System is an intelligent building an integral part. The traditional control method is used DDC (Direct Digital Controller) mode, the various temperature and humidity measure points and control points connected to one or more DDC, the implementation of multi-real time. As more modern intelligent building floor, a number of different floors in the air conditioning fan, temperature, humidity detection point located in each room, using DDC control has lead way too long, construction inconvenience, the system real-time communication and reliability of the disadvantages of not .

In a variety of communication methods, field bus for industrial control industrial control technology is the field of data communications solution the best solution to the problem. Fieldbus technology is the late 80s in the twentieth century developed an advanced field of industrial control technology. It combines digital communications, intelligent instruments, computer technology, network technology in one, a fundamental breakthrough in the traditional "point" type of analog or digital - the limitations of analog signal control for real "distributed control, centralized management "provides the technical guarantee.

CAN bus in the central air-conditioning control system

Fieldbus communication protocol structure is provided under the International Organization for Standardization Open Systems Interconnection model (ISO / OSI) to set. The use of CAN bus system is the first application in China are one of the fieldbus, which uses ISO / OSI seven layer within the framework of the physical and data link layer. CAN bus criterion used by the multi-master mode, any node on the network can take the initiative to other nodes send messages, network real-time systems work sites can be divided into different priority requirements. Data link layer frame structure with short, each frame is 8 bytes, easy error correction. Lost during the arbitration or an error sending the frame can be automatically re-sent automatically from the bus node failure. CAN bus standard supports full-duplex communication, using twisted pair and fiber optic transmission medium, transmission rate up to 1Mbps, up to 110 nodes. The main feature of the abolition of the traditional station address code, and replace the data block is encoded communications. Its fault tolerance and anti-jamming capability, transfer safe.

A central air-conditioning control system as a whole constitute

Central Air Conditioning System of the overall block diagram shown in Figure 1. The figure, the host computer using IBM-PC compatible, the receiver is responsible for system control and management, send control commands, the system real-time display of the work process. The cell controller as the next bit plane, produced by ATMEL AT89C51 microcontroller as the microprocessor, the unit responsible for air-conditioning fan unit field data testing and working state control. Cell controller cents SJA1000 CAN Bus Controller is responsible for receiving data from the CAN bus, and up through the CAN bus bit machine to send data. PC through the PC bus expansion slot inserted in the intelligent CAN bus CAN bus communication adapter card connection, and through CAN bus connected with the cell controller. Cell controller can also be from the host machine, directly on-site manual control.

System works principle is: the unit of the cell controller Jinxing each test point circuit test, the test figures at CAN bus protocol standard Fa Song Ji host machine; 上位 machine through the intelligent CAN Bus Adapter Jieshou From the cell controller data, according to the operator's instructions or system software pre-set control procedures to the cell controller to send control commands from the cell controller on the air conditioning fan units for real-time control. If from the host computer, cell controller will set the control parameters according to the software directly to the air conditioning fan units for automatic control. Operator unit controller via a small keypad on the control parameters of the scene changes.

CAN bus in the central air-conditioning control system

2 Hardware Design

System hardware includes intelligent CAN bus communication adapter cards and cell controller. Figure 2 Intelligent CAN bus communication adapter card block diagram. It provides a host computer and the CAN bus interface, high performance embedded microprocessor 80C188, CAN bus controller 82C200 and 82C250 CA line transceiver for data exchange and communications processing. PHILIPS 82C200 is the company's products, complete physical layer and data link layer of all the features. Electronic control unit (ECU) of the application layer from the microprocessor to provide, 82C200 to provide a multi-purpose interface. Dual-port RAM IDT7230 as PC machines with CAN-bus Kong Zhiqi data commons can provide two kinds of Xianghuduli the port, Meigeduankou have their own address lines, data lines and Kongzhi line, Bingqiejuyou two separate interrupt logic to implement the handshake between the two CPU control signal. She Zhiqiang pair of port by hardware and software into the PC RAM mapping machine's Wu Li deposit, Shi Shu Ju Xiang Dangyu transceiver to read and write data directly to the Neicun, thus enhancing the data exchange rate, Bing Tong Yi Bao Zheng both CPU Tongshi right memory cell reading and writing O'clock accuracy of the data.

In addition, the intelligent CAN Bus Adapter also has interrupt selection, main memory base address selection, LED indicating system status and the status of CAN transceiver functions.

System work, the host computer to control commands sent by the ISA bus, CAN bus communication adapter to the smart card, written by the drive circuit dual-port RAM, and an interrupt signal. CAN communication controller 82C200 interrupt signal received from the dual port RAM, remove the data, and to CAN bus protocol standard, the output driver circuit, optical isolation circuits and CAN bus transceiver 82C250 CAN bus to send to complete from the host computer to cell controller data exchange. PC receive data process and the process of sending an order similar to, but in the opposite direction.

Figure 3 for the cell controller circuit block diagram. The figure, the microprocessor color ATMEL AT89C51 microcontroller produced, CAN bus controller used SJA1000, CAN bus transceiver is still used 82C250, control CAN bus data exchange. Work, CAN bus controller SJA1000 CAN bus from the host computer to receive commands and data sent to interrupt notification CPU89C51. CPU interrupt signal received, it will SJA1000 received data into RAM, and the data on the I / O interface circuit to issue the appropriate command, control, fan units, humidifiers and other components for the implementation of appropriate action. If the host computer requires the unit status information, the CPU starts the data collection procedures, control I / O interface circuit test points on each road test data, issued by the CAN bus controller to the CAN bus, the host computer to receive. I / O interface circuit provides 8 digital inputs, 8 digital outputs, 16 analog inputs and 4 analog output interface for connecting unit test points and control points each.

CAN bus in the central air-conditioning control system

X25045 hardware watchdog circuit for system monitoring, to prevent the program running to fly, and provide 512-byte EEPROM to protect critical system control parameters to improve the cell controller's disturbance.

Digital display can show each return air fan humidity, air temperature, return air humidity, transducer frequency, throttle opening, valve opening, alarm signal systems such as the type and amount of state information. Keypad to set parameters for modifying, changing the display type, so that cell controller from the PC in the case of control functions can still be completed.

3 Software Design

System software management software from the PC and cell controller software. PC management software is in the Windows98 operating platform, using Visual Basic6.0 development of, including system monitoring, traffic management, data processing, control commands, dynamic display modules, with Interface You Hao, intuitive display, convenient operation. System run time, the test points and control points of the location to visualize graphically displayed in positions of machine monitor, detect and control in their respective positions Pang Shu Ju Dong Tai display, who can be trained by the simple control of the whole system. Cell controller control software using 8051 assembly language programming, the EEPROM 89C51 curing Fair, mainly for data acquisition, data communication, I / O interface control, digital display control functions. According to the various seasons of indoor temperature and humidity of different requirements, the software pre-selected set of control parameters in different seasons and may be modified at any time through the small keyboard. Actual operation, the humidity control accuracy of ± 0.5 ℃, humidity control accuracy of ± 2% RH.

Central air conditioning control 系統, the under-machine communication between using CAN bus, the system can be Dada improve the reliability, Shi Shi Xing and expansion of high precision and humidity, humidity control, Juyou wide of the extension and application.