Experiments based on CAN bus electrical system design guide

Abstract: Based on the CAN (Controller Area Network) protocol and its application in research, using CAN communications controller, CAN transceiver, as well as enhanced micro-controller components, developed and developing applications based on CAN bus system - - Electrical test guidance system


In the production of field control system, intelligent equipment and Chang Gui electrical equipment Di installation, commissioning and maintenance requires considerable technical staff Shu Liang Di electrical, how Gao Xiao, volume, 規范 to train Gao Ji Jiao electrical apparatus manufacturers Caozuorenyuan yes urgent problem. It requires equipment with communication capabilities, training process for teachers to acquire the dynamic indicators, to understand the actual experimental conditions students can control the experiment process to achieve guidance.

Based on the CAN (Controller Area Network) protocol and its application in research, using CAN communications controller, CAN transceiver, as well as enhanced micro-controller components, developed and developing applications based on CAN bus system - Electrical Engineering Laboratory guidance system, the electrical network laboratory experiment out of teaching courses, thereby changing the shortage of conventional teaching methods for students to be more independent, flexible and complete the experimental task, and can be extended according to their experimental conditions for the establishment of open experiment training facilities and lay a good foundation base, but also to make students understand the real value of the network experiments to understand the CAN bus control technology basics.

1 CAN bus network communication protocol layer model

Applications for different areas of application of choice of different norms, the general areas of application, a "command - response" model of communication protocols, we would achieve reliable and effective "master - slave" type of communication 網絡. If you need a great deal of data exchange or communication flexible CAN network, you can use some of the standard multi-master communication protocol, such as HilonB agreement or agreements with CAN2.0 the definition of a remote frame. In the field of automotive electronics products, usually directly by reference or other standard specification J1939. Communication design in power, the regular use of DeviceNETV2.0 specification, the specification has been adopted by national standards in China. Communication in the field of intelligent buildings, the general use of Modbus protocol or continue to use the RS-485 mode of "master - slave" protocol.

The system for establishing the actual CAN bus communication network, the use of the underlying hardware to achieve the CAN physical layer, data link layer control. Application CAN2.0A / B agreement communication error detection mechanisms such as the CAN bus communication network to ensure the reliability of an established user protocol layer communication protocols, and network traffic data stream interpretation and management. The user protocol layer (application layer) communication protocol by the data frame and remote frame format defined to achieve, and are "master - slave" type of structure
2 Hardware system components and design of the hardware module

Fieldbus based electrician experimental guidance system hardware consists of the host, interface cards, smart node (slave) component. Host Zhongyou application and database, etc. Wen Jian; CAN Interface Card is the bridge to achieve communication, 同時 in networking Ta also serves as a node; Zhinengjiedian You based on field bus, single chip technology for data collection and transmission modules and physical operations Jiexianzhuangzhi etc.. Node can be under the control of the computer's electrical experiments on the students intelligent guidance.

2.1 Data Acquisition and Transmission Module

Data acquisition and transmission module can be divided into five main parts, namely: the composition of the host portion of the MCU AT89S52; by the SJA1000, PCA82C250, optical isolation circuit composed of CAN bus control and interface section; from the 5V reference voltage source, driver transistor, LED lights, digital tubes, power and display parts; using four 8255 as the I / O port expansion, and with operator back-end interface circuit digital data conversion and acquisition part; actual operatives bit.

AT89S52 MCU as a host, is responsible for initialization of the SJA1000, SJA1000 achieved by controlling the receive and transmit data such as communication, the implementation of the experimental data collection, using P1 port to control the dynamic scanning display relevant data to guide the experiment. Choose 74L, S373 as an address latch with a 74LS138 on the 8255, SJA1000 for chip select.

2.1.1 CAN bus control and interface section

From the machine running the process, as required to complete a number of host CPU tasks requires a certain degree of flexibility at the same time, the system needs to have some scalability, therefore, the CAN controller from the machine selection Philips company SJA1000. Chosen as the CAN bus PCA82C250 transceiver, it is the physical layer CAN protocol controller and the question of interface, with anti-transient, anti-RF and anti-electromagnetic interference performance, internal limiting circuit with short circuit on the transmission output level protection functions. In the node (station machine) was inserted between the coupler and the media circuit, that is, the TX0 and RX0 SJA1000 is not directly related to the TXD and RXD 82C250 connected, but after high-speed optocoupler 6N137 connected with 82C250. 6N137 separated for high-speed optical devices, as the outside line and asked the isolation system, using two completely separate power supply VCC and VDD are two parts of the optocoupler circuit power supply, so as to achieve complete isolation between the signals, so that effectively improve the system of anti-jamming capability and internal security of the system. SJA1000 of ADO ~ AD7 the P0 port to connect to the AT89S52, CS connected to the Y4 74LS138 port, Y4 is 0, CPU chip memory address optional in the SJA1000, CPU through these addresses can perform the appropriate read and write operations SJA1000, SJA1000 of RD, WR, ALE AT89S52 respectively connected to the corresponding pin can be connected INT AT89S52 the INT0 or INT1. AT89S52 can be interrupted or query access SJA1000, INT can also be connected to other ports AT89S52 using query access SJA1000. Interface circuit shown in Figure 1.
2.1.2 Data Conversion and acquisition part

1) Data Conversion Circuit

According to electrical control theory analysis and research, from which optimized kind of general wiring methods, to the point Dui Ying Yi Ci by order of operations to the CPU's I / O port provides Yidingguize the 5 V level, you can 完成 Cai Yang and Shu Zi amount of conversion. Students for the operator and the actual position of the positive terminal connector, the rear is connected to the signal line, signal line and the other end of the port 8255 of a fixed phase.

2) the sampling circuit

Station side machine 4 8255 as I / O port expansion, and through 20 kΩ pull-down resistor and the corresponding back-end operator position terminal phase. Initialization in 8255, allowed to work in the way of ordinary time, this time, if a terminal is high, then the corresponding 8255 I / O port can be collected high. If all terminals are high, then the total current will be close to 7805 the maximum output current. Therefore, the need to use split-phase, sub-circuit method, the experiment guide operation, completion of the pilot's guidance tasks. 2.1.3 MCU access to the hardware addresses of the various parts of the circuit

Hardware circuit design is completed, the access address can be determined according to the specific situation. In this paper, P2.5 ~ 2.7 port to control 74LS138, 8255, respectively 4 and SJA1000 to chip select and access. The access address as shown in Table 1.

Experiments based on CAN bus electrical system design guide

3 CAN-bus electrical system node test software

3.1 Data acquisition and display in the node to achieve

In this paper, AT89S52 MCU as the station (node) system control, data acquisition and display of the core, using Keil uVision2 integrated development environment for software development and debugging.

As the machine needs to be done from the display, data acquisition and transmission capabilities, so at least by two interrupt source control, the INT0 and T0. Of which: INT0 is used to indicate CAN Bus data reception and transmission process such as external interrupt; T0 control display scan clock. Data sampling process is divided into two situations: First, automatic initialization of the initial sampling; Second, during the running of the program, when the received data frame, the automatic implementation of a sample.
1) showed that some of the functions and process analysis

Shows there are three kinds of circuit function: display initialization is successful, the experimental error and the steps the students instructions and other information. This information is user-based hardware and software needs of their own definitions. In this paper, 74LS47 decoder driver IC to drive and display control. By software running, so P1 port control 6, respectively yang side of the digital control off, while the P0 port to the 74LS47 decoder driver circuit to provide data to realize the display of dynamic scan control. Initializing a custom display for the normal 004 321, during normal operation display issue number, phase number, grade or step wiring error number when an error flag.

2) the principle of data acquisition and process analysis

The principles of data collection is: CPU through the port P2 corresponding Qi pin control to its counterpart in the Fenxiang first terminal Tigong 5 V Dianping, the other contacts by Yi Ding Xiang Lian Yongxinhaoxian rules so that each power level Duan Zi Shang Chuxian 0 or high, so the corresponding terminal state can be read by 8255. That a certain sequence of wiring can be read in the corresponding 8255 data in different sampling. 8255 Each port can read an 8-bit binary number (1 byte), these steps associated with the experimental data, so that each operation have different data. The system needs 4 8255, obtained a sample of 12 8-bit binary number.

RAM space in the microcontroller to set up a 20-byte array as a collection of data storage space. In the power-on reset, so that 8255 are initialized to the ordinary reading methods to initialize the array to write data. Normal operation, each received a data frame to conduct a data collection. The data collected directly by CAN bus communication frame format, the contents of the array is updated, to prepare to read and upload. Data acquisition memory address and content shown in Table 2.

Experiments based on CAN bus electrical system design guide

3.2 Communication Software

Main points in this article using PC15121 interface card as the interface device, in communication with the protocol established, the main station and the communication from the station can call the interface functions of the product to achieve. From the station (station) CAN nodes control software is modular in design. There are five modules: SJA1000 initialization module, SJA1000 receive data module, SJA1000 send data module, SJA1000 error processing module; systems and other mission modules.

3.3 The procedures for the operation of smart nodes

From the main function for hardware initialization, enter the normal display, waiting for an interrupt event occurs, receive data frames, data processing and delivery was, waiting to receive remote frames and return the required data frames and data acquisition. The main program flow shown in Figure 2. External interrupt service program flow shown in Figure 3.

Experiments based on CAN bus electrical system design guide

In the host program design, interface and data processing algorithms process design is the key. Among them, the host interface card can be used as an intelligent node, network, data communication is mainly the card operation.

4 Conclusion

This article on the CAN bus network hardware and software systems analysis and research, using one kind of networking protocol based on CAN bus and data transmission mode and experimental Zhidao 其 used in electrical systems to "Zhu 1 from" Tongxinmoshi Network communication, to achieve the expected goal. Equipment to meet the test environment.

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