Design of CAN/LIN Gateway Based on AT89C51 MCU

Introduction

Fieldbus technology has been widely used in industrial control, especially CAN (Control Area Network) bus, which has the advantages of high reliability, low cost and easy implementation, and occupies a large share in the actual engineering application of fieldbus. With the development of bus technology, LIN (Local Interconnect Network) bus is a low-cost serial communication network, whose goal is to provide auxiliary functions for the existing fieldbus control network, especially the bus application in the automobile control network. Therefore, there must be a LIN bus and other bus communication interface implementation. Taking CAN bus as an example, this paper proposes a CAN-LIN gateway design based on AT89C51CC03 single-chip microcomputer.

LIN is a low-cost serial communication network used to control distributed electronic systems in automobiles. The goal of LIN is to provide auxiliary functions for existing automobile networks (such as CAN bus). Therefore, LIN bus is an auxiliary bus network. In situations where CAN bus bandwidth and multi-function are not required, such as communication between smart sensors and brake devices, using LIN bus can greatly save costs. LIN communication is based on SCI (UART) data format, using single master controller/multiple slave device mode, using only one 12V signal bus and a node synchronization clock line without a fixed time reference.

Gateway Hardware Design

The entire gateway module includes six submodules: LIN interface, CAN interface, CAN baud rate setting, LIN baud rate setting, power module, and status light (Figure 1). Figure 1 System structure block diagram

AT89C51CC03 is an 8-bit microcontroller with built-in CAN controller from Atmel. This design is based on the AT89C51CC03 microcontroller, selects TJA1020 as the LIN bus transceiver, uses the microcontroller UART interface, and selects PCA82C250 as the CAN bus transceiver in the CAN module design part. The specific circuit connection is shown in Figure 2, Figure 3, and Figure 4. Figure 2 Microcontroller circuit Figure 3 CAN interface circuit Figure 4 LIN interface circuit

We designed a 5-bit DIP switch in the circuit. Since the LIN bus and CAN bus transmission are different in different working systems, the software needs to be changed. Therefore, a 5-bit DIP switch is used for baud rate setting in this design, three bits for LIN baud rate setting, and two bits for CAN baud rate setting. At the same time, in order to show the working status of the gateway, a working indicator light is specially designed. It flashes at a certain frequency when receiving and sending signals. When a fault occurs, the two lights are lit at the same time.

To enhance the anti-interference capability of CAN nodes, the TXDC and RXDC pins of the microcontroller are not directly connected to the TXD and RXD pins of the PCA82C250AT, but are connected through the high-speed optocoupler 6N137 (Figure 3). This achieves good electrical isolation between nodes on the bus. The two power supplies VCC and VDD used in the optocoupler circuit must be completely isolated, otherwise the use of optocouplers will lose its meaning.

Gateway software design

The gateway software design mainly includes the main control program module, CAN module software design and LIN module software design. The CAN module software design mainly has three sub-functions, one is CAN initialization CAN_INIT(), and the other two are CAN_RE_ISR() and CAN_SEND(). CAN_INIT() is mainly used to set the CAN communication baud rate and CAN basic settings. The baud rate can be set according to the value of the dip switch. After the system is powered on, it will automatically scan through the self-test program, check the pre-set baud rate table, and set the CAN communication baud rate.

CAN_RE_ISR() is responsible for information reception and processing, and CAN_SEND() is responsible for information sending.

The LIN module software design mainly includes several files: LIN.H, LIN.C, TEMR0.H TEMRO.C, where LIN.H and LIN.C respectively implement LIN specification settings, UART baud rate settings, and LIN information reception and transmission, and TEMR0.H TEMRO.C is used to generate the LIN bus baud rate. The main control program design mainly completes the entire gateway information forwarding function. When a CAN receive interrupt occurs, the LIN send flag is set to prepare to forward the CAN information to the LIN network; similarly, when a LIN receive interrupt occurs, the CAN send flag is set to prepare to send LIN information to the CAN network. [page]

The entire software is written in C51 and debugged using KEIL's simulation software. Finally, the complete program is burned into the AT89C51CC01 flash space.

Conclusion

This paper proposes a CAN-LIN gateway design based on AT89C51CC01 single-chip microcomputer, which solves the problem of information transmission between CAN bus control network and LIN bus control network in field bus control, and provides a basis for flexible application of field bus. This design has been tested on site, and the experimental results show that the gateway runs well, works reliably and stably, and has been applied to actual work.