Abstract: This paper introduces the research on vehicle-mounted monitoring terminal based on embedded system, presents the overall system structure and functions of each module, describes the hardware design of the system, and details the hardware and software design of the CAN bus in the embedded system. Keywords: vehicle-mounted monitoring system, embedded system, CAN bus 1 Introduction In recent years, with the continuous development and utilization of land resources, the scale of infrastructure construction in China has further expanded, and the construction machinery market has shown a sustained growth trend. However, the domestic construction machinery industry is still in a relatively backward production mode. Therefore, the construction machinery industry needs intelligent and high-performance monitoring products that meet the requirements of the industry. It is essential to integrate high-tech such as embedded technology, bus technology, and network technology into the monitoring system of the construction machinery industry. To this end, this paper designs a construction machinery monitoring system terminal based on embedded system and bus technology, and discusses in detail the composition of the monitoring system terminal and the design of the CAN bus. 2 Overall Composition of Monitoring System Terminal The monitoring terminal is responsible for monitoring all units of the front-end control system, including safety monitoring, electro-hydraulic proportional and other units, and performs human-machine interaction through LCD display and keyboard. At the same time, it connects to video monitoring equipment to monitor the situation on site at any time. [align=center]Figure 1 Overall Structure of the Monitoring System Terminal[/align] As shown in Figure 1, the monitoring system terminal includes: an onboard monitoring system control module, a human-machine interface module, a storage module, a video monitoring module, and a CAN bus control module. The functions of each part are as follows: 1. The onboard monitoring system control module is the core component of the entire terminal, using an ARM7202 embedded processor with an ARM720TDMA core to complete the control functions of the entire system. 2. The storage module stores the operating system kernel, bootloader, application programs, and drivers, and caches various data generated during execution to ensure stable system operation. 3. The human-machine interface module includes an LCD display and keyboard input, allowing users to intuitively monitor and control the system. 4. To directly monitor the on-site working conditions, the system integrates a video monitoring module. A camera is connected via a video capture card, converting the captured images into digital signals and compressing them into JPEG format files, which are then input into the processor for user monitoring. 5. The system monitors the control systems of each front-end unit via the CAN bus. 3 Hardware Design 3.1 Overall Hardware Structure As shown in Figure 2, the monitoring terminal consists of: an embedded processor 7202, a storage system, a reset circuit, a crystal oscillator circuit, a JTAG debugging interface, an LCD display interface, an RS-232 serial interface, and a CAN bus interface. [align=center] Figure 2 Hardware Structure Diagram of the Monitoring Terminal[/align] The functions of each part are as follows: 1. The crystal oscillator circuit provides the operating clock for the system. 2. The reset circuit is used to complete the system power-on reset and user button reset during system operation. 3. The storage system consists of FLASH memory and SDRAM memory. FLASH memory is used to store debugged user applications, embedded operating systems, and other user data that need to be saved after system power failure. SDRAM memory serves as the main area for system operation. 4. The JTAG interface allows access to all components inside the chip, enabling system debugging and programming. 5. The LCD interface is used to connect to the display device required for human-machine interaction. 6. The CAN controller provides a CAN bus interface for the system, facilitating data and instruction transmission with the control systems of the front-end units. 7. The RS-232 serial communication interface is used for connecting the video compression card and transmitting video images. 3.2 Hardware Design of CAN Module Through the CAN module interface, the ARM processor can directly access the CAN register group. These registers can configure the CAN core module, CAN information processing module, and access information RAM. This system uses Philips' TJA1050 as a transceiver, which is the transceiver between the CAN interface and the CAN bus. Its function is to convert the 3.3V logic level to the CAN logic level, that is, to convert the transmitted and received signals into signals that can be recognized by the CAN bus and ARM. [align=center] Figure 3 Circuit Design of CAN Module[/align] 4 Software Design of CAN Module in ARM In terms of construction and characteristics, the 7202 CAN controller is basically no different from the standard CAN module, except for some differences in the number of registers and the offset of the base address. [align=center] Figure 4 CAN Module Operation Sequence[/align] As shown in Figure 4, four steps need to be completed before starting bus operation. First, enable the CAN module by writing 0x01 to the CAN Enable Register. Since ARM pins are multiplexed, the pins used by the CAN module must be switched to special mode before enabling the CAN module. Next, initialize the CAN module, primarily by correctly configuring the Command Mask Register. This register is used to configure the data transmitted and received by the CAN module. Then, configure the baud rate. Calculate the values ​​of the variables in the formula based on the desired CAN bus baud rate. The CAN baud rate calculation formula is as follows: (Tseg2 + Tseg1 + SJW + 3) * BRP = CAN_CLK / Fbps. The four variables on the left are in the BRP register, while CAN_CLK on the right is a fixed value, 48MHz in this case. Finally, configure the information memory. The configuration of the data is related to the specific application information, specifically the settings of each register in the information buffer register group. It should be noted that the first three steps are completed in initialization mode, while the last step is performed in normal mode. After completing these four steps, you can operate the CAN module. The Linux operating system treats CAN operations as file operations. For files, the most basic operations are open, close, read, and write. For the CAN module, read and write operations respectively implement the reading and sending of received data, while opening and closing the file respectively initializes and releases some hardware resources of the CAN module. Configuration operations such as configuring baud rate and configuring message mode are performed by the ioctl function. `static int _int can_init(void) { Initialize default baud rate, register driver }` `int can_open(struct inode *inode, struct file *filp) { Set CAN working register, initialize read operation queue, register CAN module interrupt }` `static int can_ioctl(struct inode *inode, struct file *file, unsigned int cmd, unsigned long arg) { Select the appropriate operation based on the cmd parameter }` The above lists the initialization, opening, and configuration functions for CAN operations. Other functions include read, write, and close functions. The final function to be implemented is the CAN module interrupt. Within the interrupt, the main task is to change the read/write position flags to achieve blocking I/O operations. In this way, users can use the CAN bus by applying these operation functions. 5. Innovations of the Author This design utilizes an embedded system and a CAN bus to achieve integrated, information-based, and intelligent on-board monitoring of engineering machinery. Through the application of the CAN bus in the embedded system, it can easily realize front-end safety monitoring, electro-hydraulic proportional and other unit monitoring, and can also perform human-machine interaction and image acquisition, showing great application prospects. References: [1] Tao Wei, Wei Hongxing, Liu Miao. Research on intelligent communication and positioning system for engineering machinery. Engineering Machinery, 2003 (7): 1-3 [2] Chen Yi, Tian Jie, Wang Jingang. 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