Abstract: With the development of information industries such as the internet, remote operation and remote monitoring of intelligent devices have become the direction of modern life, and remote communication is a problem worthy of research. This paper takes the example of a remotely controlled robotic arm to introduce the basic architecture and implementation process of remote serial communication, and analyzes the design and implementation of the 89C51 direct controller hardware and software. Keywords: remote; serial communication; microcontroller; robotic arm Introduction Networked operation and remote control have become research directions for many enterprises and research institutions. To manage and control field equipment, it is necessary to establish communication connections with these devices and exchange relevant data to achieve the purpose of management, control, and monitoring. Similarly, in the embedded field, remote monitoring must also be based on a network. Robots operating underwater or in harsh environments require remote control at specific times. Network-based remote control of robotic arms has become possible. In remote control, communication is a technical issue worthy of discussion. Traditional communication is limited to communication without a network, such as communication between two PCs, or a PC as the host computer and a microcontroller as the slave computer. In remote-controlled robotic arm systems, Internet-based remote serial communication is used. Remote serial communication refers to long-distance communication between the client and the lower-level machine or communication object via a serial port. Traditional remote communication is only a part of it, transmitting commands from the client to the lower-level machine and then to the control components to achieve remote monitoring. 1. Basic Architecture and Implementation of Remote Serial Communication System (I) Overview of Basic Architecture In software system architecture, C/S and B/S are the two mainstream technologies in the world's development model. The C/S model adopts a two-layer architecture, namely client and server. This architecture can make full use of the advantages of the hardware environment at both ends, and rationally allocate tasks to the client and server. The client handles the display interface and transaction processing, while the server handles data processing and response to requests. Client software needs to be installed on the client to access the server. This not only makes software upgrades inconvenient, but also increases the client's load and investment costs. B/S (Browser/Server) structure is a browser and server structure. It is a variation or improvement of the C/S structure that emerged with the rise of Internet technology. In this architecture, the user interface is implemented through a browser, with a small portion of the transaction logic implemented on the front end (browser), but the main transaction logic is implemented on the server side (server). Data processing is handled by the database server, forming a so-called three-tier structure. This greatly simplifies the client computer load, reduces the cost and workload of system maintenance and upgrades, and lowers the overall cost for users. However, direct data communication with the controlled object cannot be achieved solely in the B/S mode. Remote serial communication for data communication with the controlled object based on the B/S mode adopts a four-tier architecture, adding a control layer. The browser is the presentation layer, the web server is the functional layer, the database server is the data layer, and the control layer transmits instructions from the web server to the control server. The control server acts as the host computer, controlling the slave computer via serial port, down to the control execution unit. This not only adds a control layer but also expands the functional and data layers. This architecture combines the excellent characteristics of the B/S mode with added control service functions, fully utilizing existing network and industrial site resources and organically integrating them to achieve remote communication with the controlled device via serial port. The presentation layer, functional layer, data layer, and control layer are interconnected yet relatively independent. Each layer is connected via the Internet and communicates information via HTTP and serial communication protocols. As shown in Figure 1, (II) Functions and Implementation of Each Component in Remote Serial Communication (1) Browser: The user logs into the web server through a browser. After entering the username and password and verifying them against the data in the database, the user becomes a legitimate user and then enters control data in the corresponding form. After pressing the submit button, the data is transmitted to the web server. The browser then acts as the display end, showing the feedback location of the remote execution component. (2) Web Server: It can receive control data sent from the browser, process the corresponding data, and send the data to the control server, or directly act as the control server and send the data to the execution component via the serial port. (3) Database Server: It stores the username and password of legitimate users for verification. At the same time, when sending execution data, if specific conversion data is needed, it can also be obtained directly from the database. It realizes the data processing of the system and feeds back the running results to the web server. (4) Control Server: Acts as the host computer that sends commands directly to the execution unit via serial port, or is directly handled by the web server itself. Receives data from the browser via the web server. Sends the data to the slave computer via serial communication protocol and handshake signal. (5) Slave Computer: Receives execution data from the control server (host computer) via serial communication protocol, and then drives the execution unit to work via the corresponding drive circuit. (6) Execution Unit: Works according to the transmitted instructions, and converts the current position and attitude of the execution unit into data via sensors, then sends it back to the control server via serial port, until it reaches the browser, so that the user can remotely control the execution unit and obtain the effect after execution even when not at the execution unit site. In the browser, after login verification, the data is transmitted to the web server via HTTP protocol, and then to the control server. The control server, acting as the host computer, opens the serial port and sends the data to the slave computer via communication protocol. The slave computer receives the data sent by the host computer according to the communication protocol, starts the D/A converter, and controls the execution unit. At the same time, it feeds back the attitude of the execution unit to the host computer via sensors. The lower-level machine can be a microprocessor such as a single-chip microcomputer, DSP, or ARM. 2. Implementation of the remote control robot system The remote control of the robot based on the web is required to operate the robot in harsh working environments such as high temperature and underwater. The operation data is input remotely through the browser and transmitted to the main control machine through the network. The main control machine is a general PC. The main control machine sends the data to the lower-level machine through the serial port. The robot system uses the 89C51 single-chip microcomputer as the direct control computer. The posture of the robot is fed back to the remote control machine through the monitoring equipment on site. At the same time, the on-site data is collected by the sensor and returned to the control machine. Figure 2 is a schematic diagram of the remote control robot system. After logging into the server of the main control machine in the browser and obtaining a valid identity, the data is sent. After receiving the information, the main control machine sends the data to the direct control machine 89C51 through the serial port. (I) Hardware components of the single-chip microcomputer system (1) The core is based on the 89C51 microprocessor, and the RAM6254, latches, clock circuits, reset circuits, etc. are expanded. (2) Serial communication circuit: When the main controller transmits data to the 89C51, serial communication is used. The commonly used serial communication bus interface is RS-232C, which is specified by the American Electrical Industry Association (EIA). Since the serial ports TXD and RXD of the microcontroller are both TTL level, while the PC is configured with the RS-232C standard serial interface, level conversion must be performed during application. In the robot control system, MAX232 is used as the interface conversion chip. (3) Digital-to-analog conversion circuit: Through the serial port, the main controller sends the robot's action command data to the 89C51. The 89C51 sends the data to the D/A conversion circuit data port through the bus. In this system, the DA0832 digital-to-analog conversion chip is used to implement this. (4) Drive circuit: The working power of the robot comes from the hydraulic system. The servo valve is used to realize the loop control of the robot. To drive the servo valve, the corresponding drive circuit is designed. (5) Analog-to-digital conversion circuit: The actual operation data of the robot is collected by the angle potentiometer and displacement sensor. After the sensor is calibrated, the collected displacement and angle analog signals are converted into digital signals and transmitted to 89C51, and then sent upward. The AD0809 analog-to-digital conversion chip is used in this system. (II) Implementation of the main control computer and single-chip microcomputer software system (1) Main control computer program The main control computer is a PC. The operating interface is developed using VC++. The serial port communication protocol is initialized through the serial port control MSComm. The data sent from the WEB to control the robot is retrieved from the background database SQLServer. The angle of each joint of the robot is controlled. At the same time, the data sent back by 89C51 is received. The flowchart of the software system is shown in Figure 3. (2) 89C51 Microcontroller Main Program: The 89C51 microcontroller is used as the direct control computer. The main program is written in C language. It initializes the serial port, allocates a memory buffer to store the received data, enables interrupts, and waits for external data to be sent and received in the form of interrupts. The flowchart of the 89C51 main program is shown in Figure 4. (3) 89C51 Interrupt Handling Subroutine: The interrupt subroutine first clears the interrupt flag, then determines whether the interrupt is caused by receiving or sending, and handles it according to the corresponding interrupt source. The flowchart of the 89C51 interrupt handling subroutine is shown in Figure 5. 3. Conclusion: The innovation of this paper lies in linking the 89C51 microcontroller with the operation of the robot arm. Through network remote communication, the remote control of the robot arm laboratory is realized, providing a specific example for the research of remote control operation. Currently, the system realizes the online sending of data to the main control computer and storing it in the database. It is necessary to manually call the data on the main control computer to realize the control of the robot arm. The ability to completely eliminate human intervention and directly control the operation through the network is still under further research. Experimental applications and market proofs show that in today's and future modern network era, remote communication will inevitably appear in the lives of future humans, and has considerable research significance and practical value. 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