How Does a Serial Server Achieve Modbus to TCP Protocol Conversion? Detailed Operation Steps

In the field of Industrial Internet of Things (IIoT), communication and data exchange between devices are the core links in building efficient and intelligent systems. As a classic communication protocol in the industrial automation sector, the Modbus protocol is widely used for data transmission among various industrial devices due to its simplicity, openness, and ease of implementation. However, with the development of network technology, the Modbus TCP protocol based on Ethernet has gradually become the mainstream, offering higher data transmission rates and support for more complex network topologies. So, how can we use a serial server to achieve protocol conversion from Modbus RTU to Modbus TCP? This article will take PUSR's serial server USR-N540 as an example to provide a detailed introduction to the operation steps.

1. Differences Between Modbus RTU and Modbus TCP

Before delving into protocol conversion, let's first understand the basic differences between Modbus RTU and Modbus TCP.

• Modbus RTU: Based on serial communication (such as RS-485), it has relatively low data transmission efficiency and is suitable for simple point-to-point or point-to-multipoint networks. Its data frames are encoded in binary form and contain slave addresses, function codes, data, and checksum information (usually CRC cyclic redundancy check).
• Modbus TCP: Based on Ethernet, it uses the TCP/IP protocol stack for data transmission. It adds an MBAP (Modbus Application Protocol Header) in front of the Modbus application layer data, which includes information such as transaction identifiers, protocol identifiers, lengths, and unit identifiers. This information is used to accurately identify and transmit Modbus data over the network. Modbus TCP supports higher data transmission rates and more complex network topologies, making it suitable for modern industrial automation systems.

2. Why Is Protocol Conversion Necessary?

In practical applications, many industrial devices still communicate using the Modbus RTU protocol, while the network environments of modern enterprises are mostly based on the TCP/IP protocol. To achieve seamless integration of these devices with existing networks, protocol conversion is required. As a bridge connecting traditional serial devices to modern networks, serial servers can meet this demand.

3. Introduction to USR-N540 Serial Server

The USR-N540 is a powerful industrial-grade four-port serial server that supports protocol conversion from Modbus RTU to Modbus TCP. It adopts a high-performance processor and possesses stable and reliable network communication capabilities, making it widely used in fields such as industrial automation, energy management, and intelligent buildings.

4. Detailed Operation Steps

4.1 Hardware Connection

• Serial Connection: Connect the Modbus RTU device (such as a PLC or sensor) that requires protocol conversion to the serial interface of the USR-N540 using an RS-485 serial cable. Ensure that the wiring of the serial cable is correct, with A+ connected to A+ and B- connected to B-.
• Network Connection: Use a network cable to connect the Ethernet interface of the USR-N540 to a local area network (LAN) switch or router, ensuring that the network connection is normal.

4.2 Configuration Software Installation and Device Search

• Software Installation: Download and install the configuration software for the USR-N540 from PUSR's official website.
• Device Search: Open the configuration software and click the "Search Device" button. The software will automatically search for USR-N540 devices within the LAN.

4.3 Network Parameter Configuration

• IP Address Setting: Depending on the network environment, set a static IP address for the USR-N540 or choose to obtain an IP address dynamically via DHCP. If a static IP is chosen, manually fill in information such as the IP address, subnet mask, gateway, and DNS server address.
• Port Setting: By default, the USR-N540 uses port 23 as the service port for Modbus TCP. This can be modified to another port as needed.

4.4 Modbus Gateway Configuration

• Protocol Conversion Selection: In the configuration software, find the "Modbus Gateway" or "Protocol Conversion" option and select "Modbus RTU to Modbus TCP".
• Serial Parameter Setting: According to the requirements of the connected Modbus RTU device, set the serial parameters of the USR-N540, including baud rate, data bits, stop bits, and parity bits. Ensure that these parameters are consistent with those of the Modbus RTU device.
• Polling Setting: If the Modbus polling function is required, parameters such as polling timeout and polling interval can be set in the configuration software.

4.5 Saving Configuration and Restarting the Device

• Saving Configuration: After completing all configurations, click the "Save Configuration" button to save the configuration information to the USR-N540.
• Restarting the Device: To make the configuration take effect, restart the USR-N540 device.

4.6 Testing and Verification

• Using Modbus Testing Software: Open Modbus testing software (such as Modbus Poll or Modbus Slave), set the connection parameters for Modbus TCP (including the IP address and port number of the USR-N540), and then attempt to read or write data from the Modbus RTU device.
• Observing Indicator Status: The USR-N540 device is equipped with RJ45 Link/Data indicators and RS232&RS485 transmit/receive indicators. By observing the status of these indicators, you can quickly determine whether the network connection and serial communication are normal.

5. Application Value

The application of the USR-N540 serial server in Modbus to TCP protocol conversion not only solves the problem of traditional devices being unable to access modern networks but also brings numerous practical values to enterprises:

• Enhancing Device Compatibility: Through protocol conversion, the USR-N540 enables devices that originally only supported the Modbus RTU protocol to seamlessly integrate into a TCP/IP-based network environment, improving device compatibility and scalability.
• Reducing Retrofitting Costs: Compared to replacing entire devices or systems, using the USR-N540 for protocol conversion is more cost-effective and has a shorter cycle, helping enterprises quickly achieve device upgrades and network integration.
• Improving Management Efficiency: By connecting devices to the network, enterprises can achieve remote monitoring and management of devices, reducing the workload of manual inspections and on-site maintenance, and improving management efficiency.
• Enhancing Market Competitiveness: Adopting advanced IIoT technologies, such as the USR-N540 serial server, can enhance an enterprise's technological level and market competitiveness, winning more business opportunities for the enterprise.

Serial servers play a crucial role in Modbus to TCP protocol conversion. Through reasonable configuration and debugging, we can easily achieve the integration of Modbus RTU devices with modern networks. As a powerful industrial-grade four-port serial server, the USR-N540 not only possesses stable and reliable network communication capabilities but also provides rich configuration options and flexible application scenarios.