Serial Device Server: TCP/IP Protocol Conversion - How to Achieve Transparent Transmission from Serial Ports to Networks? Submit Inquiries for Configuration Tutorials!

Introduction: The "Protocol Fault" in Industrial Communication and the Solution for Transparent Transmission
In a production line upgrade project for a manufacturing enterprise, technicians faced a core challenge: 30 old PLC devices only supported RS-485 serial communication, while the newly introduced MES system required real-time data collection and remote control via Ethernet. Using traditional solutions would have necessitated re-laying serial cables and deploying industrial switches, with a high risk of system paralysis due to incompatible device interfaces.

Ultimately, by deploying the serial device server USR-N520, which supports TCP/IP protocol conversion, the enterprise completed system integration in just 48 hours. Data transmission delays remained stable at under 8ms, and no modifications were made to any existing device code. This case highlights a core pain point in industrial scenarios: How can transparent transmission between serial devices and networks be achieved through protocol conversion technology during equipment iteration and system upgrades?

1. The "Three Technical Pillars" of Transparent Transmission
1.1 Protocol Encapsulation: "Language Translation" from Serial Frames to TCP/IP Packets
The core of transparent transmission lies in encapsulating raw data from serial devices (such as Modbus RTU frames) into TCP/IP protocol packets. Key steps include:

• Frame Header Parsing: Identifying the start character (e.g., 0x7E), address field, and data length in serial data.
• Protocol Mapping: Converting Modbus RTU function codes (e.g., 0x03 for reading holding registers) into Modbus TCP message headers (transaction identifiers, protocol identifiers, etc.).

Data Encapsulation: Adding the target IP, port number, and checksum to generate a complete TCP/IP data packet.
Case Study: The USR-N520 features a deeply optimized TCP/IP protocol stack that supports automatic Modbus RTU-to-TCP conversion with a delay of less than 1ms, without requiring firmware modifications to the device.
1.2 Data Caching and Flow Control: Intelligent Scheduling to Avoid "Data Congestion"
In high-speed transmission scenarios, data caching and flow control are crucial for ensuring stable transparent transmission:

• Circular Buffers: Utilizing a dual-buffer mechanism where one buffer receives data while the other processes it, preventing data loss.
• Flow Thresholds: Automatically triggering flow control signals (e.g., RTS/CTS hardware flow control or XON/XOFF software flow control) when the amount of data in the receive buffer exceeds a threshold.

Retransmission Mechanisms: Ensuring reliable data transmission through TCP's ACK acknowledgment mechanism.
Technical Implementation: The USR-N520 supports both hardware flow control (RTS/CTS) and software flow control (XON/XOFF), with a baud rate range covering 600bps to 230.4Kbps, accommodating devices with different speed requirements.
1.3 Multithreaded Concurrent Processing: The "Parallel Engine" for Improved System Responsiveness
Transparent transmission requires simultaneous handling of serial data reception, protocol conversion, and network transmission tasks. Multithreading technology can significantly enhance system efficiency:

• Reception Thread: Listens to the serial buffer and reads device data in real-time.
• Conversion Thread: Parses serial frames and encapsulates them into TCP/IP packets.
• Transmission Thread: Sends the encapsulated data to the target server via Ethernet.
  Code Example (Based on the QThread Library):

cpp

classSerialPortThread:publicQThread{Q_OBJECTpublic:voidrun()override{while(!isInterruptionRequested()){// Listen for serial dataQByteArray data=serialPort.readAll();// Trigger protocol conversion signalemitdataReady(data);}}signals:voiddataReady(constQByteArray&data);};classProtocolConverter:publicQObject{Q_OBJECTpublicslots:voidconvertData(constQByteArray&data){// Parse Modbus RTU frameModbusRtuFrame rtuFrame=parseRtuFrame(data);// Convert to Modbus TCP frameModbusTcpFrame tcpFrame=rtuToTcp(rtuFrame);// Trigger transmission signalemittcpDataReady(tcpFrame.toByteArray());}signals:voidtcpDataReady(constQByteArray&data);};

2. Serial Device Server USR-N520: An "Industrial-Grade Solution" for Transparent Transmission
In the field of serial device servers, the USR-N520 stands out as a preferred choice for transparent transmission scenarios due to its "high performance, high compatibility, and high reliability":

• Dual Serial Ports Operating Independently: Supports 2 RS-232/485/422 interfaces, each configurable with independent baud rates, data bits, and parity bits.
• Protocol Conversion Engine: Built-in Modbus RTU/TCP bidirectional conversion functionality, supporting multi-host polling and protocol transparency.
• Industrial-Grade Design: Operates within a temperature range of -40℃ to 85℃, with EMC protection meeting IEC 61000 standards, suitable for harsh industrial environments.
• Dual Socket Backup: Each serial port supports 2 simultaneous Socket connections, enabling access to different servers for redundant data transmission.
  Typical Application Scenarios:
• Legacy Device Networking: Connecting PLCs, sensors, and other devices for remote data collection and MES integration.
• Energy Management: Integrating electricity meters, inverters, and other devices to build an energy internet.
• Smart Buildings: Consolidating air conditioning, lighting, and other systems for unified control and energy optimization.

3. The "Five-Step Implementation Method" for Transparent Transmission
3.1 Hardware Connection: Establishing Physical Communication Links

• Serial Device Connection: Use wires to connect the device's serial port (e.g., RS-485 A/B lines) to the corresponding interface on the USR-N520.
• Power Supply Connection: Power the USR-N520 using a switch power supply (DC 5V-36V) and confirm that the POWER indicator light is on.
• Network Connection: Use a network cable to connect the USR-N520's Ethernet port to a switch or router.
  3.2 Parameter Configuration: Setting Communication Protocols and Network Parameters
• Static IP Configuration:
  • Set the computer's IP to a static IP (e.g., 192.168.0.100) with a subnet mask of 255.255.255.0 and a gateway of 192.168.0.1.
  • Access the USR-N520's management interface via a web browser (default IP 192.168.0.7) and modify the device's IP to the same subnet (e.g., 192.168.0.113).
• Serial Port Parameter Settings:
  • Baud Rate: Set according to device requirements (e.g., 9600bps).
  • Data Bits: 8 bits.
  • Parity Bit: None.
  • Stop Bits: 1 bit.
• Operating Mode Selection:
  • TCP Server Mode: The USR-N520 listens on a specified port (e.g., 21018) for client connections.
  • TCP Client Mode: The USR-N520 actively connects to the target server's IP and port.
    3.3 Protocol Conversion Configuration: Enabling Modbus Gateway Functionality
• In the management interface, navigate to the "Modbus Parameters" settings page.
• Enable the "Modbus Gateway" function and select "Simple Protocol Conversion."

Turn on the "TCP to RTU" option, save the configuration, and restart the device.
3.4 Testing and Verification: Confirming Transparent Data Transmission

• Serial Port Debugging Tool: Use tools like UartAssist to connect to the USR-N520's serial port and send test data (e.g., Modbus RTU request frames).
• Network Debugging Tool: Use tools like NetAssist to connect to the USR-N520's TCP port and verify receipt of the converted Modbus TCP frames.
• Data Consistency Check: Compare the data sent via the serial port with the data received over the network to confirm no packet loss or errors.

3.5 Operation and Maintenance Optimization: Establishing Monitoring and Fault Response Plans

• Real-Time Monitoring: Monitor device status, communication quality, and traffic via SNMP or the USR-N520's management platform.
• Log Analysis: Regularly review system logs to identify potential issues.
• Fault Response Plan: Develop emergency plans for scenarios such as device offline status or protocol incompatibility, such as enabling dual Socket backup.

4. Contact Us: Obtain Your Customized Transparent Transmission Solution
The implementation of transparent transmission requires in-depth customization based on specific scenarios. For example:

• Device Quantity: If connecting 50+ devices, choose a solution that supports multi-serial port expansion (e.g., USR-N520 dual serial ports or USR-N580 eight serial ports).
• Protocol Complexity: Prioritize devices that support automatic protocol identification if dealing with diverse device protocols.
• Environmental Adaptability: Select industrial-grade protective devices for outdoor or high-temperature environments.

Contact us, and we will provide you with:

• Needs Assessment: Customize a transparent transmission solution based on your device types, protocols, and system environment.
• Device Selection Recommendations: Recommend suitable serial device server models (e.g., USR-N520) and configuration parameters.
• Configuration Tutorials: Provide detailed parameter setting steps and protocol conversion guidelines.
• Operation and Maintenance Support: Assist remotely with device debugging, fault troubleshooting, and performance optimization.

From a manufacturing enterprise achieving seamless integration of 30 old PLC devices with an MES system using the USR-N520 to an energy company building a cross-regional energy management system through transparent transmission technology, countless cases prove that a scientific transparent transmission solution is the "core engine" for upgrading industrial communication.