Introduction

In modern industrial automation and IoT deployments, a vast number of field devices (such as PLCs, electricity meters, sensors, card readers, and variable frequency drives) still communicate via RS485 serial ports. Connecting these "isolated" devices to Ethernet networks or the cloud is a core requirement for industrial internet construction.

However, many serial servers on the market suffer from limited functionality (transparent transmission only), too few ports (only 1-2 serial ports), or lack industrial-grade protection (isolation, wide temperature, surge protection), making them unsuitable for complex and demanding industrial environments.

The NA241 / NA241S / NA281 / NA281S DIN-rail multi-port serial server series from Chengdu EBYTE Electronic Technology Co., Ltd. is designed to address precisely these pain points. Offering up to 4 or 8 RS485 ports, integrated switch functionality, signal isolation, built-in termination resistors, and wide-voltage power supply, these devices serve as the ideal "bridge" for connecting serial devices to the cloud.

1. Product Overview: Four Models for Different Levels of Harsh Environments

The NA241 / NA241S / NA281 / NA281S are EBYTE's self-developed DIN-rail multi-port serial server series, integrating a complete TCP/IP protocol stack. Their primary function is bidirectional transparent transmission between serial (RS485) data and Ethernet data, along with Modbus protocol conversion, enabling serial devices to connect to networks and the cloud.

Core Positioning: A high-performance multi-port serial networking device that combines multiple industrial protection features.

The key differences between the four models are shown below:

Quick Product Guide:

• NA241: 4 ports, with isolation, with termination resistors — strongest protection.

• NA241S: 4 ports, no isolation, with termination resistors — cost-effective choice.

• NA281: 8 ports, with isolation, no termination resistors — multi-port + strong protection.

• NA281S: 8 ports, no isolation, no termination resistors — pure multi-port requirement.

2. Features and Model Comparison

Common Core Features

The software functionality across the entire series is identical, with the same usage methods. The only differences lie in hardware protection and port count. Core features include:

1. Powerful Networking Capabilities

• Dual Ethernet Ports: Two standard RJ45 ports (ETH1 and ETH2), supporting 10/100M auto-negotiation.

• Built-in Switch Function: The two Ethernet ports can function as a switch, eliminating the need for an external switch when daisy-chaining multiple devices, simplifying cabling.

• Full Protocol Stack Support: TCP Server, TCP Client, UDP Server, UDP Client, HTTP Client, MQTT Client (default: TCP Server).

2. Rich Serial Port Capabilities

• 4/8 RS485 Ports: Each port uses a 5.08mm push-in terminal block for secure wiring.

• Flexible Serial Parameters: Baud rate from 2400 to 115200 bps, supports None, Odd, and Even parity.

3. Multiple Configuration Methods

• 3 Configuration Methods: PC configuration tool, AT commands, and web page configuration — accommodating different user preferences.

4. Powerful Modbus Gateway Functionality

• 5 Modbus Gateway Modes: Simple protocol conversion, multi-master mode, storage-type gateway, configurable gateway, and auto-upload.

• Modbus TCP to Modbus RTU Conversion: Enables active reporting from RTU devices.

5. Comprehensive Value-Added Features

• Supports Heartbeat Packets and Registration Packets (network/serial port modes, 7 registration packet modes).

• Supports short connections, serial buffer clearing, timeout reboot, and auto-reconnect on disconnection.

• Hardware one-key factory reset.

• Online firmware upgrade (UDP upgrade / serial port upgrade).

6. Industrial-Grade Electrical Characteristics

• Wide Voltage Supply: DC 8~28V (with reverse polarity protection).

• Wide Temperature Range: -40°C to +85°C.

• Rich LED Indicators: PWR, NET, ETH1/ETH2, LINK1~8, DATA1~8 for quick status diagnosis.

Model Comparison — In-Depth Analysis

Key Differences Explained

Signal Isolation

• Isolated models (NA241/NA281): Each serial port has independent power + signal isolation. In industrial sites, different sensors/PLCs may have significant potential differences in reference ground (common-mode voltage). Isolation effectively blocks "ground loop" current, protecting serial chips from damage while significantly improving communication stability and noise immunity.

• Non-isolated models (NA241S/NA281S): Lower cost, suitable for scenarios with short device distances, small ground potential differences, and low interference.

Built-in Termination Resistor

• NA241/NA241S (all 4 ports): For long-distance RS485 communication (>100m), signal reflection can cause data errors. The built-in 120Ω termination resistor (enabled by shorting the R and B terminals) absorbs signal reflections, improving long-distance communication quality.

• NA281/NA281S (none): For 8-port scenarios, connections are typically short-distance (<50m) dense connections where signal reflection is less of an issue. If needed, users can add an external 120Ω resistor on the farthest device's 485 line.

Port Count

• 4 ports (NA241/NA241S): Typically sufficient for small to medium-scale data acquisition and control.

• 8 ports (NA281/NA281S): Suitable for large-scale automated production lines, equipment room environmental monitoring, and other scenarios requiring numerous serial device connections.

Technical Specifications at a Glance

Application Scenarios: Where NA Series' Hardcore Capabilities Are Needed

Scenario 1: Factory Automation Data Collection

Requirement: Numerous legacy PLCs and smart instruments (RS485 only) in a workshop need real-time upload of operational status and production data to the MES system.

Solution: Use NA241 or NA281 (depending on port count) to connect via 485 bus for data collection and upload to the MES server via Ethernet. The dual Ethernet ports with switch functionality allow daisy-chaining more collectors.

Recommended Model: NA241 (4-port isolated) or NA281 (8-port isolated) for strong electromagnetic interference environments.

Scenario 2: Equipment Room Power & Environment Monitoring

Requirement: An equipment room contains dozens of serial devices (air conditioners, UPS, temperature/humidity sensors, access control) with significant ground potential differences between devices.

Solution: Deploy one NA281 (8-port) with isolated serial ports to connect multiple devices, ensuring ground loops do not damage expensive equipment room hardware. The Modbus gateway function enables easy data reporting to the monitoring platform.

Recommended Model: NA281 (8-port isolated) — meets multi-device access + strong protection requirements.

Scenario 3: Smart Building and HVAC Control

Requirement: A building integrates numerous Modbus RTU devices (fan coil units, motorized valves, temperature control panels) requiring centralized TCP/IP-based control.

Solution: Use NA241 as a "mini-gateway" to connect nearby area devices, supporting MQTT/HTTP client communication with the building automation platform.

Recommended Model: NA241 (4-port, with termination resistors for more stable long-distance communication).

Scenario 4: Photovoltaic Station and Energy Storage Monitoring

Requirement: Inverters, combiner boxes, and electricity meters are scattered across vast outdoor areas with long communication distances, strong electromagnetic interference, and varying ground potentials between devices.

Solution: NA241's isolated serial ports and built-in termination resistors significantly improve long-distance RS485 communication reliability.

Recommended Model: NA241 (4-port isolated + termination resistors).

Scenario 5: Smart Grid and Energy Management

Requirement: Data collection from energy meters, multi-function power instruments, and power controllers demands high reliability and data security.

Solution: NA281S (8-port) can densely connect multiple electricity meters, supporting Modbus TCP to RTU conversion for reporting to the energy management platform.

Recommended Model: NA281S (8-port, highest cost-effectiveness).

 EBYTE Core Advantages

• Unified Software Across the Series: The NA241/241S/281/281S share identical software functionality. Users only need to choose the hardware protection level and port count. Develop once, reuse all code and configurations — reducing learning and development costs.

• Hardcore Industrial Features: Signal isolation, built-in termination resistors, wide voltage (8-28V), wide temperature (-40~85°C), dual Ethernet ports with switch functionality — features that are often "optional" or "missing" in competing products are standard in the NA series.

• Multi-Protocol & Multi-Platform Compatibility: Simultaneously supports TCP/UDP/MQTT/HTTP protocols, enabling quick integration with mainstream cloud platforms such as Alibaba Cloud, Baidu Cloud, OneNET, and Huawei Cloud.

• Powerful Modbus Capabilities: Supports 5 Modbus gateway modes, particularly suitable for complex bus scheduling and active reporting scenarios.

• User-Friendly Design: 5.08mm terminal blocks ensure secure wiring; 8 independent LINK and DATA LEDs facilitate on-site diagnostics; 3 configuration methods accommodate different development habits.

• Easy Deployment: DIN-rail mounting design allows direct installation on standard DIN rails alongside PLCs, switches, and other equipment within a single cabinet.

Frequently Asked Questions (FAQ) — Expanded

Q1: Is signal isolation (NA241/NA281) really necessary in practical applications?

A: Absolutely necessary, especially in the following scenarios: devices powered by different power supplies, communication distances exceeding 50 meters, devices located outside electrical cabinets, or environments with motors/VFDs and other strong interference sources. Isolation effectively blocks "ground loop current" caused by potential differences, protecting serial chips from damage and reducing data errors caused by common-mode interference. For industrial projects pursuing long-term stability, we strongly recommend choosing isolated models NA241 or NA281.

Q2: How do I enable the built-in termination resistor (NA241/NA241S)?

A: During wiring, short the R terminal (e.g., R1) and the B terminal (e.g., B1) of the corresponding serial port to enable the built-in 120Ω termination resistor. Once enabled, it absorbs signal reflections, suppressing overshoot and ringing, thereby improving long-distance RS485 communication quality.

Applicable scenarios: When the communication distance exceeds 100 meters or when more than 32 devices are on the RS485 bus, it is recommended to enable termination resistors at both ends of the bus.

Q3: The device cannot be found by the search tool. How do I troubleshoot?

A:

1. Confirm the device is powered on (PWR LED is lit).

2. Check that your PC's IP address is on the same subnet as the device's default IP (192.168.3.7).

3. Disable your PC's firewall and antivirus software, as they may block the device discovery broadcast packets.

4. Connect your PC directly to the device using an Ethernet cable (or through a switch/router).

5. If still not found, press and hold the Reload button to restore factory settings.

Q4: How do I configure Modbus RTU to TCP conversion?

A: Using the PC configuration tool:

1. Navigate to the "Modbus Parameters" page.

2. Select "Modbus Gateway" → "Simple Protocol Conversion".

3. Enable the "TCP to RTU" function.

4. Configure the serial port parameters for the corresponding channel.

5. Once configured, the device will automatically convert received Modbus TCP requests into Modbus RTU commands sent to the serial port, and convert RTU responses back to TCP data packets.

Q5: Is there any difference in software configuration between NA241/241S (4-port) and NA281/281S (8-port)?

A: None whatsoever. The 4-port devices have channels 1~4, while the 8-port devices have channels 1~8, but the configuration interface, commands, and functionality are completely identical. The software and firmware are fully interchangeable between the two series. Users simply need to be mindful of the channel count during configuration.

Q6: What is the default IP address of the device, and how do I change it?

A: The default IP is 192.168.3.7, subnet mask 255.255.255.0, and gateway 192.168.3.1. You can modify these settings using the PC configuration tool or via the web interface (enter http://192.168.3.7 in a browser). Both static IP and DHCP dynamic acquisition are supported.

Q7: How do I configure the device via the web interface?

A:

1. Ensure your PC and the device are on the same IP subnet.

2. Open a browser and enter the device's default IP: http://192.168.3.7.

3. The default username and password are both admin.

4. Once logged into the web configuration interface, you can modify network parameters, serial port parameters, operating modes, and more as needed.

Q8: What is the maximum number of TCP client connections supported?

A: A single TCP server channel supports up to 5 simultaneous client connections. Each of the 8 channels can be independently configured to different operating modes (e.g., one channel as TCP Server, another as TCP Client, etc.).

Q9: Does the device support MQTT for cloud platform connectivity?

A: Yes. The NA series supports MQTT Client mode, allowing serial device data to be published directly to MQTT brokers on cloud platforms such as Alibaba Cloud IoT, AWS IoT, and Azure IoT Hub. This makes it ideal for IoT cloud-based applications.

Q10: Can the device be used outdoors or in extreme temperature environments?

A: Yes. With an operating temperature range of -40°C to +85°C and a wide voltage supply of DC 8~28V, the NA series is fully suitable for outdoor cabinets, unattended stations, and other extreme environment applications. For outdoor installations, additional surge protection on the Ethernet ports is recommended.

Q11: What is the difference between "Simple Protocol Conversion" and "Multi-Master Mode" in Modbus gateway?

A:

• Simple Protocol Conversion: The device acts as a transparent Modbus gateway. When a Modbus TCP request arrives, it is directly forwarded to the serial port as Modbus RTU. This is the simplest mode, suitable for single-master scenarios.

• Multi-Master Mode: Allows multiple TCP masters (clients) to simultaneously access the same serial device(s). The device manages request queuing and response distribution, preventing data collisions. This is ideal when multiple SCADA or monitoring systems need to poll the same serial devices.

Q12: What should I do if the device frequently disconnects or data transmission has errors?

A: Check the following:

1. Termination resistors: For long-distance RS485 communication (>100m), ensure termination resistors are enabled at both ends of the bus.

2. Baud rate matching: Verify that the baud rate, data bits, stop bits, and parity settings match on both the serial server and the connected devices.

3. Grounding: Ensure proper grounding of all devices. Poor grounding is a common cause of communication errors in industrial environments.

4. Cable quality: Use shielded twisted-pair cable for RS485 connections, especially in high-interference environments.

5. Power supply: Verify that the power supply voltage is stable and within the 8~28V range. Insufficient voltage can cause intermittent operation.

The NA241/NA241S/NA281/NA281S series represents EBYTE's benchmark product line in the industrial serial server market. With a product matrix of "4/8 RS485 ports + dual Ethernet ports with switch functionality + signal isolation + built-in termination resistors," it precisely addresses the critical industrial requirements of multi-device access, strong interference immunity, long-distance communication, wide temperature operation, and device protection. Whether building a factory data acquisition network or upgrading a legacy equipment room monitoring system, the NA series provides a powerful, mature, and reliable solution.