1. Overview
The USR N540 is a 4-port RS485 serial device server that supports the Modbus RTU to Modbus TCP gateway function. This article explains in detail how to configure the Modbus gateway on the USR-N540.
2. Hardware Connection
- Connect the Ethernet port to a computer or switch
- Connect the RS485 ports to downstream devices (PLCs, instruments, etc.)
- Power supply: DC 5-36 V
3. Web Configuration Interface
- Enter the module's default IP in the browser: 192.168.0.7
- Enter the username and password (default admin/admin)
- Enter the configuration interface
4. Modbus Gateway Configuration
4.1 Serial Port Parameter Configuration
| Parameter | Description |
|---|---|
| Baud rate | Must match the downstream device (e.g. 9600) |
| Data bits | 8 bits |
| Parity | Must match the downstream device |
| Stop bits | 1 bit |
4.2 Operating Mode Selection
- Select the "Modbus Gateway" mode
- TCP port number: 502 (the standard Modbus TCP port)
- Supports bidirectional conversion between Modbus RTU and Modbus TCP
4.3 Multi-Port Mapping
| Serial Port | Number of TCP Connections | Description |
|---|---|---|
| RS485-1 | Up to 4 | First serial port |
| RS485-2 | Up to 4 | Second serial port |
| RS485-3 | Up to 4 | Third serial port |
| RS485-4 | Up to 4 | Fourth serial port |
5. FAQ and Troubleshooting
- Check whether the serial port parameters match those of the downstream device
- Confirm that the operating mode is set to Modbus Gateway
- Check whether the TCP port is already occupied
- Note that each serial port supports at most 4 TCP clients
6. Summary
Key points for configuring the USR N540 Modbus gateway:
- Configure the serial port parameters to match the downstream device
- Select the Modbus Gateway operating mode
- The default TCP port is 502
- The 4 RS485 ports work independently without interfering with one another
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