ModbusGateway (English)

English fork of louisir/ModbusGateway with full English UI.

ModbusGateway is a Qt-based Modbus software gateway for forwarding requests and responses between Modbus TCP and Modbus RTU. It supports both TCP Master → RTU Slave and RTU Master → TCP Slave modes, with GUI settings for the serial port, TCP listen/target address, and real-time TCP/RTU frame logs.

Features

• TCP Master → RTU Slave: Modbus TCP masters access Modbus RTU slave devices over a serial/USB-RS485 adapter.
• RTU Master → TCP Slave: Modbus RTU masters access a Modbus TCP slave.
• TCP frame parsing based on the MBAP length field (handles fragmentation and coalescing).
• Automatic Modbus RTU CRC16 append and validation.
• Serialized RTU request queue (prevents concurrent access to the same RS-485 bus).
• Supported function codes: 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x0F, 0x10.
• Modbus exception responses and gateway timeout exceptions (fixed 2000 ms).
• Real-time hex logs for both TCP and RTU sides.

Requirements

• Qt 5.15 or Qt 6.x
• Modules: Core, Gui, Widgets, Network, SerialPort
• C++17 compiler (MinGW or MSVC on Windows)

Build (Windows)

Option A – Qt Creator (easiest)

1. Install Qt (open-source) with MinGW and the SerialPort module.
2. Open ModbusGateway.pro in Qt Creator.
3. Select a kit that includes Qt SerialPort.
4. Click Build → Run.

Option B – Command line (MinGW)

# Adjust path to your Qt installation
$env:PATH = "C:\\Qt\\6.8.3\\mingw_64\\bin;C:\\Qt\\Tools\\mingw1310_64\\bin;" + $env:PATH

qmake ModbusGateway.pro
mingw32-make -j4

The executable will be in the build directory (often release\\ModbusGateway.exe).

Create a portable package

windeployqt --release release\\ModbusGateway.exe

Usage

1. Start the application.
2. Select mode:
   • TCP Master → RTU Slave (most common for USB-RS485 sticks)
   • RTU Master → TCP Slave
3. Configure serial port (COM port of your USB-RS485 adapter), baud rate, parity, etc.
4. Set TCP IP and port (default listen on port 502).
5. Click Start.
6. Connect your Modbus TCP client (Node-RED, SCADA, QModMaster, …) to 127.0.0.1:502.

Limitations

• Only one TCP client is accepted at a time in TCP→RTU mode.
• Response timeout is fixed at 2000 ms.
• Broadcast address 0 is not forwarded in RTU→TCP mode.

Original project

Upstream: https://github.com/louisir/ModbusGateway
This fork changes the UI language to English and keeps the same license and functionality.

License

See LICENSE.