📡 ModbusNet: A .NET Library for Modbus Communication

A modern, lightweight, and production-ready .NET library for communicating with Modbus devices using Modbus ASCII (Serial), Modbus RTU (Serial), and Modbus TCP/IP protocols.

Built for industrial automation, IoT gateways, SCADA systems, and embedded .NET applications.

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✅ Features

• Three transport modes:
  • ✅ Modbus ASCII over serial ports (with LRC error checking)
  • ✅ Modbus RTU over serial ports (with CRC-16 and inter-frame timing)
  • ✅ Modbus TCP over Ethernet (with MBAP framing and async I/O)
• Full function code support:
  • Read/Write Coils & Discrete Inputs
  • Read/Write Holding & Input Registers
  • Mask Write, Read-Write Multiple, FIFO Queue
  • File Record Access, Diagnostics (serial-only), Device Identification
• Robust error handling:
  • Automatic exception decoding (Modbus exception codes)
  • LRC/CRC validation with custom exceptions (ModbusExceptionLRC, ModbusExceptionCRC)
• Thread-safe & async-ready:
  • SendRequestReceiveResponseAsync() for TCP and ASCII
  • Semaphore-locked writes to prevent frame corruption
• Clean architecture:
  • IModbusMaster interface for testability
  • Factory-based creation (ModbusFactory)
  • Settings-driven configuration (ModbusSettings)
• Extensible design:
  • Easy to add new function codes or transports

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🚀 Quick Start

1. Configure Settings

var settings = new ModbusSettings
{
    ConnectionType = ConnectionType.TCP,
    IpAddress = "192.168.1.10",
    Port = 502,
    RetryCount = 3,
    RetryDelayMs = 100
};

For serial (RTU or ASCII):

var settings = new ModbusSettings
{
    ConnectionType = ConnectionType.RTU, // or ASCII
    PortName = PortName.COM4,
    BaudRate = 9600,
    Parity = Parity.Even,
    DataBits = DataBits.db8,
    StopBits = StopBits.One
};

2. Create a Master

// TCP
var master = ModbusFactory.CreateTcpMaster(settings);

// RTU
var master = ModbusFactory.CreateRtuMaster(settings);

// ASCII
var master = ModbusFactory.CreateAsciiMaster(settings);

3. Use It!

// Read 10 holding registers starting at address 0
ushort[] registers = master.ReadMultipleHoldingRegisters(slaveAddress: 1, startAddress: 0, numberOfPoints: 10);

// Write a single coil
master.WriteSingleCoil(slaveAddress: 1, address: 5, value: true);

// Read-Write atomically
ushort[] readData = master.ReadWriteMultipleRegisters(
    slaveAddress: 1,
    startReadAddress: 0,
    numberOfPointsToRead: 3,
    startWriteAddress: 10,
    writeData: new ushort[] { 100, 200, 300 }
);

💡 All methods validate inputs, handle retries, and throw meaningful exceptions on error.

🧩 Supported Function Codes

The ModbusNet library provides full support for standard Modbus function codes across all three transport modes: ASCII, RTU, and TCP. Operations are organised by data type and use case, enabling robust communication with industrial devices.

Category	Function Code	Method Name
Discrete Inputs	0x02	ReadDiscreteInputs()
Coils	0x01	ReadCoils()
	0x05	WriteSingleCoil()
	0x0F	WriteMultipleCoils()
Input Registers	0x04	ReadInputRegisters()
Holding Registers	0x03	ReadMultipleHoldingRegisters()
	0x06	WriteSingleHoldingRegister()
	0x10	WriteMultipleHoldingRegisters()
	0x17	ReadWriteMultipleRegisters()
	0x16	MaskWriteRegister()
	0x18	ReadFifoQueue()
File Record	0x14/0x1	ReadFileRecord(), WriteFileRecord()
Diagnostics (Serial)	0x07–0x11	Serial-only diagnostics
Device ID	0x2B	ReadDeviceIdentification()

📌 Diagnostics (0x07, 0x08, etc.) are only available in serial modes (RTU/ASCII).

⚙️ Configuration (ModbusSettings)

Property	Description
ConnectionType	TCP, RTU or ASCII
IpAddress, Port	For TCP mode
PortName, BaudRate, etc	For serial modes
AsciiStartDelimiter	Usually ":"
AsciiEndDelimiter	Usually "\r\n"
RtuInterCharTimeMs	Inter-character timeout (auto-calculated if baud < 19200)
RtuInterFrameTimeMs	Inter-frame delay
RetryCount	Max retries on timeout (default: 3)
RetryDelayMs	Delay between retries (default: 50 ms)

🔄 RTU timing is automatically calculated for baud rates below 19200 per Modbus spec.

📦 Project Structure

ModbusNet/
├── ModbusNet/               # Core library (IModbusMaster, transports, messages, utils)
├── ModbusNet.Samples/       # Console examples
├── ModbusUI/                # WinForms test UI 
└── ModbusNet.Tests/         # Unit tests (not required for usage)

Testing & Sample Codes

The solution includes:

• A WinForms GUI (ModbusUI) for visual testing of all three protocols.
• A sample console project (ModbusNet.Samples) showing basic usage patterns.

🔒 The core library has no UI dependencies — the GUI is purely for testing/demo.

License

Distributed under the MIT License. See LICENSE for details.

🙌 Contributing

Contributions are welcome! Feel free to:

• Report bugs
• Suggest enhancements
• Implement other function codes
• Improve documentation

📬 Need Help?

Open an issue or contact the maintainers.

ModbusNet brings industrial-grade Modbus communication to modern .NET developers with simplicity, correctness, and performance.