NModbus is a C# implementation of the Modbus protocol.
Provides connectivity to Modbus slave compatible devices and applications.
Supports serial ASCII, serial RTU, TCP, and UDP protocols.
NModbus4 it's a fork of NModbus(https://code.google.com/p/nmodbus).
NModbus4 differs from original NModbus in following:
 
1. removed USB support(FtdAdapter.dll)
2. removed log4net dependency
3. removed Unme.Common.dll dependency
4. assembly renamed to NModbus4.dll
5. target framework changed to .NET 4

The MIT License (MIT)
 
Copyright (c) 2006 Scott Alexander, 2015 Dmitry Turin
 
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
 
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

NModbus4.Wrapper is driven from NModbus4 for integrated usage.
Difference of NModbus4.Wrapper from NModbus4 is: 
 
1. integrate class (RTU, TCP, UDP...) into ModbusService
2. support C# data types (bool, int, float)
3. support threading when using Client

The MIT License (MIT)
 
Copyright (c) 2023 Peponi
 
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
 
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

NuGet\Install-Package NModbus4.Wrapper

string interfaceName = "Test";
ModbusType modbusType = ModbusType.TCP_Slave;
int slaveNo = 1;
EthernetInformation ethernetInformation = new EthernetInformation
{
    Address = "127.0.0.1",
    Port = 50001
};
Endian endian = Endian.Big;
 
ModbusInterface interfaceData = new ModbusInterface(interfaceName, modbusType, slaveNo, ethernetInformation, endian);
ModbusService modbus = new ModbusService(interfaceData, CheckConnectionStatus);
 
modbus.ModbusLog += Modbus_LogWrite;
modbus.ModbusDataReceived += Modbus_ModbusDataReceived;
modbus.ModbusCommunicationException += Modbus_ModbusCommunicationException;
modbus.ModbusGeneralException += Modbus_ModbusGeneralException;
 
modbus.Connect();
 
void CheckConnectionStatus(ModbusInterface modbusInterface, bool connectStatus)
{
    if (connectStatus)
    {
        // Do something...
    }
    else
    {
        // Reconnect, or other things to do..
    }
}

modbus.Dispose();

if (modbus != null) modbus.Dispose();
 
modbus = new Modbus(interfaceData, CheckConnectionStatus);
 
modbus.ModbusLog += Modbus_LogWrite;
modbus.ModbusDataReceived += Modbus_ModbusDataReceived;
modbus.ModbusCommunicationException += Modbus_ModbusCommunicationException;
modbus.ModbusGeneralException += Modbus_ModbusGeneralException;
 
modbus.Connect();

// 1. Single case
 
var commData = new CommunicationData(DataStorage.HoldingRegister, 0, default(double), modbus.Interface.EndianOption);
 
if (modbus.ReadData(ref commData))
{
    // Data process...
}
else
{
    // Do something for error handling...
}
 
// 2. List case
 
List<CommunicationData> commDatas = new List<CommunicationData>();
 
commDatas.Add(new CommunicationData(DataStorage.HoldingRegister, 0, default(float), modbus.Interface.EndianOption));
commDatas.Add(new CommunicationData(DataStorage.HoldingRegister, 2, default(bool), modbus.Interface.EndianOption));
commDatas.Add(new CommunicationData(DataStorage.HoldingRegister, 3, default(int), modbus.Interface.EndianOption));
 
if (modbus.ReadData(ref commDatas))
{
    // Data process...
}
else
{
    // Do something for error handling...
}

// 1. Single case
 
var commData = new CommunicationData(DataStorage.HoldingRegister, 0, 10.12, modbus.Interface.EndianOption);
 
if (!await modbus.WriteDataAsync(commData))
{
    // Do something for error handling...
}
 
// 2. List case
 
List<CommunicationData> commDatas = new List<CommunicationData>();
 
commDatas.Add(new CommunicationData(DataStorage.HoldingRegister, 0, 3.465F, modbus.Interface.EndianOption));
commDatas.Add(new CommunicationData(DataStorage.Coil, 0, true, modbus.Interface.EndianOption));
commDatas.Add(new CommunicationData(DataStorage.HoldingRegister, 2, 534, modbus.Interface.EndianOption));
 
if (!await modbus.WriteDataAsync(commDatas))
{
    // Do something for error handling...
}