C# Easy Modbus Communication

1. Preamble

Hello, everyone! I'm paid worker. Previously, I gave you a series of knowledge about RS485 and Modbus.

Finally, someone has clarified RS485.
Finally, someone's got Modbus figured out.
Through and through! Finally got ModbusRTU figured out!
In this case, the ModbusTCP protocol is too simple
Today talk to you about how to implement Modbus communication in C#.

2. Open source communication libraries

Communication library is the encapsulation of the communication protocol, generally in the form of dll dynamic link library exists, for the programmer, only need to call the library's various methods to realize the data read and write.

There are two kinds of communication libraries, one is open source, even if open source, but also pay attention to the open source license, open source is not necessarily free, the other is to develop their own package, which requires a certain degree of development capabilities.

Modbus communication has a lot of open source communication libraries, which is more widely used is NModbus4, NModbus4 is an open source and free Modbus communication library, its open source license is MIT, is a relatively loose software licensing terms, can be commercially available.

3、ModbusRTU communication

1, in the project solution explorer, select [Reference] right-click, in the pop-up interface, click [Manage NuGet packages] option, as shown in the following figure:

2, in the open tab, select [Browse], and then enter NModbus4 to search, after the search, select the latest stable version 2.1.0, click [Install] can be:

3. Encapsulate a method to open and close the serial port on the basis of NModbus4:

private SerialPort serialPort;
private ModbusSerialMaster master;
public void Open(string portName, int baudRate, Parity parity, int dataBits, StopBits stopBits)
{
    if (this.serialPort != null && this.)
    {
        this.();
    }
    this.serialPort = new SerialPort(portName, baudRate, parity, dataBits, stopBits);
    this.();
    this.master = (this.serialPort);
    this. = 2000;
    this. = 2000;
    this. = 500;
    this. = 3;
}
 public void Close()
 {
     if (this.serialPort != null && this.)
     {
         this.();
     }
     this.master = null;
 }

4. Encapsulate various methods of reading and writing on the basis of NModbus4, here read the holding registers as an example, other methods are similar:

public byte[] ReadHoldingRegisters(byte slaveId, ushort start, ushort length)
{
    try
    {
        ushort[] data = this.(slaveId, start, length);
        List<byte> result = new List<byte>();
        foreach (var item in data)
        {
            ((item).Reverse());
        }
        return ();
    }
    catch (Exception ex)
    {
        throw new Exception("[Read Holding Register] failed:" + );
    }
}

Based on NModbus4 to realize ModbusRTU communication, do not need to pay attention to the protocol and message, only need to the NModbus4 library secondary packaging.

4、ModbusTCP communication

NModbus4 not only supports ModbusRTU communication, but also supports ModbusTCP communication as well. The encapsulation process of ModbusTCP is very similar to that of ModbusRTU, mainly because of the following two differences:

ModbusRTU is based on serial communication and therefore mainly uses the SerialPort class, while ModbusTCP is based on Ethernet communication and mainly uses the TcpClient class.
ModbusRTU must include the slave address in both the read and write methods, whereas ModbusTCP can make SlaveAddress optional.

ModbusTCP communication library encapsulation process is as follows: 1. Encapsulate a TCP connection and disconnection method on the basis of NModbus4:

private TcpClient tcpClient;
private ModbusIpMaster master
public void Connect(string ip, int port)
{
    tcpClient = new TcpClient();
    ((ip), port);
     = ();
     = 2000;
     = 2000;
     = 500;
     = 3;
}
 public void DisConnect()
 {
     if ( != null && )
     {
         ();
     }
      = null;
 }

2, encapsulate a method to read the output coil, other read and write methods are similar:

public bool[] ReadOutputCoils(ushort start, ushort length, byte slaveAddress = 1)
{
    try
    {
        return this.(slaveAddress, start, length);
    }
    catch (Exception ex)
    {
        throw new Exception("[Read Output Coil] Failed:" + );
    }
}