基于C#实现Modbus RTU通信

一、环境配置与依赖安装

# NuGet包安装（支持.NET Framework 4.5+）
Install-Package NModbus4
Install-Package System.IO.Ports

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二、核心代码实现

1. 串口初始化与连接

using System.IO.Ports;
using Modbus.Device;

public class ModbusRtuMaster
{
    private SerialPort _serialPort;
    private IModbusSerialMaster _master;

    public void Connect(string portName, int baudRate = 9600, Parity parity = Parity.None, 
                       int dataBits = 8, StopBits stopBits = StopBits.One)
    {
        try
        {
            _serialPort = new SerialPort(portName, baudRate, parity, dataBits, stopBits)
            {
                ReadTimeout = 3000,
                WriteTimeout = 3000
            };
            
            _serialPort.Open();
            _master = ModbusSerialMaster.CreateRtu(_serialPort);
            _master.Transport.Retries = 3; // 设置重试次数
            _master.Transport.WriteTimeout = 2000;
            _master.Transport.ReadTimeout = 2000;
        }
        catch (Exception ex)
        {
            Console.WriteLine($"连接失败: {ex.Message}");
            throw;
        }
    }

    public void Disconnect()
    {
        _master?.Close();
        _serialPort?.Close();
    }
}

2. 数据读取操作

public ushort[] ReadHoldingRegisters(byte slaveId, ushort startAddr, ushort count)
{
    try
    {
        return _master.ReadHoldingRegisters(slaveId, startAddr, count);
    }
    catch (ModbusException ex)
    {
        Console.WriteLine($"Modbus错误: {ex.ErrorCode}");
        return null;
    }
    catch (IOException ex)
    {
        Console.WriteLine($"通信异常: {ex.Message}");
        return null;
    }
}

// 示例调用
var data = master.ReadHoldingRegisters(1, 0, 10); // 从站1读取保持寄存器0-9

3. 数据写入操作

public void WriteSingleRegister(byte slaveId, ushort address, ushort value)
{
    _master.WriteSingleRegister(slaveId, address, value);
}

public void WriteMultipleCoils(byte slaveId, ushort startAddr, bool[] values)
{
    _master.WriteMultipleCoils(slaveId, startAddr, values);
}

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三、关键功能实现

1. CRC16校验（Modbus标准）

public static class Crc16
{
    public static byte[] Compute(byte[] data)
    {
        ushort crc = 0xFFFF;
        foreach (byte b in data)
        {
            crc ^= (ushort)b;
            for (int i = 0; i < 8; i++)
            {
                if ((crc & 0x0001) != 0)
                {
                    crc >>= 1;
                    crc ^= 0xA001;
                }
                else
                {
                    crc >>= 1;
                }
            }
        }
        return new[] { (byte)crc, (byte)(crc >> 8) };
    }

    public static bool Validate(byte[] dataWithCrc)
    {
        if (dataWithCrc.Length < 2) return false;
        byte[] data = dataWithCrc.Take(dataWithCrc.Length - 2).ToArray();
        byte[] crc = Compute(data);
        return crc[0] == dataWithCrc[dataWithCrc.Length - 2] 
            && crc[1] == dataWithCrc[dataWithCrc.Length - 1];
    }
}

2. 帧间延迟计算

private int CalculateInterFrameDelay()
{
    int charBits = 1 + _serialPort.DataBits + 
                  (_serialPort.StopBits == StopBits.One ? 1 : 2) + 
                  (_serialPort.Parity == Parity.None ? 0 : 1);
    return (int)(3500.0 * charBits / _serialPort.BaudRate); // 3.5字符时间
}

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四、错误处理与调试

1. 异常处理策略

try
{
    var data = ReadHoldingRegisters(1, 0, 10);
    if (data == null) throw new InvalidOperationException("读取失败");
}
catch (TimeoutException)
{
    Console.WriteLine("通信超时，请检查设备状态");
    Reconnect();
}
catch (InvalidOperationException ex)
{
    Console.WriteLine($"操作失败: {ex.Message}");
}

2. 自动重连机制

private void Reconnect()
{
    Disconnect();
    Thread.Sleep(1000);
    Connect(_config.PortName, _config.BaudRate);
}

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五、性能优化

1批量操作优化

// 批量读取多个寄存器区域
public Dictionary<ushort, ushort[]> BatchRead(
    params (byte SlaveId, ushort StartAddr, ushort Count)[] requests)
{
    var results = new Dictionary<ushort, ushort[]>();
    Parallel.ForEach(requests, request => 
    {
        var data = ReadHoldingRegisters(request.SlaveId, request.StartAddr, request.Count);
        lock (results) results[request.SlaveId] = data;
    });
    return results;
}

2异步通信实现

public async Task<ushort[]> ReadAsync(byte slaveId, ushort startAddr, ushort count)
{
    return await Task.Run(() => ReadHoldingRegisters(slaveId, startAddr, count));
}

参考代码 C#利用modbus rtu模式与下位机通讯 www.youwenfan.com/contentcsr/112701.html

六、完整项目结构

ModbusRTUDemo/
├── src/
│   ├── ModbusMaster/          // 主站核心逻辑
│   ├── SerialPortConfig.cs    // 串口配置管理
│   └── ProtocolHandler.cs     // 协议解析器
├── tests/
│   ├── ModbusTests.cs         // 单元测试
│   └── StressTests.cs         // 压力测试
└── docs/
    └── 开发指南.md

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七、调试与测试工具

1. 虚拟串口工具

   使用VSPD创建虚拟串口对（如COM3<->COM4），方便调试

2. Wireshark抓包分析

   过滤Modbus RTU协议，观察完整的请求/响应帧结构

3. Modbus从站模拟

   使用Modbus Slave工具创建测试从站设备

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八、扩展应用场景

1.多从站管理

public class ModbusNetwork
{
    private Dictionary<byte, ModbusRtuMaster> _slaves = new();
    
    public void AddSlave(byte address, string portName)
    {
        var master = new ModbusRtuMaster();
        master.Connect(portName);
        _slaves[address] = master;
    }
}

2.数据缓存机制

public class DataCache
{
    private Dictionary<ushort, (DateTime Timestamp, ushort Value)[]> _cache = new();
    
    public void UpdateCache(ushort[] data, ushort startAddr)
    {
        _cache[startAddr] = data.Select((v, i) => 
            (DateTime.Now, v)).ToArray();
    }
}

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九、最佳实践建议

1. 参数配置规范

   • 波特率：9600/19200/115200（根据设备手册选择）

   • 数据格式：8N1（默认配置）

   • 超时时间：读操作1000ms，写操作500ms

2. 安全防护措施

   • 添加设备认证机制

   • 实现数据加密传输

   • 设置访问权限控制