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OPC UA → Modbus TCP 桥接

老设备只支持 Modbus, 新设备只暴露 OPC UA. 写一个轻量桥: 订阅 OPC UA → 写 Modbus 寄存器. 用 C# + NModbus 示例.

配套示例

依赖​

dotnet add package DarraOpcUa
dotnet add package NModbus

完整代码​

using DarraOpcUa_Client;
using NModbus;
using System;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.Threading.Tasks;

class Program
{
    // 映射表: OPC UA NodeId → Modbus 寄存器地址
    record TagMap(string NodeId, ushort Reg, string Type);

    static readonly TagMap[] Mapping = new[]
    {
        new TagMap("ns=2;s=Boiler1.Temperature", 0,   "Float"),  // 占 reg 0/1
        new TagMap("ns=2;s=Boiler1.Pressure",    2,   "Float"),  // 占 reg 2/3
        new TagMap("ns=2;s=Boiler1.IsRunning",   100, "Bool"),   // coil 100
    };

    static async Task Main()
    {
        const string opcuaEndpoint = "opc.tcp://localhost:4840";
        const int    modbusPort    = 502;

        // 1. 启动 Modbus TCP Slave
        var listener = new TcpListener(IPAddress.Any, modbusPort);
        listener.Start();
        var factory = new ModbusFactory();
        var slaveNet = factory.CreateSlaveNetwork(listener);
        var slave = factory.CreateSlave(unitId: 1);
        slaveNet.AddSlave(slave);
        _ = slaveNet.ListenAsync();
        Console.WriteLine($"[OK] Modbus TCP Slave listen on :{modbusPort}");

        // 2. 启动 OPC UA Client
        using var ua = new DarraOpcUa(opcuaEndpoint);
        ua.Connect();
        Console.WriteLine($"[OK] OPC UA connected to {opcuaEndpoint}");

        // 3. 订阅 + 类型转换写 Modbus
        using var sub = ua.CreateSubscription(500);
        sub.DataChanged += (s, e) =>
        {
            var map = Mapping.FirstOrDefault(m => m.NodeId == e.NodeId);
            if (map == null || !e.Status.IsGood) return;

            try
            {
                switch (map.Type)
                {
                    case "Float":
                        var f = float.Parse(e.ValueString);
                        var bytes = BitConverter.GetBytes(f);
                        slave.DataStore.HoldingRegisters[map.Reg]     = BitConverter.ToUInt16(bytes, 0);
                        slave.DataStore.HoldingRegisters[map.Reg + 1] = BitConverter.ToUInt16(bytes, 2);
                        break;
                    case "Bool":
                        slave.DataStore.CoilDiscretes[map.Reg] = bool.Parse(e.ValueString);
                        break;
                }
                Console.WriteLine($"  {e.NodeId} = {e.ValueString} -> Modbus[{map.Reg}]");
            }
            catch (Exception ex) { Console.WriteLine($"  map error: {ex.Message}"); }
        };

        sub.AddMany(Mapping.Select(m => m.NodeId).ToList());

        Console.WriteLine("\nBridge 运行中, Ctrl+C 退出...");
        await Task.Delay(Timeout.Infinite);
    }
}

分段说明​

第 1 步: Modbus Slave 启动​

var slaveNet = factory.CreateSlaveNetwork(listener);
var slave = factory.CreateSlave(unitId: 1);
slaveNet.AddSlave(slave);
_ = slaveNet.ListenAsync();

NModbus 支持单监听口多个 unitId, 多设备桥接时 unitId 区分.

第 2 步: 类型转换 (重点)​

var f = float.Parse(e.ValueString);
var bytes = BitConverter.GetBytes(f);
slave.DataStore.HoldingRegisters[map.Reg]     = BitConverter.ToUInt16(bytes, 0);
slave.DataStore.HoldingRegisters[map.Reg + 1] = BitConverter.ToUInt16(bytes, 2);

关键陷阱: Modbus 寄存器是 16 位, OPC UA Float (32 位) 必须拆 2 个寄存器, Double (64 位) 拆 4 个. 字节序 (Big / Little Endian, Word Swap) 各厂家不一致, 调试时拿 Modbus Master 工具 (Modbus Poll) 对一下.

第 3 步: 反向桥接 (Modbus → OPC UA Write)​

slave.ModbusSlaveRequestReceived += (s, ev) =>
{
    if (ev.Message.FunctionCode == 6 /* Write Single Reg */)
    {
        // ev 内取 reg 值, 找映射表, 调 ua.Write(...)
    }
};

Modbus Master 写过来时, 通过 ModbusSlaveRequestReceived 事件转发到 OPC UA Write.

注意事项​

  • HoldingRegisters / InputRegisters / Coils / DiscreteInputs 四张表独立, 设计映射前先想清楚.
  • NModbus 不支持 Modbus RTU over TCP, 要 RTU 用 NModbus.Serial 或 EasyModbusTCP.
断线哨兵值

OPC UA 断线时 Modbus 寄存器不会自动清零 — 上层应用可能误以为数据正常. 建议挂 ua.Events.Disconnected 把对应寄存器写一个"无效值哨兵" (如 0xFFFF).

相关链接​