用C#写一个RS485通讯的MODBUS通讯功能块

以下是一个基本的C#代码示例，用于实现RS485通讯的MODBUS通讯功能块：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO.Ports;

namespace ModbusCommunication
{
    public class ModbusRS485
    {
        private SerialPort serialPort;

        public ModbusRS485(string portName, int baudRate, Parity parity, int dataBits, StopBits stopBits)
        {
            serialPort = new SerialPort(portName, baudRate, parity, dataBits, stopBits);
            serialPort.Handshake = Handshake.None;
            serialPort.ReadTimeout = 500;
            serialPort.WriteTimeout = 500;
            serialPort.Open();
        }

        public byte[] ReadInputRegisters(byte slaveAddress, ushort startAddress, ushort numberOfPoints)
        {
            byte[] data = new byte[8];
            data[0] = slaveAddress;
            data[1] = 0x04;
            data[2] = (byte)(startAddress >> 8);
            data[3] = (byte)(startAddress & 0xFF);
            data[4] = (byte)(numberOfPoints >> 8);
            data[5] = (byte)(numberOfPoints & 0xFF);

            ushort crc = ModbusHelper.CalculateCRC(data, 6);
            data[6] = (byte)(crc & 0xFF);
            data[7] = (byte)(crc >> 8);

            serialPort.Write(data, 0, 8);

            int byteCount = numberOfPoints * 2 + 5;
            byte[] response = new byte[byteCount];
            serialPort.Read(response, 0, byteCount);

            if (response[0] != slaveAddress || response[1] != 0x04 || response[2] != byteCount - 5)
            {
                throw new Exception("Invalid response.");
            }

            crc = ModbusHelper.CalculateCRC(response, byteCount - 2);
            if (crc != (ushort)(response[byteCount - 2] | (response[byteCount - 1] << 8)))
            {
                throw new Exception("Invalid CRC.");
            }

            byte[] result = new byte[numberOfPoints * 2];
            for (int i = 0; i < numberOfPoints * 2; i++)
            {
                result[i] = response[3 + i];
            }

            return result;
        }

        public void WriteSingleRegister(byte slaveAddress, ushort registerAddress, ushort value)
        {
            byte[] data = new byte[8];
            data[0] = slaveAddress;
            data[1] = 0x06;
            data[2] = (byte)(registerAddress >> 8);
            data[3] = (byte)(registerAddress & 0xFF);
            data[4] = (byte)(value >> 8);
            data[5] = (byte)(value & 0xFF);

            ushort crc = ModbusHelper.CalculateCRC(data, 6);
            data[6] = (byte)(crc & 0xFF);
            data[7] = (byte)(crc >> 8);

            serialPort.Write(data, 0, 8);
        }
    }

    public static class ModbusHelper
    {
        public static ushort CalculateCRC(byte[] data, int length)
        {
            ushort crc = 0xFFFF;

            for (int i = 0; i < length; i++)
            {
                crc ^= data[i];

                for (int j = 0; j < 8; j++)
                {
                    if ((crc & 0x0001) == 0x0001)
                    {
                        crc >>= 1;
                        crc ^= 0xA001;
                    }
                    else
                    {
                        crc >>= 1;
                    }
                }
            }

            return crc;
        }
    }
}

这个代码示例仅仅提供了基础的读取输入寄存器和写单个寄存器的功能，你可以在此基础上扩展更多的Modbus通讯功能。需要注意的是，不同的Modbus设备可能需要不同的数据格式和通讯协议，所以在实际使用中需要根据设备的具体要求进行修改。