c# codesys modbus rtu

Sure! Here's an example of how you can use C# with CODESYS to communicate over Modbus RTU:

using System;
using System.IO.Ports;

namespace ModbusRTUExample
{
    class Program
    {
        static void Main(string[] args)
        {
            // Modbus RTU serial port settings
            string portName = "COM1";
            int baudRate = 9600;
            Parity parity = Parity.None;
            int dataBits = 8;
            StopBits stopBits = StopBits.One;

            // Create a serial port object
            SerialPort port = new SerialPort(portName, baudRate, parity, dataBits, stopBits);

            try
            {
                // Open the serial port
                port.Open();

                // Modbus RTU message format: slave address + function code + data + CRC16
                byte slaveAddress = 1;
                byte functionCode = 4;
                ushort startingAddress = 0;
                ushort numberOfRegisters = 10;

                // Build the Modbus RTU message
                byte[] message = new byte[8];
                message[0] = slaveAddress;
                message[1] = functionCode;
                message[2] = (byte)(startingAddress >> 8);
                message[3] = (byte)startingAddress;
                message[4] = (byte)(numberOfRegisters >> 8);
                message[5] = (byte)numberOfRegisters;

                // Calculate the CRC16 checksum
                ushort crc = CalculateCRC(message, 6);
                message[6] = (byte)(crc & 0xFF);
                message[7] = (byte)(crc >> 8);

                // Send the Modbus RTU message
                port.Write(message, 0, message.Length);

                // Receive the response from the slave device
                byte[] response = new byte[1024];
                int bytesRead = port.Read(response, 0, response.Length);

                // Process the response data
                for (int i = 0; i < bytesRead; i++)
                {
                    Console.WriteLine("Byte " + i + ": " + response[i]);
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine("Error: " + ex.Message);
            }
            finally
            {
                // Close the serial port
                if (port.IsOpen)
                    port.Close();
            }

            Console.ReadLine();
        }

        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;
        }
    }
}

This example shows how to communicate with a Modbus RTU slave device using a serial port connection. You will need to modify the `portName`, `baudRate`, `parity`, `dataBits`, and `stopBits` variables to match your specific serial port settings. Additionally, you can customize the Modbus RTU message by modifying the `slaveAddress`, `functionCode`, `startingAddress`, and `numberOfRegisters` variables. The example also includes a CRC16 calculation function to calculate the checksum for the Modbus RTU message.