nmodbus - Message frame must contain at least 6 bytes of data

Question

I am trying to communicate with a PLC over modbus via RS232, but it simply keeps saying that my message from should contain at least 6 bytes of data. First of all I am sorry for the outlining I always seem to struggle with the code input..., I used the same class for a TCP/IP modbus connection which seems to work quite good, now I am trying to do the same via RTU RS232 I added both of my classes in the edit, thanks in advance I hope someone can help me out.

namespace ConsoleApplication2
{
    class Program
    {
        public static ModBusDriver modbusDriver;

    static void Main(string[] args)
    {
        SerialPort port = new SerialPort("COM1");
        port.BaudRate = 38400;
        port.DataBits = 8;
        port.ReadTimeout = 600;
        port.WriteTimeout = 600;
        port.Parity = Parity.None;
        port.StopBits = StopBits.One;

        modbusDriver = new ModBusDriver(port);
        modbusDriver.connect(1);
        byte slaveAddress = 1;
        modbusDriver.WriteMultipleCoils(slaveAddress, 8193, new bool[6] { false, false, false, false, false, false });
        Console.WriteLine("done");
        Console.Read();
    }

Modbusdriver.cs

using Modbus.Device;
using System;
using System.IO.Ports;
using System.Net.Sockets;
using System.Threading;

namespace CoCoSModBusDriver
{

    // based on nmodbus4: 
    // -https://github.com/NModbus4/NModbus4
    class ModBusDriver
    {
        public int connected;
        private bool gotClient = false;
        public IModbusSerialMaster modbusConnector;
        public SerialPort serialPort;

        public ModBusDriver(SerialPort port)
        {
            serialPort = port;
            modbusConnector = ModbusSerialMaster.CreateRtu(port);
        }

        public void connect(int retries)
        {

            int retryCounter = 0;
            while (retryCounter < retries || retries == -1)
            {
                try
                {
                    serialPort.Open();
                }
                catch (Exception ex)
                {
                    retryCounter++;
                    Thread.Sleep(5000);
                }
            }
        }

        public void WriteMultipleCoils(byte slaveAdress, ushort startAdress, bool[] data)
        {
            try
            {
                modbusConnector.WriteMultipleCoils(slaveAdress, startAdress, data);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex);
            }
        }
    }
}

Answer 1

You are missing the slave address in the request. From the IModbus master interface:

    /// <summary>
    ///    Writes a sequence of coils.
    /// </summary>
    /// <param name="slaveAddress">Address of the device to write to.</param>
    /// <param name="startAddress">Address to begin writing values.</param>
    /// <param name="data">Values to write.</param>
    void WriteMultipleCoils(byte slaveAddress, ushort startAddress, bool[] data);

Answer 2

You should use ModbusSerialMaster class. There is a good example at mesta automations homepage.