private static void Main(string[] args)
        {
            try
            {
                ModbusSerialRtuMasterWriteRegisters();
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }

            Console.WriteLine("Press any key to continue...");
            Console.ReadKey();
        }

        /// 

        /// Simple Modbus serial RTU master write holding registers example.
        /// 
        public static void ModbusSerialRtuMasterWriteRegisters()
        {
            using (SerialPort port = new SerialPort("COM3"))
            {
                // configure serial port
                port.BaudRate = 9600;
                port.DataBits = 8;
                port.Parity = Parity.None;
                port.StopBits = StopBits.One;
                port.Open();

                var factory = new ModbusFactory();
                IModbusMaster master = factory.CreateRtuMaster(port);

                byte slaveId = 1;
                ushort startAddress = 100;
                ushort[] registers = new ushort[] { 1, 2, 3 };

                // write three registers
                master.WriteMultipleRegisters(slaveId, startAddress, registers);
            }
        }