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int i;
        private void cmdReceive_Click(object sender, EventArgs e)
        {
            serialPort1.Open();
            //for (i = 0; i < 100; i++)
            {
                i++;
                rtxtReceive.Text += serialPort1.ReadLine() + Environment.NewLine;//"\n";
                //serialPort1.Close();

            }
            serialPort1.Close();
        }