private static Plc s7Instance;

public MainForm()
{
  InitializeComponent();
}

private void btnConnect_Click(object sender, System.EventArgs e)
{
  if (btnConnect.Text == "Connect")
  {
    if (s7Instance == null)
      s7Instance = new Plc(CpuType.S71500, txtPlcIPAddress.Text.Trim(), 0, 1);

    s7Instance.Open();
    btnConnect.Text = "Disconnect";
  }
  else
  {
    s7Instance.Close();
    btnConnect.Text = "Connect";
    txtBool01.Clear();
    txtInt01.Clear();
    txtStr01.Clear();
    txtStr02.Clear();
  }
}

private void btnReadData_Click(object sender, System.EventArgs e)
{
  if (s7Instance == null || !s7Instance.IsConnected)
  {
    MessageBox.Show("Your PLC is not connected now!", "Error", MessageBoxButtons.OK);
    return;
  }

  // bool
  var boolData = (bool)s7Instance.Read(DataType.DataBlock, 1, 0, VarType.Bit, 1);
  txtBool01.Text = boolData ? "1" : "0";
  // int
  var intData = (short)s7Instance.Read(DataType.DataBlock, 1, 2, VarType.Int, 1);
  txtInt01.Text = intData.ToString();
  // string
  var count = (byte)s7Instance.Read(DataType.DataBlock, 1, 4 + 1, VarType.Byte, 1); // +1表示读取偏移值的长度
  var str01Data = Encoding.Default.GetString(s7Instance.ReadBytes(DataType.DataBlock, 1, 4 + 2, count)); // +2表示读取偏移值（跳过）的字符
  txtStr01.Text = str01Data;
  // wstring
  var str02Data = (string)s7Instance.Read(DataType.DataBlock, 1, 260, VarType.S7WString, 254);
  txtStr02.Text = str02Data;
}

public static class S7DataWriter
{
  /// <summary>
  /// 获取西门子PLC字符串数组--String类型
  /// </summary>
  public static byte[] GetPlcStringByteArray(string str)
  {
    byte[] value = Encoding.Default.GetBytes(str);
    byte[] head = new byte[2];
    head[0] = Convert.ToByte(254);
    head[1] = Convert.ToByte(str.Length);
    value = head.Concat(value).ToArray();
    return value;
  }

  /// <summary>
  /// 获取西门子PLC字符串数组--WString类型
  /// </summary>
  public static byte[] GetPlcWStringByteArray(string str)
  {
    byte[] value = Encoding.BigEndianUnicode.GetBytes(str);
    byte[] head = BitConverter.GetBytes((short)508);
    byte[] length = BitConverter.GetBytes((short)str.Length);
    Array.Reverse(head);
    Array.Reverse(length);
    head = head.Concat(length).ToArray();
    value = head.Concat(value).ToArray();
    return value;
  }
}

private void btnWriteData_Click(object sender, System.EventArgs e)
{
  if (s7Instance == null || !s7Instance.IsConnected)
  {
    MessageBox.Show("Your PLC is not connected now!", "Error", MessageBoxButtons.OK);
    return;
  }

  // bool
  var boolValue = txtBool01.Text.Trim() == "1" ? true : false;
  s7Instance.Write(DataType.DataBlock, 1, 0, boolValue);
  // int
  var intValue = Convert.ToInt16(txtInt01.Text);
  s7Instance.Write(DataType.DataBlock, 1, 2, intValue);
  // string
  s7Instance.Write(DataType.DataBlock, 1, 4, S7DataWriter.GetPlcStringByteArray(txtStr01.Text.Trim()));
  // wstring
  s7Instance.Write(DataType.DataBlock, 1, 260, S7DataWriter.GetPlcWStringByteArray(txtStr02.Text.Trim()));

  MessageBox.Show("Write data successfully!", "Info", MessageBoxButtons.OK);
}