相应源码如下所示:

public void SaveConfig(string key, string value)
{
    try
    {
	string fileName = "Web.Config";
	XmlDocument document = new XmlDocument();
	document.Load(fileName);
	((XmlElement)document.SelectSingleNode(@"//AppSetting/add[@key='" + key + "']")).SetAttribute("Value", value);
	document.Save(fileName);
    }
    catch (Exception ex)
    {
	throw new Exception(ex.Message);
    }
}

using System;
using System.IO.Ports;
using System.Threading;

namespace TripodDemo
{
    /// <summary>
    /// 串口操作通用类,抽象类防止类别直接实例化
    /// </summary>
    public abstract class ComPort : IDisposable
    {
        /// <summary>
        /// 使用变量锁定对象
        /// </summary>
        private object objComm = new object();

        /// <summary>
        /// 串口对象
        /// </summary>
        private SerialPort com;

        private bool disposed = false;

        #region SerialPort
        public ComPort()
        {
            com = new SerialPort("COM1", 9600);
            OpenCom();
        }

        public ComPort(SerialPort sp)
        {
            com = sp;
            OpenCom();
        }

        private void OpenCom()
        {
            try
            {
                if (!com.IsOpen)
                {
                    com.ReadTimeout = 3000;
                    com.WriteTimeout = 3000;
                    com.Open();
                }
            }
            catch (Exception ex)
            {
                throw new Exception(ex.Message);
            }
        }
        #endregion

        #region Dispose & Close
        public void Dispose()
        {
            Dispose(true);
        }

        private void Dispose(bool disposing)
        {
            if (!disposed && disposing && com != null && com.IsOpen)
            {
                com.Close();
                disposed = true;
            }
        }

        public void Close()
        {
            Dispose(true);
        }
        #endregion

        #region 发送数据
        /// <summary>
        /// 发送数据
        /// </summary>
        /// <param name="bwrite">写数据</param>
        /// <param name="returnDataLen">读数据长度</param>
        /// <param name="bread">读数据</param>
        /// <param name="msel">超时毫秒</param>
        /// <returns>是否执行成功</returns>
        public bool SendData(byte[] bwrite, int returnDataLen, out byte[] bread, int msel)
        {
            lock (objComm)
            {
                bread = new byte[returnDataLen];
                long l = DateTime.UtcNow.Ticks + msel * 10000;
                com.DiscardInBuffer();
                com.DiscardOutBuffer();
                com.Write(bwrite, 0, bwrite.Length);

                while (com.BytesToRead < returnDataLen && DateTime.UtcNow.Ticks < l)
                {
                    Thread.Sleep(1);
                }

                //串口无反应
                if (com.BytesToRead < returnDataLen)
                {
                    return false;
                }

                try
                {
                    com.Read(bread, 0, bread.Length);
                    return true;
                }
                catch (TimeoutException)
                {
                    return false;
                }
            }
        }
        #endregion
    }

    public class SerialQ01 : ComPort
    {
        #region 构造函数
        public SerialQ01()
            : base()
        {
            //constructor
        }

        public SerialQ01(SerialPort sp)
            : base(sp)
        {
            //constructor
        }
        #endregion

        #region 读时间
        public bool ReadDeviceTime(byte macno, out string time)
        {
            int retLen = 10;
            byte[] bread;

            //构建命令
            byte b1 = 0xAA;
            byte b2 = 0x00;
            byte b3 = 0x32;

            byte[] bwrite = { b1, b2, b2, macno, macno, b3, b3 };
            bool bRet = SendData(bwrite, retLen, out bread, 1000);

#if DEBUG
            foreach (byte b in bread)
            {
                System.Diagnostics.Debug.WriteLine(b.ToString("X2"));
            }
#endif

            time = string.Empty;
            if (bRet)
            {
                if (bread[0] == 0xCC && bread[1] == 0x30 && bread[2] == 0x30)
                {
                    time = string.Format("20{0}-{1}-{2} {3}:{4}", bread[3].ToString("X2"), bread[4].ToString("X2"), bread[5].ToString("X2"), bread[6].ToString("X2"), bread[7].ToString("X2"));
                    return true;
                }
                else
                {
                    return false;
                }
            }
            else
            {
                return false;
            }
        }
        #endregion

    }
}