private void cycle() //自定义的函数 
{ 
  int[] arrayboudrate = new int[9] { 300,1200,2400,4800,115200,9600,19200,38400,57600}; 
  for (i=0;i  <=100;i++)  
   {  

     sp1.BaudRate = arrayboudrate[i1]; 
     //.... //设置串口参数 
     try 
     { 
        sp1.open();//打开串口，开始接收数据 

        timer1.Enabled=false;//如果正常,时间控件为无效状态

         //在这里写代码判断是否接满了你所说的多少位

     }
     catch
     {

        timer1.Enabled=true;//发生错误,时间控件启动
        timer1.Interval = 5000;
      
     } 
  }
}  

private void timer1_Tick(object sender, EventArgs e)  
{
    cycle();//执行该方法
}

------解决方案--------------------

   bool iscontinue = false;
   private void cycle() //自定义的函数  
{  
 int[] arrayboudrate = new int[9] { 300,1200,2400,4800,115200,9600,19200,38400,57600};  
 for (i=0;i  <=100;i++) 
  { 

    sp1.BaudRate = arrayboudrate[i1];  
    .... //设置串口参数  
    try  
    {  
        iscontinue = false;
        timer1.Interval = 5000; 
        timer1.start()；
       sp1.open();//打开串口，开始接收数据  
    }
    catch
    {
        iscontinue = true;
    }
     if(iscontinue) continue;
     else
      {  
        if (接收的字符串与协议匹配)  
            终止循环  
          else  
            continue;  
      }  
  } 
} 

private void timer1_Tick(object sender, EventArgs e) 
{ 
   iscontinue = true;
     timer1.stop();
}

------解决方案--------------------
up