出现读取超时啦。。。。。。。。。

多寄存器读 接受数据偶尔会出现读取超时 超时时间不定 波特率19200  代码可能有BUG  大神帮我看看吧 
                 for (int i = 0; i < len; i++)
                 {
                     c = sw.ElapsedMilliseconds;
                     serialPort1.Read(num, i, 1);
                     d = sw.ElapsedMilliseconds;                    
                     if ((d - c) > databyteout)//databyteout = 3
                     {
                         WritePrivateProfileString("error", "C:", "C=" + c, FileNameerror);//记录时间
                        WritePrivateProfileString("error", "D:", "D=" + d, FileNameerror);
                         Form2.isok = false;
                         Form2.boolcheck = false;
                         WritePrivateProfileString("error", "error" + DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss"), "字间超时！" + num[i] + " " + i, FileNameerror);//记录读取超时的寄存器值
                        MessageBox.Show("字间超时！");
                         serialPort1.DiscardInBuffer();
                         return;
                     }
                 }