图中的串口测试工具可以接收到一条反馈码，我自己写的winform却接收不到，哪位大神了解串口工具的源码或者知道我的代码怎么改嘛，哪位大神指点一下，万分感谢！
int n = sc._serialPort.BytesToRead;
StringBuilder builder=new StringBuilder();
byte[] rec = new byte[n]; //新建一个接受数组
sc._serialPort.Read(rec, 0, n); //将串口接收到的数据写入接收数组
//sc.DataReceived(object sender, EventArgs e, rec);
builder.Append(Encoding.ASCII.GetString(rec));
这个是我自己写的，获取不到东西，还有一个是别人提供的写好的
public SerialPort _serialPort = null;
//定义委托
public delegate void SerialPortDataReceiveEventArgs(object sender, SerialDataReceivedEventArgs e, byte[] bits);
//定义接收数据事件
public event SerialPortDataReceiveEventArgs DataReceived;

            void _serialPort_DataReceived(object sender, SerialDataReceivedEventArgs e)
    {
        if (DataReceived != null)
        {
            byte[] _data = new byte[_serialPort.BytesToRead];
            _serialPort.Read(_data, 0, _data.Length);
            DataReceived(sender, e, _data);
            //a += _data.Length;
            //rec += System.Text.Encoding.Default.GetString(_data)+_data.Length;
        }
    }
            可是这两种都接收不到东西，请大神指教一下我应该怎么改写这两个函数或者是怎样写