向上滚动代码，不间断,JavaScript

<div id="demo" style="width:250px;height:82px;border:1px solid #900;overflow:hidden;">
        <ul id="demo1">
          <li>白家印象-资讯频道1</li>
          <li>白家印象-资讯频道2</li>
          <li>白家印象-资讯频道3</li>
          <li>白家印象-资讯频道4</li>
        </ul>
        <ul id="demo2"></ul>
        <script type="text/javascript">
        var speed=50;
        document.getElementById("demo2").innerHTML=document.getElementById("demo1").innerHTML;
        function Marquee(){
        if(document.getElementById("demo2").offsetTop-document.getElementById("demo").scrollTop<=0)
           {
               document.getElementById("demo").scrollTop-=document.getElementById("demo1").offsetHeight;
           }
           else
           {
               document.getElementById("demo").scrollTop++;
           }
        }
        var MyMar=setInterval(Marquee,speed);
        document.getElementById("demo").onmouseover=function() {clearInterval(MyMar);}
        document.getElementById("demo").onmouseout=function() {MyMar=setInterval(Marquee,speed);}
      </script>
      </div>