                        课程
                    
                        /前端开发
                        
                            /JavaScript
                        
                        /信息滚动效果制作

我的代码怎么运行处BUG了，滚动不到最后就又开始滚动了而且还越滚越快？

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Document</title>
<style type="text/css">
        body {
font-size: 12px;
line-height: 24px;
text-algin: center;        /* 页面内容居中 */
}
* {
margin: 0px;
padding: 0px;            /*  去掉所有标签的marign和padding的值  */
}
        #box{
         width:410px;
         height: 230px;
         margin: 0 auto;
          margin-top: 50px;
          border: 5px solid gray;
          border-radius: 10px;
          overflow: hidden;
        }
        #box h3{
         background: red;
         height: 65px;
         line-height: 65px;;
         color: white;
         font-size:25px;
         padding:10px;
         padding-left: 20px;
         margin-top:0;
        }
        #box h3 a{
         font-size: 10px;
         text-decoration: none;
         float: right;
         color: white;
        }
        #moocBox{
         width: 410px;
         height: 150px;
         margin-top: 5px;
         overflow: hidden;     
        }
        #moocBox ul{
            list-style-type: none;
            padding: 0 40px;
        }
        #moocBox ul li{
         margin-top: 5px;
         height: 24px;
        }
        #moocBox ul li a{
         text-decoration: none;
         color:black;
         font-size: 12px;
        }
        #moocBox ul li a:hover{
         color:red;
        }
        #moocBox ul span{
         color: gray;
         float: right;
        }
</style>  
</head>
<body>
<div id="box">
       <h3>最新课程 <a href="#">更多》》</a></h3>
<div id="moocBox">
<ul id="cn1">
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</ul>
</div>
</div>
</body>
    <script type="text/javascript">
     var box=document.getElementById("moocBox");
     box.innerHTML+=box.innerHTML;
     var iHegiht=24;
     function startMove(){
     box.scrollTop++;
     time=setInterval("scrollUp()",50)
     }
     function scrollUp(){
     box.scrollTop++;
     if(box.scrollTop % iHegiht==0){
     clearInterval(time);
     setTimeout("startMove()",2000)
     }else{
     box.scrollTop++;
     if (box.scrollTop>=box.offsetHeight/2) {
     box.scrollTop=0;
     }
     }
     }
     setTimeout("startMove()",2000);//初始化
    </script>
</html>