jquery无缝向上滚动实现代

<!DOCTYPE html>
<html>
<head>
<style type="text/css">
.renav{
width:200px;
height:150px;
overflow:hidden;
}
.renav li{
height:21px;
border-bottom:solid 1px blue;
list-style-type:none;
}
</style>
<body>
<div class="renav">
<ul>
<li><a>罗氏</a></li>
<li><a>瑞声达</a></li>
<li><a>未添加1</a></li>
<li><a>未添加2</a></li>
<li><a>未添加3</a></li>
<li><a>未添加4</a></li>
<li><a>西门子</a></li>
<li><a>欧姆龙</a></li>
</ul>
</div>
        <script src="http://cdn.static.runoob.com/libs/jquery/2.1.1/jquery.min.js"></script>
<script>
    $(function(){
var $this = $(".renav");
var scrollTimer;
$this.hover(function(){
clearInterval(scrollTimer);
},function(){
scrollTimer = setInterval(function(){
scrollNews( $this );
}, 2000 );
}).trigger("mouseout");
});
function scrollNews(obj){
var $self = obj.find("ul:first");
var lineHeight = $self.find("li:first").height();
$self.animate({ "margin-top" : -lineHeight +"px" },600 , function(){
$self.css({"margin-top":"0px"}).find("li:first").appendTo($self);
})
}
</script>
</body>
</html>