这是一个文字向上滚动的例子，请问如何改成向下滚动？<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>文字向上滚动</title>
<style type="text/css">
.box{width:500px; height:150px;line-height:25px; border:#bbb 1px solid; overflow:hidden;}
.box ul{margin:0; padding:0}
.box li{font-size:12px; }
</style>
</head> <body>
<div class="box" id="marqueebox0">
<ul>
<li>11111111</li>
<li>22222222</li>
<li>33333333</li>
<li>44444444</li>
<li>55555555</li>
<li>66666666</li>
</ul>
</div>
<script type="text/javascript">
function startmarquee(lh,speed,delay,index){
var t;
var p=false;
var o=document.getElementById("marqueebox"+index);
o.innerHTML+=o.innerHTML;
o.onmouseover=function(){p=true}
o.onmouseout=function(){p=false}
o.scrollTop = 0;
function start(){
t=setInterval(scrolling,speed);
if(!p){ o.scrollTop += 1;}
}
function scrolling(){
if(o.scrollTop%lh!=0){
o.scrollTop += 1;
if(o.scrollTop>=o.scrollHeight/2) o.scrollTop = 0;
}else{
clearInterval(t);
setTimeout(start,delay);
}
}
setTimeout(start,delay);
}
startmarquee(50,30,3000,0); </script>
</body>
</html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>文字向上滚动</title>
<style type="text/css">
.box{width:500px; height:150px;line-height:25px; border:#bbb 1px solid; overflow:hidden;}
.box ul{margin:0; padding:0}
.box li{font-size:12px; }
</style>
</head> <body>
<div class="box" id="marqueebox0">
<ul>
<li>11111111</li>
<li>22222222</li>
<li>33333333</li>
<li>44444444</li>
<li>55555555</li>
<li>66666666</li>
</ul>
</div>
<script type="text/javascript">
function startmarquee(lh,speed,delay,index){
var t;
var p=false;
var o=document.getElementById("marqueebox"+index);
o.innerHTML+=o.innerHTML;
o.onmouseover=function(){p=true}
o.onmouseout=function(){p=false}
o.scrollTop = 0;
function start(){
t=setInterval(scrolling,speed);
if(!p){ o.scrollTop += 1;}
}
function scrolling(){
if(o.scrollTop%lh!=0){
o.scrollTop += 1;
if(o.scrollTop>=o.scrollHeight/2) o.scrollTop = 0;
}else{
clearInterval(t);
setTimeout(start,delay);
}
}
setTimeout(start,delay);
}
startmarquee(50,30,3000,0); </script>
</body>
</html>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>文字向上滚动</title>
<style type="text/css">
.box{width:500px; height:150px;line-height:25px; border:#bbb 1px solid; overflow:hidden;}
.box ul{margin:0; padding:0}
.box li{font-size:12px; }
</style>
</head> <body>
<div class="box" id="marqueebox0">
<ul>
<li>11111111</li>
<li>22222222</li>
<li>33333333</li>
<li>44444444</li>
<li>55555555</li>
<li>66666666</li>
</ul>
</div>
<input value = "1" id="tt">
<input value = "1" id="tt2">
<script type="text/javascript">
function startmarquee(lh,speed,delay,index){
var t;
var p=false;
var o=document.getElementById("marqueebox"+index);
o.innerHTML+=o.innerHTML;
o.onmouseover=function(){p=true}
o.onmouseout=function(){p=false}
o.scrollTop = o.scrollHeight;
function start(){
t=setInterval(scrolling,speed);
if(!p){ o.scrollTop -= 1;document.getElementById("tt").value = o.scrollTop;document.getElementById("tt2").value = document.getElementById("tt2").value * 1 + 1;}
}
function scrolling(){
if(o.scrollTop % lh != 0){
o.scrollTop -= 1;
if(o.scrollTop <= 0){
o.scrollTop = o.scrollHeight;
}
}else{
clearInterval(t);
setTimeout(start,delay);
}
}
setTimeout(start,delay);
}
startmarquee(50,30,3000,0); </script>
</body>