var layerHeight = 195; // 定义滚动区域的高度.

var iFrame = 1; // 定义每帧移动的象素.

var iFrequency = 50; // 定义帧频率.

var timer; // 定义时间句柄.

if(document.getElementById("layer2").offsetHeight >= layerHeight)

document.getElementById("layer1").style.height = layerHeight;

else

document.getElementById("layer1").style.height = document.getElementById("layer2").offsetHeight;

document.getElementById("layer3").innerHTML = document.getElementById("layer2").innerHTML;
   

function move(){

if(document.getElementById("layer1").scrollTop >= document.getElementById("layer2").offsetHeight){

document.getElementById("layer1").scrollTop -= (document.getElementById("layer2").offsetHeight - iFrame);

}

else {

document.getElementById("layer1").scrollTop += iFrame;

}

}


timer = setInterval("move()",iFrequency);

document.getElementById("layer1").onmouseover=function() {clearInterval(timer);}

document.getElementById("layer1").onmouseout=function() {timer=setInterval("move()",iFrequency);}