Set Max Length From -MultiLine TextBox(asp.net)

function checkTextAreaMaxLength(textBox,e, length)
{

var mLen = textBox["MaxLength"];
if(null==mLen)
mLen=length;

var maxLength = parseInt(mLen);
if(!checkSpecialKeys(e))
{
if(textBox.value.length > maxLength-1)
{
if(window.event)//IE
e.returnValue = false;
else//Firefox
e.preventDefault();
}
}
}
function checkSpecialKeys(e)
{
if(e.keyCode !=8 && e.keyCode!=46 && e.keyCode!=37 && e.keyCode!=38 && e.keyCode!=39 && e.keyCode!=40)
return false;
else
return true;
}
maxL=200;
var bName = navigator.appName;
function taLimit(taObj) {
if (taObj.value.length==maxL) return false;
return true;
}

function taCount(taObj,Cnt) {
objCnt=createObject(Cnt);
objVal=taObj.value;
if (objVal.length>maxL) objVal=objVal.substring(0,maxL);
if (objCnt) {
if(bName == "Netscape"){
objCnt.textContent=maxL-objVal.length;}
else{objCnt.innerText=maxL-objVal.length;}
}
return true;
}
function createObject(objId) {
if (document.getElementById) return document.getElementById(objId);
else if (document.layers) return eval("document." + objId);
else if (document.all) return eval("document.all." + objId);
else return eval("document." + objId);
}

----------------------------------example-----------
TextBox ID="txtReason" onKeyPress="return taLimit(this)" onKeyUp="return taCount(this,'myCounter')" ToolTip="Please enter reason" onkeyDown="checkTextAreaMaxLength(this,event,'200');" CssClass="textbox2" runat="server" TextMode="MultiLine"


You have SPAN id=myCounter-200-SPAN characters remaining
for your description.