Ajax re-loading variable DIVs

I'm using this script to re-load a DIV (id = roomdiv) in a room booking page.

It works fine, but reloads all rooms in the page - which is slow if there are lots of rooms on the page.

What I would like to do is reload an individual room.

I think I need to pass the roomno variable from the changeroom function into the stateChanged2 function but I have no idea how to do it.

function changeroom(cell,periodno,dayno,weekno,roomno,t)
{ 
document.getElementById(cell).innerText="Wait";
document.getElementById(cell).style.color='000000';
document.getElementById(cell).style.fontWeight='bold';
xmlHttp=GetXmlHttpObject();
if (xmlHttp==null)
  {
  alert ("Your browser does not support AJAX!");
  return;
  } 
var url="room.asp";
url=url+"?p="+periodno+"&d="+dayno+"&w="+weekno+"&r="+roomno+"&t="+t;
url=url+"&sid="+Math.random();
xmlHttp.onreadystatechange=stateChanged2;
xmlHttp.open("GET",url,true);
xmlHttp.send(null);
}



function stateChanged2() 
{ 
if (xmlHttp.readyState==4)
{ 
document.getElementById("roomdiv").innerHTML=xmlHttp.responseText;
}
}

Code (markup):

I would ultimately like to be able to have this in the statechanged2 function:

function stateChanged2(roomno) 
{ 
if (xmlHttp.readyState==4)
{ 
document.getElementById("roomdiv"+roomno).innerHTML=xmlHttp.responseText;
}

Code (markup):

I know it has something to do with this line

xmlHttp.onreadystatechange=stateChanged2;

Code (markup):

and thought maybe this might work:

xmlHttp.onreadystatechange=stateChanged2(roomno);

Code (markup):

but it doesn't.

Any ideas? Anyone make sense of my ramblings?