var xmlHttp;
function initxmlhttp(){
	  var xmlhttp
	  try {
	    xmlhttp=new ActiveXObject("Msxml2.XMLHTTP");
	   } catch (e) {
	     try {
	        xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
	     } catch (E) {
	        xmlhttp=false;
	     }
	  }
	if (!xmlhttp && typeof XMLHttpRequest!='undefined') {
	        try {
	                xmlhttp = new XMLHttpRequest();
	        } catch (e) {
	                xmlhttp=false;
	        }
	}
	if (!xmlhttp && window.createRequest) {
	        try {
	                xmlhttp = window.createRequest();
	        } catch (e) {
	                xmlhttp=false;
	        }
	}
	  return xmlhttp;
}

function callBack_exchange() {
 if (xmlHttp.readyState == 4) {
  if (xmlHttp.status == 200) {
   document.getElementById("exchange_results").value = xmlHttp.responseText;
  }
 }
}

function exchange(changeurl) {
 var exchange = document.getElementById("exchange_value");
 var exchange1 = document.getElementById("exchange1");
 var exchange2 = document.getElementById("exchange2");
 var url = changeurl+"exchange.php?exchangevalues=" + exchange.value + "&exchange1=" + exchange1.value + "&exchange2=" + exchange2.value;
 xmlHttp = initxmlhttp();
 xmlHttp.open('GET', url, true);  
 xmlHttp.onreadystatechange = callBack_exchange;
 xmlHttp.send(null);
 
}