function getRequest(sender)
 {
    var xmlHttp = (window.XMLHttpRequest) ? new XMLHttpRequest() : new ActiveXObject('Microsoft.XMLHTTP');
    xmlHttp.open('POST', 'index.php', true);
    xmlHttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
    
    xmlHttp.onreadystatechange = function()
    {
       if (xmlHttp.readyState == 4 && xmlHttp.status == 200)               
       {
       	document.getElementById('ajax_data').innerHTML = (xmlHttp.responseText);
       } 
    }
    xmlHttp.send(sender);
 }
 function getValue(param)
 {
    var postArg = 'op=' + param;
    return postArg;
 }