sAjaxsource modified url (search) making 3 times Ajax call to server instead of 1 in datatable

Hi my code is like this,first ajax call is working fine ,if i enter the new value in search box and pressing the enter then it is making two ajax calls first with old search value and then new search value.i want to make only one ajax call with new search value, please help on this.

var oTable =$("#deviceListTable").dataTable({
"bPaginate": true,
"sPaginationType" : "full_numbers",
"bLengthChange": false,
"bFilter": true,
"bSort": true,

"bInfo": true,
"bAutoWidth": false,
"sScrollY": "150px",
"bScrollCollapse": false,
"bJQueryUI": true,
"bProcessing": true,
"bServerSide": true,
//"sSearch" : isearch,
"sAjaxSource": "./ajaxDevicelist.htm?&fromDate="+fromDate+"&toDate="+toDate+"&IsExport=false&mySearch="+isearch,
"sDom": 'T<"clear">lfrtip',
"oTableTools": {
"aButtons": [
{
"sExtends": "text",
"sButtonText": "Export to Excel",
"fnClick": function ( nButton, oConfig, oFlash ) {
window.location.href="./ajaxDevicelist.htm?&fromDate="+fromDate+"&toDate="+toDate+"&IsExport=true";
}
},
{
"sExtends": "text",
"sButtonText": "Download Configs",
"fnClick": function ( nButton, oConfig, oFlash ) {
dialogval.dialog( "open" );
}
}
]
},
"aoColumnDefs":[/*{
"aTargets": [5],
"fnRender": function (o,val) {
return "<a href='#' onclick=getid('"+ val +"')><center><img src='images/export.png' name='but' title='click here to download/view all configuration data' alt='download' ></center></a>";
}
},*/
{
"aTargets": [5],
"fnRender": function (o,val) {
return "<center><input type='checkbox' id='deviceid' name='devicename' value='"+val+"' /></center>";
}
},
{ "bSortable": false, "aTargets": [ 5 ] }
]
});
$("div.dataTables_filter input").keyup( function (e) {
if (e.keyCode == 13) {
oTable.fnClearTable(this);
isearch= $('#deviceListTable_filter label input:text').val();

console.log("isearch value is :"+isearch);

var oSettings = oTable.fnSettings();
oSettings.sAjaxSource = "./ajaxDevicelist.htm?&fromDate="+fromDate+"&toDate="+toDate+"&IsExport=false&mySearch="+isearch;
console.log("isearch value is :"+isearch);

oTable.fnDraw();

}
} );