function objetoAjax(){
var xmlhttp=false;
try {
xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try {
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
} catch (E) {
xmlhttp = false;
}
}

if (!xmlhttp && typeof XMLHttpRequest!='undefined') {
xmlhttp = new XMLHttpRequest();
}
return xmlhttp;
}
//----------------------------------------------------------------------------------------------
function enviaDatos(){
divResultado = document.getElementById('div_valor');

_operacion=document.f_busqueda._operacion.value;
_moneda=document.f_busqueda._moneda.value;

ajax=objetoAjax();
ajax.open("POST", "calcula_valor.php",true);
ajax.onreadystatechange=function() {
if (ajax.readyState==4) {
divResultado.innerHTML = ajax.responseText
}
}
ajax.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
ajax.send("t_operacion="+_operacion+"&t_moneda="+_moneda)
}
//----------------------------------------------------------------------------------------------