var req;

function leer_doc(url) {
	req = false;
	 
    // llama XMLHttpRequest objecto 
    if (window.XMLHttpRequest) {
        req = new XMLHttpRequest();
       if (req.overrideMimeType) {
                req.overrideMimeType('text/xml');          
        }
	
    // Si no funciona intenta utiliar el objeto IE/Windows ActiveX 
    } else if (window.ActiveXObject) {
        isIE = true;
        req = new ActiveXObject("Microsoft.XMLHTTP");    
	}
	
	if(req){
		req.open('GET', url, true);
		req.send(null);
	}	
	 
}