function init_ajax(){
	if (window.XMLHttpRequest){		
		return new XMLHttpRequest();     // Firefox, Safari, ...
	}
	else if (window.ActiveXObject){
		return new ActiveXObject('Microsoft.XMLHTTP');    // Internet Explorer 
	}
	else{
		return false;
	}
}

function get_ajax(p,xhr){	
	xhr.open("GET",p,true);
	xhr.send(null);
}

function get_ref(id) {	
	var xhr = init_ajax();	
	var url = 'http://www.coperior.fr/site/ajax_reference.php?id=' + document.getElementById('marque').value;	
	get_ajax(url,xhr);
	xhr.onreadystatechange = function(){		
		if(xhr.readyState == 4){
			mText = xhr.responseText;			
			document.getElementById('charge_ref').innerHTML=mText;
		}
	}
}