如何通过ajax将多个值传递给codeigniter的控制器

Question

function getdata(x,y)
{

    var xmlhttp=new XMLHttpRequest();

    xmlhttp.onreadystatechange=function(){

        if(xmlhttp.readystate==4) {
            document.getElementByID("txt").innerHTML=xmlhttp.responseText;
        }
    };

    xmlhttp.open("GET","base_url()/vendor/home/getdata"+x +y,true);

    xmlhttp.send();

}

I am passing two values x,y to the function from a view. Then I want to pass it to controller as in the program. But y is concantenated to x. If I use , or & operator, it is not passing values to controller. Which operator should I use to pass both values x and y to controller?