XMLHttpRequest receive binary data

Hello, I can not handle binary data ( getXmlHttp ), as they can be converted to Int. The task is as follows: there is a server that issues the schedule data in binary form to the request, I have to accept them, process them, convert them to integer type, and put them on the chart. Don't swear badly, I'm new to JavaScript ! Below is a screenshot from the debugger:

Here is the code:

     function ask_values ​​() {
             req = getXmlHttp ();
             req.open ('POST', 'GetChart.cgi?', true);
             req.onreadystatechange = updatePage;
             req.send ('0')
         }

         function updatePage () {
             if (req.readyState == 4) {

                 var uInt8Array = new Uint8Array (req.response);
                 /*console.log (req.response );*/
                 add_voltage_data (uInt8Array);

             }
         }