php - 更新クエリを mysql から PDO に変換するには?

Question

このクエリを pdo に変換したい : 誰でも助けていただければ幸いです

function updateonlinesession(){         
if(isset($_SESSION['username']['id'])){
$uid = $_SESSION['username']['id'];
$page = $_SERVER['REQUEST_URI'];
$ip = $_SERVER['REMOTE_ADDR'];
$username = $_SESSION['logged'];

("UPDATE site_user SET dateupdated  = now(),ip = '$ip' WHERE 
username = '".mysql_real_escape_string($_SESSION['username'])."'"); 
}

}
This is What I have tried 
<?php 

function updateonlinesession(){         
if(isset($_SESSION['username']['id'])){
$uid = $_SESSION['username']['id'];
$page = $_SERVER['REQUEST_URI'];
$ip = $_SERVER['REMOTE_ADDR'];
$username = $_SESSION['logged'];

$update =("UPDATE site_user SET dateupdated  = now(),ip = '$ip' WHERE 
username = '"($_SESSION['username'])."'");  
$updated_once= $con->($update);
$updated_once->execute();
}

}
?>