使用PHP在PDO_FIREBIRD中找不到驱动程序

I am getting Error: Could not find Driver while connecting to Firebird DB using PHP. My driver setting in PHP.INI file are OK with enabled extensions. It is showing PDO_firebird clicked. I have also copied firebirdclient dll file in system32 folder. tried doing anything i can but still its showing the same error. My firebird db file is in the same location. port for locathost access is 85. Anyone's help will be really obliged. Code i am writting with the help of some suggestion is as under:

<?php
$server = 'localhost:c:/xpos_db/';
$username = 'sysdba';
$password = 'masterkey';
$db = 'xposdata.fdb';
try {
    $dbh = new PDO("firebird:host=$server;dbname=$db", $username, 
    $password);
    $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    echo "Connected Successfully";
} catch (PDOException $e) {
print "Problemo!: " . $e->getMessage() . "<br/>";
die();
} 
?>