How to send Hexadecimal value to serial port using Php

Question

Can any one help me , I have NFC PAD device . I have prepared code in PHP and sends data to this device. This device respond properly but with wrong code because this device receives data in hexadecimal. I have also tried after converting string to Hex but did not find any result.

Can any one explain me How we send Hex data over serial port in PHP.

My code is :

<?php 

exec("mode com9: BAUD=9600 PARITY=n DATA=8 STOP=1 to=off dtr=off rts=off");
$fp =fopen("com9", "w");
fwrite($fp, "Hello");
fclose($fp);

?>