PHP hexadecimal matrix map

Question

I have hexadecimal content saved inside a string, however I would like to get a value that is located at a specific address (ex. 0xD3)

I have the following code to read the .bin file and show it's content:

$handle = @fopen($file, "r");
        if ($handle) {
            while (!feof($handle)) {

                $hex = bin2hex(fread ($handle , 16 ));
                print $hex."\n";

                $input_output .= $hex;

            }

            fclose($handle);

        }

I am looking for a way to map the addresses in order to find the values I want to. Ideas ? thanks in advance