Zero padded hex strings as a pair of 2 (8bit).

<?php 
function dec2hex($int) {
  $hex = dechex($int);
  if (strlen($hex)%2 != 0) {
    $hex = str_pad($hex, strlen($hex) + 1, '0', STR_PAD_LEFT);
  }
  return $hex;
}

dec2hex(2); // 02
dec2hex(10); // 0a
dec2hex(256); // 0100
?>