<?php
$strToSend = "\xfe\x04\x01";
$CRC16 = GetCRC16($strToSend. "\x00\x00"); // ergibt "BED2"
echo "Checksum 1: ". sprintf("%X", $CRC16). "\r\n";


$strReceived = "\xfe\x04\x01\xbe\xd2";
$CRC16 = GetCRC16($strReceived); // ergibt 0
echo "Checksum 2: ". sprintf("%X", $CRC16). "\r\n";


function GetCRC16($s)
{
$CRCreg = 0xffff00;
for ($cp=0; $cp<strlen($s); $cp++)
{
  $CRCreg |= ord($s[$cp]);
  for ($bp=0; $bp<8; $bp++)
  {
   $CRCreg <<= 1;
   if ($CRCreg & 0x1000000) $CRCreg ^= 0x100200; // hier ist das Polynom 0x1002 enthalten
   $CRCreg &= 0xffffff;
  }
}
return $CRCreg >> 8;
} 
?>