#!/bin/perl

use strict;
use warnings;

my $hexdata = "fe0401";
 
my @split = unpack( "A2" x (length($hexdata)/2), $hexdata );

my $strToSend = ("\\x". join ("\\x",@split)."\\x00\\x00");

print $strToSend,"\n";
my $CRC16 = GetCRC16($strToSend); # ergibt "BED2"
print "Checksum A: ". sprintf("%x", $CRC16). "\n";


$strToSend = "\xfe\x04\x01";
print $strToSend,"\n";

$CRC16 = GetCRC16($strToSend. "\x00\x00"); # ergibt "BED2"
print "Checksum 1: ". sprintf("%x", $CRC16). "\n";

sub GetCRC16 {
   my $s = shift;
   
   my $CRCreg = 0xffff00;
   
   for (my $cp=0; $cp<length($s); $cp++) {
    $CRCreg |= ord( substr($s,$cp,1) );
    
    for (my $bp=0; $bp<8; $bp++) {
        $CRCreg <<= 1;
        if ($CRCreg & 0x1000000) {
        $CRCreg ^= 0x100200; # hier ist das Polynom 0x1002 enthalten
        }
        $CRCreg &= 0xffffff;
    }
   }
   return $CRCreg >> 8;
}

1;