while(1){
   $ca++;
   ($BlockingFlags,$InBytes,$OutBytes,$ErrorFlags) = $PortObj->status;
   die "lost port\n" unless defined $ErrorFlags;
   unless($InBytes){
      last if($ca > 25);
      select(undef,undef,undef,0.01);
      next;
    }
    if($string_in = $PortObj->read($InBytes)){
          # hat geklappt mach was
          last;
    }
}