function Passive($pasv=NULL) {
    if(is_null($pasv)) $this->_passive=!$this->_passive;
    else $this->_passive=$pasv;
    if(!$this->_port_available and !$this->_passive) {
      $this->ftp_base::SendMSG("Only passive connections available!");
      $this->_passive=TRUE;
      return FALSE;
    }
    $this->ftp_base::SendMSG("Passive mode ".($this->_passive?"on":"off"));
    return TRUE;
  }