public function exportVouchers($iStart)
    {
        $iExported = false;

        if ($oSerie = $this->_getVoucherSerie()) {
            $oDb = \OxidEsales\Eshop\Core\DatabaseProvider::getDb(\OxidEsales\Eshop\Core\DatabaseProvider::FETCH_MODE_ASSOC);

            $sSelect = "select oxvouchernr from oxvouchers where oxvoucherserieid = " . $oDb->quote($oSerie->getId());
            $rs = $oDb->selectLimit($sSelect, $this->iExportPerTick, $iStart);

            if (!$rs->EOF) {
                $iExported = 0;

                // writing header text
                if ($iStart == 0) {
                    $this->write(\OxidEsales\Eshop\Core\Registry::getLang()->translateString("VOUCHERSERIE_MAIN_VOUCHERSTATISTICS", \OxidEsales\Eshop\Core\Registry::getLang()->getTplLanguage(), true));
                }
            }

            // writing vouchers..
            while (!$rs->EOF) {
                $this->write(current($rs->fields));
                $iExported++;
                $rs->fetchRow();
            }
        }

        return $iExported;
    }