//set slave id according to each mb_tx
    ret = modbus_set_slave(this_mb_link->modbus, this_mb_tx->mb_tx_slave_id);
    if (ret != 0) {
+       (**this_mb_tx->num_errors)++;

        ERR(this_mb_tx->cfg_debug, "mb_tx_num[%d] mb_links[%d] cannot set slave [%d]",
            this_mb_tx_num, this_mb_tx->mb_link_num, this_mb_tx->mb_tx_slave_id);
        return retOK; //not connected
    }