a digital television transmitter / receiver and a method of processing data in the dtv transmitter / receiver are disclosed . in the dtv transmitter , a pre - processor pre - processes the enhanced data by coding the enhanced data for forward error correction and expanding the fec - coded enhanced data . a data formatter generates enhanced data packets including the pre - processed enhanced data and inserts known data to at least one of the enhanced data packets . a first multiplexer multiplexes the enhanced data packets with main data packets including the main data . and , an rs encoder rs - codes the multiplexed main and enhanced data packets , the rs encoder adding systematic parity data to each main data packet and adding rs parity place holders to each enhanced data packet . herein , the rs encoder may insert non - systematic rs parity data or null data into the rs parity place holders included in each enhanced data packet .