A digital television (DTV) transmitter and a method of coding data in the DTV transmitter are disclosed. A data formatter generates an enhanced data packet including the enhanced data and a known data sequence. A data randomizer randomizes the enhanced data packet. A RS encoder RS-codes the randomized data packet by adding first parity data, and a data interleaver interleaves the RS-coded data packet. A trellis encoding unit trellis-encodes the interleaved data packet. Herein the trellis encoding unit includes a TCM encoder for generating a first output bit by trellis-encoding a first input bit and generating a second output bit by bypassing the first input bit, and a pre-coder for generating a third output bit by pre-coding a second input bit, wherein memories included in the TCM encoder and the pre-coder are initialized when the known data sequence is inputted to the trellis encoding unit.