A digital broadcast system and a method of processing data are provided. The transmitting system of the digital broadcast system includes an encoder for encoding mobile data for FEC to build RS frames, a signaling encoder for encoding TPC data including the RS frame mode information, a divider for dividing at least one of the RS frames into a plurality of portions, a block processor for converting one portion to a plurality of SCCC blocks, a converter for converting the SCCC blocks to data blocks, a group formatter for forming data groups, a packet formatter for forming data packets including data in the data groups, a multiplexer for multiplexing main data packets including main data and the data packets, a trellis encoder for performing trellis encoding on data in the multiplexed data packets and a transmission unit for transmitting the broadcast signal including a parade of the data groups.