Abstract: A method for converting a succession of data words into an output bit stream comprising a succession of code words uses a table of code words and associated next state values. For each data word the table provides a code word and associated next state value for each of a plurality of present state values. The code words are either of a first type that correspond to only one data word or of a second type that correspond to more than one data word. The next state value associated with each code word of the second type belongs to one of a first group of states. The next state values ensure that adjacent code words chosen in accordance with the next state values satisfy a run length constraint. Code words belonging to the first group of states can be identified by a unique bit structure.