A note on the method of poles for code construction

The method of poles is a method for constructing a rate 1:1 finite state code from K-ary data into a constrained channel S, where S is recognized by a given local automaton and S has capacity at least log(k). We characterize those automata to which the method of poles applies in the case where h(S)=log(k). The code produced by the method of poles has a sliding-block decoder. We also give an upper bound on the window length of the decoder that applies when h(S)⩾log(k)