1. A communication system, including: a receiver; a transmitter; and a serial link between the transmitter and the receiver, wherein the transmitter is coupled to receive input data, configured to generate a sequence of selected code words by encoding the input data, and configured to transmit the sequence of selected code words to the receiver over the serial link, wherein each of the selected code words is a member of a robust subset of a full set of code words, the full set includes predetermined disjoint clusters of the code words, the input data can be encoded as a conventional sequence of code words of the full set, and the sequence of selected code words is less susceptible to inter-symbol interference during transmission over the link than would be the conventional sequence of code words, wherein the robust subset consists of preferred words of the full set, the code words of the full set that are not preferred words are non-preferred words, each of the preferred words is indicative of an input data value, each of the clusters includes a preferred word set consisting of at least one of the preferred words, at least one of the clusters also includes at least one of the non-preferred words, each said preferred word set is indicative of a different input data value, and the receiver is configured to map each received code word that is a member of one of the clusters to the input data value determined by the preferred word set of said one of the clusters.