1. An integrated circuit, comprising: an encoder circuit to encode a series of 2-bit data words into a series of 4-bit code; and a transmitter circuit to transmit in succession the series of 4-bit code words over a set of 4 links that convey respective bits in each of the series of code words; wherein the encoder is configured to select a code word out of a set of six symbols for each of the series of data words, the set of six symbols including a first group of two symbols, a second group of two symbols, and a third group of two symbols, and wherein the encoder is further configured to encode the series of 2-bit data words such that any two consecutive code words in the series of 4-bit code words are selected from two different groups of symbols.