1. A system for serial communications comprising: encoder means for outputting, as a serial bit stream, conservative encoded codewords each having a predefined number of transitions, responsive to a parallel data input; decoder means for outputting, in parallel, decoded data words responsive to the serial bit stream of conservative encoded codewords; wherein, each codeword has a plurality of transitions as serially transmitted, and wherein the ratio is known between the total number of bits per codeword transmitted and the total number of transitions per codeword in the serial bit stream.