Optimality of bus-invert coding

F. Z. Rokhani, Wen Chih Kan, John Kieffer, Gerald E Sobelman

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Dynamic power dissipation on I/O buses is an important issue for high-speed communication between chips. One can use coding techniques to reduce the number of transitions, which will reduce the dynamic power. Bus-invert coding is one popular technique for interchip buses, where the dominant contribution is from the self-capacitance of the wires. This algorithm uses an invert line to signal whether the bus data are in its original or an inverted form. While the method appears to be a greedy algorithm, we show that it is, in fact, an optimal strategy. To do so, we first represent the bus and invert line using a trellis diagram. Then, we show that applying bus-invert coding to a sequence of words gives the same result as would be obtained by using the Viterbi algorithm, which is known to be optimal. We also show that partitioning an M-bit bus into P subbuses and using bus-invert coding on each subbus can be described as applying the Viterbi algorithm on a P-state trellis.

Original languageEnglish (US)
Pages (from-to)1134-1138
Number of pages5
JournalIEEE Transactions on Circuits and Systems II: Express Briefs
Issue number11
StatePublished - 2008


  • Bus coding
  • Low power
  • Off-chip buses
  • Trellis diagram
  • Viterbi decoding

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