Theoretical analysis of bus-invert coding

The bus-invert method, proposed by M. R. Stan and W. P. Burleson [l], is a simple and yet effective method to reduce data-bus switching activity if the switching of data lines is spatially and temporally independent and uniformly distributed. Suppose the bus is n-bit wide. The bus-invert method can reduce not only the average switching activity of the I/O bus, but also the peak switching activity from n to n/2 transitions per bus cycle. The best result, saving 25% of the switching activity, can be obtained with n=2. Dividing the bus lines into several groups of small size can take this advantage, but it also increases the number of invert lines (extra lines showing to the receiver about inverting of data values). M. R. Stan and W. P. Burleson [l] correctly established the relationship between the bus-invert method and limitedweight codes [2] and showed that the average number of