The energy consumption at the I/O pins is a significant part of the overall chip consumption. This paper presents a method for encoding an external address bus which lowers its activity and, thus, decreases the energy. This method relies on the locality of memory references. Since applications favor a few working zones of their address space at each instant, for an address to one of these zones only the offset of this reference with respect to the previous reference to that zone needs to be sent over the bus, along with an identifier of the current working zone. This is combined with a modified one-shot encoding for the offset. An estimate of the area and energy overhead of the encoder/decoder are given; their effect is small. The approach has been applied to two memory-intensive examples, obtaining a bus-activity reduction of about 2/3 in both of them. Comparisons are given with previous methods for bus encoding, showing significant improvement.

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