The power dissipation at the off-chip bus has become a significant part of the overall power dissipation in micro-processor based digital systems. This paper presents irredundant address bus encoding methods which reduce signal transitions on the instruction address buses by using adaptive codebook methods. These methods are based on the temporal locality and spatial locality of instruction address. Since applications tend to JUMP/BRANCH to limited sets of addresses, proposed encoding methods assign the least signal transition codes to the addresses of JUMP/BRANCH operations in the past. In addition, our methods can be easily applicable for conventional digital systems since they are irredundant encoding methods. Our encoding methods reduce the signal transitions on the instruction address buses, which results in the reduction of total power dissipation of digital systems. Experimental results show that our methods can reduce the signal transition by an average of 88%.