In this paper, we propose an adaptive low-power bus encoding algorithm based on weighted code mapping (WCM) and the delayed bus technique. The WCM algorithm transforms an original bus data vector to a low-energy code through one-to-one mapping. The code mapping is determined by the data probabilistic distribution in the original sequence. The WCM algorithm considers both the self and coupling capacitance of the bus wires. In addition, we found that applying the delayed-bus technique can further reduce the bus energy. A window-based adaptive encoding algorithm is proposed to improve the energy saving by adaptively changing the code mapping when significant data changes are detected. Experimental results show that the proposed algorithm outperforms the existing heuristic bus encoding algorithms by 20~60% in energy dissipation.