In this work the authors propose a data coding protocol that leads to power reduction for block data transfer in off-chip buses. I/O pads driving off-chip buses contribute to a major portion of power dissipation in chips. Also, block data transfer is preferred in most systems like caches, DMA etc. In this proposed work, the prior knowledge of the block of data to be transmitted, when it is stored in the buffer, is exploited in a serial fashion to reduce transitions on every bus line. Statistical analysis shows up to 31.9% reduction in transitions. Benchmark results show that it leads to 29% reduction in power consumption. The technique provides added error detection on the lines of parity bit technique, with similar average error detection capability.