This paper describes a 16-b fixed point digital signal processor(DSP), especially its multiply-accumulate(MAC) unit, memories, and instruction set.By adopting a redundant binary multiplier and a variable pipeline structure, this DSP's MAC unit, compared to a conventional MAC unit, consumes about 15% less power and operates 24% faster. Furthermore, its doublespeed MAC mechanism can realize twice the performance of a single MAC operation while consuming only 69% more power. By being able to more finely control which portions of memory are activated, the data ROM and data RAM's precharge current was reduced to about 1/8 of the conventional ROM and RAM's. We redesigned the instruction set and reduced its width from 32 b to 24 b based on the analysis of data generated by simulating an application program on our previous DSP. The reduction in instruction width made our on-chip instruction memory size 33% smaller than the previous one. This chip is fabricated with a 0.5- µm double-metal-layer CMOS process and achieves 80-MOPS-peak double speed multiply-accumulate performance.