This paper has the character of an extended manufacturer’s applications note on the NEC &mgr;PD7720 single-chip digital signal processor. It begins by reviewing very briefly the well-established design procedures for digital filters in terms of both s-plane to z-plane transformations and impulse-response methods. It then gives a detailed description of the NEC digital signal processing chip, including its architecture, instruction set, I/O capabilities, and possible host interconnect. Finally, it shows how a simple second-order recursive Butterworth lowpass filter may be implemented at a 5 kHz sample rate, taking data directly from an external 8-bit A/D converter.

The authors achieve their stated goal of illustrating the main features of the 7720 signal processor, how it can be used in conjunction with the 8085 microprocessor, and its application to digital signal processing. They do so in a clear, comprehensive, tutorial fashion. The paper will undoubtedly be useful to those faced with a similar task. However, this reviewer was disappointed that the authors did not adopt a more critical approach and compare the architecture and capabilities of this device with its market competitors.