Dedicated Digital Processors: Methods in Hardware/Software Co-Design

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Digital Computer Basics

1.1 DATA ENCODING

A digital system is an artificial physical system that receives input at a number of sites and times by applying input ‘signals’ to it and responds to these with output that can later be measured by some output signals. A signal is a physical entity measurable at some sites and depending on time. The input signals usually encode some other, more abstract entities, e.g. numbers, and so do the outputs. In a simple setting, the numbers encoded in the output may be described as a function of the input numbers, and the artificial system is specifically designed to realize this function. More generally, the output may also depend on internal variables of the system and the sites and times at which it occurs may be data dependent. The main topic of this book is how to systematically construct a system with some wanted processing behavior, e.g. one with a prescribed transfer function.

The application of such a system with a particular transfer function first involves the encoding of the input information into physical values that are applied at the input sites for some time by properly preparing its input signals, then some processing time elapses until the output signals become valid and encode the desired output values, and finally these encoded values are extracted from the measured physical values. For the systems considered, the input and output signals will be electrical voltages measured between pairs of reference sites and restricted ...