A survey of published information on universal logic arrays

Abstract

Increasing commercial pressure for (i) standard monolithic circuit layouts and (ii) reduced design times for custom design requirements, is placing increasing emphasis upon the desirability of using standard arrays which may readily be committed for particular requirements. This general survey briefly reviews existing logic concepts in the field of “universal” arrays, many of which have no present (or foreseeable?) commercial viability. However, for completeness, all known general concepts have been surveyed in this document for reference purposes. Note, software-based systems (i.e. microprocessors) are specifically excluded from this survey, being entirely outside our present area of interest. One of the fundamental problems of the random-logic area is how best to use the resources of l.s.i. technology but at the same time maintain the flexibility of the single logic gate approach, custom design of special logic requirements and realization in unique monolithic form being in general a completely uneconomic approach for small-quantity requirements. A more viable approach, however, is to consider programmable devices, that is l.s.i. circuits which are general-purpose networks and which finally may be arranged so as to perform specific duties. In this area we will first look at two main contenders, the programmable read-only-memory (“PROM”) and the programmable logic array (“PLA”), following which we will consider other theoretical possibilities which have not to date been commercially exploited.