User-programmable logic-chasing the gate array

Integrated circuits (ICs) come in a wide range of technologies, and can implement a bewildering variety of functions. For the systems builder, however, there is one aspect of an IC that, irrespective of technology or function, is likely to be of overriding importance: whether it can be bought as a standard `off-the-shelf´ component, or whether it must be implemented as some form of ASIC (application-specific IC). Here, the author shows that to a degree, the various forms of user-programmable logic, e.g. PLAs (programmable logic array) and PALs (programmable array logic), can offer the best of both worlds, as they are effectively standard parts that can be customised without recourse to a lengthy and expensive factory-based procedure. He shows that due to current advances in semiconductor processing and device architecture, integration levels for user-programmable logic are rising dramatically, attaining levels of functionality that rival low- to medium-complexity gate arrays