Chapter 7 - Programmable Logic Devices

Abstract

This chapter emphasizes the class of devices called programmable logic devices (PLDs) that can be thought of as universal logic implementers in the sense that they can be configured (actually programmed) by the user to perform a variety of specific logic functions. The option to use PLDs offers the logic designer a wide range of versatile devices that are commercially available for design purposes. Some PLDs are made to perform only combinational logic functions while others can perform both combinational and sequential logic functions. The chapter also identifies the PLDs that are capable of performing both combinational and sequential logic functions; however, it limits the exemplar applications to combinational logic design. Four commonly used PLDs that are considered by this chapter are the read-only memory (ROM) devices and their subgroups, the field programmable logic array (FPLA) devices, the programmable array logic (PAL) devices and their subgroups, and field programmable gate arrays (FPGAs) and subgroups. Other PLDs include erasable programmable logic devices (EPLDs), including erasable programmable ROMs; generic array logic (GAL) devices; and field programmable logic sequencers (FPLSs). Except for FPGAs, most of the PLDs mentioned have some commonality, namely a two-level AND/OR configuration.