3 - Electronic logic circuits

Abstract

This chapter discusses how electronic circuits, called gates, can be made to perform the basic logical functions, AND, OR, and NOT. Using these, two commonly used devices are designed—the decoder and the multiplexer. The chapter also describes how circuits made from gates can be made to store binary values and how these flip-flops are used to make state machines. The design of this machine is determined by the four variables P, C, B, and A giving 16 rows in the state transition table. (To make the design process less laborious computer-based design tools can be made to do this task more quickly and more reliably). In the early 1980s, it was recognized that it was possible to make use of this similarity by making a circuit on silicon, containing a number of AND gates whose outputs are connected to an OR gate. All the inputs, and their complements, are connected to all the AND gate inputs using connections that are fuses and so can be removed.