Digital Logic Design, 4th Edition

6

Latches and flip-flops

6.1 Introduction

A digital logic circuit or system is usually made up of combinational elements such as NAND and NOR gates and memory elements which may, for example, be discrete flip-flops or latches. Alternatively, an interconnection of these devices may be found in a shift register, a counter, or in a variety of MSI and LSI packages.

With the introduction of memory elements as components in digital systems, an additional variable, time, has been introduced and must be taken into account when designing digital systems. In effect, logic operations can be performed sequentially, information being stored in a memory element and released at some specified instant later so that it can take part in a controlled combinational ...