Counters and Registers
Counters and registers belong to the category of MSI sequential logic circuits. They have similar architecture, as both counters and registers comprise a cascaded arrangement of more than one flip-flop with or without combinational logic devices. Both constitute very important building blocks of sequential logic, and different types of counter and register available in integrated circuit (IC) form are used in a wide range of digital systems. While counters are mainly used in counting applications, where they either measure the time interval between two unknown time instants or measure the frequency of a given signal, registers are primarily used for the temporary storage of data present at the output of a digital circuit before they are fed to another digital circuit. We are all familiar with the role of different types of register used inside a microprocessor, and also their use in microprocessor-based applications. Because of the very nature of operation of registers, they form the basis of a very important class of counters called shift counters. In this chapter, we will discuss different types of counter and register as regards their operational basics, design methodology and application-relevant aspects. Design aspects have been adequately illustrated with the help of a large number of solved examples. A comprehensive functional index of a large number of integrated circuit counters and registers is given towards the end of the chapter.