Introduction of Registers

Chapter 4: Registers

Introduction

AU: Dec.-19

• A group of flip-flops can be used to store a word, which is called register.

• A flip-flop can store 1-bit information. So an n-bit register has a group of n flip-flops and is capable of storing any binary information/number containing n-bits.

Buffer Register

• Fig. 4.1.1 shows the simplest register constructed with four D flip-flops. This register is also called buffer register.

• Each D flip-flop is triggered with a common negative edge clock pulse.

• The input bits set up the flip-flops for loading.

• When the first negative clock edge arrives, the stored binary information becomes, Q_AQ_BQ_CQ_D = ABCD

• In this register, four D flip-flops are used. So it can store 4-bit binary information. 

• The number of flip-flop stages in a register determines its total storage capacity.

Controlled Buffer Register

•We can control input and output of the register by connecting tri-state devices at the input and output sides of register as shown in Fig. 4.1.2. So this register is called'controlled  buffer register'.

•Here, tri-state switches are used to control the operation.

•When you want to store data in the register, you have to make  signal low to activate the tri-state buffers.

•When you want the data at the output, you have to make  signal low to activate the buffers.

• Controlled buffer registers are commonly used for temporary storage of data within a digital system.

•As seen above the 4-bit register can store 4-bit binary information. In general, n-bit register can store n-bit binary information.

Review Questions

1. What is register?

2. What is buffer register?