Introduction

By now we have discussed instruction sets and register organisation followed by a discussion on micro-operations and a simple arithmetic logic unit circuit. We have also discussed the floating point ALU and arithmetic processors, which are commonly used for floating point computations.

In this unit we are going to discuss the functions of a control unit, its structure followed by the hardwired type of control unit. We will discuss the microprogrammed control unit, which are quite popular in modem computers because of flexibility in designing. We will start the discussion with several definitions about the unit followed by Wilkes control unit. Finally, we will discuss the concepts involved in micro-instruction execution.

Objectives

After going through this unit you will be able to:

• define what is a control unit and its function;
• describe a simple control unit organization;
• define a hardwired control unit;
• define the micro-programmed control unit; 
• define the term micro-instruction; and
• identify types and formats of micro-instruction