Chapter 1 Introduction

By: Masud-ul-Hasan

Fetching & Executing An Instruction

•Fetching involves the following steps:

a)Contents of PC are placed on address bus

b)READ signal is activated

c)Data (instruction opcode) are read from RAM and placed on data bus

d)Opcode is latched into the CPU’s internal instruction register

e)PC is incremented to prepare for the next fetch from memory

•Execution involves decoding the opcode and generating control signals to gate internal registers in and out of the ALU and to signal the ALU to perform the specified operation.