Introduction

The microprocessor is the logical evolution of the circuit designer’s need for circuits that have more functionality. Logic gates can be used to make a flip-flop, but it is easier and more efficient to use a flip-flop IC. Furthermore, a memory device can be made from flip-flops, but it is easier and more efficient to use a memory IC. Likewise, complex logic systems can be made from IC components, but the microprocessor was invented to integrate the function of many logic ICs into one multipurpose logic IC.

 History

Year

Company

Processor

1971

Intel

4004 (4 bit)

1974

Intel

8080 (8 bit)

1975

Motorola

6800 (8 bit)

 

With the increase in the number of bits came the benefits of increased speed and computing power. These bits determine the amount of data that can be input to or output from the processor. Currently, 32 bit processors are the norm.

 

Microprocessor Systems

 

A microprocessor is a Very Large Scale Integrated (VLSI) logic IC whose logical function is controlled be an instruction code. This instruction code is a specific combination of logic bits needed for a microprocessor to execute its logic operations. These codes may include instructions to perform logical, arithmetic or input/output operations.

 

A microprocessor system is one type of computer system. All computer systems have three basic functional blocks: a processing unit, memory, and input/output. In practice these components are connected together using either address bus, data bus or control lines. This is illustrated in Figure 6-1.

 

 fig6-1.gif (40828 bytes)

 Figure 6-1 Basic Microprocessor System

 

Central Processing Unit (CPU): Performs the computational tasks of the microprocessor system and the operation and timing of all the other microprocessor tasks. It contains:

Arithmetic and Logic Unit (ALU): Processes all arithmetic and logic functions

Control Unit: Responsible for the over all system timing and operation control and execution of the software program instructions.

Memory: This is typical Read only Memory (ROM) or Random Access Memory (RAM)

Input/Output units: Data is passed to and from external devices these units.

Address Bus: The address bus contains all the address lines of the microprocessor. All external memory and I/O devices requiring addressing are connected to the appropriate microprocessor address lines via the address bus. The address bus is unidirectional.

Data Bus: The transmission of all data to and from the microprocessor occurs on the data bus. Note that the data bus must be bi-directional.