Control systems: Microprocessor systems
The CPU performs three functions: it controls the systemís operation; it performs algebraic and logical operations; and it stores information (or data) whilst it is processing. The CPU works in conjunction with other chips, notably those that provide random access memory (RAM), read-only memory (ROM), and input/output (I/O).
The key process in the development of increasingly powerful microprocessor chips is known as microlithography. In this process the circuits are designed and laid out using a computer before being photographically reduced to a size where individual circuit lines are about 1/100 the size of a human hair. Early miniaturization techniques, which were referred to as large-scale integration (LSI), resulted in the production of the first generation of 256K-bit memory chip (note that such a chip actually has a storage capacity of 262,144-bits where each bit is a binary 0 or 1). Today, as a result of very-large-scale integration (VLSI), chips can be made that contain more than a million transistors.
The first microprocessor systems were developed in the early 1970ís. These were simple and crude by todayís standards but they found an immediate application in the automotive industry where they were deployed in engine management and automatic braking systems. Today, microprocessor systems are found in a huge variety of applications from personal computers to washing machines!
The block diagram of a typical microprocessor system is shown below. To find out what each feature does just move your mouse pointer over it!
The central processing unit (CPU) is generally the microprocessor chip itself. This device contains the following main units:
In order to ensure that all the data flow within the system is orderly, it is necessary to synchronise all of the data transfers using a clock signal. This signal is often generated by a clock circuit (similar to the clock in a digital watch but much faster). To ensure accuracy and stability the clock circuit is usually based on a miniature quartz crystal.
All microprocessors require access to read/write memory in which data (e.g. the results of calculations) can be temporarily stored during processing. Whilst some microprocessors (often referred to as microcontrollers) contain their own small read/write memory, this is usually provided by means of a semiconductor random access memory (RAM).
Microprocessors generally also require more permanent storage for their control programs and, where appropriate, operating systems and high-level language interpreters. This is usually provided by means of semiconductor read-only memory (ROM).
To fulfil any useful function, a microprocessor system needs to have links with the outside world. These are usually supplied by means of one, or more, VLSI devices which may be configured under software control and are therefore said to be programmable. The input/output (I/O) devices fall into two general categories; parallel (where a byte is transferred at a time along eight wires), or serial (where one bit is transferred after another along a single wire).
The basic components of a microprocessor system (CPU, RAM, ROM, and I/O) are linked together using a multiple connecting arrangement known as a bus. The address bus is used to specify memory locations (i.e. addresses), the data bus is used to transfer data between devices, and the control bus is used to provide timing and control signals (such as read and write, reset and interrupt) throughout the system).
A practical micontroller is shown below. To see how this relates to the diagram shown earlier just move your mouse pointer over the components:
|Copyright © 2002 Mike Tooley - All rights reserved.|