Control systems: Microprocessor systems


A microprocessor is a single chip of silicon that performs all of the essential functions of a computer central processor unit (CPU) on a single silicon chip. Microprocessors are found in a huge variety of applications including engine management systems, environmental control systems, domestic appliances, video games, fax machines, photocopiers, etc.

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:

  • storage locations (called registers) that can be used to hold instructions, data, and addresses during processing
  • an arithmetic logic unit (ALU) that is able to perform a variety of arithmetic and logical function (such as comparing two numbers)
  • a control unit which accepts and generates external control signals (such as read and write) and provides timing signals for the entire system.

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:

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  Copyright © 2002 Mike Tooley - All rights reserved.  

 

Microprocessor CPU Semiconductor Read-only Memory (ROM) Semiconductor Random Access Memory (RAM) Quartz crystal (to set clock frequency) Input/output (I/O) interface devices Serial I/O port Power supply components Serial interface The system clock provides an accurate time reference for all data transfers within the system The CPU executes the control program and carries out logic and arithmetic operations The ROM stores the control program and any permanent data that is required The RAM stores transient data and variables used during program execution The I/O device provide a means of interfacing the system to the outside world Parallel I/O is used to transfer parallel data (usually in bytes, i.e. 8 bits at a time) into and out of the system The serial port is used to transfer a stream of data into and out of the system one bit at a time The CPU places addresses on the address bus whenever it needs to read from or write to a memory or I/O location Data is transferred into the CPU via the data bus when the CPU is performing a read operation and out of the CPU via the data bus when the CPU is performing a write operation The control bus is used to convey control signals such as READ, WRITE, RESET and INTERRUPT Microprocessor CPU Semiconductor Read-only Memory (ROM) Semiconductor Random Access Memory (RAM) Quartz crystal (to set clock frequency) Input/output (I/O) interface devices Serial I/O port Power supply components Serial interface The system clock provides an accurate time reference for all data transfers within the system The CPU executes the control program and carries out logic and arithmetic operations The ROM stores the control program and any permanent data that is required The RAM stores transient data and variables used during program execution The I/O device provide a means of interfacing the system to the outside world Parallel I/O is used to transfer parallel data (usually in bytes, i.e. 8 bits at a time) into and out of the system The serial port is used to transfer a stream of data into and out of the system one bit at a time The CPU places addresses on the address bus whenever it needs to read from or write to a memory or I/O location Data is transferred into the CPU via the data bus when the CPU is performing a read operation and out of the CPU via the data bus when the CPU is performing a write operation The control bus is used to convey control signals such as READ, WRITE, RESET and INTERRUPT