Hardware Organisation of Computers and Microprocessors

HARDWARE ORGANISATION OF COMPUTERS AND MICROPROCESSORS

COMPUTER ORGANISATION

This deals with the optimization of performance-based products i.e. hardware is optimized in order to achieve the most performance at the least expense. Hardware refers to the physical and electronic equipment used for the input, processing, output, and storage activities performed in a computer system. The hardware components consist of:

Input technologies Central processing unit (CPU) - data path and control Memory (primary and secondary storage) Output technologies Communication technologies

These components are linked together by a communication network or bus.

STANDARD ORGANISATION OF A COMPUTER

FIGURE 1.0 : STANDARD ORGANISATION OF A COMPUTER SHOWING THE FIVE CLASSIC COMPONENTS

FIGURE 1.5. A desktop computer. The liquid crystal display (LCD) screen is the primary output device, and the keyboard and mouse are the primary input devices. On the right side is an Ethernet cable that connected the laptop to the network and the Web. The laptop contains the processor, memory, and additional I/O devices. This system is a MacBook Pro 15" laptop connected to an external display.

CENTRAL PROCESSING UNIT (CPU)

This performs the actual computation inside a computer. It processes information and executes programs. It performs arithmetic and logic operations on data, times and controls the rest of the computer system. The CPU is a microprocessor made up of millions of microscopic transistors embedded in a circuit on a silicon wafer or chip. The microprocessor has different parts, which perform different functions. The control unit sequentially accesses program instructions, decodes them, and controls the flow of data to and from the ALU, the registers, the caches, primary storage, secondary storage, and various output devices. The arithmetic-logic unit (ALU) performs the mathematic calculations and makes logical comparisons. The registers are high-speed storage areas that store very small amounts of data and instructions for short periods of time. The microprocessor is a CPU with a single integrated circuit. The microprocessor logically comprises two main components: datapath and control, the respective brawn and brain of the processor. The datapath performs the arithmetic operations, and control tells the datapath, memory, and I/O devices what to do according to the instructions of the program.

FIGURE 1.4: PARTS OF A MICROPROCESSOR

The figure above illustrates the following

The inputs are data and brief instructions about what to do with the data. The instructions come from software within the parts of the computer. They could be typed by the user on the keyboard, or read from a data file in another part of the computer. They are stored in registers until when sent for processing.

Data and instructions travel in the chip via electrical pathways called buses. The size of the bus—analogous to the width of a highway—determines how much information can flow at any time.

The control unit directs the flow of data and instructions within the chip. The arithmetic-logic unit (ALU) receives the data and instructions from the

registers and makes the desired computation. These data and instructions have been translated into binary form, that is, only 0s and 1s. The CPU can process only binary data.

The data in their original form and the instructions are sent to storage registers and then are sent back to a storage place outside the chip, such as the computer’s hard drive. Meanwhile, the transformed data go to another register and then on to other parts of the computer (e.g. to the monitor for display, or to be stored).

FIGURE 1.5: HOW THE CPU WORKS

A CPU has three functional sections which are:

1. Arithmetic and Logic unit (ALU): It is used for arithmetic and logic operations that are performed on numbers. It performs the mathematic calculations and makes logical comparisons.

2. Registers: These are fast temporary storage devices for data, instructions or intermediate results of calculations. They store very small amounts of data and instructions for short periods of time.

3. Control section: This times and regulates all elements of the computer system, translates register patterns into computer activities.

The control unit is the main part of the processor. It performs its task by repeatedly cycling through the following steps:1. Read (fetch) the next instruction from memory.2. Examine the instruction to determine what it is and to find any possible errors.3. Execute the instruction.These steps are known as the fetch-execute cycle. In order to read the next instruction from memory, the control unit needs to know the location (memory address) of the instruction. This address is kept in a special register called the program counter (PC). The PC is a special register and is normally located in the control unit. It always contains the address of the next instruction, not the current one. When the next instruction is fetched, it is stored in the instruction register (IR), another special-purpose register that always contains the current instruction. Note that as soon as the next instruction is fetched and is stored in the IR it becomes the current instruction.

Figure 1.2: The main components used in the fetch-execute cycle

CPU ELEMENTS

Program Counter or PC: This contains the address of the instruction that will be executed next.

Stack: This is a data structure of last in first out type. A stack is described by a special register – stack pointer. It can be used explicitly to save/restore data. It is used implicitly by procedure call instructions (if available in the instruction set).

IR: This is an instruction register that holds the current instruction being processed by the microprocessor. It is not exposed through the instruction set architecture. It is an organization element.

COMPUTER MEMORY

The amount and type of memory that a computer possesses has a great deal to do with its general utility, often affecting the type of program it can run and the work it can do, its speed, and both the cost of the machine and the cost of processing data. There are two basic categories of computer memory. The first is primary storage, so named because small amounts of data and information that will be immediately used by the CPU are stored there. The second is secondary storage, where much larger amounts of data and information (an entire software program, for example) are stored for extended periods of time. CPUs process only 0s and 1s. All data are translated through computer languages into series of these binary digits, or bits. A particular combination of bits represents a certain alphanumeric character or simple mathematical operation. Eight bits are needed to represent any one of these characters.This 8-bit string is known as a byte. The storage capacity of a computer is measured in bytes. (Bits are used as units of measure typically only for telecommunications capacity, as in how many million bits per second can be sent through a particular medium.) The hierarchy of byte memory capacity is as follows:• Kilobyte. Kilo means one thousand, so a kilobyte (KB) is approximately one thousand bytes. Actually, a kilobyte is 1,024 bytes (210 bytes).• Megabyte. Mega means one million, so a megabyte (MB) is approximately one million bytes (1,048,576 bytes, or 1,024 * 1,024, to be exact). Most personal computers have hundreds of megabytes of RAM.• Gigabyte. Giga means one billion; a gigabyte (GB) is actually 1,073,741,824 bytes

(1,024 * 1,024 * 1,024 bytes). The storage capacity of a hard drive (a type of secondary storage) in modern personal computers is often many gigabytes.• Terabyte. One trillion bytes (actually, 1,078,036,791,296 bytes) is a terabyte.

P r i m a r y S t o r a g ePrimary storage, or main memory, stores for very brief periods of time three types of information: data to be processed by the CPU, instructions for the CPU as to how to process the data and operating system programs that manage various aspects of the computer’s operation. Primary storage takes place in chips mounted on the computer’s main circuit board (the motherboard), located as close as physically possible to the CPU chip. As with the CPU, all the data and instructions in primary storage have been translated into binary code. There are four main types of primary storage:

(1) Register: As indicated earlier, registers are part of the CPU. They have the least capacity, storing extremely limited amounts of instructions and data only immediately before and after processing.

Random access memory (RAM): It stores more information than the registers and is farther away from the CPU, but it stores less than secondary storage and is much closer to the CPU than is secondary storage. It comprises of memory chips soldered onto printed circuit boards or plugged into sockets on the motherboard. It is also called read/write memory. It deals with both hardware and software: firmware. When you start most software programs on your computer, the entire program is brought from secondary storage into RAM. As you use the program, small parts of the program’s instructions and data are sent into the registers and then to the CPU. Again, getting the data and instructions as close to the CPU as possible is key to the computer’s speed, as is the fact that the RAM is a type of microprocessor chip. The chip is much faster (and more costly) than are secondary storage devices. RAM is temporary and volatile; that is, RAM chips lose their contents if the current is lost or turned off (as in a power surge, brownout, or electrical noise generated by lightning or nearby machines). RAM chips are located directly on the computer’s main circuit board or in other chips located on peripheral cards that plug into the main circuit board. The two main types of RAM are dynamic RAM (DRAM) and static RAM (SRAM). DRAM memory chips offer the greatest capacities and the lowest cost per bit, but are relatively slow. SRAM costs more than DRAM but has a higher level of performance, making SRAM the preferred choice for performance-sensitive applications, including the external L2 and L3 caches (discussed next) that speed up microprocessor performance

(1) Cache memory: This is a type of high-speed memory that a processor can access more rapidly than main memory (RAM). It augments RAM in the following way: Many modern computer applications (Microsoft XP, for example) are very complex and have huge numbers of instructions. It takes considerable RAM capacity (usually a minimum of 128 megabytes) to store the entire instruction set. Or you may be using an application that exceeds your RAM. In either case, your processor must go to secondary storage (similar to a lengthy trip to the garage) to retrieve the necessary instructions. To alleviate this problem, software is often written in smaller blocks of instructions. As needed, these blocks can be brought from secondary storage into RAM. This process is still slow, however. Cache memory is a place closer to the CPU where the computer can temporarily store those blocks of instructions used most often. Blocks used less often remain in RAM until they are transferred to cache; blocks used infrequently stay stored in secondary storage. Cache memory is faster than RAM because the instructions travel a shorter distance to the CPU. In our tool analogy, cache memory might represent an additional box with a selected set of needed tools from the kitchen toolbox and the garage. There are two types of cache memory in the majority of computer systems— Level 1 (L1) cache is located in the processor, and Level 2 (L2) cache is located on the motherboard but not actually in the processor. L1 cache is smaller and faster than L2 cache. Chip manufacturers are now designing chips with L1 cache and L2 cache in the processor and Level 3 (L3) cache on the motherboard.

(2) Read-only memory (ROM): This is the place (a type of chip) where certain critical instructions are safeguarded. ROM is nonvolatile and retains these instructions when the power to the computer is turned off. The read-only designation means that these instructions can be read only by the computer and cannot be changed by the user. Examples of ROM instructions are those needed to start or “boot” the computer once it has been shut off. There are variants of ROM chips that can be programmed (PROM), and some that can be erased and rewritten (EPROM). These are relatively rare in mainstream organizational computing, but are often incorporated into other specialized technologies such as video games (PROM) or robotic manufacturing (EPROM). Another form of rewritable ROM storage is called flash memory. This technology can be built into a system or installed on a personal computer card (known as a flash card).

These cards, though they have limited capacity, are compact, portable, and require little energy to read and write. Flash memory via flash cards is very popular for small portable technologies such as cellular telephones, digital cameras, handheld computers, and other consumer products.

The logic of primary storage in the computer is just like the logic of storing things in your house. The stored data which will be used immediately gets stored in very small amounts as close to the CPU as possible. Remember, as with CPU chip design, the shorter the distance the electrical impulses (data) have to travel, the faster they can be transported and processed. That which requires special protection will be stored in an exceptionally secure manner.

S e c o n d a r y S t o r a g eSecondary storage is designed to store very large amounts of data for extended periods of time. Secondary storage can have memory capacity of several terabytes or more and only small portions of that data are placed in primary at any one time. Secondary storage has the following characteristics:

• It is nonvolatile.• It takes much more time to retrieve data from secondary storage than it

does from RAM because of the electromechanical nature of secondary storage devices.

• It is much more cost effective than primary storage (see Figure 3.6).• It can take place on a variety of media, each with its own technology.• The overall trends in secondary storage are toward more direct-access

methods, higher capacity with lower costs, and increased portability.Under secondary (auxiliary) storage, we have:

• Magnetic diskette (Floppy disk)• Optical storage device: Types are compact disk read-only memory (CD-

ROM), digital video disk (DVD), and fluorescent multilayer disk (FMD-ROM).• Magnetic tape

Memory cards: PC memory cards are credit-card-size devices that can be installed in an adapter or slot in many personal computers. The PC memory card functions as if it were a fixed hard disk drive. The cost per megabyte of storage is greater than for traditional hard disk storage, but the cards do have advantages, which are:

• They are less failure-prone than hard disks,

• They are portable, and • They are relatively easy to use.

Expandable storage: Expandable storage devices are removable disk cartridges. The storage capacity ranges from 100 megabytes to several gigabytes per cartridge, and the access speed is similar to that of an internal hard drive. Although more expensive than internal hard drives, expandable storage devices combine hard disk storage capacity and diskette portability. Expandable storage devices are ideal for backup of the internal hard drive, as they can hold more than 80 times as much data and operate five times faster than existing floppy diskette drives.

INPUT TECHNOLOGIES

These allow people and other technologies to put data into a computer.

H u m a n D a t a - E n t r y D e v i c e sHuman data-entry devices allow people to communicate with the computer. Some of these devices are very common, such as the keyboard and the mouse. Others, such as the touch screen, stylus, trackball, joystick, and microphone, are used for somewhat more specialized purposes.

KEYBOARDS: These are the most common input device. The keyboard is designed like a typewriter but with many additional function keys. Most computer users utilize keyboards regularly.MICE AND TRACKBALLS: A mouse is a handheld device used to point a cursor at a desired place on the screen, such as an icon, a cell in a table, an item in a menu, or any other object. Once the arrow is placed on an object, the user clicks a button on the mouse, instructing the computer to take some action. The use of the mouse reduces the need to type in information or use one of the function keys.A variant of the mouse is the trackball, which is often used in graphic design. The user holds an object much like a mouse, but rather than moving the entire device to move the cursor (as with a mouse), he or she rotates a ball that is built into the top of the device. Portable computers have some other mouse-like technologies, such as the glide-and-tap pad, used in lieu of a mouse. Many portables also allow a conventional mouse to be plugged in when desired.

Another variant of the mouse, the optical mouse, replaces the ball, rollers, and wheels of the mechanical mouse with a light, lens, and a camera chip. It replicates the action of a ball and rollers by taking photographs of the surface it passes over, and comparing each successive image to determine where it is going.The pen mouse resembles an automobile stick shift in a gear box. Moving the pen and pushing buttons on it perform the same functions of moving the cursor on the screen as a conventional pointing device. But the pen mouse base stays immobile on the desk. With a pen mouse, the forearm rests on the desk, saving wear and tension. Because the mouse is not lifted or moved, the fingers, not the arm, do the work.TOUCH SCREENS: These are a technology that divides a computer screen into different areas. Users simply touch the desired area (often buttons or squares) to trigger an action. These are common in computers built into self-service kiosks such as ATM machines and even bridal registries.STYLUS: This is a pen-style device that allows the user either to touch parts of a predetermined menu of options (as with a wearable computer, discussed above) or to handwrite information into the computer (as with some PDAs). (See the photo of the PDA and stylus on page 76.) The technology may respond to pressure of the stylus, or the stylus can be a type of light pen that emits light that is sensed by the computer.JOY STICK: This is used primarily at workstations that display dynamic graphics. It is also used to play video games. The joy stick moves and positions the cursor at the desired place on the screen. MICROPHONE: This is becoming a popular data-input device as voice-recognition software improves and people can use microphones to dictate to the computer. These are also critical technologies for people who are physically challenged and cannot use the more common input devices.

SOURCE DATA AUTOMATION: Its function is to input data with minimal human intervention. These technologies speed up data collection, reduce errors, and gather data at the source of a transaction or other event. Below are the common types:CASH-TRANSACTION DEVICES: Various input devices are common in association with cash transactions. The most common are ATMs and POS terminals.

Automated teller machines (ATMs) are interactive input/output devices that enable people to make bank transactions from remote locations. ATMs utilize touch screen input as well as magnetic card readers.Point-of-sale (POS) terminals are computerized cash registers that also often incorporate touch screen technology and bar-code scanners (described below). These devices allow the input of numerous data such as item sold, price, method of payment, name or Zip code of the buyer, and so on. Some inputs are automated; others may be entered by the operator.OPTICAL SCANNERS: Bar-code scanners, used in retail stores, scan the black and white bar code lines typically printed on labels on merchandise. They are very popular for tracking inventory and shipping.An optical mark reader is a special scanner for detecting the presence of pencil marks on a predetermined grid, such as multiple-choice test answer sheets. Similarly, magnetic ink character readers (MICRs) are used chiefly in the banking industry. Information is printed on checks in magnetic ink that can be read by the MICR technology, thus helping to automate and greatly increase the efficiency of the check-handling process.Optical character recognition (OCR) software is used in conjunction with a scanner to convert text into digital form for input into the computer. Although the scanner can digitize any graphic, the OCR software can recognize the individual characters, so that they can be manipulated. As a practical example, the scanner by itself could “take a picture” of this page of text and convert it into digital information that the computer could store as a picture of the text. OCR-equipped scanning technologies are very useful when printed documents not only must be preserved but also would benefit from any manipulations or modifications. OCR technologies would enable you to scan data, process them with the OCR software, and then put them into a database, spreadsheet, or word-processing format. OCR software is usually incorporated in stylus-input devices. Other source data automation devices: Voice-recognition systems are used in conjunction with microphones to input speech to computers. Voice-recognition software (VRS) attempts to identify spoken words and translate them into digital text. Sensors are extremely common technologies embedded in other technologies.They collect data directly from the environment and input them into a computer system. Examples might include your car’s airbag activation sensor or fuel mixture/pollution control sensor, inventory control sensors in retail stores, and the myriad types of sensors built into a modern aircraft.

Cameras can now operate digitally, capturing images and converting them into digital files. There are digital still-image cameras, and there are now many types of digital motion-picture cameras. Many computer enthusiasts and practical business people find it useful to attach small digital cameras to their personal computers. When linked to the Internet, and using special software such as Microsoft’s NetMeeting, such a system can be used to conduct desktop videoconferencing.

OUTPUT TECHNOLOGIESThe output generated by a computer can be transmitted to the user via several devices and media. Below are common types of output technologies.

M o n i t o r sMonitors are the video screens used with most computers that display input as well as output. Like television sets, monitors come in a variety of sizes and color/resolution quality. And like television sets, the common desktop monitor uses cathode ray tube (CRT) technology to shoot beams of electrons to the screen. The electrons illuminate tiny points on the screen known as pixels. The more pixels on the screen, the better the resolution, i.e. the less space between pixels, the finer the dot pitch—the better the resolution.Here are some other useful facts about monitors:• Portable computers use a flat screen that uses liquid crystal display (LCD) technology, not CRT.• LCDs use less power than CRT monitors but cost six to eight times what an equivalent CRT does.• LCD monitors may be passive matrix, which have somewhat less display speed and brightness compared to active matrix monitors, which function somewhat differently (and cost significantly more).Organic light-emitting diodes: Organic light-emitting diodes (OLEDs) provide displays that are brighter, thinner, lighter, and faster than liquid crystal displays (LCDs).

Retinal scanning displays: As people increasingly use mobile devices, many are frustrated with the interfaces. The interfaces are too small, too slow, and too awkward to process information effectively. As a result,Web sites become unusable, e-mails are constrained, and graphics are eliminated. One solution does away with screens altogether. A firm named Microvision

(mvis.com) projects an image, pixel by pixel, directly onto a viewer’s retina. This technology, called retinal scanning displays (RSDs), is used in a variety of work situations, including medicine, air traffic control, and controls of industrial machines. RSDs can also be used in dangerous situations, for example, giving firefighters in a smoke-filled building a floor plan.

FIGURE 2.9: A retinal scanning display (RSD) device.

P r i n t e r sPrinters come in a variety of styles for varying purposes. The three main types are impact printers, nonimpact printers, and plotters.Impact printers: Impact printers work like typewriters, using some kind of striking action. A raised metal character strikes an inked ribbon that makes a printed impression of the character on the paper. These devices cannot produce high-resolution graphics, and they are relatively slow, noisy, and subject to mechanical failure. Although inexpensive, they are becoming less popular.Nonimpact printers: Nonimpact printers come in two main styles. Laser printers are higher-speed, high-quality devices that use laser beams to write information on photosensitive drums, whole pages at a time; then the paper passes over the drum and picks up the image with toner (similar to ink). Laser printers produce very-high-resolution text and graphics, making them suitable for a broad range of printing needs from simple text to desktop publishing. Inkjet printers work

differently, by shooting fine streams of colored ink onto the paper. These are less expensive than laser printers, but offer somewhat less resolution quality. Plotters: Plotters are printing devices that use computer-directed pens for creating high-quality images. They are used in complex, low-volume situations, for example, creating maps and architectural drawings. Some plotters are quite large, suited for producing correspondingly large graphics.

V o i c e O u t p u tVoice output is now possible via sophisticated synthesizer software that can be installed in most personal computers. A voice output system constructs the sonic equivalent of textual words, which can then be played through speakers. Other types of software can manage spoken communication in different ways. For example, one can purchase programs that integrate telephone voice mail with the computer, so that the computer can record and make limited responses to incoming calls.

FIGURE 3.0: Multimedia authoring system with a great variety of input sources and output displays

ELEMENTS OF AUTOMATIC CONTROL

CONTROL SYSTEMThis is a system of integrated elements whose function is to maintain a

process variable at a desired value or within a desired range of values. This deals basically with control, which is a series of actions directed for making a variable system adhere to a reference value (that might be either constant or variable). The major characteristic of control is to interfere, to influence or to modify the process. This control function or the interference to the process is introduced by an organization of parts (including operators in manual control) that, when connected together is referred to as the Control System. Within our daily lives, we accomplish numerous objectives such as;

In the domestic domain, we need to regulate the temperature and humidity of homes and buildings for comfortable living.

For transportation, we need to control the automobile and airplane to go from one point to another accurately and safely.

Industrially, manufacturing processes contain numerous objectives for products that will satisfy the precision and cost-effectiveness requirements.

A human being is capable of performing a wide range of tasks, including decision making. Some of these tasks, such as picking up objects and walking from one point to another, are commonly carried out in a routine fashion. Under certain conditions, some of these tasks are to be performed in the best possible way. For instance, an athlete running a 100-yard dash has the objective of running that distance in the shortest possible time. A marathon runner, on the other hand, not only must run the distance as quickly as possible, but, in doing so, he or she must control the consumption of energy and devise the best strategy for the race. The means of achieving these "objectives" usually involve the use of control systems that implement certain control strategies.

In recent years, control systems have assumed an increasingly important role in the development and advancement of modern civilization and technology. Practically every aspect of our day-to-day activities is affected by some type of control system. Control systems are found in abundance in all sectors of industry, such as quality control of manufactured products, automatic assembly lines, machine-tool control, space technology and weapon systems, computer control, transportation systems, power systems, robotics, Micro-Electro-Mechanical Systems (MEMS), nanotechnology, and many others. Even the control of

inventory and social and economic systems may be approached from the theory of automatic control.

This is based on Control Theory, which is an interdisciplinary branch of engineering and mathematics that deals with the behavior of dynamical systems with inputs. The external input of a system is called the reference. When one or more output variables of a system need to follow a certain reference over time, a controller manipulates the inputs to a system to obtain the desired effect on the output of the system. The control theory’s function is to calculate solutions for the proper corrective action from the controller that result in system stability, that is, the system will hold the set point and not oscillate around it.

FIGURE 1.1: Basic components of a control system

Basic Components of a Control SystemThe basic ingredients of a control system can be described by:

1. Objectives of control.2. Control-system components.3. Results or outputs.

The basic relationship among these three components is illustrated in Fig. 1 -1.Technically, the objectives can be referred to as inputs, or actuating signals, u, and the results are be called outputs, or controlled variables, y. Basically, the objective of the control system is to control the outputs in some prescribed manner by the inputs through the elements of the control system.

Examples of Control-System Applications

Intelligent SystemsApplications of control systems have significantly increased through the development of new materials, which provide unique opportunities for highly efficient actuation and sensing, thereby reducing energy losses and environmental impacts. State-of-the-art actuators and sensors may be implemented in virtually any system, including biological propulsion; locomotion; robotics; material handling; biomedical, surgical, and endoscopic; aeronautics;

marine; and the defense and space industries. Potential applications of control of these systems may benefit the following areas:

• Machine tools: Improve precision and increase productivity by controlling chatter.

• Flexible robotics: Enable faster motion with greater accuracy.• Photolithography: Enable the manufacture of smaller microelectronic

circuits by controlling vibration in the photolithography circuit-printing process.

• Biomechanical and biomedical: Artificial muscles, drug delivery systems, and other assistive technologies.

• Process control: For example, on/off shape control of solar reflectors or aerodynamic surfaces.

Control in Virtual Prototyping and Hardware in the LoopThe concept of virtual prototyping has become a widely used phenomenon in the automotive, aerospace, defense, and space industries. In all these areas, pressure to cut costs has forced manufacturers to design and test an entire system in a computer environment before a physical prototype is made. Design tools such as MATLAB and Simulink enable companies to design and test controllers for different components (e.g., suspension, ABS, steering, engines, flight control mechanisms, landing gear, and specialized devices) within the system and examine the behavior of the control system on the virtual prototype in real time. This allows the designers to change or adjust controller parameters online before the actual hardware is developed. Hardware in the loop terminology is a new approach of testing individual components by attaching them to the virtual and controller prototypes. Here the physical controller hardware is interfaced with the computer and replaces its mathematical model within the computer!

Smart Transportation SystemsThe automobile and its evolution in the last two centuries is arguably the most transformative invention of man. Over years innovations have made cars faster, stronger, and aesthetically appealing. We have grown to desire cars that are "intelligent" and provide maximum levels of comfort, safety, and fuel efficiency. Examples of intelligent systems in cars include climate control, cruise control, anti-lock brake systems (ABSs), active suspensions that reduce vehicle vibration over rough terrain or improve stability, air springs that self-level the vehicle in high-G turns (in addition to providing a better ride), integrated vehicle dynamics

that provide yaw control when the vehicle is either over- or under steering (by selectively activating the brakes to regain vehicle control), traction control systems to prevent spinning of wheels during acceleration, and active sway bars to provide "controlled" rolling of the vehicle. The following are a few examples.Drive-by-wire and Driver Assist Systems: The new generations of intelligent vehicles will be able to understand the driving environment, know their whereabouts, monitor their health, understand the road signs, and monitor driver performance, even overriding drivers to avoid catastrophic accidents. These tasks require significant overhaul of current designs.Drive-by-wire technology replaces the traditional mechanical and hydraulic systems with electronics and control systems, using electromechanical actuators and human-machine interfaces such as pedal and steering feel emulators—otherwise known as haptic systems.Hence, the traditional components—such as the steering column, intermediate shafts, pumps, hoses, fluids, belts, coolers, brake boosters and master cylinders—are eliminated from the vehicle. Haptic interfaces that can offer adequate transparency to the driver while maintaining safety and stability of the system. Removing the bulky mechanical steering wheel column and the rest of the steering system has clear advantages in terms of mass reduction and safety in modern vehicles, along with improved ergonomics as a result of creating more driver space. Replacing the steering wheel with a haptic device that the driver controls through the sense of touch would be useful in this regard. The haptic device would produce the same sense to the driver as the mechanical steering wheel but with improvements in cost, safety, and fuel consumption as a result of eliminating the bulky mechanical system.Driver assist systems help drivers to avoid or mitigate an accident by sensing the nature and significance of the danger. Depending on the significance and timing of the threat, these on-board safety systems will initially alert the driver as early as possible to an impending danger. Then, they will actively assist or, ultimately, intervene in order to avert the accident or mitigate its consequences. Provisions for automatic over-ride features when the driver loses control due to fatigue or lack of attention will be an important part of the system. In such systems, the so-called advanced vehicle control system monitors the longitudinal and lateral control, and by interacting with a central management unit, it will be ready to take control of the vehicle whenever the need arises. The system can be readily integrated with sensor networks that monitor every aspect of the conditions on the road and are prepared to take appropriate action in a safe manner.

Integration and Utilization of Advanced Hybrid Powertrains: Hybrid technologies offer improved fuel consumption while enhancing driving experience. Utilizing new energy storage and conversion technologies and integrating them with powertrains would be prime objectives of this research activity. Such technologies must be compatible with current platforms and must enhance, rather than compromise, vehicle function. Sample applications would include developing plug-in hybrid technology, which would enhance the vehicle cruising distance based on using battery power alone, and utilizing sustainable energy resources, such as solar and wind power, to charge the batteries. The smart plug-in vehicle can be a part of an integrated smart home and grid energy system of the future, which would utilize smart energy metering devices for optimal use of grid energy by avoiding peak energy consumption hours.High Performance Real-time Control, Health Monitoring, and Diagnosis: Modern vehicles utilize an increasing number of sensors, actuators, and networked embedded computers. The need for high performance computing would increase with the introduction of such revolutionary features as drive-by-wire systems into modern vehicles. The tremendous computational burden of processing sensory data into appropriate control and monitoring signals and diagnostic information creates challenges in the design of embedded computing technology. Towards this end, a related challenge is to incorporate sophisticated computational techniques that control, monitor, and diagnose complex automotive systems while meeting requirements such as low power consumption and cost effectiveness.The following represent more traditional applications of control that have become part of our daily lives.

Steering Control of an AutomobileAs a simple example of the control system, as shown in Fig. 1-1, consider the steering control of an automobile. The direction of the two front wheels can be regarded as the controlled variable, or the output, y; the direction of the steering wheel is the actuating signal, or the input, u. The control system, or process in this case, is composed of the steering mechanism and the dynamics of the entire automobile. However, if the objective is to control the speed of the automobile, then the amount of pressure exerted on the accelerator is the actuating signal, and the vehicle speed is the controlled variable. As a whole, we can regard the simplified automobile control system as one with two inputs (steering and accelerator) and two outputs (heading and speed). In this case, the two controls

and two outputs are independent of each other, but there are systems for which the controls are coupled. Systems with more than one input and one output are called multivariable systems.

Idle-Speed Control of an AutomobileAs another example of a control system, we consider the idle-speed control of an automobile engine. The objective of such a control system is to maintain the engine idle speed at a relatively low value (for fuel economy) regardless of the applied engine loads (e.g., transmission, power steering, air conditioning). Without the idle-speed control, any sudden engine-load application would cause a drop in engine speed that might cause the engine to stall. Thus the main objectives of the idle-speed control system are

(1) To eliminate or minimize the speed droop when engine loading is applied and

(2) To maintain the engine idle speed at a desired value. Fig. 1-2 shows the block diagram of the idle-speed control system from the standpoint of inputs-system-outputs. In this case, the throttle angle a and the load torque TL (due to the application of air conditioning, power steering, transmission, or power brakes, etc.) are the inputs, and the engine speed to is the output. The engine is the controlled process of the system.Sun-Tracking Control of Solar CollectorsTo achieve the goal of developing economically feasible non-fossil-fuel electrical power, the U.S. government has sponsored many organizations in research and development of solar power conversion methods, including the solar-cell conversion techniques. In most of these systems, the need for high efficiencies dictates the use of devices for sun tracking.Fig. 1-3 shows a solar collector field. Fig. 1-4 shows a conceptual method of efficient water extraction using solar power. During the hours of daylight, the solar collector would produce electricity to pump water from the underground water table to a reservoir (perhaps on a nearby mountain or hill), and in the early morning hours, the water would be released into the irrigation system.One of the most important features of the solar collector is that the collector dish must track the sun accurately. Therefore, the movement of the collector dish must be controlled by sophisticated control systems. The block diagram of Fig. 1-5 describes the general philosophy of the sun-tracking system together with some of the most important components. The controller ensures that the tracking collector is pointed toward the sun in the morning and sends a "start track"

command. The controller constantly calculates the sun's rate for the two axes (azimuth and elevation) of control during the day. The controller uses the sun rate and sun sensor information as inputs to generate proper motor commands to slew the collector.

CLASSIFICATION OF CONTROL SYSTEMSControl systems are classified with respect to:

1. technique involved to perform control (i.e. human/machines): manual/automatic control

2. Time dependence of output variable (i.e. constant/changing): regulator/servo, (also known as regulating/tracking control)

3. Fundamental structure of the control (i.e. the information used for computing the control): Open-loop/feedback control, (also known as open-loop/closed-loop control).

MANUAL CONTROL SYSTEM: This is a system in which a machine is controlled by the human element (human being). An example is shown below.

A diagram of the system is shown below.

Figure a

To begin with the shower is cold. To start the heating process the valve in the hot water line is opened. The operator can then determine the effectiveness of the control process by standing in the shower. If the water is too hot, the valve should be closed a little or even turned off. If the water is not hot enough then the valve is left open or opened wider.

Another example is a man driving a car.

Functions of a Manual Control System

This control system which is completed by the operator possesses the following functions:

Measurement

This is essentially an estimate or appraisal of the process being controlled by the system. In this example, this is achieved by the right hand of the operator.

Comparison

This is an examination of the likeness of the measured values and the desired values. This is carried out in the brain of the operator.

Computation

This is a calculated judgment that indicates how much the measured value and the desired values differ and what action and how much should be taken. In this example, the operator will calculate the difference between the desired temperature and the actual one. Accordingly the direction and amount of the adjustment of the valve are worked out and the order for this adjustment is sent to the left hand from the brain of the operator. If the outlet water temperature is lower, then the brain of the operator will tell the left hand to open the steam valve wider. If there is any disturbance, or variation of flow rate in water to the shower inlet, some adjustment must be made to keep the outlet water temperature at a desired value.

Correction

This is ultimately the materialization of the order for the adjustment. The left hand of the operator takes the necessary actions following the order from brain.

DISADVANTAGES

The accuracy and the continuous involvement of operators.

AUTOMATIC CONTROL SYSTEM

This is the application of control theory for regulation of processes without direct human intervention. Automatic control is widely employed in many technological and biological systems to perform operations not feasible for a man because of the necessity of processing a large amount of data in a limited time; it is also used to increase the productivity of labor and the quality and accuracy of regulation and to free men from controlling systems that operate under conditions which are relatively inaccessible or hazardous to health. An automatic control system

(ACS) sustains or improves the functioning of a controlled object. In a number of cases the auxiliary operations for the ACS—starting, stopping, monitoring, adjusting, and so on—can also be automated. An ACS functions mainly as a member of a production or some other complex. ACS’s are classified mainly according to the control objectives, the type of control circuit, and the method of transmitting the signals.

The simplest example of an ACS is a system for the direct regulation of a motor’s speed of rotation (see Figure 1). The control objective is to maintain a constant speed of rotation of a flywheel; the controlled object is the motor, the control effect is the position of the regulating slide of the throttle, the CD is the centrifugal governor, which has a sleeve that is shifted by the centrifugal forces when the speed of rotation of the shaft, which is rigidly connected to the flywheel, deviates from the specified value. When the sleeve is shifted, the position of the throttle’s slide is changed. A block diagram of this example (Figure 2) is representative of many ACS’s regardless of their physical characteristics. The system shown is a closed, single-loop continuous system of automatic control for a mechanical action that can be linearized for analysis. Examples of automatic control systems are aircraft autopilot, integrated circuits, traffic flow control etc.

Figure 1

AUTOMATIC CONTROL THEORY (ACT) deals with the design principles of automatic control systems and the rules for the processes taking place in them, which are investigated by means of dynamic simulations of the real systems,

taking into account the operating conditions, the specific purpose, and the structural features of the controlled object and the automatic devices, so that efficient and accurate control systems can be designed.

An example of an automatic control system is shown below

Figure

In this system (compared to figure b);

A temperature measurement device is used to measure the water temperature, which replaces the right hand of the operator. This improves the accuracy.

Instead of manual valves, we use a special kind of valve, called a control valve, which is driven by compressed air or electricity. This will replace the left hand of the operator.

A temperature controller replaces the brain of the operator. This has the functions of comparison and computation and can give orders to the control valve.

The signal and order connections between the measurement device, control valve and controller are transferred through cables and wires, which replace the nerve system in the operator.

FUNCTIONS OF AUTOMATIC CONTROL

Control Sensing Metrics Measurement Comparison Computation Correction

APPLICATION OF AUTOMATIC CONTROL SYSTEM

• industrial processes, manufacturing, robots• consumer goods, home appliances, CD players• computers, networks, communication systems• transportation systems: cars, planes, spacecraft• Chemical processes• Engine management systems• Integrated circuit manufacturing• X-by-Wire systems

Hardware of a Control System

Sensor – This is a piece of equipment used to measure system variables. It serves as the signal source in automatic control.

Controller – This is a piece of equipment used to perform the functions of comparison and computation.

Control Element – This is a piece of equipment used to perform the control action or to exert direct influence on the process. It receives signals from the controller and performs some type of operation on the process. Generally it is simply a control valve.

Software of a Control System

Associated with a control system are a number of different types of variables.

Controlled Variable: This is the basic process value which is being regulated by the system. It is maintained at a specified value or within a specified

range. It is the one variable that we are especially interested in e.g. the outlet water temperature in the example above. In feedback control, the controlled variable is usually the measured variable.

Set-point: This is the predetermined desired value for the controlled variable. The objective of the control system is to regulate the controlled variable at its set-point.

Manipulated Variable: This is the adjustable value which can be altered, in order to achieve the control objective. It is acted on by the control system to maintain the controlled variable at the specified value or within the specified range. In the above example, this was the input hot water flow rate.

Conclusively, in the control system we adjust the manipulated variable to maintain the controlled variable at its set-point. This meets the requirement of keeping the stability of the process and suppressing the influence of disturbances.

CLASSES OF AUTOMATIC CONTROL

SERVO (TRACKING CONTROL): This is an automatic control system designed to follow a changing reference. An example is a remote controlled car.

REGULATOR: This is an automatic control system designed to maintain an output fixed (regardless of the disturbances present) e.g. cruise control.

OPEN-LOOP CONTROL (NON-FEEDBACK CONTROL): This system does not measure the actual output and there is no correction to make that output conform to the desired output. It is such that the control action is independent of the output. An example is an electric toaster.

CLOSED-LOOP CONTROL (FEEDBACK CONTROL): This system includes a sensor to measure the output and uses feedback of the sensed value to influence the control input variable. It is such that the control action is dependent on the output. Feedback is the information in a closed-loop control system which is about the condition of a process variable. An example is the water tank of a flushing toilet.

Figure

Open loop system (a) and closed loop system (b)

ELEMENTS OF AUTOMATIC CONTROL

• An error detection element: It first compares the value of the controlled variable to the desired value, and then signals an error if a deviation exists between the actual and desired values

• A final control element: It responds to the error signal by correcting the manipulated variable of the process.

• Comparison unit: computes the difference between the desired and actual output variables to give the controller a measure of the system error

• Control element: computes the desired control input variable• Correction element: device that can influence the control input variable

of the process (aka: actuator)• Process element: component whose the output is to be controlled• Measurement element: measures the actual output variable. It senses

and evaluates the controlled variable.

FIGURE

Figure

Figure 4: Relationships of Functions and Elements in an Automatic Control System