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CHAPTER 18 Computer and Network Fundamentals

CHAPTER 18 Computer and Network Fundamentals. OBJECTIVES. After studying Chapter 18, the reader will be able to: Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “A” (General Electrical/Electronic Systems Diagnosis).

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CHAPTER 18 Computer and Network Fundamentals

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  1. CHAPTER 18 Computer and Network Fundamentals

  2. OBJECTIVES After studying Chapter 18, the reader will be able to: • Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “A” (General Electrical/Electronic Systems Diagnosis). • Explain the purpose and function of onboard computers. • List the various parts of an automotive computer. • List five input sensors. • List four devices controlled by the computer (output devices).

  3. Actuator Analog-to-digital (AD) converter Binary Central processing unit (CPU) Clock generator Controller Controller area network (CAN) Digital Duty cycle EEPROM E2 PROM Electronic control assembly (ECA) Electronic control module (ECM) Electronic control unit (ECU) Engine mapping High-side drivers (HSD) Input conditioning Keep-alive memory (KAM) Low-side drivers (LSD) Multiplexing Network Nonvolatile RAM Output drivers Powertrain Control Module (PCM) Programmable read-only memory (PROM) Random-access memory (RAM) Read-only memory (ROM) Serial data Splice pack Terminating resistors Volatile KEY TERMS

  4. COMPUTER CONTROL • Modern automotive control systems consist of a network of electronic sensors, actuators, and computer modules designed to regulate the power train and vehicle support systems. • The Powertrain Control Module (PCM) is the heart of this system. • It coordinates engine and transmission operation, processes data, maintains communications, and makes the control decisions needed to keep the vehicle operating.

  5. THE FOUR BASIC COMPUTER FUNCTIONS • The operation of every computer can be divided into four basic functions. • Input • Processing • Storage • Output

  6. FIGURE 18–1 All computer systems perform four basic functions: input, processing, storage, and output. THE FOUR BASIC COMPUTER FUNCTIONS

  7. FIGURE 18–2 A potentiometer uses a movable contact to vary resistance and send an analog voltage to the PCM. THE FOUR BASIC COMPUTER FUNCTIONS

  8. FIGURE 18–3 A replaceable PROM used in an older General Motors computer. Notice that the sealed access panel has been removed to gain access. THE FOUR BASIC COMPUTER FUNCTIONS

  9. FIGURE 18–4 A typical output driver. In this case, the PCM applies voltage to the fuel pump relay coil to energize the fuel pump. THE FOUR BASIC COMPUTER FUNCTIONS

  10. THE FOUR BASIC COMPUTER FUNCTIONS • LOW-SIDE DRIVERS • HIGH-SIDE DRIVERS • PULSE WIDTH MODULATION

  11. FIGURE 18–5 A typical low-side driver (LSD) which uses a control module to control the ground side of the relay coil. THE FOUR BASIC COMPUTER FUNCTIONS

  12. FIGURE 18–6 A typical module-controlled high-side driver (HSD) where the module itself supplies the electrical power to the device. The logic circuit inside the module can detect circuit faults including continuity of the circuit and if there is a short-to-ground in the circuit being controlled. THE FOUR BASIC COMPUTER FUNCTIONS

  13. FIGURE 18–7 Both the top and bottom pattern have the same frequency. However, the amount of on-time varies. Duty cycle is the percentage of the time during a cycle that the signal is turned on. THE FOUR BASIC COMPUTER FUNCTIONS

  14. DIGITAL COMPUTERS • In a digital computer, the voltage signal or processing function is a simple high/low, yes/no, on/off signal. • The digital signal voltage is limited to two voltage levels: high voltage and low voltage. • Since there is no stepped range of voltage or current in between, a digital binary signal is a “square wave.”

  15. DIGITAL COMPUTERS • A digital computer changes the analog input signals (voltage) to digital bits (binary digits) of information through an analog-to-digital (AD) converter circuit. • The binary digital number is used by the computer in its calculations or logic networks. • Output signals usually are digital signals that turn system actuators on and off.

  16. FIGURE 18–8 Many electronic components are used to construct a typical vehicle computer. Notice the quantity of chips, resistors, and capacitors used in this General Motors computer. DIGITAL COMPUTERS

  17. DIGITAL COMPUTERS • PARTS OF A COMPUTER • CENTRAL PROCESSING UNIT (CPU) • COMPUTER MEMORY • COMPUTER PROGRAMS • CLOCK RATES AND TIMING • COMPUTER SPEEDS • BAUD RATE • CONTROL MODULE LOCATIONS

  18. FIGURE 18–9 Typical ignition timing map developed from testing and used by the vehicle computer to provide the optimum ignition timing for all engine speeds and load combinations. DIGITAL COMPUTERS

  19. FIGURE 18–10 The calibration module on many Ford computers contains a system PROM. DIGITAL COMPUTERS

  20. FIGURE 18–11 The clock generator produces a series of pulses that are used by the microprocessor and other components to stay in step with each other at a steady rate. DIGITAL COMPUTERS

  21. FIGURE 18–12 This Powertrain Control Module (PCM) is located under the hood on this Chevrolet pickup truck. DIGITAL COMPUTERS

  22. FIGURE 18–13 This PCM on a Chrysler vehicle can only be seen by hoisting the vehicle because it is located next to the radiator, and in the airflow to help keep it cool. DIGITAL COMPUTERS

  23. COMPUTER INPUT SENSORS • The vehicle computer uses the signals (voltage levels) from the following engine sensors: • Engine speed (RPM or revolutions per minute) sensor • MAP (manifold absolute pressure) sensor • MAF (mass airflow) sensor • ECT (engine coolant temperature) sensor • O2S (oxygen sensor) • TP (throttle position) sensor • VS (vehicle speed) sensor • Knock sensor

  24. COMPUTER OUTPUTS • A vehicle computer can do just two things. • Turn a device on. • Turn a device off. • The computer can turn devices such as fuel injectors on and off very rapidly or keep them on for a certain amount of time. • Typical output devices include the following. • Fuel injectors • Ignition timing • Transmission shifting • Idle speed control • Evaporative emission control solenoids

  25. MODULE COMMUNICATION AND NETWORKS • Since the 1990s, vehicles use modules to control most of the electrical component operation. • A typical vehicle will have 10 or more modules and they communicate with each other over data lines or hard wiring, depending on the application.

  26. MODULE COMMUNICATION AND NETWORKSSERIAL DATA • Serial data is data that is transmitted by a series of rapidly changing voltage signals pulsed from low to high or from high to low. • Most modules are connected together in a network because of the following advantages: • A decreased number of wires is needed, thereby saving weight, cost, as well as helping with installation at the factory, and decreased complexity, making servicing easier. • Common sensor data can be shared with those modules that may need the information, such as vehicle speed, outside air temperature, and engine coolant temperature.

  27. FIGURE 18–14 A network allows all modules to communicate with other modules. MODULE COMMUNICATION AND NETWORKSMULTIPLEXING • Multiplexing is the process of sending multiple signals of information at the same time over a signal wire and then separating the signals at the receiving end. • This system of intercommunication of computers or processors is referred to as a network.

  28. MODULE COMMUNICATION AND NETWORKSMULTIPLEXING • This multiplexing has a number of advantages, including: • The elimination of redundant sensors and dedicated wiring for these multiple sensors. • The reduction of the number of wires, connectors, and circuits. • Addition of more features and option content to new vehicles. • Weight reduction, increasing fuel economy. • Allows features to be changed with software upgrades instead of component replacement.

  29. MODULE COMMUNICATION AND NETWORKSMULTIPLEXING • The three most common types of networks used on General Motors vehicles include: • 1. Ring link networks • 2. Star link • 3. Ring/Star hybrid

  30. FIGURE 18–15 A ring link network reduces the number of wires it takes to interconnect all of the modules. MODULE COMMUNICATION AND NETWORKSMULTIPLEXING

  31. FIGURE 18–16 A star-link-type network where all of the modules are connected together using splice packs. MODULE COMMUNICATION AND NETWORKSMULTIPLEXING

  32. SAE COMMUNICATION CLASSIFICATIONS • The Society of Automotive Engineers (SAE) standards include three categories of in-vehicle network communications, including the following. • CLASS A • CLASS B • CLASS C

  33. FIGURE 18–17 A typical bus system showing module CAN communications and twisted pairs of wire. SAE COMMUNICATION CLASSIFICATIONS

  34. What Is a Bus? • A bus is a term used to describe a communication network. Therefore, there are connections to the bus and bus communications, both of which refer to digital messages being transmitted among electronic modules or computers.

  35. MODULE COMMUNICATION DIAGNOSIS • Most vehicle manufacturers specify that a scan tool be used to diagnose modules and module communications. • Always follow the recommended testing procedures, which usually require the use of a factory scan tool. • Some tests of the communication bus (network) and some of the service procedures require the service technician to attach a DMM, set to DC volts, to monitor communications. • A variable voltage usually indicates that messages are being sent and received.

  36. FIGURE 18–18 Checking the terminating resistors using an ohmmeter at the DLC. MODULE COMMUNICATION DIAGNOSIS

  37. FIGURE 18–19 Sixteen-pin OBD II DLC with terminals identified. Scan tools use the power pin (16) ground pin (4) for power so that a separate cigarette lighter plug is not necessary on OBD II vehicles. OBD II DATA LINK CONNECTOR

  38. SUMMARY • The Society of Automotive Engineers (SAE) standard J-1930 specifies that the term Powertrain Control Module (PCM) be used for the computer that controls the engine and transmission in a vehicle. • The four basic computer functions include input, processing, storage, and output. • Read-only memory (ROM) can be programmable (PROM), erasable (EPROM), or electrically erasable (EEPROM). • Computer input sensors include engine speed (RPM), MAP, MAF, ECT, O2S, TP, and VS. • A computer can only turn a device on or turn a device off, but it can do the operation very rapidly.

  39. REVIEW QUESTIONS • What part of the vehicle computer is considered to be the brain? • What is the difference between volatile and nonvolatile RAM? • List four input sensors. • List four output devices.

  40. CHAPTER QUIZ • What unit of electricity is used as a signal for a computer? • Volt • Ohm • Ampere • Watt

  41. CHAPTER QUIZ 2. The four basic computer functions include ________. • Writing, processing, printing, and remembering • Input, processing, storage, and output • Data gathering, processing, output, and evaluation • Sensing, calculating, actuating, and processing

  42. CHAPTER QUIZ 3. All OBD II vehicles use what type of read-only memory? • ROM • PROM • EPROM • EEPROM

  43. CHAPTER QUIZ 4. The “brain” of the computer is the ________. • PROM • RAM 3 • CPU • AD converter

  44. CHAPTER QUIZ 5. Computer processing speed is measured in ________. • Baud rate • Clock speed (Hz) • Voltage • Bytes

  45. CHAPTER QUIZ 6. Which item is a computer input sensor? • RPM • Throttle position angle • Engine coolant temperature • All of the above

  46. CHAPTER QUIZ 7. Which item is a computer output device? • Fuel injector • Transmission shift solenoid • Evaporative emission control solenoid • All of the above

  47. CHAPTER QUIZ 8. The SAE term for the vehicle computer is ________. • PCM • ECM • ECA • Controller

  48. CHAPTER QUIZ 9. What two things can a vehicle computer actually perform (output)? • Store and process information • Turn something on or turn something off • Calculate and vary temperature • Control fuel and timing only

  49. CHAPTER QUIZ 10. Analog signals from sensors are changed to digital signals for processing by the computer through which type of circuit? • Digital • Analog • AD converter • PROM

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