10%20Introduction%20to%20Bus%20Systems, BMW educational info, Dokumentacja
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//-->Table of ContentsIntroduction to Bus SystemsSubjectPageIntroduction to Bus Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3Multiplexing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5Bus Communication Speeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7Bus System Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8Bus System Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9Diagnosis Bus (D-Bus) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10Diagnostic Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11Gateways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13Controller Area Network (CAN-Bus) . . . . . . . . . . . . . . . . . . . . . . . . . . .14CAN-Bus Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16Terminal Resistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16CAN Communication Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17Information and Body Bus (I and K-Bus) . . . . . . . . . . . . . . . . . . . . . . .18Bus System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20Troubleshooting the I/K-Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21Failure of the Bus cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22Failure of one of the control units attached to the I/K-Bus. . . . . . . .24Failure of the voltage supply to individual modules. . . . . . . . . . . . . . .24Interference in the Bus Cables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24Peripheral Bus (P-Bus) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25Troubleshooting the P-Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27M-Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28Communication Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29M-Bus Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29M-Bus Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30Initial Print Date: 12/04Revision Date:Introduction to Bus SystemsModel: All from E38 to PresentProduction: AllAfter completion of this module you will be able to:• Describe the operation of a basic bus system.• Understand how signals and sensor information are shared betweencontrol units in a bus system.• Identify bus systems currently used in BMW Group vehicles.• Understand how bus networking technology is applied in BMW vehicles.• Understand diagnostic techniques.2Introduction to Bus SystemsIntroduction to Bus SystemsUp until the introduction of the E31, all of the information transferred between controlunits was transmitted on dedicated signal lines. As the various electronic systems grewmore complex, the size of the wiring harness increased beyond practical limits.Signals such as engine RPM, coolant temperature, throttle position, road speed etc. eachused a dedicated signal line going to the control module that required this information.Each of these lines differed in the method of signal transmission. Some of the methodsused were variable duty cycle, switched DC signals and signals with variable frequencies.This created a need for larger and more complex wiring harnesses.Engine TemperatureEngine RPM (TD)Engine Load (tL)Injector on Time (ti)Throttle Position (DKV)Transmission RangeTorque Reduction (ME)TCC Lockup StatusA solution to this problem was found by introducing bus networks to BMW Group vehi-cles. A bus system uses multiplexing technology similar to that used in the electronicsand telecommunications industry. Multiplexing is a system of transmitting several mes-sages on the same circuit or channel.This technology allows control modules to transfer data bi-directionally at high speed andenables control modules to share sensor information. This also allows control modules tosend and receive control commands at a faster rate than with conventional methods.3Introduction to Bus SystemsWith the amount and complexity of features now available in modern vehicles, multiplex-ing is a necessary technology. There are numerous benefits to in-vehicle bus networkssuch as:• A reduction in the size of the wiring harness by decreasing the number of interfacesbetween control units to one or two wires.• Greater system reliability by reducing the number of connectors and components.• A reduction in the number of redundant sensors by allowing the sharing of sensorinformation.• Reduction of costs for components, assembly and troubleshooting.• Flexibility in system configuration for addition of new systems.Control module communication using individual signal linesDMEClusterEGSDSCSteeringAngleSensorControl module communication using a bus networkDMEClusterEGSDSCSteeringAngleSensor4Introduction to Bus SystemsMultiplexingMultiplexing relies on the use of digital communication between control units. A digitalsignal consists of a series of high and low voltage signals which represent “bits” of infor-mation.Using the example of morse code for explanation, the letters SOS are represented inmorse code as three dots - three dashes - three dots. Expressed as an electrical signalSOS would be represented as three short pulses - three long pulses - three short pulses.SCUOSCUThe basis for digital communication is binary code. Binary code uses only 2 digits -0 and 1. Electrically, 1 is represented by a voltage pulse and 0 is represented by a lowvoltage signal usually 0 volts.In digital communication, each pulse represents a “bit” of data. Eight “bits” of informationin a series of pulses makes up one “byte”. A byte represents a character in a line ofinformation (data).ElectricalSignal8Corresponding"Bits"0 1 0 1 0 1 0 18 Bits =One Byte5Introduction to Bus Systems
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