automotive engineering 5 lin bus

UniTrain-I course "Automotive engineering 5: LIN bus"

Course number: SO4204-7E Version 1.0

Author: Thomas Kähler

Lucas-Nülle GmbH · Siemensstraße 2 · D-50170 Kerpen (Sindorf) · Tel.: +49 2273

567-0

www.lucas-nuelle.com www.unitrain-i.com

Copyright © 2008 LUCAS-NÜLLE GmbH.

All rights reserved.

LIN bus

LIN bus

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Course objectives

This course on LIN buses does not attempt to draw any definitive or enduring conclusions because, despite broad standardization, networking of individual control units is still greatly subject to the fancies of automotive manufacturers.

The course's experiments are instead meant to impart an understanding of the fundamentals of data transmission via the LIN bus employed here. The experiences you gather in this process should inspire further examinations and ideas.

Because the course's topics are not progressively layered, they can be studied in any required sequence, enabling you to discover the world of LIN buses from a variety of avenues.

Though the oscillograms may vary in accordance with measurement settings and locations, they remain generally applicable. Of importance here is to discuss the experiment results and their rationales with your colleagues and instructor.

The tools provided here also permit examinations of LIN buses on real vehicles.

Course contents

� Introduction to the LIN bus and its differences vis-à-vis other data buses. � Investigation of the transmission of information and commands on the LIN bus. � Conduction of measurements on the LIN bus. � Examination of faults on the LIN bus.

Prerequisites

� Familiarity with the fundamentals of electrical engineering (current, voltage and resistance).

� Experience in measuring voltages with multimeters and oscilloscopes. � Knowledge of digital and binary/digital technology, as described in detail in the

courses on CAN buses and optical data buses.

Training objectives

Welcome to the UniTrain-I course titled "Automotive engineering 5: The LIN bus"! The LUCAS-NÜLLE team wishes you lots of fun and success in working through the course topics and conducting the experiments. The next few pages provide an overview of the course's contents and required equipment.

Training objectives

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Some animations require an installed Flash player. If your system

does not have a Flash player, you can download the latest version

from Adobe.

Equipment

SO4203-

2A

UniTrain-I

interface

SO4203-

2B

UniTrain-I

experimenter

SO4203-

2J

UniTrain-I

measurement

accessories

SO4203-

6C

UniTrain-I LIN-

master control

unit

SO4203-

6D

UniTrain-I LIN-

slave power

window

SO4203-

6E

UniTrain-I LIN-

slave exterior

mirror

SO5121-

8J

UniTrain-I

potentiometer,

47 kOhm

Equipment

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This course titled "Automotive engineering 5: The LIN bus" comes with 3 experiment

cards for creating a LIN cluster, as a LIN network is sometimes called.

The control unit acts as the master, while the power window and exterior mirror act as

slaves.

A LIN network functions only if its master control unit can communicate with at least

one slave, regardless of which card is employed as the slave.

Experiment cards

Move the mouse pointer over the cards to view details on their individual

components.

Experiment cards

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Card SO4203-6C designated "LIN-master control unit" contains the LIN-master and

sensors (switches) for operating the power windows, exterior mirrors, central locking

and indicator lights.

This card simulates the master control unit on the driver's door. Actions selected here

are communicated via the LIN line to the corresponding slave devices which execute

the selected actions.

LIN-master control unit

Technical data

Notes on the electrical system:

� The operating voltage is

supplied via the LabSoft

experimenter.

� The CAN network terminal is not

yet enabled.

Dimensions:

� 160 x 100 mm (width x height)

Move the mouse pointer over the diagram to view details on the card's individual

components.

LIN-master control unit

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Card SO4203-6D designated "LIN-slave power window" includes actuators for the

window motor and central locking, as well as a sensor for registering the window's

position.

The card can receive its power via the LabSoft experimenter or a separate ground

line permitting operation independently of the experimenter.

Actions are initiated exclusively via the LIN-master. Refer to the page on protection

against manipulation.

LIN-slave power window

Technical data


� The voltage is supplied via the

positive terminal.

Dimensions:

� 160 x 100 mm (width x height)


components.

LIN-slave power window

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Card SO4203-6E designated "LIN-slave exterior mirror" comprises actuators for the

exterior mirrors, side indicator lights and mirror heating.

The card can receive its power via the LabSoft experimenter or the separate ground

line permitting operation independently of the experimenter.

Actions are initiated exclusively via the LIN-master. Refer to the page on protection

against manipulation.

LIN-slave exterior mirror

Technical data


� The card is supplied with power

from the LIN-master via voltage

and ground terminals.

Dimensions:

� The card is firmly attached to

the exterior mirror.


components.

LIN-slave exterior mirror

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The system has two analogue measurement channels, to be found in the "ANALOG

IN" section on the UniTrain-I interface.

The voltages, currents and other signals transmitted via the accompanying 2-mm

cables can be displayed, for instance, by the virtual oscilloscope or virtual voltmeter

on the PC.

The LIN monitor translates messages into a legible language: Hexadecimal or binary

code. This makes it possible to analyse the messages.

Measuring instruments

Measuring instruments

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The virtual oscilloscope consists of a dual-channel storage instrument whose control

elements are practically identical to those of a real oscilloscope. The two

measurement channels can be displayed simultaneously.

Because one channel is sufficient for the measurements in this course, you can use

the "ON" button of channel B to deactivate it for the sake of clarity.

Open the virtual oscilloscope via the menu item "Instruments" > "Measuring devices"

> "Oscilloscope" from the menu bar at the top of the screen, or by clicking on the

corresponding icon.

Oscillograms needing to be evaluated as part of measurement results can be

transferred conveniently by means of a "drag & drop" operation to the placeholders

provided for this purpose. Only parameters like the time and voltage division need to

be entered manually.

Further details on the handling of the virtual oscilloscope can be found under the

menu item "Help" > "Help topics".

Virtual oscilloscope

Note that the virtual voltmeter and oscilloscope cannot be operated

simultaneously.

Virtual oscilloscope

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The virtual voltmeter is modelled along the lines of a real voltmeter. Because a

voltmeter usually has just one measuring channel, the training system includes a

separate voltmeter for each of the two channels.

Open the virtual voltmeter via the menu item "Instruments" > "Measuring devices" >

"Voltmeter A" or "Voltmeter B" from the menu bar at the top of the screen, or by

clicking on the corresponding icon.

Measurement values needing to be evaluated as part of experimental results can be

transferred conveniently via "drag & drop" operations to corresponding fields. This

avoids manual typing of the values. Further details on handling the virtual voltmeters

are found under the menu item "Help" > "Help topics".

Virtual voltmeter

Note that the virtual voltmeter and oscilloscope cannot be operated

simultaneously.

Virtual voltmeter

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The LIN monitor is used to display messages transmitted via the

experimental bus system.

It is similar to the analyser found in common systems for diagnosing LIN

buses.

The LIN monitor is connected directly to the LIN master via the Unitrain

experimenter's plugs. This eliminates the need for cable connections to

the measurement channels (ANALOG IN). Communication in a LIN

network is initiated exclusively by the master. This makes the LIN network

immune to external manipulations.

The LIN monitor is opened via the menu item "Instruments" > "Measuring

devices" > "LIN monitor" from the menu bar at the top of the screen, or by

clicking on the corresponding icon. Further details on the handling of the

virtual oscilloscope can be found under the menu item "Help" > "Help

topics".

LIN monitor

LIN monitor

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As a result of the rapid increase in the number of control units and the growing

volume of information required for control of the individual functions of the

� drive systems (engine, gearbox, clutch, ...)

� safety systems (ABS, ESP, airbag, assisted steering, ...)

� comfort systems (heating/air conditioning, central locking, mirror adjustment, ...)

� information systems (navigation, warning and status displays, ...)

� media systems (radio, video, telephone, ...),

there is also a considerable increase in the amount of cabling required.

It is necessary to make certain information available to a number of control units and

to coordinate the functions of the individual control units. The control units of modern

vehicles are therefore connected together in a complex network. This network is

again divided into various subnetworks or subsystems.

The division of the overall network into single subnetworks simplifies troubleshooting.

The different subnetworks can also be adapted to their special requirements (safety,

transmission speed, costs, ...).

So, in a vehicle, there are multiple subnetworks, all connected to form one overall

network.

Translation between the protocols of the different bus systems is carried out by the

so-called gateways.

The example below shows the network of an AUDI A6.

Control unit networking in the vehicle


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The LIN bus has established itself in the automobile sector in recent years as an

inexpensive network protocol. Its performance does not reach that of CAN or

FlexRay, of course, but is adequate for many applications in the comfort area, where

a low transmission capacity suffices and demands for transmission security are low.

The LIN bus (Local Interconnect Network) networks control units for comfort elements

which are spatially or functionally located near to each other. Such comfort elements

are

� the doors with electrical window winders, electrically adjustable mirrors, side

flashers and central locking

� the automatic air conditioning, with various temperature sensors, blowers and

flaps

� the automatic screen wipers, with rain/light sensorand wiper motors

� the sliding roof with its positioning motors.

Formerly, the individual elements and systems were individually wired together, but

with the increasing number of functions to be found in modern vehicles, the cable

webs would no longer be manageable.

The pictures below illustrate the reduction of the cable webs in an exterior mirror like

that included in the course.

The LIN bus in the vehicle


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However, as the LIN bus is very easily accessible from outside, it must be protected

against manipulations.

The LIN Consortium was founded in 1998 by the firms Audi, BWW, Mercedes-Benz,

Volkswagen, Volvo, Volcano and Motorola. Thanks to the cooperation between the

major German automobile groups, the LIN bus soon became a standard which has

found widespread use in modern vehicles.


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Every communication is initiated by the master. LIN employs a time slice

procedure, creating a time schedule table in the master, in which a time window is set

up for each message. The master interrogates the individual slaves according to this

table. Some individual slaves can be interrogated more frequently than others

according to their urgency.

Exception: If the LIN Cluster is in Sleep mode, it can be woken by a Wake-Up

signal. The Wake-Up signal is a dominant signal with a length of 250 µs - 5 ms (5 bit

periods).

It is not a message in the real sense of the word. After a pause of 100 - 150 ms, the

waking node, which may also be a slave, expects the Synchronisation break from the

master, which initiates the actual communication. If it receives no synchronisation

break, the wake-up signal is sent again.

The master then works through all the control units according to its time schedule.

Here, for instance, think of the central locking system which, for Safety reasons,

cannot be connected to the CAN bus.

Three different communication relationships are possible:

1. A slave module responds to a request from the master (see Window status)

Example: The master, through the header, requests information on the status

of the windows before it issues the command to open or to close them. It

receives the window status in the response attached by the slave.

2. The master sends a message to one or more slaves (see Central locking)

Example: The master commands two or more control units to execute an action

simultaneously. Header and response are sent by the master to one or more

slaves.

3. The master initiates the communication between two slaves.

The communications concept


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Example: In the header, the master commands one slave, e.g. the rain sensor,

to send information on rain activity to a second slave, e.g. the wiper motor. In

the case of a corresponding windscreen status, the wiper motor switches on.


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First, set up the power supply to the Unitrain Interface and connect the interface with

your computer via the USB interface.

Then set up the experiment as shown in the animation below.

The experimental setup

You will create a networked system like that in a vehicle. This course

employs the example of a LIN network in the driver's door.

This experimental setup is used for the whole course.


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The experimental setup represents a linear structure, as shown in the diagram below.


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The LIN bus is a voltage coded bus system.

The information is transferred from the master control unit to the slave control unit by

means of voltage signals. These voltage signals can be made visible with suitable

instruments.

Access control takes place according to the master-slave principle. Every

communication is initiated by the master. The slaves respond to appropriate

instructions or requests.

This has the advantage that the slave module can be manufactured cheaply, as it

only requires small computing and memory capacities.

The master has the function of a gateway in the overall vehicle network. It translates

CAN messages for forwarding to a slave control unit and vice versa. It also carries

out the diagnosis of the LIN bus and records errors, which can be called up via the

CAN bus.

The data are transmitted in bits via an unshielded single conductor cable.

Communication of control units


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First, set up the LIN cluster as described and test the system.

Task 1:

Measure the voltage of the LIN bus, either with the virtual voltmeter or with a separate

measuring instrument. Parametrise the measuring instrument yourself.

With what voltage is the LIN bus operated?

Task 2:

Make an oscillogram of the voltage curve of an LIN message.

Set an appropriate measurement time for the measurement with the virtual

oscilloscope, taking into account the data transfer rate and the message length.


You will study the power supply of the control units and the voltage coding of the LIN bus with corresponding measuring instruments.

nmlkj approx. 2,5 V

nmlkj approx. 5 V

nmlkj approx. 11,5 V

nmlkj approx. 15 V

Evaluation


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The measurement time required can be roughly calculated. Help is available on

the page Message duration and measurement time.

Drag and drop the oscillogram into the diagram below and enter the time per division

(TIME/Div) and the voltage per unit (CHN/Div) in in the corresponding fields!

What voltage is the High level?

What voltage is the Low level?

: ???

: ???

: ???

Vb : ???

Coupling: ???

nmlkj approx. 1 V

nmlkj approx. 11.5 V

nmlkj approx. 1 V

nmlkj approx. 11.5 V


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Evaluation


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First, set up the experiment.

Experiment 1:

Open the virtual oscilloscope and set the measurement parameters. Help in

determining the time per division is available on the page Message duration and

measurement time.

Measure the voltage at the LIN slave with the oscilloscope and then change the

resistance.

Which level changes with a resistance in the LIN data cable?

From what voltage is communication no longer possible?

Voltage tolerances

You will study the voltage range within which data transmission through the LIN bus is still possible.

Connect the variable resistance additionally

into the LIN data cable.

nmlkj The Low level (dominant level)

nmlkj The High level (recessive level)

Voltage tolerances

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Drag and drop the oscillogram into the diagram!

Experiment 2:

Now connect the resistance between the LIN bus and ground and repeat the

experiment!

Which voltage value will change?

nmlkj From approx. 2 V



Evaluation

: ???

: ???

: ???

Vb : ???

Coupling: ???

nmlkj The High level (recessive level) is pulled down.

nmlkj The High level is pulled up.Think this over

before

carrying out

Voltage tolerances

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Drag and drop the oscillogram into the diagram!

Below what voltage is communication no longer possible?

nmlkj The Low level (dominant level) is pulled down.

nmlkj The Low level is pulled up.

the

experiment!

Evaluation

: ???

: ???

: ???

Vb : ???

Coupling: ???

nmlkj approx. 12 V

nmlkj approx. 9 V

nmlkj approx. 6 V

nmlkj approx. 3 V

Also measure

with the

voltmeter!

Evaluation

Voltage tolerances

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The LIN bus is conceived as a single wire bus and requires no shielding. The large

voltage rise secures the communication against electromagnetic interference (EMI)

according to the area of application and, because of the rise and fall times, also

makes the whole bus slow.

The voltage of the recessive level is almost at vehicle voltage (approx. 14 V), while

the dominant level is approx. 0 V, i.e. ground.

For stable data transfer, a maximum voltage tolerance of 20 % is permissible for the

sending control units. The recessive level must therefore be approx. 11 V, while the

dominant level may be approx. 3 V.

So that it is capable of evaluating the information without error, the receiver of the

message is designed for larger tolerances. Here, the maximum deviation from the

supply voltage may be 40 %. The recessive level must therefore be approx. 8 V and

the dominant level 5 V.

Voltage tolerances when sending and receiving


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Characteristic for the LIN bus is a combination of

� one Master control unit and

� up to 16 Slave control units.

As a rule, slave control units are connected with the master in a star or linear

configuration. Different masters can then be networked together via a CAN bus,

through which they can communicate with one another.

The master and the slaves have different tasks in the network:

The master

� controls the data transfer and the transmission speed

� mediates the communication between the slave control units and, if necessary,

translates the information to the CAN protocol (gateway)

� carries out the diagnosis for the LIN bus

� receives the wake-up signal from a slave control unit.

The slaves are intelligent sensors or actuators. They

� wait for commands and requests from the master

Topology of the LIN bus


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� synchronise themselves with the clock pulse of the master

� execute commands from the master or respond with appropriate information.


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First, set up the experiment as described at the beginning of the course!

Which topologies are used for the LIN bus?

Which topologies can be created with the enclosed circuit boards?

Does the arrangement of the control units have an influence on the function of the

data bus?


In this experiment, you will examine different configurations of the control units.

Which structure does the setup

circuit correspond with? ???

gfedc linear or bus structure

gfedc active star structure

gfedc passive star structure

gfedc ring structure

gfedc linear or bus structure

gfedc active star structure

gfedc passive star structure

gfedc ring structure

nmlkj No, the arrangement of the control units has no influence

on the function.

nmlkj Yes, the arrangement influences the function.

nmlkj The question cannot be answered in this way.

Vary the

circuit setup!


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Information on the different topologies can be found in the Appendix.

Evaluation


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The communication of the LIN takes place according to the master-slave principle,

i.e. a master control unit initiates the communication to the slaves. As a sub-bus, the

LIN is always placed below a control level, in automobiles, below the CAN bus

As in the CAN bus, identification is not location related, but content related. That

means that all control units receive the message sent and filter out the messages

intended for them.

The data are sent by the master, either time or event controlled according to a

defined procedure. An arbitration like that for the CAN bus is therefore not necessary.

The structure of a message (Frame) is defined by the LIN message format. The

message consists of

� the message header and

� the message response.

The screenshot below shows the data record "Status Window Wipers". Thanks to

a resistance in the data cable, the header from the LIN master can be clearly

distinguished from the response of the LIN slave.

The LIN protocol

The LIN protocol

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The message header is always sent by the LIN master, for only the master can start

the communication. The header is divided into four sections:

� the synch break, during which the LIN slaves prepare to receive the message

� the synch delimiter, after which the synch field begins

� the synch field, which serves to synchronise all slave control units to the clock

pulse of the LIN master control unit, and

� the identifier field, in which the content of the message is defined.

The message header

The message header

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The message content (response) is either sent by the LIN master if an instruction to

an actuator follows or by the LIN slave if the master control unit requests information

from a sensor.

The message content ends with a checksum, in which, put simply, the sum of all the

data bytes is represented. On the basis of the checksum, the message can be

checked for errors.

The message content

The message content

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The data transfer rate describes the number of data bits sent per second. It

represents a measure for the performance of a data network. You will find an

overview of bus systems frequently used in automobiles here.

At 1000 Bit/s to 20 kBit/s, the LIN bus is among the slow bus systems. In European

vehicles, a transfer rate of 19.2 kBit/s has established itself. In America, the preferred

transfer rate is 10.4 kBit/s.

On the page The LIN protocol, the individual parts of a message were described. The

parts have a length of:

Data transfer rate and message length

Message header

� Synchronisation break

� Synchronisation delimiter

� Synchronisation field

� Identifier field

Message content

Message length

at least 13 dominant Bits

at least 1 recessive Bit

Bit sequence always 0101010101, i.e. 10 Bit

8 Bits

max. 8 data fields, each consisting of10 Bits,

i.e. max. 80 Bits

approx. 120 Bit

Data transfer rate and message length

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Follow up your thoughts on a calculator, e.g. from Start/Program

Files/Accessories/Calculator

In order to set the oscilloscope, it is a good idea to make a rough estimate of the

values to be measured. Particularly important here are the measurement time or the

time per division (TIME/Div).

This time is dependent on the speed with which the voltages change, here the data

rate in bit/s.

The standard data rate of the LIN is 19.2 or 19.2 . It follows that, for the

transfer of one bit, the following time is taken:

With a message length of approx. 120 Bit, this gives a transfer time of 6.2 .

In the case of a split of the complete message into 10 divisions, a time of 500 µs

should therefore be selected.

Now go back to the page Communication of control units and set the oscilloscope

according to your own deliberations.

Message duration and measurement time

You will determine the duration of a message, in order to set the

oscilloscope.

The experiment on this page is more of a mental experiment.

Message duration and measurement time

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As only the voltage curves can be displayed in the oscillograms, while the individual

bits and, therefore, the messages themselves are hard to analyse, the

mechatronician is provided with special tools. Such an LIN Analyser is

already integrated in this UniTrain course as the LIN Monitor and is available to you in

the menu "Instruments".

The data are displayed, as usual, not as bits, but in hexadecimal notation.

Hexadecimal coding is not dealt with in this course. It has already been described in

detail in the courses "The CAN bus" and "Optical data buses in the vehicle".

Data analysis

Data analysis

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Use the standard experimental setup and open the LIN Monitor.

Switch the monitor on and, under "Display", select the function "collect". The

protocols sent are displayed and counted.

Experiment 1: Analysis of messages

Now operate the window winder in both directions.

Which identifier has the window winder?

Assign the functions to the corresponding data fields!

Assign other identifiers to their corresponding functions.

Analysis and sending of messages

nmlkj 0F

nmlkj 1F

nmlkj 31

Watch the LIN

Monitor.

Window winder switch not pressed ???

Raise window ???

Lower window ???

Mirror heating ???

Central locking ???

Flasger switch ???

Mirror adjustment ???


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Experiment 2: Sending of messages

After you have analysed the data with regard to their identifier and the message

content, you can create your own messages according to the recognised pattern with

the LIN Monitor and start the functions from your PC.

As opposed to the CAN bus, however, you do not access the LIN bus directly (see

Security against manipulation), but get the LIN master to transmit the message.

Open the LIN Monitor and then the "Send" window in the field "Command" and test

what you have learnt!

Evaluation

Important: In the window "Options", both "Status Window Winder" and

"Subscriber-check Mirror" must be switched off!


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Name the sections of the LIN protocol!

In the LIN protocol, a distinction is made between two kinds of message. Assign

the correct names to the functions!

Knowledge test

Synch break ???

Synch delimiter ???

Synchronisation field ???

Identifier field ???

Data field ???

Message header ???

Message content (Response) ???

In the header, the LIN

master control unit

requests a LIN slave

Knowledge test

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Assign the corresponding messages to the statements!

control unit to send

information, e.g.

measured values ???

Through the identifier, the

LIN master requests a LIN

slave control unit to

execute an action, e.g.

Mirror heating ON

???

Vom LIN-Slave wird The response (message

content) is appended by the LIN slave to the header

from the LIN master . ???

The LIN master sends the response. ???

Evaluation

Knowledge test

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The output stage of the LIN Transceiver consists of a diode, a resistance and a

transistor.

The LIN control units are connected together via three cables:

� the power supply in the range from approx. 9 V to 15 V,

� the data cable and

� the ground.

Rx stands for Receive data and Tx for Transmit data and the term "Transceiver" is

formed from both words/tasks.

The function:

The circuit between USupply and ground is supplied with the required

voltage. The resistance serves as a load resistance, preventing high currents.

The diode prevents a current from the LIN bus into the supply network in the case of

a low supply voltage to a LIN module.

When no control unit is sending, i.e. all sender transistors are blocked, the voltage on

the LIN bus is practically the supply voltage. The voltage is somewhat lower as a

result of a slight voltage drop over the diode and the load resistance.

If a control unit is sending, there is a voltage on the base of the sender transistor.

This becomes conductive and pulls the bus potential almost to ground potential. Only

the voltage drop over the transistor remains.

Generation of signals


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The High level is recessive because it is only reached when the sender transistors of

all LIN nodes are blocked.

The Low level is dominant because a sending LIN module pulls down the whole bus

level.


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Verification of the data transfer is carried out by the LIN master simultaneously with

the transmission. The data sent via the cable "Tx" are simultaneously received via the

cable "Rx" and read (see Generation of signals).

In a defined routine, the LIN master checks the individual sections of its transmission

and continues when no error is detected. On the other hand, if the LIN master detects

an error in the transfer, it starts the data transmission again.

Verifying the data transfer


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In this way, the LIN master is in a position to detect bit transmission errors or

hardware faults (e.g. bus-ground short circuit). The LIN master assumes, however,

that everyone can understand the data transmission if it understands it itself. If no

communication takes place between LIN master and LIN slave, the LIN master also

repeats the transmission of its message (interrogation).

If the problem persists in spite of multiple transmission attempts, the LIN master

makes an entry in the error memory, which can be read out over the CAN bus.


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The question arises, especially for the door module described in this course, of how

to prevent access being gained to the LIN bus through the exterior mirror and the

vehicle being opened.

In contrast with the CAN bus, in which each bus sharing unit is a master, so can send

data at any time, the master has sole responsibility for data transmission in the LIN

bus. It has sole responsibility for communication and the LIN slaves may

only respond if the LIN master sends a corresponding message header. A

new control unit in the LIN cluster must be registered with the LIN master and added

to the message table.

So ithe is possible to fit LIN slaves in or outside the vehicle body shell without its

being possible to open the doors without authorisation by means of a LIN instruction.

The control units of the CAN bus are always located inside the vehicle.

LIN slaves outside the vehicle may, for example, be:

� exterior mirrors

� temperature sensors

� transmitters for garage openers

� receivers for remote controls

� parking aid sensors

� ...

Security against manipulation

Security against manipulation

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The diagnosis of the LIN bus takes place via the CAN interface of the diagnostics

plug. Errors within the LIN cluster can be stored in the master control unit and read

out via the CAN bus. LIN slaves do not possess an error memory of their own. Direct

access to the LIN bus is not possible.

If, in the course of verifying the data transfer, an error is detected, the LIN master

makes an entry in the error memory which can be read out via the CAN bus. This

includes the location of the error and an error text.

Error diagnosis in the LIN bus

Error location Error text Reason for error entry

LIN slave control

unit

e.g. exterior

mirror

no signal/ no

communication

Failure of data transfer from LIN slave control

unit over a period defined in the LIN master

software due to

- cable break or short circuit

- defective power supply to the LIN slave

control unit

- incorrect part variant LIN slave or LIN master

- defect in the LIN slave control unit

LIN slave control

unit

e.g. exterior

mirror

implausible signal

Error in checksum due to incomplete transfer

of messages.

- electromagnetic interference on the LIN

cable

- capacity and resistance change on the LIN

cable (e.g. moisture/dirt on plug casing)

- software problem (incorrect part variants)

Error diagnosis in the LIN bus

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The nature and manner of the error entry is not standardised and it can naturally only

refer to errors which are already known. Errors which the software developers have

not thought of cannot, of course, be listed in the error memory.

For this reason, the mechatronician needs comprehensive knowledge

of the system, which is to be be acquired in the following tasks.

As the LIN bus is a voltage coded bus, the familiar measuring instruments

� voltmeter

� oscilloscope

are available to the mechatronician for error diagnosis. For the experiments, the

virtual instruments of this system or alternative generally available external measuring

instruments can be used.

In the following experiments, you should use both instruments and evaluate the

results with regard to the diagnosis.

Note that, naturally, it is not only the data transfer that can be disturbed, but also

the function of the sensors/switches and actuators!

Error analysis

Error analysis

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How are the load resistances of the transceiver checked?

Help on: Load resistances of the transceiver

If you have had difficulty in answering the questions, please work again through the

pages Communication of control units and Voltage tolerances.

Diagnosis

A contact resistance in the LIN

data cable can be recognised

from ???

A short circuit over a resistance

from the LIN data cable to plus

can be recognised from ???

A short circuit over a resistance

from the LIN data cable to

minus can be recognised from ???

nmlkj Resistance measurement with Ohmmeter.

nmlkj Voltage measurement with Voltmeter.

nmlkj Current measurement with Ammeter.

Evaluation

Diagnosis

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Bauen Sie zunächst den LIN-Cluster vollständig, wie unter Versuchsaufbau

beschrieben, auf.

Beim Aufruf der entsprechenden Seite werden automatisch Fehler in den LIN-Cluster

geschaltet. Ihre Aufgabe ist es, die Fehler soweit wie möglich einzugrenzen und die

Fehlerquelle zu beschreiben. Begründen Sie Ihre Wahl und beschreiben Sie

Reparaturmöglichkeiten.

Das System lässt eine Fehlerbehebung nicht zu, da die Fehler durch das

Experimentiersystem geschaltet werden!

Versuchsdurchführung

In den folgenden Experimenten werden Sie Fehler in dem LIN-Cluster suchen und eine Systematik zur Eingrenzung des Fehlers entwickeln.


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Beachten Sie, dass Sie Fehler in einem komplexen System finden sollen. Dazu ist es hilfreich, das System in Subsysteme zu unterteilen und diese Subsystem zu überprüfen.

Machen Sie sich deutlich, wie eine Aktion (z.B. Außenspiegel heizen), ausgelöst wird.

1. Schaltersignal wird an LIN-Master gesendet. 2. LIN-Master übersetzt das Signal in die LIN-Botschaft. 3. Die LIN-Botschaft wird zu LIN-Slave gesendet. 4. Der LIN-Slave übersetzt die Botschaft in eine Schaltfunktion. 5. Die Aktion wird ausgeführt.

Im Folgenden gilt es, zu überprüfen, ob die einzelnen Schritte ausgeführt werden. Da man an verschiedene Messpunkte nicht direkt herankommt (z.B. Übersetzen des Signals in eine Botschaft), ist es wichtig die übrigen Fehlerquellen auszuschließen.

Sie werden also nicht nur direkt eine Fehlerquelle erkennen, sondern ebenso durch ein Ausschlussverfahren ein fehlerhaftes Bauteil isolieren.

Dabei ist es Ihre Aufgabe eine Systematik zu entwickeln. Es gibt viele verschiedene Wege, die zum Ziel führen. Diskutieren Sie Ihren Weg mit dem Ihrer Kollegen.

Tipps zur Fehlersuche

Tipps zur Fehlersuche

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Fehlerbeschreibung

Sie stellen fest, dass sich der Fensterheber nicht mehr ansteuern lässt.


1. Lesen Sie zuerst die Beschreibung der Versuchsdurchführung

aufmerksam durch.

2. Nutzen Sie alle erforderlichen Instrumente und Mittel, um die

Fehlerursache zu finden. Bei Bedarf beachten Sie die Tipps zu

Fehlersuche.

3. Halten Sie alle relevanten Daten in der Versuchsauswertung fest.

4. Benennen Sie die Fehlerursache stichpunktartig in der

Versuchsauswertung. Nennen Sie auch Gründe für ihre

Entscheidung.

5. Sollten Sie zu keinem Ergebnis kommen, nutzen Sie die Hilfe.

Versuchsauswertung

Fehlerursache und Reparaturvorschlag:

Halten Sie folgende Punkte fest:

- Ihre Beobachtungen

- Ihre Messwerte und Schlussfolgerungen

- Ihr Ergebnis mit Reparaturvorschlag

Fehlersuche 3

Fehlersuche 3

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Fehlerbeschreibung

Sie stellen fest, dass sich der Fensterheber nicht mehr ansteuern lässt.



aufmerksam durch.



Fehlersuche.




Entscheidung.

5. Sollten Sie zu keinem Ergebnis kommen, nutzen Sie die Hilfe.

Versuchsauswertung






Fehlersuche 4

Fehlersuche 4

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Fehlerbeschreibung

Sie stellen fest, dass sich der Außenspiegel nicht mehr verstellen lässt.



aufmerksam durch.



Fehlersuche.




Entscheidung.

Versuchsauswertung






Fehlersuche 5

Fehlersuche 5

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Fehlerbeschreibung

Sie stellen fest, dass die Zentralverriegelung nicht funktioniert.



aufmerksam durch.



Fehlersuche.




Entscheidung.

Versuchsauswertung






Fehlersuche 6

Fehlersuche 6

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Ein LIN-Cluster verbindet speziell intelligente Sensoren und Aktoren zu einem

Subsystem. LIN-Cluster werden in übergeordneten Datenbussen (z.B. einem CAN-

Bus) verbunden.

� Low-Cost-Bussystem für einfache Sensor-Aktor-Anwendungen mit

bidirektionaler Ein-Draht-Leitung (wie k-Line)

� Maximal 16 Busteilnehmer, wegen begrenzter Anzahl von Botschafts-Identifiern

� Buslänge aus elektrischen Gründen maximal 40 m

� Ein Master-Steuergerät sendet periodisch Botschaftsheader; genau eines der

anderen (Slave-)Steuergeräte führt eine Anweisung aus oder antwortet mit

max. 8 Datenbytes

� Senden aller Botschaften periodisch in einem festen Zeitraster mit

unterschiedlichen Wiederholperioden. Das Senderaster ist im Master als

Botschaftstabelle (schedule table) statisch konfiguriert. Es sind

unterschiedliche Botschaftstabellen für verschiedene Betriebszustände möglich

� Der Inhalt der Botschaft wird durch den Identifier kenntlich gemacht; der

Empfänger erkennt die Relevanz anhand des Identifiers (inhaltsbezogene

Adressierung)

� Anforderungen an die Bittakt-Genauigkeit und Protokoll-Timing sind gering. Die

Slaves haben keinen eigenen Quarz, sie passen sich dem Mastertakt an

(Synchronisation im Botschaftsheader)

� Einfache Fehlerüberwachung durch Rücklesen der Bussignale und der

Prüfsumme. Die Fehlerbehandlung ist hersteller- und anwenderabhängig und

damit nicht einheitlich festgelegt

� Das Mastersteuergerät des LIN-Clusters ist Gateway zu anderen Bus-

Systemen im Fahrzeug, z.B. CAN-Bus

Zusammenfassung

Zusammenfassung

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You will find supplementary information and hints for the experiments. Follow the

links in the course.

Appendix

Anhang

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Copyright © 2008 LUCAS-NÜLLE GmbH.

This course "Automotive Engineering 5: LIN bus" is protected by copyright. All rights pertaining thereto are reserved. Any reproduction of the document as a file or in written form be it photocopy, microfilm or any other method or conversion into a machine-compatible language, in particular for data processing systems, without the expressed written approval of the LUCAS-NÜLLE GmbH is strictly forbidden.

The software as described above is made available on the basis of a general licensing agreement or in the form of a single license. The use or reproduction of the software is only permitted in strict compliance with the contractual terms stated therein.

If changes have been performed in a manner which was not strictly authorised by the LUCAS-NÜLLE GmbH, any product liability or warranty claims pertaining thereto are null and void.

Copyright © 2002-2008 LUCAS-NÜLLE GmbH

Congratulations! This is the last page. You have completed the course "Automotive Engineering 5: LIN bus".

Copyright

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automotive engineering 5 lin bus

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