PP Data Bus Systems

8/12/2019 PP Data Bus Systems

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Data Bus Systems


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Data transfer

What are the possible options for data transfer in vehicles at present?Option No. 1:

Each item of information is exchanged over

a separate wire.

Option No. 2:

All information is exchanged between

control units along a maximum of twowires: the CAN data bus. The figure below shows you option No. 1,

where each item of information is transferred

along a separate wire.

A total of five wires are required for data

transfer in this case.


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The same data is transferred along the two

bidirectional wires of the CAN data bus.


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The CAN data busis a type of data transfer between control units. It links the individual control units to

form an integrated system.

The more information a control unit has regarding the state of the overall system, thebetter it can co-ordinate the individual functions.

The following components in the drive trainform an integrated system:

the engine control unit,

the automatic gearbox control unit and

the ABS control unit

The following components in the

convenience

system form an integrated

system:

the central control unit

and

the door control

units


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Benefits of the data bus:

If the data protocol is extended to include additional information, onlysoftware modifications are necessary.

Low error rate through continuous verification of the transmitted

information by the control units as well as additional safeguards in the

data protocols.

Fewer sensors and signal lines through the multiple use of a sensor

signal.

High-speed data transfer is possible between control units.

More space available through smaller control units and smaller controlunit

plugs.

The CAN data bus conforms tointernational standards and therefore

facilitates data interchange between different makes of control unit


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The principle of data transfer

A subscriber (control unit) speaks

data into the line network while theother subscriberslisten in to this

data.

Some subscribers will be interested

in this data and will utilise it.

The other subscribers will choose to

ignore this data.


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The CAN transceiver

is a transmitter and receiver in one. It converts the data which the CAN controller

supplies into electrical signals and sends this data over the data bus lines.

Likewise, it receives data and converts this data for the CAN controller.

The data bus terminal

is a resistor. It prevents data sent from being reflected at the ends and returning as an

echo. This would corrupt the data.

The data bus lines

are bidirectional and transfer

the data. They are referred to

as CAN High and CAN Low.


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Data transfer process:


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What does the CAN data bus transfer?

The data protocol:


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How is a data protocol produced?

Status of the light

switch

with the value 1

Switch closed

Lamp on

Status of the light switch

with the value 0

Switch opened

Lamp is not on


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Explanatory notes:

If bits 1 and 2 are transmitted with 0 Volts, the information in the table Electric

windows now in motion or Coolant temperature is 10C.


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CAN data bus allocation

If more than one control unit wants to send its data protocol simultaneously, the system

must decide which control unit comes first. The data protocol with the highest priority is

sent first.

For safety reasons, the data protocol supplied by the ABS/EDL control unit for safetyreasons is more important than the data protocol supplied by the automatic gearbox

control unit (driving comfort).

The priorities of three different data protocols are shown in the table below.


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Example


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Crankshaft sensor

Electronique

Contrle Moteur

1010 1100 0100 1010

Engine speed value

Motronic ECU

Distribution of InformationsExample Peugeot


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1010 1100 0100 1010

Engine speed value

Motronic ECU

Distribution of Informations


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ESP ECU

Motronic

ECU


1010 1100 0100 1010

Engine speed value


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Multiplexbus

Motronic ECU

ESP ECU

1010 1100 0100 1010

Engine speed value



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Multiplexbus

INTERFACE

INTERFACE

Motronic ECU

ESP ECU


1010 1100 0100 1010

Engine speed value


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1010 1100 0100 1010

INTERFACE

INTERFACE

Motronic ECU

ESP ECU


1010 1100 0100 1010

Engine speed value

Multiplexbus


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Wheel sensor

0100 1111 0101 0011

1010 1100 0100 1010

Wheel speed value

0100 1111 0101 0011

INTERFACE

INTERFACE

Motronic ECU

ESP ECU

ABS


1010 1100 0100 1010

Engine speed value

Multiplexbus


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0100 1111 0101 0011

1010 1100 0100 1010

INTERFACE

INTERFACEINTERFACE

1010 1100 0100 1010

Motronic

ECU

ESP ECUTransmission

ECU


1010 1100 0100 1010

Engine speed value

0100 1111 0101 0011

Multiplexbus

Wheel speed value


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0100 1111 0101 0011

1010 1100 0100 1010

INTERFACE

INTERFACEINTERFACE

INTERFACE

Central ECU

0100 1111 0101 0011

1010 1100 0100 1010

1010 1100 0100 1010

Motronic ECU

ESP ECUTransmission

ECU


1010 1100 0100 1010

Engine speed value

0100 1111 0101 0011

Multiplexbus

Wheel speed value


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0100 1111 0101 0011

1010 1100 0100 1010

INTERFACE

INTERFACEINTERFACE

INTERFACE

1010 1100 0100 1010

INTERFACE

Motronic

ECU

ESP ECUTransmission

ECU

Central ECU / Gateway


1010 1100 0100 1010

Engine speed value

0100 1111 0101 0011

Multiplexbus

Wheel speed value

0100 1111 0101 0011

1010 1100 0100 1010


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0100 1111 0101 0011

1010 1100 0100 1010

INTERFACE

INTERFACEINTERFACE

INTERFACE

1010 1100 0100 1010

INTERFACE

Motronic ECU

ESP ECU Multiplexbus 2

Transmission

ECU



1010 1100 0100 1010

Engine speed value

0100 1111 0101 0011

Multiplexbus 1

Wheel speed value

0100 1111 0101 0011

1010 1100 0100 1010

INTERFACE


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0100 1111 0101 0011

1010 1100 0100 1010

INTERFACE

INTERFACEINTERFACE

INTERFACE

1010 1100 0100 1010

INTERFACE

Motronic

ECU

ESP ECU

INTERFACE

Instrument Cluster

Multiplexbus 2

Transmission

ECU



1010 1100 0100 1010

Engine speed value

0100 1111 0101 0011

Multiplexbus 1

Wheel speed value

0100 1111 0101 0011

1010 1100 0100 1010


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0100 1111 0101 0011

1010 1100 0100 1010

INTERFACE

INTERFACEINTERFACE

INTERFACE

1010 1100 0100 1010

INTERFACE

Motronic ECU

ESP ECU

0100 1111 0101 0011

1010 1100 0100 1010

INTERFACE

Instrument

Cluster

Transmission

ECU



1010 1100 0100 1010

Engine speed value

0100 1111 0101 0011

Multiplexbus 1

Wheel speed value

0100 1111 0101 0011

1010 1100 0100 1010

Multiplexbus 2


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0100 1111 0101 0011

1010 1100 0100 1010

INTERFACE

INTERFACEINTERFACE

INTERFACE

1010 1100 0100 1010

Motronic ECU

ESP ECU

INTERFACE

0100 1111 0101 0011

1010 1100 0100 1010

INTERFACE

Instrument

Cluster

INTERFACE

Transmission

ECU



1010 1100 0100 1010

Engine speed value

0100 1111 0101 0011

Multiplexbus 1

Wheel speed value

0100 1111 0101 0011

1010 1100 0100 1010

Multiplexbus 2


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0100 1111 0101 0011

1010 1100 0100 1010

Motronic ECU

INTERFACE

INTERFACEINTERFACE

INTERFACE

1010 1100 0100 1010

ESP ECU

INTERFACE

0100 1111 0101 0011

1010 1100 0100 1010

INTERFACE

Instrument

Cluster

INTERFACE

INTERFACEMultiplexbus 3

Transmission

ECU



1010 1100 0100 1010

Engine speed value

0100 1111 0101 0011

Multiplexbus 1

Wheel speed value

0100 1111 0101 0011

1010 1100 0100 1010

Multiplexbus 2

Gateway function


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MultiplexbersichtABS / ESP Motronic ECUSteering wheel

sensorTransmission Others

4 5 H3 H4 4 64 66 853 82

Radio

Phone

Instrument cluster

Aircondition

CD-Changer

Park system

Multi function

Display

Navigation

2

4

3

6

9

3

1

1/2

9

1

8

7

14

1

5

26

25

13

18

7

4

19

24

20

Airbag

Autom. Switch on

Headlights

Central

ECU

Diesel-Additiv

44 54

ECU

Drivers door

3 20

ECU passengers

door

20 3

Drivers seat

memory

C5 A5A7

7

5

3

33

30

373 1

21

23

31

10

8

33

4 6 15 17 9

16

1

3

14

5

6V NR

21213

Gateway function

Voltage of an high speed CAN


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Voltage

time

Voltage of an high speed CAN

2,5 V

2,5 V

3,5 V

1,5 V


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V lt f l d CAN


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Voltage of a low speed CAN

Voltage

time

1,75 V

3,25 V

0,5 V

4,5 V


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The

start field

marks the start of the data protocol. A bit with approx. 5 Volts (depending on system) issent over the CAN High Line and a bit with approx. 0 Volts is sent over the CAN Low

Line.


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The status field

defines the level of priority of the data protocol. If, for instance, two control units want to

send their data protocol simultaneously, the control unit with the higher priority takes

precedence.


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The check field

displays the number of items of information contained in the data field. This field allows

any receiver to check whether it has received all the information transferred to it.


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In the Data field

information is transferred to the other control units.


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In the confirmation

field

the receivers signal to the transmitter that they have correctly received the data protocol.

If an error is detected, the receivers notify the transmitter of this immediately. The

transmitter then sends the data protocol again.


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The end field

marks the end of the data protocol. This is the last possibility to indicate errors which

lead to a repeat transfer.

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