Tecnologie Informatiche ed Elettroniche per le Produzioni

Animali(corso TIE)

CORSO LAUREA MAGISTRALE IN SCIENZE E TECNOLOGIE DELLA PRODUZIONE ANIMALE

Massimo LazzariScienze veterinarie per la salute, 

la produzione animale e la sicurezza alimentare - VESPAUniversità degli Studi di Milano

Rete CAN-ISOBUS sulle macchine

Massimo LazzariScienze veterinarie per la salute, 

la produzione animale e la sicurezza alimentare - VESPAUniversità degli Studi di Milano

CORSO LAUREA MAGISTRALE IN SCIENZE E TECNOLOGIE DELLA PRODUZIONE ANIMALE

TIE per le Produzioni Animali

DEFINIZIONI

DEFINIZIONI

DEFINIZIONI

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COMPONENTI DI UN MODERNO TRATTORE

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COLLEGAMENTO IN RETE A STELLA

COMPONENTI DI UN MODERNO TRATTORE

COLLEGAMENTO CON BUS DI RETE

COMPONENTI CAN-ISOBUS

Each module is a separate computer, all working together (CAN Working Set) through a communication Bus, which transfers information from one module to the others.

VTTask ControllerMgt. Computer

Gateway GPS

Hitch

Implement BridgeImplement ECU and

ImplementECU

ImplementECU

Transmission

TractorECU

Engine

Implement Bus

Tractor Bus

CONTROLLER AREA NETWORK (CAN)

There were two major development paths for CAN communication standards:

1. LBS/DIN in Europe and

2. SAE J1939 in North America.

A joint standard was a dream.

LBS/DIN evolved around using a common user interface, UI (Virtual Terminal)

SAE J1939 evolved around controlling engines and transmissions.

Both used common electronic hardware developed by Robert Bosch, GmbH.

ISOBUS ISO 11783

ISO 11783 an International Electronics Communications Standard for CAN Bus

communications in Agriculture and Forestry applications. An OPEN Standard.

ISO 11783 merges J1939 and (LBS)DIN 9684 resulting in a common CAN protocol standard.

ISO 11783

SAE J1939

CAN 2.0b (29 bit)

(LBS)

CAN 2.0a (11 bit)

DIN 9684

ISOBUS ISO 11783

Implement Control Screen is shown on the Tractor Virtual Terminal when chosen by the Operator.

Graphics displayed on the Virtual Terminal are defined by the Implement Control Module.

Operator uses soft keys or touch screen to manipulate the implement.

VIRTUAL TERMINAL

VIRTUAL TERMINAL

COLLEGAMENTO AI SOFTWARE GESTIONALI

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Let’s simulate a Vehicle Network…

Rule: Only transmit your message when nobody else is transmitting

You are an OIL TEMPERATURE SENSOR/TRANSMITTER Your identifier ID = 100 Your task If you hear REQUEST ID 100

Say ID 100, 82.0 (you may choose other temperatures, make sure to write them down)

COLLEGAMENTO AI SOFTWARE GESTIONALI

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Here is our communication protocol

ID Function Messages Meaning 0 Heart rate monitor X, Int X = heart rate in bpm 1 Collision detector X, binary 0 = ok, 1 = Collision detected 2 Seatbelt tensioner X, binary 0 = ok, 1 = Tension seatbelt 3 Airbag controller X, binary 0 = ok, 1 = Activate airbag 100 Oil temp sensor X, Float X = Engine oil temperature in deg Celsius 101 Humidity sensor X, Int X = Relative Air humidity % 102 GPS Receiver X,Y, float Latitude, 8 chars Longitude, 8 chars 1000 Satellite transmitter X, float 1001 Satellite Relay unit X, float Relays x from 1000 (car) to 1002 (hospital) 1002 Ambulance A, X,Y 0=Stationary, 1 = Drive to X,Y (GPS coord).

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Controller Area Network• A broadcast, differential serial bus standard, originally developed in the 1980s by Robert Bosch GmbH,

for connecting electronic control units (ECUs) in vehicles. • Very robust• Two wire bus• Messages are short (8 data bytes max) • Priority based arbitration used for Collision Avoidance• Bit stuffing for synchronization: if 5 equal bits, the following one is opposite polarity• Error detection mechanism through Cyclic Redundancy Check (CRC)• Bit rates up to 1 Mbit/s• The CAN data link layer protocol is standardized in ISO 11898-1 (2003). All the other protocol layers are

left to the network designer's choice.• ISO 11783 (ISOBUS) is the agricultural network protocol

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Controller Area Network cont.• 4 ms per bit = 250 bit/s (Required for ISOBUS standard)• Data Length Code (DLC) contains nr of data bytes• If RTR bit is high,

– no data bytes, DLC = # bytes requested• 11-bit (CAN 2.0a) and 29 bit (CAN 2.0b) ID messages on same bus• IDE (Identifier Extension bit) distinguishes between 11 and 29 bit frames

1

0

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CAN Frames Standard (a) & Extended (b)

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Demo time

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Transmitter

Receiver

Analog Inputs

CAN bus

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CAN 2.0b Request Transmission Frame

Mark the bits in your handout (3 min)

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Answer

01010101 01011110 10101010 00001001 11000100 00010101 00001000 10111111 1

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Step 1 Get rid of the stuffing bits

• Stuffing bits are put in to ensure synchronization

• If you see 5 consecutive zeros or ones, the next one is a stuffing bit

• Throw it out!

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De-stuffing the CAN Frame

0101010101011110101010100000 1 00111000100000 1 0101000010001011111111

0101010101011110101010100000001110001000000101000010001011111111

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Chop the Frame up into pieces

0 Start of Frame

XXXXXXXXXXX 11- bit Standard IdentifierX Substitute Remote Request BitX Identifier Extension Bit (1 = Extended Frame)

XXXXXXXXXXXXXXXXXX 18 Bit Extended Identifier

X RTR Bit (1 = Request Transmission)XX ReservedXXXX Data Length Code (Nr of bytes that follows)

XXXXXXXX Data Byte 1XXXXXXXX Data Byte 2XXXXXXXX Data Byte 3XXXXXXXX Data Byte 4

XXXXXXXXXXXXXXX Cyclic Redundancy Check (CRC) (15 bits)1 CRC delimiter

X Acknowledge slot bit 1 Acknowledge delimiter

1111111 End of frame (7 ones)

0101010101011110101010100000001110001000000101000010001011111111

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Interpret the CAN Frame

0 Start of Frame

10101010 101 11- bit Standard Identifier1 Substitute Remote Request Bit1 Identifier Extension Bit (1 = Extended Frame)

10 10101010 00000011 18 Bit Extended Identifier

1 RTR Bit (1 = Remote Transmission Request)00 Reserved0100 Data Length Code (Nr of bytes requested)

XXXXXXXX Data Byte 1XXXXXXXX Data Byte 2XXXXXXXX Data Byte 3XXXXXXXX Data Byte 4

000010100001000 Cyclic Redundancy Check (CRC) (15 bits)1 CRC delimiter

0 Acknowledge slot bit 1 Acknowledge delimiter

1111111 End of frame (7 ones)

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A word on error detection

• Cyclic Redundancy Check– Transmitter computes Transmitter checksum

based on data– Receiver receives both data and Transmitter

check sum– Receiver computes Receiver checksum based

on data– If Transmitter checksum == Receiver checksum

• Data is valid with very high probability

– P(Error unnoticed) = 4.7 *10-11

Transmitter Receiver

Message

Algorithm

Checksum Transmitter

Message

Algorithm

Checksum Receiver

Checksum Transmitter

Compare

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Message arbitration is used to resolve conflicts due to collisions: most important message must go through

• If more than one message is being transmitted simultaneously a collision occurs

• Bit-by-bit arbitration process: If a node has a lower (dominant) bit it wins arbitration, the others lose and shut down

• At (2) Node 2 loses arbitration and shuts down. At (3) Node 1 loses arbitration and shuts down. Node 3 (lowest number, highest priority) goes through

AND Function

0 0 0 0

0 0 1 0

0 1 0 0

0 1 1 0

1 0 0 0

1 0 1 0

1 1 0 0

1 1 1 1

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What is a protocol ?• Give some examples of protocols among humans•

– Communication pilot-tower– Meetings (Roberts Rules of Order)– Rules of games– Etiquette rules– Unwritten rules (job interview)

• Some Network protocols– TCP (Transmission Control Protocol) – IP (Internet Protocol) – DHCP (Dynamic Host Configuration Protocol) – HTTP (Hypertext Transfer Protocol) – FTP (File Transfer Protocol) – POP3 (Post Office Protocol 3) – SMTP (Simple Mail Transfer Protocol) – IMAP (Internet Message Access Protocol) – ISO 11783 (ISOBUS)

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You are sending a mining truck overseas• Sender

– Split up the truck in smaller parts– Add routing information– Add additional packing information– Add reassemble information– Send “packages sent” message to receiver– Deliver packages to UPS

• Receiver– Receive messages from UPS– Wait until all packages have come in– Check if you have everything– Reassemble the truck– Send acknowledge message to sender

• This transmission process requires a protocol• UPS = ISO 11898 CAN physical layer

– We don’t care how it does it– We want it reliable– We want it fast

• ISO 11783 (ISOBUS) is the protocol

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CAN in Agriculture

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Virtual terminal in John Deere tractor

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Summary• Why do we need a Vehicle network?

Improved control of engine performance and emissionsImproved comfortAutomated diagnostics (OnStar)Improved safety

• Controller Area Network– Communication network for vehicles and other noisy environments– Error handling

• Bit stuffing• CRC

– Frames• 11bit (2.0a) and 29 bit • Prioritization using arbitration mechanism

• Protocols, rules of communication– ISO 11898 (CAN Physical layer)– ISO 11783 (ISOBUS communication)

• Link: http://www.can-cia.org/

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The End