In-Vehicle Networking

January 9, 2008 BAE 5030-363

In-Vehicle Networking

Lecture 1 Introduction to CAN (Controller Area Network) BAE 5030 – 363

Spring 2009Instructors: Marvin Stone

Biosystems and Agricultural EngineeringOklahoma State University

January 9, 2008 BAE 5030-363

Automotive Body Network

CAN

CAN

Power Train

Light

Sub-Bus

ITS

Window Lift

InteriorLight

Lock

Mirror

Lock

Mirror

Lock

Lock

Seat

Htng

Seat

Htng

Instruments

CentralBody Ctrl

Climate

Universal Motor

Universal Panel

Light

Roof

1 backbone, 13 nodes8 subnets, 1-8 local nodes52 nodes total

St-Wheel Panel

x6Htng

Htng

Seat

Wiper

Trunk

WHtg

Universal Light

January 9, 2008 BAE 5030-363

Hierarchical networks are here today

VW Phaeton• Electrical parts: 11,136• Communication: 61 ECUs in total• External diagnosis: 31 ECUs via serial communication• Optical bus for high bandwidth Infotainment-data • sub-networks based on proprietary serial bus• 35 ECUs connected by • 3 CAN-busses• sharing approximately 2500 signals• in 250 CAN messages

CAN applications are broad

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• 63 ECUs• 33 CAN nodes• 2 250 k CAN Networks

Ntech RT500 Fertilizer Applicator

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J1850pier to pier

prioritized messages

Costs and Speeds for Automotive NetworksSp

eed

[bit

/s]

LINmaster-slave

single wire busno quartz

CAN-Bevent triggeredfault tolerantdual wire

25.6M

20K

2M

1M

125K

incremental cost per node [$]1 2 4.5 10

ISO 11783CAN-Cevent triggeredQuad wire

Byteflightoptical bus

TTx (in definition)

time triggeredfault tol, dependable2x2 wire

D2B, MOSTtoken ringoptical bus

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What is CAN?

– CAN = Controller Area Network• Serial data communications protocol for real-time application

using a multiple access bus– Messages have assignable priority

» most critical can dominate during heavy load– Messages are short (controlled length)

» opportunities to insert a new message come often

– CAN provides multiplexed serial communications– Reduction in wiring complexity– Better information sharing– All communications share the same communication path

– Low probability of an undetected error• 4.7 x 10-11 x message error rate

– For a message error rate of 25/sec: 1 undetected error per 10,000 hours operation

January 9, 2008 BAE 5030-363

An overview of CAN based networking

• Elements of the CAN protocol– Message components

• Identifier / Data

– Bus Access - Arbitration / Prioritization• CSMA/CR (carrier sense multiple access / collision resolution

– Bitwize priority access strategy– Non-destructive collisions

– Error Detection / Error Confinement– Filtering– Other features

• In Frame Acknowledgement

• RTR

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Capacity Comparison

Capacity (bits/sec.)

1.00E+00

1.00E+02

1.00E+04

1.00E+06

1.00E+08

V.90 Modem J1939 / ISO11783

Ethernet10base2

Loga

rithm

ic D

ata

Rat

e (b

aud)

56K250K

10,000K

January 9, 2008 BAE 5030-363

Capacity and Performance (Based on 250 KBaud)

• Use of bus bandwidth by messages– 100 messages per second (10 ms repetition) =5%

• Torque/Speed control on engine

• Hitch control

– 10 messages per second (100 ms repetition) =0.5%• Throttle position

• GPS Lat/Lon data

• Implement application rate control (process data)

– 1 message per second (1s repetition) =0.05%• Display updates

• System status

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Message latency (Based on 250 KBaud)

• 134 bit message– @ 4s per bit = 536s = 0.5 ms per message max

• Highest priority message– must wait no more than ~0.5 ms

• Low priority messages– must wait till higher priority messages clear– latency may be long at high bus loads

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Harness Hell!

January 9, 2008 BAE 5030-363

Conventional Wiring (No Bus)

DataLogging

SensorsECUs

GPS

NozzlesNOZZLE

ECU

SerialCommunicationLinks

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A Simple CAN Application (Serial Bus)

DataLogging

SensorsECUs

GPS

NozzlesNOZZLE

ECU

Data B

us

Dat

a B

us

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Multiplexed communication

EngineController

ECU 1

TransmissionController

ECU 2

DashboardController

ECU 3

Shared Communications Bus

BusTerminator

BusTerminator

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Typical ECU Components

Micro-ControllerCAN

ProtocolController

CANBus

Driver

Memory InterfaceI/O

PowerConditioning

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ECU Connection to the bus

Micro-ControllerCAN

ProtocolController

CANBus

Driver

Memory InterfaceI/O

PowerConditioning

Micro-ControllerCAN

ProtocolController

CANBus

Driver

Memory InterfaceI/O

PowerConditioning

ECU 1 ECU 2

CAN_HCAN_LTerminator Terminator

CAN_H

CAN_L

CAN_H

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CAN - continued• Developed by Bosch GmBh

(See http://www.semiconductors.bosch.de/pdf/can2spec.pdf)

– About 1986, Version 2.0 in 1991 for auto apps.• Version 1.2 (Equivalent to 2.0A)

– 11 bit ID (not interoperable with 29 bit 2.0b)

• Version 2.0 (2.0A + 2.0B)– 2.0B - 11 and 29 bit ID

» 11 and 29 are compatible on same bus» 11 bit only 2.0B is called 2.0B passive» 29 bit (and 11bit) 2.0B called 2.0B active

– CAN provides only Data Link functions• Media access control• Logical link control

January 9, 2008 BAE 5030-363

Components of a “CAN Protocol”

ISO 7498 – Open Systems Interconnection (OSI)

Netw

ork M

anag

emen

tNet

wo

rk M

anag

emen

t Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Physical Layer

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Physical Layer

CAN CAN Data Link LayerData Link Layer

To form a complete communications system you need more than CAN

January 9, 2008 BAE 5030-363

Network Protocols based on CAN

• SAE J1939• Heavy Duty Diesel Systems

– On-Highway Truck– Agricultural Equipment– Construction Equipment– Generator Sets

• ISO 11783• Ag and Forestry Equipment

• NMEA 2000/IEC 61162-3• Marine / GPS / Navigation

• CANopen• Broad industrial applications - (CiA)• EN 50325-4

• DeviceNet• Industrial automation – PLCs (Allen Bradley)

• CAN Kingdom• Meta protocol - (Kvaser)

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Physical Signaling Example (ISO 11878)

CAN Arbitration

Identifier (29 bits) Data (8 bytes)1 0 1 1 0 0 0 1 1 1 ...ECU 1

ECU 2

BusResult

1 0 1 1 1 1 1 1 1 0 0 0 0 0 1 1 1 ...

1 0 1 1 1 1 1 1 1 0 0 0 0 0 1 1 1 ...

ECU 2 ceases transmissionand prepares to resend later

Arbitration Field NO Arbitration

1 0 1 1 0 0 0 1 1 1 ...

1 0 1 1 1

VCAN_H

VCAN_L

Vdiff

recessive dominant recessive

1 Bit

Lower numbered identifiers assume higher priority

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Consequences of identifier prioritization in CAN

• Unique Identifiers– Developer must assure all identifiers within a bus system are

unique

• Resyncronization– CAN controllers assure message transmissions always start

at the same time among controllers on the bus

• All messages queued are sent simultaneously– System appears to have one large queue where highest

priority message is sent first

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CAN Frame Components

11 bits or 29 bits

Identifier Data

0 to 8 bytes (0 to 64 bits)

CAN Frame (up to 134 bits)

Serial bit streamStart

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SOF

1

Identifier

11

SRR

1

IDE

1

DLC

4

Data Field

0 - 64

ACKField

2Bits

CRCDelimiter

1

Arbitration Field32 Bits

r0

1

ControlField6 Bits

DataField

CRC

15 7

EOF

Bit Stuffing

CAN Extended Data Frame

Maximum frame length with bit stuffing = 150 bits

r1

1

IdentifierExt.

RTR

118

B. CAN Extended Frame Format

No BitStuffing

CAN Frame Format - CAN 2.0B

11 bits or 29 bits

Identifier Data

0 to 8 bytes (0 to 64 bits)

CAN Frame (up to 134 bits)

January 9, 2008 BAE 5030-363

Acknowledgement

• In-Frame acknowledgement– Any receiver of a message that receives a message correctly

asserts a dominant acknowledge bit within the frame of the message being sent.

• Transmitter can know message was received by some receiver– Further message confirmation must be built at a higher level in the

protocol– Transmitter alone on a bus will go bus OFF

• Receiver with an error– Transmits an error frame immediately after the message causing a

Frame Error for all receivers

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Remote transmission request (RTR)

• Request message hardware feature– Allows setting a bit of an identifier to request a controller with

a matching identifier to send the message– Can allow a response of a queued message without CPU

interaction– Commonly not exploited in higher level standardized

protocols

January 9, 2008 BAE 5030-363

Error Detection

• 5 Error Types Detected– Bit Error (Sent bit doesn’t match monitored bit)– Stuff Error (more than 6 successive in one state)– CRC error– Form Error– Acknowledge Error

• Probability of an undetected error– 4.7 x 10-11 x message error rate

• for a message error rate of 25/sec, 1 undetected error per 10,000 hours operation

January 9, 2008 BAE 5030-363

Message Filtering - Example

MASK

MATCH

1 = Care, 0= Don’t Care

Accept if:(ID AND MASK) XOR MATCH = 0

11100000000

IDENTIFIER10111100100

10100000000

ID AND MASK10100000000 =

(ID AND MASK) XOR MATCH00000000000 =

Pattern must match

January 9, 2008 BAE 5030-363

Bus Timing

• Bus bit rate is controlled by bit time– 1 MBaud 1 s/bit– 250 KBaud 4s/bit

• Bit time is controlled by– Time Quanta (TQ)

– Bit segment settings (no. of TQ per bit)– Bit Time = TQ * (Sync_Seg + Prop_Seg + Phase_Seg1 + Phase_Seg2)

January 9, 2008 BAE 5030-363

Bit Timing

Microchip CAN Seminar, 2006

January 9, 2008 BAE 5030-363

Propagation segment

• Twice the sum of Driver, cable , and comparator delay (See Microchip AN754)

• Propagation delay of cable– Typically 60-70% of c for 120 Ohm cables– Example:

• Driver/Comparator delays – See datasheet– 50 ns

LC

1

tprop = 2 (⋅ tcmp + tbus + tdrv)

Nominal Velocity Velocity, Light Velocity, cable delay per meter Bus Length Bus delay(%) (m/s) (m/s) (s) (m) (ns)

n c v = nc t = 1/v l d = 2lt60% 3.00E+08 1.80E+08 5.56E-09 40 2.22E+02

January 9, 2008 BAE 5030-363

Error handling


January 9, 2008 BAE 5030-363

Collaborative Error Frame Generation

• Error Frames are generated for any error detected by a CAN protocol controller

• CAN protocol controller responds with an error echo if another node generates an error frame


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CRC errors


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Acknowledge Errors


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Form Errors


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Stuff Errors


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Bit Errors


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System Fault Confinement


In-Vehicle Networking

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