CAN bus lecture 2019

Vehicle sensor data in intelligent

transportation

Jesse Pirhonen 22.11.2019

Controller Area Network

Development of Controller Area Network bus started originally in

1983 at Robert Bosch GmbH

• Developed for automotive applications, now used in various systems

• When ECU numbers started to grow

• Added flexibility in the communication

• Communication speed increase

• Still a serial communication line• Multi-master serial bus

Motivation

• If all communication

between control units

would be done this way

it would be a mess

• Wires for each function and actuator

• Adding a control unit would require a lot of work

ISO-standards

• ISO 11898-1 for the data link layer

• ISO 11898-2 for the CAN physical layer for high-speed CAN

• ISO 11898-3 was released later and covers the CAN physical layer

for low-speed, fault-tolerant CAN

• SAE J1939 Serial Control and Communications Heavy Duty Vehicle

Network

CAN bus speed

Theoretical limit up to 1Mbit/s

• Powertrain usually 500 kbit/s

• Comfort / convenience 125 – 250 kbit/s

Comparison to other networks:

• Ethernet: all the way up to10 Gbit/s (vehicles have been using max 100 Mbit/s)

• MOST (Media Oriented Systems Transport):150Mbit/s (Most150)

• FT CAN : 125 kbit/s

• LIN: 20 kbit/s

Physical layer

Components needed for CAN communication

• Twisted pair cable with termination resistors

• ECUs, including DSP, controller and transceiver

DSP / μC:

• Data handling

• Control

CAN controller:

• Bit level filtering

• Message buffering

CAN transceiver:

• Connection related protection

• Voltage level to voltage

difference for the controller

Voltage levels

Voltage levels

• CAN_H: 2.5V – 3.5V

• CAN_L: 1.5V – 2.5V

Voltage difference

• 0 = 0V (recessive)

• 1 = 2V (dominant)

Message format

The most interesting part is the ID and DATA sections

Basically all the other sections are handled by the controller

Message data meaning

Typical raw message can be hard to read, needs to be converted

into human readable form

A good starting point can be formed with the following formula

𝑆𝑐𝑎𝑙𝑒𝑑 𝑣𝑎𝑙𝑢𝑒 = 𝑂𝑓𝑓𝑠𝑒𝑡 + 𝑆𝑐𝑎𝑙𝑒 ∗ 𝐷𝑒𝑐𝑖𝑚𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 (𝑟𝑎𝑤)

Message meaning example

Message sent with ID: 0x2A includes engine coolant temp, fuel temp

and other temp values (turbo, intercooler, etc.)

The first byte includes the temperature value of the engine

NOTE!

HEX:2A

DEC:42

BIN:101010

ID D1 D2 D3 D4 D5 D6 D7 D8

HEX 2A 18 7B 43 E6 2D 4C 4D B2

DEC 42 24 123 67 230 45 76 77 178

ID D1 D2 D3 D4 D5 D6 D7 D8

DEC 42 24 123 67 230 45 76 77 178

Message meaning example cont’d

ID D1 D2 D3 D4 D5 D6 D7 D8

DEC 42 24 123 67 230 45 76 77 178

• D1 range: 0…255

• Engine coolant

temp range: -40…130

Message meaning example cont’d

ID D1 D2 D3 D4 D5 D6 D7 D8

DEC 42 24 123 67 230 45 76 77 178

• D1 range: 0…255

• Engine coolant

temp range: -40…130

OFFSET

Message meaning example cont’d

ID D1 D2 D3 D4 D5 D6 D7 D8

DEC 42 24 123 67 230 45 76 77 178

• D1 range: 0…255

• Engine coolant

temp range: -40…130

SCALE

The main idea is to map the bit

value to match the, in this case,

the coolant temp value

Another example from heavy

machinery using J1939• DBC Format configuration file

• CAN be found in data loggers

• 29-bit ID’s used in heavy machinery are standardized to some

extent

• Passenger vehicles configurations are still most oftenproprietary

Another example from heavy

machinery using J1939

sender

message name data lenmessage ID

(29-bit identifier)

start bit

size of signal

@1+ → little-endian format

scale offset unit

min and max

1 signal (row)

One full message in DBC file

One messages can include maximum of 8 bytes → 64 bits

1 byte

Message data frame 64 bits (with ID 200)

Captured messages example

Captured messages example

cont’d• All the messages are captured from

the research vehicle Ford Focus

• Still plenty to analyze

Distributed networks

• Modern vehicles can include closer to 100 control units

• All the control units can not be connected to a single network

• Too much information

• Different speed requirements

• Vulnerable

• Multiple networks and control units between the networks are

required

HS 3

HS 2

MS

HS 1

HS 4

Vehicle networks

There are many different

networks

• Purpose of use defines the used network:• Speed

• Robustness

• Real time demand

• Number of control unit / actuators

• Data inside the node

Hardware examples for CAN

communicationPEAK systems

• https://www.peak-system.com/

Arduino Based solution

• http://wiki.seeedstudio.com/CAN-BUS_Shield_V2.0/

Software examples for CAN

communication• SocketCAN / CANutils in Linux (demo after the lecture)

• With a matching hardware provides a solid base for reading, sending and analyzing CAN frames

• Wireshark, supports analysis for other protocols and busses

• Simulink with various add-ons, requires specific hardware

• Arduino IDE, serial monitor

Books

THE CAR HACKER’S HANDBOOK, Craig Smith

• http://opengarages.org/handbook/ebook/

Automotive Mechatronics, BOSCH

• https://aalto.finna.fi/Record/alli.695445

Videos

Kvaser video set about CAN (recap)

• https://www.kvaser.com/course/can-protocol-tutorial/

SocketCAN video tutorial

• https://www.youtube.com/watch?v=Ym8xFGO0llY&t=1068s

Lecture quiz 6 Vehicle

Mechatronics L, MEC-E5006Consider the information you learnt during the lecture. Write down your

answers and use them to answer lecture quiz by Dec 9, 2019 on

MyCourses

Answer the next 3 questions (Q1…Q3)

Q1.CAN communication hardware

(1 point)What kind of hardware does one node in CAN communication include?

Name the purpose also.

Q2. Distributed networks (1 point)

Why we have multiple different buses, instead of just using one?

Q3. CAN bus utilization (1 point)

How would you utilize the CAN messages shown in the lecture slides to

come up with an improvement to an already existing system or a new

one in vehicles?