Controller Area Network (Basic Level Presentation)

CAN
Controller Area Network
Vikas Kumar M

Slide No 2
Vehicle Components
 Components for functioning of a Vehicle?
Engine
Body
Chassis
Music System
Brakes
Lighting System
Battery
Sensors
Doors
Windows
Gauges
Climate Control
Meters

Slide No 3
Components Communication
 If all the mentioned components communicate in this fashion, would be a
mess, more no of cables would require, etc.
Also if a new node is to be introduced, it will be very difficult and complex
components
ECM/BCM

Slide No 4
Topology for communication
 What is a Topology
 In general, it is a study of Shapes and Spaces, such as
 Connectedness
 Continuity
 Boundary
 Branches

Slide No 5
CAN – “Bus Topology”
 What is a Network Topology
 It is the arrangement of various elements [Links, Nodes, Etc.]
for a Network [a telecommunication n/w] to exchange Data
 So CAN is a BUS Topology

Slide No 6
Vehicle Bus Topology
 What is a Vehicle Bus
 An internal communications network that interconnects components inside a
vehicle [e.g. automobile, bus, train, industrial or agricultural vehicle, etc.]
components
Internal Communication
Network

Slide No 7
Protocol
 Now we have the Vehicle Bus for communication,
 What if there is
 NO Format on how it should be routed / communicated or passed to others
 NO Syntax on how to understand the communication
 NO Identification to track the communication

Slide No 8
Protocol
 What is a Protocol
 Protocol is a set of rules for exchanging messages within or between
components/system
 Basic requirements of protocols
 Data formats for data exchange
 Address formats for data exchange
 Address mapping
 Routing
 Acknowledgment

Slide No 9
Types of Protocol
 What are the types of Protocol?
 In general, protocols differ in so many ways that it's not
possible to give an answer
 Why you need different varieties of Protocols:
 Because it depends on who, where, how, whom

Slide No 10
CAN
 CAN (Controller Area Network)
Development of Controller Area Network bus
started originally in 1983 at Robert Bosch GmbH.

Slide No 11
Before CAN
Before CAN

Slide No 12
Development of CAN
 The development of CAN began:
 when more and more electronic devices were implemented
into modern motor vehicles
 It was designed specifically for automotive applications but now also used in other areas
 To improve the behavior of the vehicle even further,
 it was necessary for the different control systems (and their sensors) to exchange information

Slide No 13
After CAN
After CAN
One of the advantages of this topology is:
that nodes can easily be added or removed with minimal software impact

Slide No 14
CAN
 What are the Characteristics of a CAN
 It is a Vehicle BUS with:
 Serial communication Protocol
 Multi-Master Message Model
 System flexibility
 Communication speed

Slide No 15
CAN
 CAN bus is a Serial Communication Protocol
 What is Serial Communication?
 Serial communication is the process of sending data one bit at a time,
sequentially, over a communication channel
 Serial Communication is used for all long-haul communication

Slide No 16
CAN
 Why Serial Communication?
 Basic differences:
Serial Communication Parallel Communication
One data bit is transceived at a
time
Multiple data bits are transceived
at a time
Less number of cables required to
transmit data
Higher number of cables required
Long Distance Short Distance

Slide No 17
CAN
 Why Serial Communication
 A few advantages
 A serial connection requires fewer interconnecting cables (e.g., wires/ fibers) and
hence occupies less space.
 The extra space allows for better isolation of the channel from its surroundings.
 Serial is a better option because it is cheaper to implement
 In general, Common Serial Communication Protocol are:
 SPI, I2C, FireWire, Ethernet, USB, RS232, etc.

Slide No 18
Vehicle Bus Protocol
Protocol Abbreviation Nature
CAN Controlled Area Network
an inexpensive low-speed serial bus for
interconnecting automotive components
D2B Domestic Digital Bus a high-speed multimedia interface
FlexRay -
a general purpose high-speed protocol with
safety-critical features
I²C Inter-Integrated Circuit for attaching low-speed peripherals
KWP 2000 Keyword Protocol 2000
– a protocol for automotive diagnostic devices
(runs either on a serial line or over CAN)
LIN
Local Interconnect Network
a very low cost in-vehicle sub-network
MOST
Media Oriented Systems
Transport
a high-speed multimedia interface
SPI Serial Peripheral Interface
for communication with slow peripheral
devices, which are accessed infrequently
Common Vehicle Bus Protocols include:

Slide No 19
CAN
 CAN bus is a Multi Master Message Model
 What is Multi Master
 Any Node* can Transmit or Receive any message
 What is Message Model
 Data transmitted from any node on a CAN bus, does not contain ADDRESSES of
either the transmitting node, or of any intended receiving node.
 Instead it contains MESSAGE which will be labelled by an identifier

Slide No 20
CAN, Multi Master Message Model
 Basic working Principle
 Data that are transmitted from any Node, contains MESSAGE labelled with
IDENTIFIER, which is unique throughout the network
 All other nodes receive the message and each performs an acceptance test on the
identifier to determine if the message, and thus its content, is relevant to that
particular node.
 If the message is relevant, it will be processed; otherwise it is ignored.
Tx
Rx
Rx
Rx
RxRx
Tx
Rx

Slide No 21
CAN, Multi Master Message Model
 What if two or more nodes start sending a message at
same time?
 Answer:
 A node with message having a highest priority will be granted to send first
 Advantage:
 It guarantees that messages are sent in order of priority
 In addition it also ensures that No message are lost

Slide No 22
CAN Node Requirement
 Each node requires a
 Host Processor
 The host processor decides: what received messages mean and which messages it wants to transmit itself
 Sensors, actuators and control devices can be connected to the host processor.
 CAN Controller
 Receiving: the CAN controller stores received bits serially from the bus until an entire message is available, which can then
be fetched by the host processor (usually after the CAN controller has triggered an interrupt)
 Sending: the host processor stores its transmit messages to a CAN controller, which transmits the bits serially onto the bus.
 CAN Transceiver
 Receiving: it adapts signal levels from the bus to levels that the CAN controller expects and has protective circuitry that
protects the CAN controller
 Transmitting: it converts the transmit-bit signal received from the CAN controller into a signal that is sent onto the bus.

Slide No 23
CAN
 CAN Message are Transmitted/Received:
 Periodically
 On Request
 On a State change
At a uniform and
fixed bit rate
within a CAN Bus or
Network

Slide No 24
CAN
Error Free Communication
Low Wiring Cost
Low Hardware Cost
Easy expandability
Low Node-Connection Cost
Safety critical equipment Real-time System
“Twisted Pair Wire”, wiring cost is low
Connectivity with MCU doesn’t occupy much Chip area,
which keeps the MCU’s cost Low
Simple to add Nodes to the network;
Just lap in two wires at any point on the bus
Only two pins are needed on MCU and in Bus connectors
More Chips with CAN Hardware
More and more MCUs with CAN functionality are becoming available

Slide No 25
CAN
 Quantity of CAN Nodes:
 Theoretically it is unlimited
 But practically it is limited to certain number, because higher the nodes will
impact on the Delay of the response, will increase the electrical load

Slide No 26
CAN
 CAN Bus implementation
 A Common way to implement using Two-Twisted wires with two termination
Resistors of 120 ohms
Twisted Pair Connection – for bi-directional data
Terminators

Slide No 27
CAN – Twisted Pair Wire
 Reason for Twisted Pair Wires
 To Cancel out Noise generated by external fields across Wires
 Current flowing in each wire in Opposite direction, their magnetic field cancels,
so the cable radiates less
 What is a Terminator
 A device connected to one end of a bus or cable that absorbs signals
 Terminators can be passive (simple resistors) or active (more complex electronics)
depending on the type of bus being terminated

Slide No 28
CAN Termination
 CAN Bus is terminated with 120 ohms?
 The terminator is placed at the end of a transmission line to
 Eliminate reflections at the ends of bus wire
 Thus to Match Impedance*

Slide No 29
CAN
 CAN Bus is terminated with 120 ohms?
Source Destination
Source Destination
Termination

Slide No 30
CAN
 Why only 120Ω been used?
 120 Ω is going to be close most of the time for the relatively large wires
commonly used for CAN.

Slide No 31
CAN
 Non-Automotive CAN Applications:
 Ships
 Locomotives, Railway Systems
 HVAC Systems
 Elevators
 Industrial Freezers, High Speed Printing Machines
 Many Others

Slide No 33
CAN
 CAN Standard Specification
 CAN Protocol is Standardized by ISO
 ISO11898 and ISO11519-2, with no much difference except at the Physical Layer
 ISO11898 is a standard for high-speed CAN communication
 ISO11519 is a standard for low-speed CAN communication

Slide No 34
CAN
 What is Matching Impedance?
 When sending power down a transmission line, it is usually desirable that as much
power as possible will be absorbed by the load and as little as possible will be
reflected back to the source.

Controller Area Network (Basic Level Presentation)

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