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BY

B.CHATRAPATHI

(092N1A0405)

22/01/2013

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What is CAN ?

Why CAN ?

CAN Protocol

CAN Applications

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ControllerArea Network

Invented by Robert Bosch GmbH in 1980 for automotiveapplications

Asynchronous Serial Bus

Simple 2-wire differential bus

Absence of node addressing

Message identifier specifies contents and priority

Lowest message identifier has highest priority

Non-destructive arbitration system by CSMA with collisiondetection

Multi-master / Broadcasting concept

Sophisticated error detection & handling system

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The CAN is an ISO standard (ISO 11898) for serial communication

Today CAN has gained widespread use:

Industrial Automation

Automotive, etc.

The CAN standard includes:

Physical layer

Data-link layer

Some message types

Arbitration rules for bus access

Methods for fault detection and fault confinement

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Mature Standard

CAN protocol more than 16 years

Numerous CAN products and tools on the market

Hardware implementation of the protocol

Combination of error handling and fault confinement with hightransmission speed (up to 1Mb/s)

Simple Transmission Medium

Twisted pair of wires is the standard, but also just one wire willwork

Other links works, too: Opto - or radio links

Excellent Error Handling CRC error detection mechanism

Fault Confinement

Built-in feature to prevent faulty node to block system

Most used protocol in industrial and automotive world

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Protocol -

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Protocol -

7. Application Layer

5. Session Layer6. Presentation Layer

4. Transport Layer

3. Network Layer

2. Data Link Layer

1. Physical LayerCAN Protocol

HLPs: CANopen, DeviceNet, OSEK/VDX

Partially Implementedby High LayerProtocol (HLP)

CANLayers

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Protocol -

CAN Controller

CAN Transceiver

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Protocol -

Node 1 Node 2 Node 3 Bus

D D D D

D D r D

D r D DD r r D

r D D D

r D r D

r r D D

r r r r

1 Recessive (r)

0 Dominant (D)

Two logic states on the CAN bus

Bus in dominant state

Bus in recessive state

or idle

Wired-AND Function

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Protocol -

Controller CANController

CANTransceiver

CANBu

sCAN_H

CAN_L

TXD

RXD

CAN Bus is a simple 2-wire differential serial bus

CAN Bus is terminated on each side by a 120 Ohm resistor

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Protocol -

Bit Coding : NRZ (Non-Return-To-Zero code) does not ensure enough edgesfor synchronization

Stuff Bits are inserted after 5 consecutive bits of the same level

Stuff Bits have the inverse level of the previous bit.

No deterministic encoding, frame length depends on transmitted data

Number of consecutive bitswith the same polarity

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Hard synchronization at Start Of Frame bit

Re-Synchronization on each Recessive to Dominant bit

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Protocol -

CAN Bit Period Four Time Segments

Each Time Segment represents a number of Time Quanta (TQ)

1 Time Quantum 1 period of CAN Controller Clock

1 Bit Time 8 to 25 Time Quanta

SYNC_SEG: synchronize the different nodes PROP_SEG: compensate for signal delays across the network

PHASE_SEG1 & 2: compensate for edge phase errors

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Protocol -

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Protocol -

SOF: Start Of Frame

CRC: Cyclic Redundancy Code

ACK: Acknowledge

EOF: End of Frame

IFS: Inter Frame Space

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Protocol -

One undetected error every 1000 years !!!

Error statistics depend on the entire environment

Total number of nodes

Physical layout

EMI disturbance

Automotive example

2000 hours/year

Baud rate: 500 kbps

25% bus load

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HLP -

CiA (CAN in Automation)

Features

CANopen is a subset from CAL (CANApplication Layer) developed by CiA

Auto configuration the network

Easy access to all device parameters

Device synchronization

Cyclic and event-driven data transfer Synchronous reading or setting of inputs, outputs or parameters

Applications

Machine Automation

Advantages

Accommodating the integration of very small sensors and actuators

Supports inter-operability of different devices High speed real-time capability

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Applications -

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Applications -

Building Automation:

Heating control, Air Conditioning, Security, Access & LightControl

Domestic & Food distribution appliances

Washing machines, dishes cleaner, self-service bottledistributors

Automotive & Transportation

Dash Board, Power train & Car Body

Train, bus and truck equipment

Robotic

Production Automation:

Control & link of production machines

Medical

Agriculture

Harvester, seeding, sowing machines, tractor control...

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