CAN

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Controller Area Network

CAN

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CAN Agenda

What is CAN ? Why CAN ? CAN Protocol CAN Higher Layer Protocols CAN Applications AT91 CAN Microcontrollers – Roadmap

CAN

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What is CAN ? 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

CAN

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Why CAN ? 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 high

transmission speed (up to 1Mb/s) Simple Transmission Medium

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

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

CAN

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CAN Protocol

Protocol -

CAN

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ISO-OSI Reference Model

Protocol -

7. Application Layer

5. Session Layer

6. Presentation Layer

4. Transport Layer

3. Network Layer

2. Data Link Layer

1. Physical LayerCAN Protocol

HLPs: CANopen, DeviceNet, OSEK/VDX

Partially Implemented by High Layer Protocol (HLP)

CA

N L

ayer

s

CAN

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Typical CAN Node

Protocol -

µController CAN Controller

CAN Transceiver

CA

N B

usCAN_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

CAN

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Error Detection Analysis

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

CAN

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CAN High Layer Protocols

HLP -

CAN

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HLP Definition

HLP -

One undetected error every 1000 years !!!

CAN protocol defines only the physical and a low data link layer ! The HLP defines:

Start-up behavior Definition of message identifiers for the different nodes Flow control Transportation of messages > 8bytes Definition of contents of Data Frames Status reporting in the system

CAN

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CAN Kingdom

HLP -

CAN Kingdom is more than a HLP (Meta Protocol): Introduced by KVASER, Sweden A ‘King’ (system designer) takes the full responsibility of the system The King is represented by the Capital (supervising node)s CAN Kingdom provides simple unique identification of system nodes

Applications Machine Automation

Advantages Designed for safety critical applications Real time performance Scalability Integration of DeviceNet modules in CAN Kingdom possible

CAN

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CAN Applications

Applications -

CAN

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CAN: a Large Field of Applications

Applications -

Building Automation: Heating control, Air Conditioning, Security, Access & Light

Control… Domestic & Food distribution appliances

Washing machines, dishes cleaner, self-service bottle distributors…

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...

CAN

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AT91SAM7 CAN Embedded ControllersA1 - A2 - A3 - X

AT91SAM7 -

CAN

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CAN Controllers Types

3 types of CAN controllers exist: CAN Controllers 2.0 Part A: standard frames CAN Controllers 2.0 Part B Passive or ‘extended frames passive’ CAN Controllers 2.0 Part B Active or ‘extended frames active’

CAN Implementations: 2 main implementations strategy BasicCAN: cheaper CAN Controller

• 1 or 2 Rx buffers (FIFO) and 1 Tx buffer• Minimal Filtering

FullCAN: high performance CAN Controllers• Set of buffers called Mailboxes• Dedicated Mailbox Filtering

Our CANs: 2.0A/2.0B (Active) & FullCAN

AT91SAM7 -

CAN

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AT91SAM7A3 – AT91SAM7XCAN Controller

SAM7A3 / SAM7X -

CAN

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CAN Controller Structure

SAM7A3 / SAM7X -

CAN

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Mailbox Organisation

SAM7A3 / SAM7X -

Eight 32-bit registers by mailbox

Mailbox x Mode Register Mailbox x Acceptance Mask Register Mailbox x ID Register Mailbox x Family ID Register Mailbox x Status Register Mailbox x Data Low Register Mailbox x Data High Register Mailbox x Control Register

Mailbox Channel Buffer

CAN_MAMxCAN_MAMx

CAN_MMRxCAN_MMRx

CAN_MIDxCAN_MIDx

CAN_MFIDxCAN_MFIDx

CAN_MDLxCAN_MDLx

CAN_MSRxCAN_MSRx

CAN_MDHxCAN_MDHx

CAN_MCRxCAN_MCRx

Mailbox x

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Mailbox Priority

SAM7A3 / SAM7X -

Reception Modes: In this modes, the mailbox with the lowest number is serviced first.

Transmission Modes: Mailbox with the highest priority PRIOR lowest value. When several mailboxes try to transmit a message at the same time, the mailbox with

the highest priority is services first. If at least two mailboxes have the same priority (same PRIOR value), the mailbox with

the lowest number is serviced first.

Mailbox Mode Register

PRIOR 16

CAN

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Multiple Transfer or Abort Requests

SAM7A3 / SAM7X -

The CAN Transfer Command Register (CAN_TCR) allows to perform several transfer requests at the same time.

The CAN Abort Command Register (CAN_ACR) allows to perform several abort requests at the same time.

CAN

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THANK YOU !

13/04/23