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CAN
1 13/04/23
Controller Area Network
CAN
2 13/04/23
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
CAN
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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