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Understanding CAN: History, Implementation, and Application Strengths

This presentation outlines the Controller Area Network (CAN), detailing its history from its development by Bosch in 1983 to its implementation in modern automotive systems. It explains the standard message frame, arbitration process, and methods for error checking and noise protection, highlighting the strengths of CAN in real-time communication. The presentation also discusses various applications in the automotive industry, factory automation, and multimedia systems, addressing its robust error correction and low costs, making it vital for efficient communication in electronic control units.

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Understanding CAN: History, Implementation, and Application Strengths

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  1. EECS 373 Controller Area Networks Samuel Haberl Russell Kuczwara SenyuanZhong

  2. Presentation Outline • CAN history and basics • CAN standard message frame & arbitration • Error checking & noise protection • CAN implementation • Application strengths http://goo.gl/Ktm1BY

  3. CAN History • Developed by Bosch in 1983 • Presented at SAE Conference in Detroit in 1986 • Designed for automotive uses • Allows multiple controllers and sensors to communicate • 2008: all US vehicles required to implement CAN for OBD • Multiple CAN implementations and variations

  4. Where is CAN Used? • Automotive industry • Electronic control units (ECUs) • Sensors and switches • Multimedia systems • Factory automation • Low-cost machinery and electronics • Michigan Hybrid Racing Electric Drive System Photo credit: Sam Haberl

  5. CAN Basics • Multi-master, broadcast serial bus • Real Time Arbitration • Robust error-checking and noise protection • No extra wires for clock or arbitration • Cheap http://www.aa1car.com/library/can_systems.htm

  6. Masters and Targets • Each node can be a master and a target • Arbitration field indicates message type • Nodes listen to messages that they care about • Addresses composed of dominant and recessive bits • 0 – Dominant, 1 – Recessive • Lowest address (0x000) is most dominant http://goo.gl/NafrtG

  7. Standard Message Frame • Start of frame • Arbitration (identifier) • Control (data length, reserved bits) • Data field • CRC (cyclical redundancy check) • ACK (acknowledgement field) • End of frame • Intermission (time between frames) 11 or 29 Bit Image from http://www.softing.com/home/en/industrial-automation/products/can-bus/more-can-bus/data-frame.php?navanchor=3010395

  8. Arbitration 11 or 29 Bit http://electronicdesign.com/Files/29/9131/Figure_02.gif

  9. Error Checking • Form Errors • Proper message formatting is enforced • Bit Errors • Transmitter detects wrong bit while transmitting. • CRC Checksum Errors • Checksum calculated, compared to transmitted checksum • Acknowledgement Errors • ACK field must be set dominant by a receiving node • Bit stuffing Errors • Any time there are 5 of the same bits, one opposite bit sent • Error triggered by 6 identical bits

  10. Error Handling • Any node on the bus can raise an “Error frame.” • Holds bus dominant for 6 bits • Other nodes realize this is wrong, raise their error frames • Node that was transmitting re-sends message • Each node keeps individual error count • Node goes into “passive” mode at 127 errors • Node removes itself from bus after 255 errors Image from http://www.softing.com/home/en/industrial-automation/products/can-bus/more-can-bus/error-handling/active-error-frame.php?navanchor=3010501

  11. Timing http://goo.gl/nUry9c • No bus clock signal, each node has its own clock • Each bit is divided into four sections • Synchronization, Propagation, Phase 1, Phase 2 • Bit sampled between phase 1 and 2 • Receiving nodes synchronize by adjusting phases

  12. CAN Implementations Variants • CAN architecture can be implemented in many different approaches • Standards for single-wire, twisted pair, four-wire • Twisted-pair CAN is most commonly used • Twisted pair uses CAN_H and CAN_L signals • No additional wires needed • Signal generated by transceiver, not by processor http://www.networkcablinglosangeles.com/wp-content/themes/networkcablinglosangeles/images/unshielded_cable.jpg

  13. Electrical Noise • Lots of Noise in Automotive Application • Only getting worse with more automation for luxury http://upload.wikimedia.org/wikipedia/commons/0/0a/3phase-electric-motor-1.18.png

  14. Differential Signals • Two-Wire differential signal • Value represented by difference between wires, not the absolute value of one wire • Difference creates immunity to noise 0 0 1 0 ?

  15. From Master to Bus (2-Wire Implementation) • Processor uses logic-level signal • Signals sent over 2-wire bus • Use transceiver as bridge http://goo.gl/RPHJ8R

  16. Full Message Example • Sends the message with identifier 00000010100 • Sends One Byte with value “1” • 15 bit CRC field • Bit Stuffing is handled by can transceivers and is not visible

  17. A CAN Bus For Everyone • Allows multiple bitrates and buses • Bitrates affect robustness and bus length • 1 Mbit/s – High-priority • i.e. Airbags • 10 kbit/s – Low-priority • i.e. Audio System changes (volume, audio source)

  18. Multiple CAN Bus Example http://goo.gl/UFsVd1

  19. Application Strengths • Arbitration with no delay or extra wires • High-priority devices don’t wait • No extra weight or cost from wires • Robust error correction • Faulty nodes remove themselves from bus • Minimizes need for software correction • Noise immunity from twisted pair CAN • Inexpensive • 56 cents @ 2,500 qty for SN65HVD1040DR CAN Transceiver (DigiKey)

  20. References • Robert Bosch GmbH • http://esd.cs.ucr.edu/webres/can20.pdf • KVaser CAN Solutions • http://www.kvaser.com/en/about-can/the-can-protocol.html • Dearborn Group Technologies • http://www.dgtech.com/images/primer.pdf • Softing CAN Bus Products • http://www.softing.com/home/en/industrial-automation/products/can-bus/index.php?navanchor=3010024 • Vector CANtech • http://vector.com/vi_controller_area_network_en.html?gclid=CNOAroPo47oCFdFDMgod9GsAIw&et_rp=1

  21. Questions?

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