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Lecture Controller Area Networks Dr. Tony Grift grift@uiuc

Lecture Controller Area Networks Dr. Tony Grift grift@uiuc.edu. What will you learn today?. Recap binary numbers What purpose serve vehicle networks? Understand Controller Area Network physical layer (hardware) Identify and interpret components of CAN Frames

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Lecture Controller Area Networks Dr. Tony Grift grift@uiuc

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  1. Lecture Controller Area Networks Dr. Tony Grift grift@uiuc.edu

  2. What will you learn today? • Recap binary numbers • What purpose serve vehicle networks? • Understand Controller Area Network physical layer (hardware) • Identify and interpret components of CAN Frames • Understand the meaning and importance of standardized communication protocols

  3. Bits & Bytes • Data communication is digital. You only have 1’s and 0’s • Bit = binary digit • How do you translate these into decimal numbers? • Decimal number • 4532 • 2*10^0+3*10^1+5*10^2+4*10^3=4532dec • Binary numbers • 1011bin • 1*2^0+1*2^1+0*2^2+1*2^3 = 11dec • 1 byte = 8 bits • Base (either 10 or 2) is called the radix

  4. Why do we need in-vehicle networks?

  5. Modern Car components

  6. Star topology

  7. Bus topology

  8. Let’s simulate a Vehicle Network…

  9. Here is our communication protocol

  10. Controller Area Network • A broadcast, differential serial bus standard, originally developed in the 1980s by Robert Bosch GmbH, for connecting electronic control units (ECUs) in vehicles. • Very robust • Two wire bus • Messages are short (8 data bytes max) • Priority based arbitration used for Collision Avoidance • Bit stuffing for synchronization: if 5 equal bits, the following one is opposite polarity • Error detection mechanism through Cyclic Redundancy Check (CRC) • Bit rates up to 1 Mbit/s • The CAN data link layer protocol is standardized in ISO 11898-1 (2003). All the other protocol layers are left to the network designer's choice. • ISO 11783 (ISOBUS) is the agricultural network protocol

  11. Controller Area Network cont. • 4 ms per bit = 250 bit/s (Required for ISOBUS standard) • Data Length Code (DLC) contains nr of data bytes • If RTR bit is high, • no data bytes, DLC = # bytes requested • 11-bit (CAN 2.0a) and 29 bit (CAN 2.0b) ID messages on same bus • IDE (Identifier Extension bit) distinguishes between 11 and 29 bit frames 1 0

  12. CAN Frames Standard (a) & Extended (b)

  13. Demo time

  14. Transmitter CAN bus Analog Inputs Receiver

  15. CAN 2.0b Request Transmission Frame Mark the bits in your handout (3 min)

  16. Answer 01010101 01011110 10101010 00001001 11000100 00010101 00001000 10111111 1

  17. Step 1 Get rid of the stuffing bits • Stuffing bits are put in to ensure synchronization • If you see 5 consecutive zeros or ones, the next one is a stuffing bit • Throw it out!

  18. De-stuffing the CAN Frame 0101010101011110101010100000 1 00111000100000 1 0101000010001011111111 0101010101011110101010100000001110001000000101000010001011111111

  19. Chop the Frame up into pieces 0101010101011110101010100000001110001000000101000010001011111111 0 Start of Frame XXXXXXXXXXX 11- bit Standard Identifier X Substitute Remote Request Bit X Identifier Extension Bit (1 = Extended Frame) XXXXXXXXXXXXXXXXXX 18 Bit Extended Identifier X RTR Bit (1 = Request Transmission) XX Reserved XXXX Data Length Code (Nr of bytes that follows) XXXXXXXX Data Byte 1 XXXXXXXX Data Byte 2 XXXXXXXX Data Byte 3 XXXXXXXXData Byte 4 XXXXXXXXXXXXXXX Cyclic Redundancy Check (CRC) (15 bits) 1 CRC delimiter X Acknowledge slot bit 1 Acknowledge delimiter 1111111 End of frame (7 ones)

  20. Interpret the CAN Frame 0 Start of Frame 10101010 101 11- bit Standard Identifier 1 Substitute Remote Request Bit 1 Identifier Extension Bit (1 = Extended Frame) 10 10101010 00000011 18 Bit Extended Identifier 1 RTR Bit (1 = Remote Transmission Request) 00 Reserved 0100 Data Length Code (Nr of bytes requested) XXXXXXXX Data Byte 1 XXXXXXXX Data Byte 2 XXXXXXXX Data Byte 3 XXXXXXXXData Byte 4 000010100001000 Cyclic Redundancy Check (CRC) (15 bits) 1 CRC delimiter 0 Acknowledge slot bit 1 Acknowledge delimiter 1111111 End of frame (7 ones)

  21. A word on error detection • Cyclic Redundancy Check • Transmitter computes Transmitter checksum based on data • Receiver receives both data and Transmitter check sum • Receiver computes Receiver checksum based on data • If Transmitter checksum == Receiver checksum • Data is valid with very high probability • P(Error unnoticed) = 4.7 *10-11

  22. Message arbitration is used to resolve conflicts due to collisions: most important message must go through • If more than one message is being transmitted simultaneously a collision occurs • Bit-by-bit arbitration process: If a node has a lower (dominant) bit it wins arbitration, the others lose and shut down • At (2) Node 2 loses arbitration and shuts down. At (3) Node 1 loses arbitration and shuts down. Node 3 (lowest number, highest priority) goes through

  23. What is a protocol ? • Give some examples of protocols among humans • Communication pilot-tower • Meetings (Roberts Rules of Order) • Rules of games • Etiquette rules • Unwritten rules (job interview) • Some Network protocols • TCP (Transmission Control Protocol) • IP (Internet Protocol) • DHCP (Dynamic Host Configuration Protocol) • HTTP (Hypertext Transfer Protocol) • FTP (File Transfer Protocol) • POP3 (Post Office Protocol 3) • SMTP (Simple Mail Transfer Protocol) • IMAP (Internet Message Access Protocol) • ISO 11783 (ISOBUS)

  24. You are sending a mining truck overseas • Sender • Split up the truck in smaller parts • Add routing information • Add additional packing information • Add reassemble information • Send “packages sent” message to receiver • Deliver packages to UPS • Receiver • Receive messages from UPS • Wait until all packages have come in • Check if you have everything • Reassemble the truck • Send acknowledge message to sender • This transmission process requires a protocol • UPS = ISO 11898 CAN physical layer • We don’t care how it does it • We want it reliable • We want it fast • ISO 11783 (ISOBUS) is the protocol

  25. CAN in Agriculture

  26. Virtual terminal in John Deere tractor

  27. Summary • Why do we need a Vehicle network? Improved control of engine performance and emissions Improved comfort Automated diagnostics (OnStar) Improved safety • Controller Area Network • Communication network for vehicles and other noisy environments • Error handling • Bit stuffing • CRC • Frames • 11bit (2.0a) and 29 bit • Prioritization using arbitration mechanism • Protocols, rules of communication • ISO 11898 (CAN Physical layer) • ISO 11783 (ISOBUS communication) • Link: http://www.can-cia.org/

  28. The End

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