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

2. 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. 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=4532 dec Binary numbers 1011 bin 1*2^0+1*2^1+0*2^2+1*2^3 = 11 dec 1 byte = 8 bits Base (either 10 or 2) is called the radix

4. 4 Why do we need in-vehicle networks?

5. 5 Modern Car components

6. 6 Star topology

7. 7 Bus topology

8. 8 Let’s simulate a Vehicle Network…

9. 9 Here is our communication protocol

10. 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. 11 OSI model

12. 12 Complete 7 layer OSI model All People Seem To Need Data Processing

13. CAN only implements the two layers of the OSI model that are closest to the hardware 13

14. 14 Controller Area Network cont. 4  s per bit = 250 kilo 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

15. 15 CAN Frames Standard (a) & Extended (b)

16. 16 Demo time

17. 17 Transmitter Receiver Analog Inputs CAN bus

18. 18 TransmitterReceiver Requester Analog Inputs

19. 19 CAN 2.0b Request Transmission Frame Mark the bits in your handout (3 min)

20. 20 Answer 01010101 01011110 10101010 00001001 11000100 00010101 00001000 10111111 1

21. 21 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!

22. 22 De-stuffing the CAN Frame 0101010101011110101010100000 1 00111000100000 1 0101000010001011111111 0101010101011110101010100000001110001000000101000010001011111111

23. 23 Chop the Frame up into pieces 0 Start of Frame XXXXXXXXXXX 11- bit Standard Identifier XSubstitute Remote Request Bit X Identifier Extension Bit (1 = Extended Frame) XXXXXXXXXXXXXXXXXX18 Bit Extended Identifier XRTR Bit (1 = Request Transmission) XX Reserved XXXX Data Length Code (Nr of bytes that follows) XXXXXXXX Data Byte 1 XXXXXXXX Data Byte 2 XXXXXXXXData Byte 3 XXXXXXXX Data Byte 4 XXXXXXXXXXXXXXX Cyclic Redundancy Check (CRC) (15 bits) 1CRC delimiter XAcknowledge slot bit 1 Acknowledge delimiter 1111111End of frame (7 ones) 0101010101011110101010100000001110001000000101000010001011111111

24. 24 Interpret the CAN Frame 0 Start of Frame 10101010 101 11- bit Standard Identifier 1Substitute Remote Request Bit 1 Identifier Extension Bit (1 = Extended Frame) 10 10101010 0000001118 Bit Extended Identifier 1RTR Bit (1 = Remote Transmission Request) 00 Reserved 0100 Data Length Code (Nr of bytes requested) XXXXXXXX Data Byte 1 XXXXXXXX Data Byte 2 XXXXXXXXData Byte 3 XXXXXXXX Data Byte 4 000010100001000 Cyclic Redundancy Check (CRC) (15 bits) 1CRC delimiter 0Acknowledge slot bit 1 Acknowledge delimiter 1111111End of frame (7 ones)

25. 25 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

26. 26 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

27. CAN-USB interface (Lab being developed) 27

28. 28 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)

29. 29 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

30. 30 CAN in Agriculture

31. 31

32. The lightbar displays graphics to assist the operator when navigating along curved swaths. 32

33. The FieldPilot Module performs assisted steering on straight and contour paths. 33

34. 34

35. Spray application 35

36. 36

37. 37 Virtual terminal in John Deere tractor

38. 38 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/

39. 39 The End