CAN Controller Area Network

1. MotoHawk Training CAN Controller Area Network

2. OUTLINE • CAN Introduction • CAN Physical Network • CAN Message Format • MotoHawk Block Walk Through • MotoHawk “Post Office” • MotoHawk Advanced CAN Blocks • CAN Protocol Overview

3. INTRODUCTION • CAN = Controller Area Network • Communication specification implemented for automotive applications in the 1980s • Often, the term “CAN” is misused • CAN is a hardware definition for interoperability between modules • CAN specification does not state the data content of a given message • Protocols built on top of CAN state the data content (ex. J1939, GMLAN) • MotoHawk doesn’t define a protocol, but allows access to the CAN hardware to implement a protocol • By itself, CAN is not difficult (I mean it)

4. OUTLINE • CAN Introduction • CAN Physical Network • CAN Message Format • MotoHawk Block Walk Through • MotoHawk “Post Office” • MotoHawk Advanced CAN Blocks • CAN Protocol Overview

5. PHYSICAL NETWORK • Two wire robust serial communication • Up to 1Mbps data rate which is limited by wire length • 100 m @ 250Kbps • 30 m @ 1Mbps • Termination resistance required • Maximum bandwidth • 2000 messages per second @250Kbps • 4000 messages per second @500Kbps • 8000 messages per second @1Mbps • Designed bandwidth should not exceed 70% of the maximum bandwidth CAN - CAN + Wire Length 120 Ω

6. PHYSICAL NETWORK • Bus arbitration is handled with a simple strategy • All modules on the bus attempt to transmit a message at the same time • The message with the lowest address wins • This strategy is handled at the hardware level • Dominant Bits (0) vs. Recessive Bits (1) • Multiple modules on the same bus cannot transmit the same address at the same time Module 0 continues to transmit while Module 1 waits for next opportunity to transmit Module 0 Module 1 T0 T1 T2 T3

7. OUTLINE • CAN Introduction • CAN Physical Network • CAN Message Format • MotoHawk Block Walk Through • MotoHawk “Post Office” • MotoHawk Advanced CAN Blocks • CAN Protocol Overview

8. MESSAGE FORMAT • A CAN 2.0B Message can contain up to 131 bits • As application developers, 3 fields are important: • 4 bits determine the length of the data (aka payload) (Range : 0-8) • Up to 64 bits of data depending on data length • ID Format • Extended IDs are 29 bits • Standard IDs are 11 bits • Extended and Standard IDs can exist on the same bus at the same time • Standard IDs have less message overhead (higher percentage of data per message)

9. OUTLINE • CAN Physical Network • CAN Message Format • MotoHawk Block Walk Through • MotoHawk “Post Office” • MotoHawk Advanced CAN Blocks • CAN Protocol Overview

10. CAN DEFINITION BLOCK • First, the CAN hardware needs to be initialized • Baud rate and transmit queue size configured • If the baud rate and/or MotoTune protocol settings are not configured properly, then MotoTune can’t talk to the module via CAN (and therefore programming cannot be performed via CAN) • Boot key sets CAN baud rate to 250kbps

11. Send CAN Raw Block

12. CAN Exercise #1 • CAN Bus Test • Construct a calibratable CAN message transmitter • Use CANKing to monitor bus traffic System Diagram

13. OUTLINE • CAN Introduction • CAN Physical Network • CAN Message Format • MotoHawk Block Walk Through • MotoHawk “Post Office” • MotoHawk Advanced CAN Blocks • CAN Protocol Overview

14. POST OFFICE • CAN is the hardware layer, so how are transmitted messages sorted and filtered in MotoHawk? • A Post Office is the simplest analogy • Mailboxes • Letters • Addresses • Zip Codes

15. POST OFFICE • Many messages are transmitted on a bus at a given time, but a module may only be interested in a small subset • Similar to a post office where the messages are letters and the software dispatcher is the postman • A “mail box” in MotoHawk is called a “slot”

16. POST OFFICE • A “slot” has an address known as a CAN ID similar to the address on a mailbox • The MotoHawk post office needs to deliver messages to these slots • How does it happen?

17. POST OFFICE • Filtering is done with 2 masks • ID Mask : Filters a message by the address or the ID • Payload Mask : Filters a message by the data content • A mask is similar to assigning a “Don’t Care” or a “Do Care” to a particular number in the mask

18. Filtering • Filtering is done with 2 masks • ID Mask : Filters a message by the address or the ID • Payload Mask : Filters a message by the data content • A ‘1’ in the mask means that the data and the value must match exactly • For example, • if ID mask = 0x7F0 (111 11110000) • and ID = 0x7E4 (111 11100100) • If incoming ID = 0x7E0, (111 11100000) message goes to mailbox • If incoming ID = 0x7F4, (111 11110100) x message is rejected by mailbox • If incoming ID = 0x7E1, (111 11100001) message goes to mailbox

19. READ CAN RAW BLOCK

20. POST OFFICE • The “Slot Name” is the name of the mailbox at the post office • The slot has default settings for the ID, ID Mask, Payload Value, and Payload Mask • This is the design time mailbox configuration

21. POST OFFICE • The properties of the mailboxes can be changed at run time • The filters determined at design time can be strengthened (more restrictive), but cannot be weakened • In MotoHawk, the CAN Receive Slot Properties Block allows the user to change the filters at run time

22. POST OFFICE • What happens if the postal worker rings your doorbell to deliver a message? • This is an asynchronous reception of a message • The advantage is that processing time can be saved by not periodically polling this message • How does MotoHawk handle this situation? • Asynchronous reception processed with CAN Receive Slot Trigger Block • Slot name in this block must match the slot name specified in Read CAN Raw block or Read CAN Message block

23. OUTLINE • CAN Introduction • CAN Physical Network • CAN Message Format • MotoHawk Basic Transmit Block • Exercise • MotoHawk “Post Office” • MotoHawk Advanced CAN Blocks • CAN Protocol Overview

24. MOTOHAWK ADVANCED CAN • The Read and Send CAN blocks are nice, but sometimes more advanced data parsing is necessary. Common questions: • I have 12 bit scaled data that spans across multiple bytes. How do I convert it into engineering units? • I have more data that can fit into 64 bits. How do I create multi-page messages? • I’m using a protocol that has a variable ID. How do I dynamically create the ID easily? • These are valid questions and there is an answer…

25. MOTOHAWK ADVANCED CAN • MotoHawk has 2 blocks – Read CAN Message and Send CAN Message (below) • These are very powerful blocks that allow users to set up multi-page documents and parse and scale both variables and IDs

26. MOTOHAWK ADVANCED CAN >> edit motohawk_can_example.m

27. LITTLE ENDIAN vs BIG ENDIAN • Terminology originates from “Gulliver’s Travels” • “Endianness” refers to the order in which bytes are stored in memory • This table shows the 4 byte storage for 1025 (0x41) • By default, the MotoHawk CAN scripts use Big Endian byte ordering…which can lead to confusion

28. LITTLE ENDIAN vs BIG ENDIAN Given this CAN definition byte ordering for a 4 byte variable: Big Endian MSB Little Endian LSB 63...….56 55...….48 47...….40 MSB 39...….32 LSB Now, go let’s back to the script definition…

29. OUTLINE • CAN Introduction • CAN Physical Network • CAN Message Format • MotoHawk Basic Transmit Block • Exercise • MotoHawk “Post Office” • MotoHawk Advanced CAN Blocks • CAN Protocol Overview

30. CLASS EXERCISE • Create a distributed control system to control the ETC over CAN Pedal Duty Cycle PID Analog signal from potentiometer CAN message send TPS % City ID 0x81 ECU 2 CAN message receive TPS % TPS % Analog signal from ECT CAN message send City ID 0x0B Duty Cycle Duty Cycle ECU 1 CAN message receive PWM output

31. CLASS EXERCISE

32. PROTOCOL OVERVIEW • CAN gets complicated when protocols are considered • J1939, SmartCraft, CCP, GMLAN, etc. are all examples of protocols that adhere to strict rules • These protocols can be implemented using Simulink and/or Stateflow • Some message formats (J1939) have already been implemented for other projects

33. MotoTron Control SolutionsProduction Controls in a Flash