![VEHICLE NETWORKS Introduction to CAN Joseph Holly [email_address]](https://image.slidesharecdn.com/cannetworks-090730134422-phpapp01/85/CAN-Networks-1-320.jpg)
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CAN Networks
- 1. VEHICLE NETWORKS Introduction to CAN Joseph Holly [email_address]
- 2. NETWORK PROTOCOLS There are multiple vehicle networking protocols, each with its own history and function. The most common protocol in light vehicles is Controller Area Network ( CAN ). Even a single vehicle is likely to contain multiple networks and multiple protocols.
- 6. FOUR FRAME TYPES - DATA - REMOTE - ERROR - OVERLOAD
- 7. DATA Frame Two Types: STANDARD and EXTENDED STANDARD - 11-bit identifier EXTENDED - 29-bit identifier
- 8. Structure of a DATA FRAME START OF FRAME (SOF) - Indicates a new transmission to all receiving nodes - Also used by all receiving nodes for synchronization SOF ARB DATA ACK CRC CONTROL EOF
- 11. Structure of a DATA FRAME DATA FIELD – Actual message data SOF ARB DATA ACK CRC CONTROL EOF
- 12. Structure of a DATA FRAME CYCLIC REDUNDANCY CHECK (CRC) – Error-trapping method used by controller to verify successful data transmission. Every data frame is validated, retransmitted if necessary. SOF ARB DATA ACK CRC CONTROL EOF
- 13. Structure of a DATA FRAME ACKNOWLEDGEMENT FIELD – Field in which receiving nodes signal that message was properly received. If ACK is not received, originating node retransmits message. SOF ARB DATA ACK CRC CONTROL EOF
- 14. Structure of a DATA FRAME END OF FRAME (EOF) - Indicates end of transmission from originating node - Signals beginning of Intermission period. SOF ARB DATA ACK CRC CONTROL EOF
- 15. REMOTE Frame Used by any node to request data from any other node. Same structure as Data Frame, except: - Remote Frame has no message in Data Field - Control Field used to indicate size of expected return data
- 16. ERROR Frame Two Types: ACTIVE and PASSIVE When a transmitting node sends an Error Frame, it is detected by all the other nodes on the network. They respond by sending their own error flags.
- 17. Structure of an ERROR FRAME ERROR FLAG ERROR DELIMITER ERROR FLAG – Unique message sent by the node detecting an error. Any receiving node will respond with its own error flag transmission. ERROR DELIMITER – “ quiet” period following initial error flag transmission.
- 18. ERROR TYPES Greater-than-allowed number of consecutive bits of the same polarity trigger an Error Flag. Stuff Error Sending nodes verify their own transmissions and re-send if there’s an inappropriate bit. Bit Violation A dominant bit in EOF, Interframe Space, CRC Delimiter or ACK Delimiter triggers an Error. Form Violation Every receiving node should acknowledge message. If no ACK received, originating node generates Error Flag and re-sends message. ACK Error If the checksum fails at any node, the Error Flag will cause the originating node to re-send. CRC Error
- 19. OVERLOAD Frame Structurally similar to the Error Frame, but sent during the Intermission period. Originally used to allow an early ECU chip to keep up with network traffic. Not usually needed by modern processors.
- 20. CAN NETWORKS ERRORS DETECTED (none shown) MSG DATA (shown in hex) ARB ID MSG LENGTH CAN DATA on viewing software
Notes de l'éditeur
- 11-bit address allows 2048 message identifiers. 29-bit address allows up to 537 million (!!) message identifiers.
- SOF is transmitted as a single dominant bit.
- Priority is determined by ANDing the two bits together from simultaneous competing signals; if sending node detects a dominant bit where it sent a recessive bit, it cancels transmission and attempts to re-send at next opportunity. Arbitration Field is 11 bits + RTR bit in Standard, 29 bits + SRR, IDE, RTR bits in Extended. RTR bit: Identifies Remote Tranmission Request. Dominant in Data Frame, recessive in Remote Frame. SRR bit: Replaces RTR bit in Extended Frames. IDE bit: Idenfier Extension. Would be a control flag in Standard Frame, but is part of Arbitration Field in Extended frame. Transmitted dominant in Standard Frame, recessive in Extended Format.
- First flag is R1 in Standard Frame (dominant), IDE for Extended Frame (recessive). Second Flag is R0, reserved. Normally sent dominant. Four-bit Data Length Code may have values from 0 through 8. Indicates length (in bytes) of the actual data field.
- May be up to 8 bytes (64 bits) long.
- Checksum is derived from contents of SOF, Arbitration Field, Control Field, and Data Field.
- Transmitter sends first bit recessive. Receivers acknowledge data transmission by sending a dominant bit, which Transmitter detects. If no dominant bit is detected, message is retransmitted.
- Single recessive bit.
- Active error flag: six consecutive dominant bits. Passive error flag: six consecutive recessive bits.
- Error delimiter: eight recessive bits.