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Introduction to CAN Bus Technology

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In this CAN Bus Technology introduction learn about the history and applications of the technology.

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Introduction to CAN Bus Technology

  1. 1. CAN Bus Technology
  2. 2. CAN Bus Introduction <ul><li>Controller Area Network (CAN) </li></ul><ul><li>Originally developed by Robert Bosch for automobile in-vehicle network </li></ul><ul><li>Multi-drop, Multi-master serial bus provides communications between controllers, sensors, and actuators. </li></ul><ul><li>Very reliable and robust, well proven technology (introduced mid 1980s) </li></ul><ul><li>Inexpensive </li></ul>
  3. 3. CAN Bus Introduction <ul><li>CAN 2.0 A </li></ul><ul><ul><li>Standard format </li></ul></ul><ul><li>CAN 2.0 B </li></ul><ul><ul><li>Extended format </li></ul></ul><ul><li>International Standard ISO 11898 </li></ul><ul><ul><li>ISO 11898-2 High speed applications up to 1 Mbps </li></ul></ul><ul><ul><li>ISO 11898-3 Low speed applications up to 125 Kbps </li></ul></ul>
  4. 4. CAN Bus Introduction <ul><li>CAN Applications </li></ul><ul><li>Automotive </li></ul><ul><li>Military vehicles </li></ul><ul><li>Industrial machinery </li></ul><ul><li>Medical systems </li></ul><ul><li>Agricultural machinery </li></ul><ul><li>Marine control and navigation </li></ul><ul><li>Elevator control systems </li></ul>
  5. 5. CAN Bus Introduction <ul><li>Network Layered Model </li></ul>Application Presentation Session Transport Network Data Link Physical CAN defines most of the lowest two layers Higher layer protocols defined by various industry standards: DeviceNet, CANOpen, CANaerospace, MilCAN, SAE J1939, ISO1192 and others
  6. 6. CAN Bus Introduction <ul><li>CAN Characteristics </li></ul><ul><li>All messages are broadcast </li></ul><ul><li>Any node is allowed to broadcast a message </li></ul><ul><li>Each message contains an ID that identifies the source or content of a message </li></ul><ul><li>Each receiver decides to process or ignore each message </li></ul>
  7. 7. CAN Bus Introduction <ul><li>CAN Characteristics </li></ul><ul><li>Bus length / Bit rate tradeoff </li></ul><ul><li>1M bit/sec 40 meters (131 feet) </li></ul><ul><li> 500K bit/sec 100 meters (328 feet) </li></ul><ul><li> 250K bit/sec 200 meters (656 feet) </li></ul><ul><li> 125K bit/sec 500 meters (1640 feet) </li></ul>
  8. 8. CAN Bus Introduction <ul><li>CAN characteristics – Physical Medium </li></ul><ul><li>Single twisted pair wire terminated on each end </li></ul>Node A Node B 120 Ω 120 Ω
  9. 9. CAN Bus Introduction <ul><li>CAN characteristics – Signal Levels </li></ul><ul><li>Differential signaling </li></ul>Volts 3.5 2.5 1.5 CAN H CAN L recessive1 dominant 0 recessive 1
  10. 10. CAN Bus Introduction <ul><li>CAN characteristics – Bit timing </li></ul>previous bit next bit Nominal bit time sync prop phase 1 phase 2 sample point Time Quanta Local timing logic re-synchronizes with bus on each recessive to dominant transition
  11. 11. CAN Bus Introduction <ul><li>CAN Characteristics </li></ul><ul><li>Network Size </li></ul><ul><li>The maximum number of nodes is not specified. </li></ul><ul><li>Networks are limited by electrical loading, up to 64 nodes is normal </li></ul>
  12. 12. CAN Bus Introduction <ul><li>Four Message Types </li></ul><ul><li>Data Frame </li></ul><ul><ul><li>Used to transmit data </li></ul></ul><ul><li>Remote Frame </li></ul><ul><ul><li>Used to request data transmission </li></ul></ul><ul><li>Error Frame </li></ul><ul><ul><li>Sent by a node that detects an error </li></ul></ul><ul><li>Overload Frame </li></ul><ul><ul><li>Sent by a node to request a delay in transmission </li></ul></ul>
  13. 13. CAN Bus Introduction <ul><li>Message Format (standard) </li></ul>0 – 64 Data field 0 – 8 bytes 1 Start of frame 7 End of frame 4 Data length code 1 ACK delimiter 1 Reserved 1 ACK slot 1 ID extension 1 CRC delimiter 1 Remote trans. 15 CRC 11 Identifier Bits Field Bits Field
  14. 14. CAN Bus Introduction <ul><li>Message Collision Detection / Arbitration </li></ul><ul><li>All nodes must wait for an idle bus condition </li></ul><ul><li>If two nodes begin transmitting simultaneously, they then participate in a non-destructive arbitration sequence </li></ul><ul><li>The node with the lower ID number wins the arbitration and continues transmitting its message </li></ul><ul><li>The loser of the arbitration backs off and re-tries </li></ul>
  15. 15. CAN Bus Introduction <ul><li>Error Detection Capabilities </li></ul><ul><li>Bit error </li></ul><ul><li>Acknowledge error </li></ul><ul><li>Form error </li></ul><ul><li>CRC errors </li></ul><ul><li>Stuff error </li></ul>
  16. 16. CAN Bus Introduction <ul><li>Error States </li></ul><ul><li>Error-active </li></ul><ul><ul><li>Normal operating mode, node participates in communications and error reporting </li></ul></ul><ul><li>Error-passive </li></ul><ul><ul><li>Node switches to passive error reporting </li></ul></ul><ul><li>Bus-off </li></ul><ul><ul><li>Node has detected too many transmit errors, stops transmitting (fault containment) </li></ul></ul>
  17. 17. CAN Bus Introduction <ul><li>End of presentation </li></ul>

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