 What is a Controller Area Network?  History of CAN  CAN communication protocol  Physical layer  ISO  CiA  CANopen  DeviceNet  Applying CAN

 CAN = controller area network  ECU = electronically controlled unit  Dominant = 0  Recessive = 1

 CAN implements a vehicle bus to which all CAN devices are connected  Allows all devices to communicate with one another

 Cars, trucks, buses, off-road vehicles  Maritime electronics  Aircraft/aerospace electronics  Medical equipment and devices  Coffee machines  Elevators

 Developed in Germany in the 1980's by engineers working at Robert Bosch  More functionality while reducing the weight and complexity of the wiring between controllers.  Multi-processor system which has better performance, increased reliability and is more maintainable  No communication protocols at the time met the speed and reliability requirements so Bosch developed CAN specification 2.0

 Physical and data link layer are implemented in the CAN controllers  Standard CAN bypasses layers 3-6  (1) Physical layer = actual hardware  (2) Data link layer = connects data to the protocol  (7) Application layer = interacts with OS of CAN device

 Since CAN is so widely used CAN chips are cheap  Reliability and error resistance of CAN calculated in mathematical model shown to have only 1 undetected error in 1000 years  Has world wide acceptance  Higher layer protocols defined for data intensive applications

 Data frame – sends data  Remote frame – requests data  Error frame – reports an error  Overload frame – reports a node is overloaded

 SOF – 1 dominant bit  Arbitration Field – message ID + RTR

 Control Field -Length of the data field to follow -For remote frame DLC is ignored, data field is always zero

 CRC Field – CRC segment + delimiter bit  ACK Field – acknowledgement bit + delimiter bit

 SOF – 1 bit  Arbitration field – 12 or 32 bits  Control field – 6 bits  Data field – up to 8 bytes  CRC field – 16 bits  ACK field – 2 bits  EOF -7 bits  IFS – 3 bits

 Off-road vehicles require more messages  11 bit message ID -> 29 bit  Use IDE to determine format: › 0 = 11 bit › 1 = 29 bit  Extended frame has trade-offs: › Bus latency time is longer › More bandwidth required › Error detection performance decreased

 Error occurs: bit stuffing, CRC incorrect, etc.  Error flag set followed by recessive delimiter and interframe

 Errors are caught quickly and have short recovery times: Error Frame LengthBaud RateTotal error recovery time (error frame + interframe) 14 bits1 Mbit/sec uSec 14 bits500 kBit/sec uSec 14 bits250 kBit/sec uSec 20 bits1 Mbit/sec uSec 20 bits500 kBit/sec uSec 20 bits250 kBit/sec uSec

 Overload flag – 6 dominant bits so all nodes detect overload, messaging ceased

 Producer/consumer  All messages are acknowledged for consistency (error if inconsistent or unacknowledged)  Nodes can accept or decline message filitering

 CAN uses message ID of the node to prevent collisions – high priority first  Uses bitwise arbitration as follows: › Node sends SOF with dominant level  Non-sending nodes begin listening › Node sends next bit and compares output signal with actual bus level  If sent recessive, detects dominant, then begins listening, else sends next bit › Transmits the rest of the message if it transmits all arbitration bits

 Node A = (high priority)  Node B =  B send a recessive, detects dominant, then listens 1 st arbitration bit2 nd arbitration bit3rd arbitration bit Node A100 Node B11listen Bus level100

 Errors detected by: › Bit monitoring › Checksum Check › Variable bit stuffing with a stuff width of 5 › Frame check › Acknowledge Check  Defective frames are aborted and retransmitted

 Malfunctions that would disrupt the system: › Transmitting Error from malfunctioning node › Receiving Error from malfunctioning node  CAN determines permanent vs. temporary malfunctions › Transmit error counter › Receive error counter

 Based on the counters, a node is in one of the following states: › Error Active  Transmit and receive counters <128 › Error Passive  Transmit or receive counters >127 › Bus-Off  Transmit error counter >255

 ISO is the most common standard for the physical layer  Nodes connected by 2 wires: CAN_H and CAN_L  Bus level determined by: › Vdiff = Vcan_h – Vcan_l › 2V for recessive, 0V for dominant  Bus terminated by 120 Ω resistors to suppress electrical reflections on the bus  Electromagnetic interferences are minimized with the differential voltage between CAN_H and CAN_L  At a maximum baud rate of 1 Mbit/sec a bus can be up to 40m long › At <10 kbit/sec can have up to 5000 m bus

 “Road vehicles – Controller area network (CAN)” 1993  Contains: › Data link layer and physical signaling › High speed medium access unit › Low speed fault tolerant medium dependant interface › Time triggered communication

 Users + manufacturers develop and support CAN  Based on participation and initiative  Represented at ISO and IEC committees

 Higher layer protocol adds: › Network management › Device monitoring › Communication between nodes  Requires CANopen nodes to have: › Communication unit › State machine › Object dictionary

 Application layer protocol adds 4 required objects: › Identity object › Connection object › Message router object › DeviceNet object

 Hewlett-Packard  Lockheed Martin  Boeing  NASA  GE Medical  Siemens Medical  John Deere

 Vehicle Spy (Vspy)  NETCAR-Analyzer  Volcano Network Architect (VNA)  Ability to: › Read bus signals › Transmit messages › Log data › Write to ECU memory

 ECU  TCU  CCU  SSM15  SSM25  CMU

 LIN-Bus (Local Interconnect Network)  Ethernet  RS232  Universal serial bus

 CAN specification 2.0 CAN specification 2.0 › A = standard format › B = extended format  ISO › Specific requirements on the sub layers of the data link layer and physical layer  CANopen specification CANopen specification  Book: A comprehensible guide to CAN  Book: Embedded networking with CAN and CANopen

 [1]Wilfried Voss. (2005). A Comprehensible Guide to Controller Area Network. Greenfield: Copperhill Technologies Corporation.  [2]Pazul Keith. (2002). Controller Area Network (CAN) Basics. In Microchip.  [3]CiA. (2001). Can physical layer. Retrieved 1 24, 2012, from cia.de/index.php?id=systemdesign-can-physicallayerhttp:// cia.de/index.php?id=systemdesign-can-physicallayer  [4]International Standard ISO First edition Road vehicles - Controller area network (CAN).  [5]Robert Bosch. (1991). CAN Specification. Robert Bosch GmbH.  [6]National Instruments. (2012). Controller Area Network (CAN) Overview. Retrieved 2 2, 2012, from  [7]Vehicle Spy. ( ). Vehicle Spy Professional. Retrieved 2 4, 2012 from  [8]CANopen. CANopen USA. Retrieved 2 4, 2012 from  [9]Real Time Automation. DeviceNet Introduction. Retrieved 2 4, 2012 from