Controller Area Network and its Applications
Contents
1. 5 Start Frame Bit Fig 4 CAN contain built in priority for messages to avoid conflicts E Available Products If standard frames are used exclusively in an application then both kinds of CAN controllers those according to version 2 0 B passive or active as well as those according to version 2 0 A or even older versions can be used That means that for these CAN networks the full range of available CAN controllers can be used All future CAN products will still perform standard frame communication When extended frames are used in a CAN network the number of usable products is only an extract of the full range of available CAN controllers Because of the aim to offer very cheap CAN controllers it is likely that even some future CAN controllers will be created which do not support extended frame actively For most applications the cheaper price will be more beneficial than the additional feature of extended frame communication Il CAN APPLICATIONS CAN was first created for automotive use so its most common application is in vehicle electronic networking However as other industries have realized the dependability and advantages of CAN over the past 20 years they have adopted the bus for a wide variety of applications JE Abe EXPLORING RESEARCH AND INNOVATIONS International Journal of Emerging Technology and Advanced Engineering Website www ijetae com ISSN 2250 2459 ISO 9001 2008 Certified Journal2. IE Abe EXPLORING RESEARCH AND INNOVATIONS International Journal of Emerging Technology and Advanced Engineering Website www ijetae com ISSN 2250 2459 ISO 9001 2008 Certified Journal Volume 4 Issue 3 March 2014 Controller Area Network and its Applications Akshay Rane Ajit Shendge Rushikesh Shinde J yoti Patil Ramakant Patil Nilima Zade 1234Students Dept Of Electronics P V P P College of Engineering Sion Chunabatti Mumbai 400022 Asst Prof Dept Of Electronics P V P P College of Engineering Sion Chunabatti Mumbai 400022 Abstract The Control Area Network Protocol is a serial communication protocol The CAN protocol is designed in such a way that the microcontrollers and other devices can communicates with each other within a vehicle in the absence of a host computer The development of CAN protocol started originally in 1983 at Robert Bosch GmbH In 1986 at the Society of Automotive Engineers in Detroit Michigan the CAN protocol was officially released CAN protocol is a type of message based protocol which is dedicatedly designed for automotive applications but now it has vast applications in other engineering fields like aerospace maritime industrial automation and medical equipment Keywords CAN protocol Control Area Network Protocol CAN CAN networks I INTRODUCTION The CAN is serial communication protocol that supports real time systems with high reliability It detects the collis
3. Emerging Technology and Advanced Engineering Website www ijetae com ISSN 2250 2459 ISO 9001 2008 Certified Journal Volume 4 Issue 3 March 2014 A safety critical communication does not use a safe state but redundancy instead It can use redundant networks and or redundant communication Figure 5 shows an example of a safety critical communication using a redundant communication The intrinsically safe communication is simply a CAN physical layer rated for certain conditions to ensure the CAN hardware will not cause any explosions It finds applications in the petrochemical and chemical industries CAN BUS Transceiver Monitoring Controller Controller SPI or UART Fig 5 Safety critical communication Even though this paper has explained the superiority of CAN over LIN as technology evolves a newer faster and even more robust protocol is going to replace CAN in the near future In the 2lst century s first decade a communication system called FlexRay was developed by the FlexRay Consortium 375 In 2010 this group released the latest version of the protocol the FlexRayTM Communications System specifications Version 3 0 1 This new robust serial networking technology designed for advanced control applications in the automotive industry is a time deterministic scalable and fault tolerant protocol having a data rate up to 10 Mb s Like most new technologies reaching the market FlexRay is more expensive
4. Volume 4 Issue 3 March 2014 Railway applications such as streetcars trams undergrounds light railways and long distance trains incorporate CAN You can find CAN on different levels of the multiple networks within these vehicles for example in linking the door units or brake controllers passenger counting units and more CAN also have applications in aircraft with flight state sensors navigation systems and research PCs in the cockpit In addition you can find CAN buses in many aerospace applications ranging from in flight data analysis to aircraft engine control systems such as fuel systems pumps and linear actuators Medical equipment manufacturer s use CAN as an embedded network in medical devices In fact some hospitals use CAN to manage complete operating rooms Hospitals control operating room components such as lights tables cameras X ray machines and patient beds with CAN based systems Lifts and escalators use embedded CAN networks and hospitals use the CAN open protocol to link lift devices such as panels controllers doors and light barriers to each other and control them CAN open also is used in nonindustrial applications such as laboratory equipment sports cameras telescopes automatic doors and even coffee machines IHI CONCLUSION Tab 1 tries a summarizing valuation of the standard and extended frame formats regarding the number of different identifiers the bus access time the bus through
5. error state As low is dominant all other nodes will detect bit stuffing violation and send their own error flags After this nodes that want to transmit including the one sending the interrupted message will start to do so As usual the node whose message has the highest priority will win arbitration and send its message If the CAN controller is in error passive mode the error frame will consist of six passive high bits Since the error flag only consists of passive bits the bus is not affected If no other node detected an error the message will be sent uninterrupted This ensures that a node having problems with receiving cannot block the bus All of this advanced error handling is done automatically by the CAN controller without any need for the host microcontroller to do anything This is one of the big advantages of CAN IIE Ae EXPLORING RESEARCH AND INNOVATIONS International Journal of Emerging Technology and Advanced Engineering Website www ijetae com ISSN 2250 2459 ISO 9001 2008 Certified Journal Volume 4 Issue 3 March 2014 Calculation of baud rate and sample point Baud rate The baudrate of the bus can be calculated from Baudrate forysta 2 n BRP 1 Where n is the number of time quanta for one bit and is defined as n SYNCHSEG TSEG1 TSEG2 BRP is the value of the BaudRate Prescaler Warning some CAN controllers like Intel 526 has another way of calculating the number of time quantas in a b
6. Acknowledgement Error If a transmitter determines that a message has not been acknowledged then an ACK Error is flagged CAN controller error modes A CAN controller can be in one of three states I Error active the normal operating mode for a controller Messages can be received and transmitted On detecting an error an active error flag is sent see error signaling 2 Error passive a mode entered when the controller has frequent problems transmitting or receiving messages Messages can be received and transmitted On detecting an error while receiving a passive error flag is sent IIE Ae EXPLORING RESEARCH AND INNOVATIONS International Journal of Emerging Technology and Advanced Engineering Website www ijetae com ISSN 2250 2459 ISO 9001 2008 Certified Journal Volume 4 Issue 3 March 2014 3 Bus off entered if the controller has serious problems with transmitting messages No messages can be received or transmitted until the CAN controller is reset by the host microcontroller or processor The mode of the controller is controlled by two error counters the transmit error counter tx_count and the receive error counter rx_count The following rules apply 1 The CAN controller is in error active mode if tx_count lt 127 AND rx_count lt 127 2 Passive mode is used if tx_count gt 127 OR rx_count gt 127 AND tx_count lt 255 3 Bus off is entered if tx_count gt 255 Once the CAN controller ha
7. ag 372 After detecting the 14th consecutive dominant bit in the case of an active error flag or an overload flag or after detecting the 8th consecutive dominant bit following a passive error flag and after each sequence of additional 8 consecutive dominant bits every transmitter increases its tx_count by 8 and every receiver increases its rx_count by 8 7 After the successful transmission of a message getting ack and no error until end of frame is finished tx_count is decreased by 1 unless it was already 0 8 After the successful reception of a message reception without error up to the ack slot and the successful sending of the ack bit rx_count is decreased by 1 if it was between 1 and 127 If rx_count was 0 it stays O and if it was greater than 127 it will be set to a value between 119 and 127 Note If a node is the only one on the bus or during start up the only one that has become active and it transmits a message it will get an acknowledgement error and will retransmit the message This may lead to that node going to error passive mode but not to it becoming bus off due to exception under point 3 Error signaling When an error is detected by a node it sends an error flag on the bus This prevents any other node from accepting the message and ensures consistency of data throughout the network The active error flag consists of six low bits and is used if the node transmitting the error frame is in active
8. e data frame format how it is specified in the CAN protocol specification versions 1 0 1 1 1 2 and 2 0 A Fully compatible to that is the standard data format Fig 1 b how it is specified in version 2 0 B In contrast to that Fig 1 c describes the extended data format with the 11 18 29 bit identifier version 2 0 B The meaning of the three control bits is as follows RTR bit Remote Transmit Request The RTR bit differentiates between data and remote frames In data frames this bit is dominant 0 in remote frames this bit is recessive 1 SRR bit Substitute Remote Request The SRR bit is a recessive bit It is transmitted in extended frames at the position of the RTR bit of standard frames IDE bit Identifier Extension The IDE bit differentiates between standard and extended frames In standard frames this bit is dominant whereas in extended frames this bit 1s recessive Similar to Fig 1 showing the standard and extended frame formats of CAN data messages Fig 2 shows the frame formats of CAN remote messages Here the RTR bit is set to recessive CP IIE Ae EXPLORING RESEARCH AND INNOVATIONS International Journal of Emerging Technology and Advanced Engineering Website www ijetae com ISSN 2250 2459 ISO 9001 2008 Certified Journal Volume 4 Issue 3 March 2014 Versions 1 0 1 1 1 2 2 0A o 11 bit Identifier a fo fo DLC SOF RTR fe CRC ACKN EOF Version 2 0B Standard Frame Fo
9. ine the bus access 371 C The CAN error process The error is detected by the CAN controller a transmitter or a receiver An error frame is immediately transmitted The message is cancelled at all nodes exceptions exist see CAN controller error modes The status of the CAN controllers is updated see CAN controller error modes The message is re transmitted If several controllers have messages to send normal arbitration is used Error detection Error detection is handled automatically by the CAN controller The detected errors are Bit errors 1 Bit stuffing error normally a transmitting node inserts a high after five consecutive low bits and a low after five consecutive high This is called bit stuffing A receiving node that detects violation more than five consecutive bits will see a bit stuffing violation 2 Bit error A transmitting node always reads back the message as it is sending If it detects a different bit value on the bus than it sent and the bit is not part of the arbitration field or in the acknowledgement field and error is detected Message errors I Checksum error each receiving node checks CAN messages for checksum errors 2 Frame error There are certain predefined bit values that must be transmitted at certain points within any CAN Message Frame If a receiver detects an invalid bit in one of these positions a Form Error sometimes also known as a Format Error will be flagged 3
10. ions it also detects the errors retransmits corrupt messages and gives priority to the received and transmitted messages The identifier length can be either 11 bits or 29 bits and the data length can vary from 0 to 8bytes The fast growing use of the CAN protocol in the Industrial applications resulted in development of the CAN based network In CAN based distributed control system the major problem is the size of distributed area The physical length limitation of the CAN bus is 2km at the rate of 20kbps The maximum speed of the CAN protocol is Imbps for 5Ometres and 500kbps for 100metres Sleep mode and wakeup are available options for each node to reduce power consumption A Standard and Extended Frame Format Fig 1 gives an overview of the different CAN data frame types All CAN messages start with the identifier arbitration field There are one or three control bits coming along with the identifier These bits define whether It is a standard or an extended frame and whether it is a data or a remote frame 370 a Versions 1 0 1 1 1 2 2 0A g 11 bit Identifier olojo oe data CRC ACKN EOF SOF RTR RE b Version 2 0B Standard Frame Format ol 11 bit Identifier oo oc data CRC ACKN EOF O R I res TD RE c Version 2 0B Extended Frame Format o 11 bit Identifier ala 18 bit Identifier ofofo me data CRC ACKN EOF R es z R SOF aww D E Fig 1 CAN Data Frame Types Fig 1 a shows th
11. it Consult your user s manual Sample point Quantapeforesample TSEGI 1 Quanta after sample TSEG2 Often the sample point is given in percent of the bit time This is TSEG1 1 TSEG1 1 TSEG2 D How CAN Communication Works As stated earlier CAN is a peer to peer network This means that there is no master that controls when individual nodes have access to read and write data on the CAN bus When a CAN node is ready to transmit data it checks to see if the bus is busy and then simply writes a CAN frame onto the network The CAN frames that are transmitted do not contain addresses of either the transmitting node or any of the intended receiving node s Instead an arbitration ID that is unique throughout the network labels the frame All nodes on the CAN network receive the CAN frame and depending on the arbitration ID of that transmitted frame each CAN node on the network decides whether to accept the frame If multiple nodes try to transmit a message onto the CAN bus at the same time the node with the highest priority lowest arbitration ID automatically gets bus access Lower priority nodes must wait until the bus becomes available before trying to transmit again In this way you can implement CAN networks to ensure deterministic communication among CAN nodes 373 1 Device A ID 11001000111 647 hex 2 Device B IG 11011111111 BFF hex 3 Device B Loses Arbitration Device 4 Wins Arbitration and Proceeds
12. put the CPU load the availability of products and the chip size cost The result is that it is advantageous to use the standard frame format as long as the application allows to do so From today s point of view only the American automotive manufacturers have applications needing extended frames Therefore it should be recommended for all other applications to use only standard frames 374 Extended Frame Format better than average o average below average Tab 1 Comparison of CAN Standard and Extended Frame Products IV CAN Safety is a CAN based technique providing safety in field bus systems It is not related to secure communication where data encryption and decryption is used to protect systems from unauthorized access It ensures the validity of CAN messages or the safety of the hardware in relation to explosions This technology already FUTURE DEVELOPMENT exists but is not commonly used in automotive applications There are three types of CAN Safety technologies safety related communication safety critical communication and intrinsically safe communication Here there is a safe state the controller is forced into given in any failure for a safety related communication This type of safety is found in CAN open Safety protocol and DeviceNet CIP Safety protocol however a custom safety related communication can be design as well IIE Ae EXPLORING RESEARCH AND INNOVATIONS International Journal of
13. rmat 11 bit Identifier 1 jo me CRC ACKN EOF D SOF R I res RE Version 2 0B Extended Frame Format o 11 bit Identifier afal 18 bit Identifier ajojo me CRC ACKN EOF Ss RD SOF R E 7 RE R Fig 2 CAN Remote Frame Types In case that several nodes within one system start a simultaneous transmission of message frames with the same identifier the following rules are valid Data frames have a higher priority than remote frames and standard frames have a higher priority than extended frames That means that e g a standard remote frame wins arbitration against an extended data frame if the 11 most significant bits of the identifiers are equal B CAN and OSI Model Many communication bus protocols do not use all the seven layers of this OSI Model Since CAN is a closed network it doesn t need to have security and to present the data in a user interface Also it does not need to maintain sessions and logins Hence it uses only two Layers such as Physical and Data Link Layer The CAN OSI model shown in fig 3 explains the transfer of data between two nodes Application Layer Application Layer Data Link Layer Data Link Layer Physical Layer Physical Layer CAN Bus Fig 3 CAN and OSI model The Physical Layer ensures the physical connection between the nodes in the network The Data Link layer contains Frames and information to identify the frames and errors It has information also to determ
14. s entered bus off state it must be reset by the host microcontroller or processor in order to be able to continue operation In addition this is only allowed after the reception of 128 occurrences of 11 consecutive recessive bits The counters are updated as follows 1 When a receiver detects an error the rx_count will be increased by 1 except when the detected error was a bit error during the sending of an active error flag or an overload flag 2 When a receiver detects a dominant bit as the first bit after sending an error flag the rx_count will be increased by 8 3 When a transmitter sends an error flag the tx_count is increased by 8 Exception 1 If the transmitter is error passive and detects an ack error because of not detecting a dominant ack and does not detect a dominant bit while sending its passive error flag Exception 2 If the transmitter sends an error flag because a stuff error occurred during arbitration whereby the stuff bit is located before the RTR bit and should have been recessive and has been sent as recessive but monitored as dominant 4 If a transmitter detects a bit error while sending an active error flag or an overload flag the tx_count is increased by 8 5 If a receiver detects a bit error while sending an active error flag or an overload flag the rx_count is increased by 8 6 Any node accepts up to 7 consecutive dominant bits after sending an active or passive error flag or an overload fl
15. than older similar technologies such as LIN and CAN REFERENCES 1 Bosch CAN Specification Version 2 0 Robert Bosch GmbH 1991 2 Kadionik Patrice Le bus CAN Ecole Nationale Sup rieure Electronique Informatique amp Radiocommunications Bordeaux 2001 3 Held Gilbert Inter and intra vehicle communications Auerbach Publications 2008 4 Provencher Hugo Introduction au protocole de communication CAN Presentation ELE4202 Commande des processus industriels D partement deg nie lectrique Ecole Polytechnique de Mtl Automne 2009 5 MotoHawk Training CAN Controller Area Network Presentation Woodward MotoTron Control Solutions 28 October 2008 6 http progrm77 blogspot com 2012 10 can controller area network html 7 http wiki altium com pages viewpage action pageId 8753896 8 http wenku baidu com view fff270bd960590c69ec376e5 html
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