CAN Bus Technology - Case Study Example

CAN Bus Technology This paper is about the CAN bus technology. CAN bus technology is more prevalent nowadays. My aim is to present a technological overview of this technology. I will discuss CAN bus history how It has evolved, the main motive behind its development. Then I will discuss some technical points regarding this technology. Overview of CAN bus: (Kuanming, 1999) Her I will discuss the CAN bus features in a little overview: CAN bus has a line configuration with passive bus coupling There are number of microcontrollers and chips that carry this protocol CAN bus has object oriented messages, that can be broadcasted and multicoated with response check In the CAN bus number of subscribers relies simply on the capability of driver modules CAN bus is a more than one master network CAN bus has access by bitwise mediation at CSMA-CA technique CAN bus presents a particularly prominent data confidentiality History The CAN bus or controller area network was at the start developed by Robert Bosch in 1986, it is also renowned to ISO standard11898 for the applications that has up to 1 Mbps data rate, and also has ISO standard 11519 for the applications up to 125 Kbps (Tindell et al, 1994). The development of the CAN bus have deep and very useful consequence on the in-car electronics that has cumbersome and having unreliable wiring looms and connectors was reduced. The car businesses carry on to utilize CAN for a rising number of applications. CAN bus also being used in many other control applications since for it’s established reliability and robustness. 1 Literature Review Controller-area network that is also acknowledged as CAN or CAN-bus was developed as a vehicle bus standard design to consent microcontrollers and devices to have communication infrastructure with each other inside a vehicle without a host computer.2 CAN is one of the field bus which is broadest application worldwide complete named “Controller Area Network” (Kuanming, 1999) As a kind of serial communication bus by means of multi mainframe approach, the innermost design standard of CAN demands high velocity and improved capability of contradicting electromagnetism concern, still demands to make certain any mistakes which are produced in communication bus. When the distance of signal communication arrived at 10km, CAN bus still proffer digital communication velocity with 50kbit/s (Kuanming, 2001). CAN is abbreviated as controller area network or also acknowledged as CAN bus. It is a serial bus network of microcontrollers which puts together sensors, devices, and actuators in a system or sub system for synchronized control applications. The exclusive quality of this network is that there is no addressing idea utilized in CAN, as happened in the sense of old addressing in networks as in the Ethernet (Liu et al, 2006). Somewhat, messages are broadcasted to all the points in the network by means of an identifier exclusive to the network. Foundation on the identifier, the individual node makes a decision whether or not have processing on this message and as well as come to a decision regarding priority of the message in conditions of competition for bus access. This procedure permits for constant transmission when a collision is identified, different from Ethernets that will stop transmission upon collision discovery (Kuanming, 1999). The hurdles of these control systems, and the constraint to exchange data among them meant that ever more hard-wired, devoted signal lines had to be offered. Sensors had to be copied if measured parameters were desirable by diverse controllers (Lawrenz, 1997). Apart from the price of the electric wiring looms needed to put together all these components jointly, the physical bulk of the wiring looms sporadically made it impracticable to thread them about the automobile. As well to the price, the augmented number of connections fakes serious reliability, mistake diagnosis, and repair troubles throughout together production and in service (Kuanming, 2001). An innovative resolution was desirable and, in the 1983 the Robert Bosch Corporation that was a very big dealer of machinery parts and sub systems to the automotive manufacturing: to be had the solution by making out the Controller Area Network (CAN) or CAN bus (Yang, 2007). CAN bus operation This section provides comprehensive details on different CAN bus operations and functionalities. I will also discuss the frame structure and different types of the frame. Now first I will discuss the frame structure of the CAN bus. The CAN protocol holds up two dissimilar message formats. They are merely distinguished by the span of the identifier which describes the recognition of the message in addition to the priority (Hairong et al, 2001). The standard set-up of the identifier is eleven bits long and the wide-ranging identifier has a length of 29 bits.3 In the CAN protocol the only receivers do not put into effect straight acknowledgements apposite to multicasting.  Though, probable errors are noticed and signaled. The mostly error discovery a number of methods are implemented within the CAN protocol with orientation to the data link layer (Kuanming, 1999). Here below has discretion of the CAN bus frame format: Figure 1 CAN data frame. Source [http://www.profichip.com/ SOF is the bits those illustrate beginning of a frame. Identifier field have 11 or 29 bits for the redeployment of the frame. Data Length area has 4 bits those show the length of data that is presenting the data packet. Data Field holds the data which we have to send. CRC Field bits have cyclic redundancy check code that is used for the error inspection. ACK Field holds Acknowledgment Slot bit and ACK Delimiter that is a filed recessive delimiter bit. EOF Field indicates the End of Frame. It have 7 recessive bits Now I will discuss CAN bus frame types. There are four types of frames premeditated for the CAN protocol. These have different frame types, namely: Data, Remote, Overload and Error frames (Tindell et al, 1995). CAN Bus timing Each node in a controller area network has its own timing clock, and no timing clock is sent throughout data transmission. Synchronization is through by separating every bit of the frame into a number of sections: 4 Synchronization Propagation Phase 1 Phase 2 The Length of every phase segment is capable to be accustomed based on network and node situation. The model point falls among Buffer Segment 1 and Buffer Segment 2, which assists to make possible constant synchronization. Permanent synchronization in turn facilitates the target to be capable to correctly read the messages. (Hairong et al, 2001) Below there is an image that exhibits the CAN bus trimming. Figure 1CAN Bus timing source [http://en.wikipedia.org/wiki/Image:CAN_Bit_Timing2.svg] In most of the CAN bus controllers, two eight bit registers are used to program the bit rate for CAN communication. Furthermore, it is also potential to organize the bit sample point and the greatest amount of adjustment of bit width that can be applied in order to resynchronized with the bit stream on the bus. The bit timing logic (BTL) determines the timing of the bits and synchronizes with the edges of the bit stream on the CAN bus. It supervises the bus line through a differential input comparator (Liu et al, 2006). The BTL synchronizes on a transition at the start of the frame and resynchronizes on further transitions during response of the frame. The BTL also provides programmable time segments to compensate for propagation delays and phase shifts (Hairong et al, 2001). Line coding scheme CAN bus make use of Not Return to Zero encoding format. This line coding scheme have the major advantage of facilitating the bit-stuffing for data communication among the discrepancy two wire bus. The NZR coding format makes easy the less number of the transitions and elevated resilience to external disturbance (Kuanming, 2001). Prioritization A unique attribute of CAN is its prioritization scheme. Throughout the mediation point of the communication progression, every node transmits its identifier bits against the bus, one by one. Because the bus functions likewise to an "AND" logic gate, a "0" bit that is also called a foremost bit from one node will apparent a "1" bit that is called a recessive bit from a challenging node. Because all nodes monitor the bus condition, they are cognizant if they have lost arbitration and appropriately revert to a passive state, releasing the bus for the highest priority node (Liu et al, 2006). These means facilitate plain broadcast or multicast messages, in which one node is capable to send the parallel message to a number of nodes, a potentially cooperative characteristic for a "boss-worker" comparable processing architecture (Tindell et al, 1994). Comparison with Ethernet As comparing the Ethernet and CAN bus gives lots of information regarding the usefulness and effectiveness associated scenarios about the both technologies. One plus point of the Ethernet is it uses a single very prevailing processor and employ video and stepper motor PCI peripheral cards with every node with necessary abilities (Liu et al, 2006). Data transfer CAN is good for the transfer small amounts of data Ethernet is good for the transfer large amounts of data Transfer speed CAN bus have more speed because it requires instance message delivery and it less size also help in faster data transfer. Ethernet facilitate in the large data but at lower speed than CAN bus. Size For a small system where we have few nodes and there is less number of the messages transfer CAN is best. For large number of nodes Ethernet is best. Conclusion In this paper the basic characteristics of CAN based networks are introduced. Controller Area Networks applications are emerging and gaining high ground in many applications from automobile industry to automation and factory industries. It’s usage in the passenger cars, trucks and buses, marine electronics, factory automation, industrial machine control, and non-industrial control is increasing increasingly (Yang, 2007). So we can say that CAN bus has a bright future and there are lot scope in this field is still available. References 1. Liu,W. Gao,J. Ding, Y, and Xu, J. Communication scheduling for CAN bus autonomous underwater vehicles, IEEE – International conference on mechatronics and automation, vol. 1, pp. 379–383, 2006. 2. Kuanming, Wu. Application System Design and Bus Theory of CAN, Beihang University Publishing Company, 1999 3. Hairong, X. Fengyu, Z. Design of CAN Bus System Brainpower Node Based on SJA1000, Computer Automatic Measure and Control, 2001, 9(2) 4. Yang Li, Yan Weisheng, Gao Jian, Zhang Lichuan. CAN System Development Based on CANoe Measurement and Control Technology, 2007, 26(4):66-67, 75 5. Tindell, K. W. Hansson, H., and Wellings, A.J. Analyzing Real-Time Communications: Controller Area Network (CAN), Proc. Real-Time Systems Symp., pp. 259-263, 1994. 6. Bosch, R. CAN SPECIFICATION (Version 2.0)," Germany: Stuttgart, 1991. 7. Tindell, K., Burns, A. and Wellings, A.J., Calculating Controller Area Network (CAN) Message Response Times, Control Engineering Practice, Vol. 3, no. 8, pp. 1163-1169, 1995. Read More