CAN Bus Technologies - Case Study Example

CAN bus technologies In this paper I will discuss CAN bus technologies. This paper will take a look on Historical background, operation, working, implementation and advantages of the CAN bus technology. Controller Area Network (CAN) is becoming a de facto standard for data transmission in automotive applications. What is CAN Bus? Controller-area network is also known as CAN or CAN-bus was introduced as a vehicle bus standard design to permit microcontrollers and devices to have communication infrastructure with each other inside a vehicle with no a host computer.1 CAN is one of the field bus which is broadest application internationally complete named “Controller Area Network”. As a kind of serial communication bus by means of multi mainframe mode, the central design standard of CAN demands towering velocity and superior capability of contradicting electromagnetism disturb, still demands to make sure any mistakes which are fashioned in communication bus. When the distance of signal communication arrived at 10km, CAN still offers digital communication velocity with 50kbit/s (Kuanming, 2001). The backbone of the Controller Area Network is a prompt serial bus that is deliberate to present a trustworthy, well-organized, and an awfully economical link among sensors and actuators. CAN uses a twisted-pair cable to correspond at speeds up to 1 Mbits/sec, with up to 40 devices. CAN was initially developed to make simpler the wiring in automobiles. In the past, automobile manufacturers utilized to connect devices in vehicles using point-to-point wiring systems (Tindell et al, 1995). As additional electronics and controllers are deployed to observe and run vehicles, wiring started to turn out to be additional multifarious, huge, weighty and expensive. Automotive industry begins to diminish massive wires complexity with dedicated CAN link that offers low-cost, robust network, and multi-master communication system (Lawrenz, 1997). CAN bus has been utilized in the automotive industry or textile machinery, and it has as well found a exceptional method as a field-bus system surrounded by the industrial control sector, as it offers mechanisms that make it probable for devices of diverse types and makings to be integrated mutually and to communicate with each other.2 Controller Area Network: CAN is proposed as a communication network among the control units in vehicles. These days, CAN applications are gaining ground and it is enlarged to industrial computerization comprising marine and aircrafts electronics, trucks, factories, cars and many others (Tindell et al, 1995). History The CAN bus is came into view as a serial communications bus for real time control applications; functions at data rates of equal to 1 Mb/sec, and has outstanding error recognition and confinement potentials. CAN was primarily developed in 1983 by the German corporation, Robert Bosch, for operating in cars, to offer a low cost communications bus. By this the in-car electronics that have 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 because of its established reliability and robustness. 3 CAN bus is a worldwide standard and ISO 11898 standards are documented for its high-speed applications presentation and ISO 11519 standards are documented for it’s for lower-speed applications (Kuanming, 2001). Why was it developed? As in the early discussion I have stated that the origin of CAN bus has facilitated low cost and reliable communication inside the automobiles. In this section I will take a deep look on the development motive that originates this technology. The aim of every automobile company is to persuade its consumer requirements for better safety, ease, and convenience, and to fulfill with more and more severe government legislation for enhanced pollution management and minimum fuel exploitation, the car manufacturing has developed a lot of electronic systems. Like Traction Control, innermost door locking, Air Conditioning Control, powered seat, Engine Management, Anti-lock Braking and mirror controls are only a few examples (Kuanming, 2001). The difficulties of these control systems, and the conditions to exchange data among them meant that all the time more hard-wired, devoted signal lines had to be offered. Sensors had to be copied if considered parameters were advantageous by diverse controllers (Lawrenz, 1997) Apart from the price of the electric wiring looms wanted to connect all these machinery in a group, the physical immensity of the wiring looms occasionally made it impracticable to thread them about the automobile. As well to the price, the augmented number of connections fakes serious consistency, slip-up 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 trader of apparatus parts and sub systems to the automotive manufacturing: offered the explanation by identifying the Controller Area Network (CAN) or CAN bus. A lots of the world's chip producers at the present a extensive variety of semiconductor devices that put into practice the CAN bus protocol in little less cost controllers and interface devices and the majority of them found in the modern cars (Tindell et al, 1995). CAN bus operation In this section I will discuss the main functionalities and operations that can be performed by the CAN bus like, I will discuss Line coding scheme, Timing, Frame Structure, and frame types and Prioritization. First I am going to discuss the Frame Structure, and frame types. CAN frame: CAB bus has data frame comprising seven dissimilar fields with utmost data size of 134 bits that also includes stuffed bit The utmost amount of data bytes is just 8 bytes to accomplish little response times for high priority frames. In applications like that manufacturing process control, a little amount of data bytes may be a trouble when performing jobs like uploading code to an automaton. The greatest efficiency described as the amount of data bits divided per the total frame size-is 59%. Below the farm structure of the CAN bus is presented (Lawrenz, 1997). Figure 1 CAN data frame. Source [http://www.canbus.us/] Description of frame 4 1. SOF or Start of Frame: These bits suggest the start of a data or remote frame. 2. Identifier field: (have 11 or 29 bits) If we are using CAN 2.0 A then identifier is 11 bits or if we are using CAN 2.0 B then identifier is 29 bits, that is divided into 2 sub parts: 3. Data Length filed: (4 bits): this field shows the amount of bytes subsequent to the control field, this means it shows the number of bytes in the Data Field. 4. Data Field: it holds the data that we have to throw. This data can have 0 up to 8 byes utmost. 5. CRC Field: sit consists of 2 fields: it contains the chain of 15 bits that is a check code, and used for the error inspection in the sent message. 6. ACK Field: it holds of 2 fields: one is ACK that means Acknowledgment Slot bit. Second is ACK Delimiter: this is a filed recessive delimiter bit. 7. EOF Field: This End of Frame field includes 7 recessive bits, setting the limits of the end of a data or remote frame. CAN bus frame types: (Tindell et al, 1995) There are four types of frames designed for the CAN protocol. These have different frame types, namely: 1. Data 2. Remote 3. Overload 4. Error frames CAN bus protocols have bits in a frame those shows one of the following "0": dominant bit "1": recessive bit If a 0 and a 1 are sent at the same time, in two dissimilar messages, then bit "0", (dominant) will be taken into apprehension, disposal the message with the "1" bit. Bus access method: here I will take a look at the bus access method used by CAN Bus. A node may find to transmit merely when the bus is idle. If two or additional stations at the same time start transmitting, the bus access argument is determined by bit-wise arbitration by means of the arbitration field. Every station evaluates its transmitted bit period with the monitored bit stage. A station that broadcasts a recessive bit, and monitors a leading bus level, stops transmitting (Kuanming, 2001). The identifiers are transmitted bit by bit to the bus. For the rationale that a dominant value for all time overwrites a recessive value, the small binary value identifier message gains right of entry to the bus with no holdup. Frames that have misplaced arbitration will participate in an original arbitration round when the bus turned out to be idle again (Lawrenz, 1997). CAN Bus timing This section will elaborate the Timing concept in the CAN bus. I will discuss the synchronous or asynchronous concepts in this scenario. In the majority CAN controllers, 2- 8 bit registers are utilized to program the bit rate for CAN communication. As well as, it is also probable to direct the bit sample point and the maximum amount of adjustment of bit width that is able to be performed in order to re-synchronies with the bit stream on the bus. The timing of one bit period contains a number of bit timing logic or BTL cycles. In addition, the bit period is separated into 5 segments: Throughout the period the incoming border of a bit is expected. This segment corresponds to one bit timing logic cycle (Tindell et al, 1995). The bit timing logic or BTL decides the timing of the bits and synchronizes with the edges of the bit stream on the CAN bus. It checks the bus line by means of differential input comparator. The BTL synchronizes on a evolution at the opening of the frame and resynchronizes on supplementary transitions throughout reception of the frame. The bit timing logic as well as offers programmable time segments to balance for propagation delays and phase shifts (Lawrenz, 1997). ISO11898 has defined the supposed time for every bit in a CAN frame surrounding message that will be made up of 4 non overlapping time segments those I have discussed below:5 First time division is Sync-seg: is the segment which is utilized to synchronized nodes on the bus. The second time segment is Prop-Seg: this is a period of time that is engaged to compensate for physical impediment times inside the network. The third one is Phase-seg1: is a buffer segment that can be lengthened throughout re-synchronization to make up for oscillator drift and optimistic phase differences between the oscillators of the transmitting and receiving nodes. The last one is Phase-seg2: is a buffer segment that can be shortened throughout re-synchronization to make up for negative phase errors and oscillator drift. Below is an image of the Bit timing segments for the CAN BUS. Figure 2 Bit time segments source: [http://www.mjschofield.com/index.htm] Line coding scheme Now I will discuss the line coding scheme that is used by the CAN bus. Non Return to Zero or NRZ is the coding format that is used by the CAN bus. This encoding that also included the bit-stuffing for data communication among the differential two wire bus. The utilization of Non Return to Zero encoding makes sure compacted messages with a slightest number of transitions and elevated flexibility to peripheral disturbance (Kuanming, 2001). Prioritization In CAN bus networks have not the configuration of the conventional sense addressing of subscribers or station, however in its place, prioritized messages are broadcasted. A sender or transmitter transmits a message to all CAN bus attached nodes (Bosch, 1991). Every node makes a decision on the basis of the identifier established from the source means, if they should process the received message or not.  The identifier as well decides the priority that the message takes pleasure in competition for bus right to make use of.  If a node needs to transmit a message, it at the start waits in anticipation of the bus is quiet.  All nodes which desire to send information on the bus can broadcast their messages at the same time.  The others stay in the listening state (Noble, 1992). Comparison with Ethernet In this section I will present a comparison between Ethernet and CAN bus. I will discuss then in their strengths/weaknesses point of view. The first advantage of the CAN bus is its usefulness to frequently transfer small amounts of data that can be 64 bits or less, on the other hand Ethernet is good if we infrequently desire to transfer big amounts that can be 1500 bytes. But this transfer of big data in Ethernet is at lower speeds, but CAN bus can transfer at less data at more speed (Noble, 1992). Another point in favor of CAN bus is that CAN bus can be longer than a standard 100 m Ethernet segment. If we have a small system, that only have few nodes and just an inadequate number of message types, The main disadvantage of the CAN bus is that it has no exacting assistance in latency while Ethernet have a number of ways to handle the latency of the network.. (Noble, 1992) Conclusion As concluding the whole discussion I have discussed the CAN bus in such way that there is enough material to understand and know about the working of it. I have discussed its development motive, its history, main working and operation, frame structure and lots of other details. So the whole discussion have a central focus on the CAN bus operating and working. In the last section I have discussed its strengths/weaknesses with the Ethernet. I have concluded that CAN bus have a very bright future. No technology can stand against it in the automobile industry. Work Cited 1. Noble, I.E., EMC and the automotive industry, Electronics & Communication Engineering Journal, pp. 263-271, October 1992. 2. 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, 3. Lawrenz, W., CAN System Engineering From Theory to Practical Applications, Springer, New York, pp. 26, 1997. 4. Kuanming, Wu. The Theory and Design of Application System of CAN Bus. Beijing: Beijing University of Aeronautics and Astronautics Press, 2001. 18-34. 5. Bosch, R. CAN SPECIFICATION (Version 2.0), Germany: Stuttgart, 1991 Read More