CprE 458/558: Real-Time SystemsIntra-vehicular communicationSlide 3How do we connect these control devices?Fieldbus Networks: basic motivationFieldbus NetworksFieldbus AdvantagesWhat constitutes a Fieldbus?Fieldbus: OSI layer detailsWhat Fieldbus Networks are currently on the market?Controller Area Network (CAN)CAN featuresCAN architectureWorking of the CAN network: exampleTradeoff: CAN bus versus point-to-point connectionsCAN: message formatExtended CAN message formatPhysical CAN connectionImplicit collision handling in the CAN busImplicit collision handling in the CAN bus: exampleOther applications of CANReferencesCprE 458/558: Real-Time Systems (G. Manimaran) 1CprE 458/558: Real-Time Systems Controller Area Network: OverviewCprE 458/558: Real-Time Systems (G. Manimaran) 2Intra-vehicular communication•A typical vehicle has a large number of electronic control systems•The growth of automotive electronics is a result of:–Customers wish for better comfort and better safety.–Government requirements for improved emission control–Reduced fuel consumption•Some of such control systems–Engine timing–Gearbox and carburetor throttle control–Anti-block systems (ABS)–Acceleration skid control (ASC)CprE 458/558: Real-Time Systems (G. Manimaran) 3Intra-vehicular communication•The complexity of the functions implemented by these electronic control systems necessitates communication between them.•In addition, a number of systems are being developed which will cover more than one device. For example–ASC requires the interplay of the engine timing and carburetor control in order to reduce torque when drive wheel slippage occurs.–In the electronic gearbox control, the ease of gear changing can be improved by a brief adjustment to ignition timingCprE 458/558: Real-Time Systems (G. Manimaran) 4How do we connect these control devices?•With conventional systems, data is exchanged by means of dedicated signal lines.•But this is becoming increasingly difficult and expensive as control functions become ever more complex. •In the case of complex control systems in particular, the number of connections cannot be increased much further.•Solution: Use Fieldbus networks for connecting the control devicesCprE 458/558: Real-Time Systems (G. Manimaran) 5Fieldbus Networks: basic motivationWhy use Fieldbus Networks? To avoid this…Figure 1 Traditional Wiring - two pairs of cables can substitute all typical connections.CprE 458/558: Real-Time Systems (G. Manimaran) 6Fieldbus Networks•Fieldbuses are communication technologies and products used in vehicular, automation and process control industries. •Proprietary Fieldbuses–Proprietary Fieldbuses are an intellectual property of a particular company or body.•Open Fieldbuses–For a Fieldbus to be Open, it must satisfy the following criteria.–The full Fieldbus Specification must be published and available at a reasonable price. –Critical ASIC components must be available, also at a reasonable price. –Well defined validation process, open to all of the Fieldbus users.CprE 458/558: Real-Time Systems (G. Manimaran) 7Fieldbus Advantages•Reduces the complexity of the control system in terms of hardware outlay.•Resulting in the reduced complexity of the control system, project design engineering is made simpler, more efficient and conversely less expensive.•By selecting a recognized and well established system, this will make the Fieldbus equipment in you plant or plants interchangeable between suppliers. •The need to be concerned about connections, compatibility and other potential problems is eradicated.CprE 458/558: Real-Time Systems (G. Manimaran) 8What constitutes a Fieldbus?The specification of a Fieldbus should ideally cover all of the seven layers of the OSI model.CprE 458/558: Real-Time Systems (G. Manimaran) 9Fieldbus: OSI layer details•Physical Layer [1] What types of signals are present, levels, representation of 1's and 0's, what type of media, connects, etc. •Link Layer [2] Techniques for establishing links between to communicating parties. •Network Layer [3] Method of selecting the node of interest, method of routing data. •Transport Layer [4] Ensuring what was sent arrives at the receiver correcting any correctable problems. •Session Layer [5] Not applicable to Fieldbuses. •Presentation Layer [6] Not applicable to Fieldbuses. •Application Layer [7] Meaning of data. •The best way of covering layer 7 is to define standard profiles for standard devices.CprE 458/558: Real-Time Systems (G. Manimaran) 10What Fieldbus Networks are currently on the market? •some of the Fieldbus technologies currently on the market –RS-232–RS-485–CAN ( we will discuss in detail)–ARCNET–IEC 1158-2–BITBUS (IEEE 1118)–ModBus–HART–Conitel–DF1–Data Highway [+]CprE 458/558: Real-Time Systems (G. Manimaran) 11Controller Area Network (CAN)•Controller Area Network (CAN) is a fast serial bus that is designed to provide –an efficient, –Reliable and–very economical link between sensors and actuators.•CAN uses a twisted pair cable to communicate at speeds up to 1Mbit/s with up to 40 devices. •Originally developed to simplify the wiring in automobiles. •CAN fieldbuses are now used in machine and factory automation products as well.CprE 458/558: Real-Time Systems (G. Manimaran) 12CAN features•Any node can access the bus when the bus is quiet •Non-destructive bit-wise arbitration to allow 100% use of the bandwidth without loss of data •Variable message priority based on 11-bit (or 29 bit) packet identifier •Peer-to-peer and multi-cast reception •Automatic error detection, signaling and retries •Data packets 8 bytes longCprE 458/558: Real-Time Systems (G. Manimaran) 13CAN architectureCAN BUSCS1 CS2 CS3 CS4 CS5CAN Station 1 CAN Station 5CprE 458/558: Real-Time Systems (G. Manimaran) 14Working of the CAN network: exampleCprE 458/558: Real-Time Systems (G. Manimaran) 15Tradeoff: CAN bus versus point-to-point connections•By introducing one single bus as the only means of communication as opposed to the point-to-point network, we traded off the channel access simplicity for the circuit simplicty•Since two devices might want to transmit simultaneously, we need to have a MAC protocol to handle the situation.•CAN manages MAC issues by using a unique identifier for each of the outgoing messages•Identifier of a message represents its priority.CprE 458/558: Real-Time Systems