CAN Holger Zeltwanger A personal review and an outlook © CiA CAN The OSI model Text (application software) Vocabulary + phrases * Grammar rules (Translation services) Normally (Start and stop indications) not used in single- (Page numbering) segment networks (Routing) Character set Paper, pen, or laser-beam * Including “confirmation” and “encryption” procedures © CiA CAN First 11898 transceivers 15 of 35 is +16V. CAN_L and V members 6. Description of the MediumCAN_H Access Unit 6.1 Physical Medium Attachment Sublayer Specification (Transceiver) exhibited on See /3/. The maximum rating for V Galvanic isolation between the bus nodes is optional. the first CiA 6.2 Medium Dependent Interface Specification (Bus connector) joint booth 6.2.1 Electrical Parameters See /3/. The output voltage at pin 9 (external positive supply) shall be +7 V < V+ < +13 V at an output current of up to 100 mA (current consumption of module). Modules are not allowed to source current into this pin. The electrical parameters for pin 9 (V+) refer to the proposal of the working group "Physical Note: Layer". They are not yet agreed upon by the General Assembly of CAN in Automation. 6.2.2 Mechanical Parameters The connector used to plug electronic modules to the bus line is a 9-pin D-Sub connector according to /4/. Its pinning is fixed as follows Pin Signal Description 1 - Reserved 2 CAN_L CAN_L bus line (dominant low) 3 CAN_GND CAN Ground 4 - Reserved 5 (CAN_SHLD) Optional CAN Shield 6 (GND) Optional CAN Ground 7 CAN_H CAN_H bus line (dominant(dedicated high) for supply of transceiver and optocouplers, CANshow if galvanic isolation of the bus nodes applies) 8 - Reserved (error line) 9 (CAN_V+) Optional CAN external positive supply at Interkama 1992 CiA® 102 © CiA Each bus node has to provide a male connector, meeting the above-mentioned specification. Within the modules, pin 3 and pin 6 have to be interconnected. Inside of such electronic modules providing two bus connections, and inside the T-connectors, all the pins (including the reserved ones) have to be connected. The intention is, that there shall be no interruption of any of the wires in the bus cable, assuming a possible future specification of the use of the reserved pins. By using the pin V+ for supplying transceivers in case of galvanical isolation, the necessity of an extra local power isolation (e.g. DC/DC-converter) is avoided. If an error line is needed within a system, then pin 8 shall be used for this purpose. CAN CAN physical layer options 2 u ISO 11898:1993 – High-speed CAN transceiver u ISO 11519-2:1994 – Low-speed CAN transceiver u SAE J2411:2000 – Single-wire CAN transceiver u ISO 11898-2:2003 – High-speed CAN transceiver u ISO 11992-1:2003 – Truck/trailer CAN transceiver u ISO 11898-3:2006 – Low-power/low-speed CAN transceiver u ISO 11898-5:2007 – Low-power/high-speed CAN transceiver u ISO 11898-6:2013 – Selective wake-up CAN transceiver u ISO 11898-2:2016 – Up to 5-Mbit/s CAN transceiver Lessons learnt: (1) Separate strictly MAU (medium access unit) specifications from device and network system design recommendations or specifications. (2) Don’t specify additional functions in separate documents. © CiA CAN CAN (FD) network design u SAE J1939-1X – CAN high-speed (250 and 500 kbit/s) u SAE J2284-1 – CAN high-speed (125 kbit/s) u SAE J2284-2 – CAN high-speed (250 kbit/s) u SAE J2284-3 – CAN high-speed (500 kbit/s) u SAE J2284-4 – CAN high-speed (2 Mbit/s) u SAE J2284-5 – CAN high-speed (5 Mbit/s) u ISO 15765-4 – CAN diagnostic network requirements u ISO 11992-1 – Truck/trailer point-to-point network u ISO 11783-1 – ISOBUS network specification u CiA 301/303 – CANopen network design rules u IEC 62026-3 – DeviceNet network specification u Arinc 825 – CAN (FD) for airborne u CiA 601-3 – CAN FD recommendations u CiA 601-5 – CAN FD reference topology examples © CiA CAN What comes next? u “Smart” CAN transceivers with additional functions such as selective wake-up (already available), security, filtering of CAN FD frames, “dynamic” ringing suppression, etc. u CAN FD transceivers supporting bit-rates higher than 5 Mbit/s. u CAN FD network systems using bus-line topologies running at bit-rates higher than 2 Mbit/s. © CiA CAN CAN data link layer norm u ISO 11898:1993 – CAN data link layer with 11-bit IDs u ISO 11898:1995 amendment – Extended frame format u ISO 11898-1:2003 – CAN data link layer u ISO 11898-1:2015 – CAN data link layer with CAN FD Lessons learnt: (1) Original names such as CAN 2.0 will survive for a long time. Official references such as ISO 11898-1 need a long time to be accepted and used in datasheets – some parties will never use them. (2) Even when submitted for international standardization, prove first the functionality and features before implement them (this is not just true for data link Standard CAN High-speed CAN High-speed CAN controller carrier modulated signal to generate baseband signal providing in- layer protocols). (3) To standardizecontroller the host interfacecontroller is nearly phase and quadrature components. Output of demodulator is applied High-speed CAN St andard CAN impossible, buttransmit the bits minimumtransmit bits functionalStandard CAN behavior High-speed is CAN standardized receive bits receive bits to equalizer for channel compensation. For the training of the (see CiA 601-2 andSymbol CiA 603). equalizer, simple LMS (least mean square) algorithm is considered generation [10]. Carrier High-speed modulation CAN controller Standard CAN High-speed CAN receiver receiver High-speed CAN signal © CiA generator High-speed CAN receive bits CAN Bus signal generator Slicer CAN_H CAN_L Equalizer Standard CAN CAN What comes next? received bits Figure 4. Proposed high-speed transmitter Standard CAN demodulator bit detector Sp(t) Standard CAN bits D DRDRR CAN bits Passband filter Ap Sp(t) Qs(t) A 1V P 1V Signal converter 3.5V Qd(t) 2.5V Closes for D bit 1.5V Figure 6. Proposed receiver Qs(t) Simulation Results FigureSome 5. High-speed South CAN Korean signal generation scientists have The receiver of the proposed scheme uses the bit pattern of the data introduced a multi-level modulation scheme field to run the receiver for the period of 5 bit durations and hold the Carrierto be frequencyused just selection in dominant bits. This operation for one bit period. This process is repeated until the end of approach allows bit-rates of over 100 Mbit/s data field. Figure 7 shows the simulation setup. Standard CAN frame As for carrier frequency selection of modulated signal Sp(t), usingand lower can carrier run frequency Classical can be CAN beneficial communication since attenuation is with data field bits set to all D’s is generated to make CAN signal lowersimultaneously in lower frequency region with in no CAN impacts. bus environment. However, while random bit generators are used to generate bits to be carried in this can cause high frequency noise generated from the transition of Sp(t). The combined signal Qd(t) passes dispersive channel experiencing© CiA frequency-dependent distortion. Additive white the standard CAN signal to interfere with Sp(t) especially in the start and end part of high-speed CAN signal. Setting carrier frequency Gaussian noise (AWGN) is added before the signal is input to higher will reduce interference but incur higher attenuation of receiver for demodulation. Carrier frequency of Sp(t) is set to 24MHz modulated signal. Carrier frequency is a parameter to be optimized and symbol rate of Sp(t) is 36MHz. 16QAM was used for symbol according to the channel characteristics and modulation schemes. generation. For the purpose of simplicity, the carrier frequency and timing of both transmitter and receiver is assumed to be perfectly Receiver matched. Figure 6 shows the proposed receiver. The differential signal received from the bus is converted to single-ended signal, using CAN frame Can signal With all 0 Receiver generator differential-to-single conversion device, which is applied to standard data field Proposed CAN bit detector and band-pass filter for high-speed signal channel Output SNR receiver Passband Random bit demodulation, respectively. Standard CAN detector monitors the bus signal generator and detects the start of recessive-to-dominant bit transition during generator AWGN data field and enables the high-speed CAN demodulator operation to run for the period of 5 D bits. Bandpass filter in the high-speed CAN Figure 7. Simulation setup receiver removes the interference from standard CAN signal as well as out-of-band noise, providing input to the demodulator and equalizer of the proposed scheme. The demodulator down-converts CAN Transport layer protocols u CCP (CAN Calibration Protocol) u SDO (Service Data Object) protocols (CANopen) u Explicit Messages (DeviceNet) u BAM and CTS (J1939-21) u ISO 15765-2 (ISO-TP) u XCP (Extended CAN Calibration Protocol) u etc. Lessons learnt: (1) Each application domain likes to re-invent transport layer protocols. This means, up to today this lesson has not been learnt (this is sometimes also true for other higher-layer protocols). (2) Specify a byte-oriented instead of a bit-oriented protocol overhead (see the new USDO protocol for CANopen FD), this simplifies implementations. © CiA CAN Migrating to CAN FD u ISO 15765-2:2016 – Transport protocol and network layer u ISO 22900-2:2016 – Diagnostic PDU API u ASAM XCP version 1.2 – Extended calibration protocol u CANopen FD – Universal Service Data Object (USDO) u Arinc 825 – CAN FD transport layer Lessons learnt: Migrating transport layer protocols from Classical CAN to CAN FD data link layer is not a big deal.