Basics of In-Vehicle Networking (IVN)
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Major IVN technologies overview
This presentation deals with basics of LIN, CAN (FD), FlexRay
and automotive Ethernet technologies

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LIN Overview
Like in a classroom situation,
the LIN ‘master’ initiates theresponse of the otherparticipants• LIN = 12 V, single-wire serial communications protocol basedon the common SCI (UART) byte-word interface• Maximum speed = 20 kb/s (EMC/clock synchronisation)• Master controls the medium access: no arbitration or
collision management, guaranteed latency times• Clock synchronization mechanism by slave nodes (no need forquartz or ceramics resonator)• Nodes added without HW/SW changes in other slave nodes• Typically < 12 nodes, (64 identifiers & relatively low transmissionspeed)3

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LIN details
Physical Layer• Vsup between 7 V and 18 V
• Strict requirements for slope and symmetry• Duty-cycle: Min = 39.6 %, Max = 58.1% (Bus-load: time-constant between 1 µs and5 µs: 1k/1 nF 660/6.8 nF 500/10 nF) (not-synchronized oscillator <14% tolerance)

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LIN details
Communication concept• Communication initiated by the master task (message header)• Slave task activated upon recognition of identifier - starts the message response(1-8 data bytes + 1 checksum byte)• Data correctness: parity, checksum• Identifier = content, not the destination!
•Exchange of data in various ways:• M  S(s)• SM
• S  S(s)• .

5message frame
0 = “dominant” state
1 = “recessive” state
Not used = recessive

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LIN Applications• Mirrors, window lift, doors switches, door lock, HVAC motors, control
panel, engine sensors, engine cooling fan, seat positioning motors,
seat switches, wiper control, light switches, interface switches toradio/navigation/phone, rain sensor, light control, sun roof, RFreceivers, body computer/smart junction box, interior lighting, andmore
Roof :rain sensor, lightsensor, light control, sunroof

Steering Wheel: cruisecontrol, wiper, turning light,
climate control, radio,
telephone
Climate: small
motors, control
panel

Door: mirror, central ECU,
mirror switch, window lift, seat
control switch, door lockEngine:sensors, smallmotors

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Seat: seat position
motors, occupancy
sensor,controlpanel

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CAN Overview• Controller Area Network is a fast serial bus designed toprovide an efficient, reliable and very economical link
between sensors and actuators

In CAN communication, all partners
are equal and are able tocommunicate at any time. In case ofconflicts (two speaking at the sametime), arbitration is used to ensure
messages are understood.

• CAN connects the vehicle's electronic equipment• These connections facilitate the sharing of information andresources among the distributed applications• All nodes can send a message at any time, when two nodes areaccessing the bus together, arbitration decides who will continue

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CAN Applications• CAN was developed in early 1980’s for automotive and is
widely used in all car parts (Powertrain, Chassis, Body).
Every car developed in Europe, USA, and Japan has at leasta few CAN nodes; CAN is being adopted in Asia as well.
•An increasing number of products have a CAN transceiver
implemented together with other functionality (e.g. insystem basis chips, stepper motors, park assist, … )• CAN also found its way into Industrial Applications.
See http://www.can-cia.de/

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CAN – details
Characteristics• Asynchronous communication (Event Triggered)• Any node can access the bus when the bus isquiet• Non-destructive arbitration, 100% use of thebandwidth without loss of data, large latency for
low priority messages, low latency for high prioritymessages• Variable message priority based on 11-bit (orextended 29 bit) packet identifier• Automatic error detection, signaling and retries• CAN uses a twisted pair cable to communicate at
speeds up to 1 Mb/s with up to 40 devices.

Extended CAN frame (ISO 11898)
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CAN – details
Physical Layer(*)• CAN bus requires line termination• ISO 11898 standard define the impedance ofthe cable as 120 ± 12 Ω.
Twisted pair, shielded or unshielded isrequested.

(*) Single wire CAN (SEA2411, 33,3 kbit/s) and low speed CAN (ISO11898-3, 125Kbit/s) are not covered by above
description

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CAN – details

Bus arbitration in more details• If two messages are simultaneously sent over the CAN bus, the bus
takes the “logical AND” of the signal.
• Hence, the messages identifiers with the lowest binary number
gets the highest priority.
• Every device
listens on thechannel and backs
off as and when it
notices amismatch between
the bus’s bit andits identifier’s bit.

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CAN Flexible Data-rate• For increased bandwidth, CAN Flexible Data-rate has been
introduced as an extension to CAN
Two techniques are used:
1. Increase of the bit rate of the payload
2. Increase of the number of bytes in the payload

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CAN Flexible Data-rate, CAN SIC•CAN SIC – CAN with Signal Improvement Capability
CAN SIC suppress the ringing causes by the not optimized network
topology. These SIC transceivers are specified in CiA 601-4. There are twoimplementations available: one suppresses the ringing when transmitting;the other filters the ringing when receiving.
Results from ONSEMI CAN SIC solution:
Without ringing suppression

13With ringing suppression

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Flexray Overview• High data rates (up to 10 Mb/s)• Time- and event-triggered behavior• Redundancy• Fault-tolerance

As in a train-schedule, all FlexRay
traffic on the bus is nicely scheduledusing time-slots.

• Deterministic (use of “time-slots”)

FlexRay delivers the error tolerance, speed and timedeterminism performance requirements for x-by-wireapplications (i.e. drive-by-wire, steer-by-wire, brake-by-wire,etc.).

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FlexRay – Details
Physical Layer

Communication cycle

Static Segment:
Reserved slots for deterministic data that arrives at a fixed period.
Dynamic Segment: Is used for a wider variety of event-based data that does not require determinism(cfr.CAN)
Symbol Window:
Typically used for network maintenance and signaling for starting the network.
Network Idle Time: A known "quiet" time used to maintain synchronization between node clocks.
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FlexRay – Details
Frame Format

Clock Synchronization

See chapter 8 of FlexRay Protocol Specification

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Ethernet Overview: 100Base-T1, 1000Base-T1• Single twisted pair, full-duplex, 100/1000 Mbps.
• Cable length of up to at least 15 m.
• Differential signal is coupled into a twisted pair via capacitors.
• PHY converts bits to symbols (3 bits -> 2 symbols). Symbol can have value+1, 0 or -1, what corresponds to three different differential voltage levels.
• Peer to peer communication, switches are needed for more complex
network.
• To keep synchronization, communication is ongoing even if none of nodes
intend to send data.
Full-duplex channel

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Ethernet Overview: 100Base-T1
Physical layer details• One of link partners is Master (initiate training) and the second one is Slave(synchronize its clock with Master’s using clock recovery form data stream).
• As PHY uses PAM3 (3 bits -> 2 symbols) baud rate is 66 MBd/s.
• Both link partners transmits symbols simultaneously, so there might be 5
different differential voltage levels observed.
• Data to be transmitted are combined with side stream• scrambler (pseudorandom stream) for better EMC• performance (emissions).
Full-duplex channel

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Eye diagram of 100Base-T1
linkEthernet Overview: 10Base-T1S• 10 Mbps over single twisted pair cable, length of up to at least 15 m.
• Peer to peer half-duplex communication, optionally it can havecapability of:• Full-duplex peer to peer operation• Half-duplex multidrop (BUS topology like CAN, FlexRay, LIN… ) operation• Multidrop: One Master, up to at least 8 Slaves. Master initiates
communication by BEACON and then each Slave have an opportunity
to send data. This protocol is called Physical Layer Collision
Avoidance (PLCA).

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