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Embedded NetworksLocal Interconnect Network

LIN 1.3

Abraham Tezmol

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Abraham Tezmol, M.S.E.E

2

Embedded Networks

Local InterconnectNetwork (LIN 1.3)

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Abraham Tezmol, M.S. E.E.

LINWhat is LIN?

The LIN (Local Interconnect Network) is a serialcommunications protocol which efficiently supports the controlof mechatronic nodes in distributed automotive applications.

The domain is class-A multiplex buses with a single masternode and a set of slave nodes

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LINLIN Features

The main properties of the LIN bus are:

1. Single-master / multiple-slave concept

2. Low cost silicon implementation based on commonUART/SCI interface

3. Hardware, an equivalent in software, or as pure statemachine.

4. Self synchronization without quartz or ceramics resonatorin the slave nodes

5. Deterministic signal transmission6. Low cost single-wire implementation

7. Speed up to 20kbit/s

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LINWhy LIN?

Low Cost (Almost $1 per node)

Half the price of CAN

Baud Rate much slower than CAN networks.

Self synchronization in the slave nodes without crystal or ceramics

resonator

Mainly used for lower demanding applications such as side view mirrors,seats, sensors, actuators, etc.

Cuts on development costs.

Implementation based on common UART/SCI interface hardware

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LINLIN Versions

1.2 , 1.3 , 2.0 and the new 2.1

Most Products are developed using LIN version 1.3 because its ease of

use and simplicity. Nowadays, LIN 2.0 is becoming more accepted amongAutomotive developers.

2.0 or 2.1 versions are recommended for new designs.

1.3 slaves will works in 2.0 systems, but won't work from 2.0 slaves to 1.3systems.

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LINLIN and the OSI Model

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LINApplications

The LIN protocol was suggested in 1999 as a low cost sub-bus system to complementCAN in applications such as:

Vehicle Roof (Rain Sensor, Light Sensor, Light Control, Sun Roof)

Vehicle Doors (Mirror, Central Locking, Mirror Switch, Window Lift)

Engine (Sensors, Small Motors, Steering Wheel, Cruise Control Switches, Wiper,Turn

Signal, Radio, Climate Control)

Seat (Seat Position Motors, Seat heater, Occupancy Sensor)

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LIN

Master Task

Determines order and priority of messages.

Monitors Data and check byte and controls the error handler.

Serves as a reference with its clock base (stable clock necessary)

Receives Wake- Up Break from slave nodes

Slave Task

Is one of 2-16 members on the bus

Receives or transmits data when an appropriate ID is sent by themaster.

The node serving as a master can be slave, too!

Master / Slave Protocol

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LINCommunication Concept

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LINInformation Routing

In LIN systems a node does not make use of any information about the systemconfiguration, except for the denomination of the single master node.

System Flexibility: Nodes can be added to the LIN network without requiringhardware or software changes in other slave nodes.

Message routing: The content of a message is named by an IDENTIFIER.

The IDENTIFIER does not indicate the destination of the message, butdescribes the meaning of the data. The maximum number of identifier is 64,out of which 4 are reserved for special communication purposes such assoftware upgrades or diagnostics.

Multicast: As a consequence of the Message Filtering any number of nodes

can simultaneously receive and act upon messages.

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LINBit Rate

The maximum bit rate is 20kbit/s, given by the EMI limitation of the single wiretransmission medium. The minimum bit rate is 1kbit/s to avoid conflicts with thepractical implementation of time-out periods.

In order to allow implementation of low cost LIN devices, the use of followingbit-rates is recommended

Slow Medium Fast

2400 bits/sec 9600 bits/sec 19200 bits/sec

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LINMaster / Slave Protocol

Master

Has control over the whole Bus and Protocol

The master controls which message at what time is to be transferred overthe bus. It also does the error handling.To accomplish this the master

Sends Sync Break

Sends Sync Byte

Sends ID-Field

Monitors Data Bytes and Check Byte, and evaluates them onconsistence

Receives WakeUp Break from slave nodes when the bus is inactiveand they request some action.

Serves as a reference with its clock base (stable clock necessary)

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LINMaster/Slave Protocol

Slave

Is one of 2-16 Members on the Bus and receives or transmits Data whenan appropriate ID is sent by the master.

Slave snoops for ID.

According to ID, slave determines what to do.

either receive data

or transmit data

or do nothing.

When transmitting the slave

sends 1, 2, 4, or 8 Data Bytes

sends Check-Byte

The node serving as a master can be slave, too!

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LINLIN Message Frame

0 to 8 data fields checksum

message response

synch break

13 bit

synch field identifier

message header

byte field

SCI / UART format

start stop

0 1 2 3 4 5 6 7

LSB

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LINMessage Frame - Header

Synch Break:

In order to identify clearly a beginning of a message frame its first field is asynchronization break (SYNCH BREAK). A SYNCH BREAK FIELD isalways sent by the master task.

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Synch Byte:

Specific Pattern for Determination of Time Base(Determination of the time between two rising edges)

A Synch Byte precedes any Message Frame

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ID-Field:

Message Identifier: Incorporates Information about the sender, thereceiver(s), the purpose, and the Data field length.Length 6 Bit.4 classes of 1/2/4/8 Data Bytes. The length coding is in the2 LSB of the ID-Field. Each class has 16 Identifiers. A total of 64 MessageIdentifiers are possible.

2 Parity Bits protect this highly sensitive ID-Field.

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2 Parity Bits protect this highly sensitive ID-Field.

The identifiers 0x3C, 0x3D, 0x3E, and 0x3F with their respectiveIDENTIFIER FIELDS 0x3C, 0x7D, 0xFE, and 0xBF (all 8-byte messages)are reserved for command frames(e.g. sleep mode) and extended frames

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LINResponse Fields Data Field

The DATA FIELD consists of a BYTE FIELD containing eight bits of datato be transferred by a MESSAGE FRAME. The transmission happens LSBfirst.

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LINResponse Fields Checksum

The CHECKSUM FIELD contains the inverted modulo-256 sum over alldata bytes

The sum is calculated by ADD with Carry where the carry bit of each

addition is added to the LSB of its resulting sum. This guarantees security

also for the MSBs of the data bytes.

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LINIdentifier

The identifier field is sent by the master node to all LIN nodesThis identifier normally contains one of 64 different values andincludes 2 parity bits in the 8 bit data

The identifier is normally associated with a collection of signals thatare subsequently transmitted on the LIN bus

In a specific case this can initiate SLEEP mode in the LIN slavenodesin this case no further data is transmitted on the LIN bus

synch break13 bit


message header

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message response

synch break

13 bit


message header

byte field

SCI / UART format

start stop

0 1 2 3 4 5 6 7

LSB

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message response

synch break

13 bit


message header

Synchronisation

frame

Synchronisation field

Identifier byte

Message

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LINPhysical Layer - Connections

The maximum number of nodes in a LIN network is not only limited by thenumber of but also by the physical properties of the bus line:

Recommendation:

- The number of nodes in a LIN network should not exceed 16. Otherwisethe reduced network impedance may prohibit a fault free communicationunder worst case conditions. Every additional node lowers the networkimpedance by approximately 3% (30 k || ~1 k).

- The accumulated galvanicwire length in a network is less or equal 40 m.

- The bus termination resistance is typically 1k for the master node and30k for the slave nodes.

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LINPhysical Layer

The Physical Layer is a single line, wired-AND bus with pull-up resistors inevery node, being supplied from the vehicle power net (VBAT).

A diode in series with the pull-up resistor prevents the electronic control unit(ECU) from being powered by the bus in case of a local loss of battery

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LINBus Values

The bus can have two complementary logical values: dominantor recessive.

The correspondence with bit and voltage values are given in the following table:

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LINError and Exception Handling

Types of Errors

Bit-Error

Check-sum error

Identifier-Parity-Error

Slave-Not-Responding-Error

Inconsistent-Synch-Field-Error

Physical-Bus-Error

lin 1.3 - iteso

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