LIN Protocol Overview

Topology:

• Broadcast serial network

• Single Master/multiple Slave Concept
  - the master node (task) can be assigned to perform both master and slave operation
  - the medium access in a LIN base network is controlled by a master node so that no arbitration or collision management slave node is required.
  - true “plug-and-play” slave nodes implementation due to standardizesyntax for the specification by enhanced LIN features and LIN - node compatibility language.

• 12v Bus with 16 nodes or less
  - based upon LIN specification and standard driver characteristics
  - LIN is limited to 64 identifiers and relatively low transmission speed.

• Master Task
  - control over the whole Bus and Protocol: The master controls which message at what time is to be transferred over the bus.  It can also do the error handling.

- to accomplish this the master

• sends Sync Break, Sync Byte & ID-Field
• monitors Data Bytes and Check Byte, and evaluates them on consistence
• receives Wakeup Break from slave nodes when the bus is inactive and they request some action
• serves as a reference with it’s clock base (stable clock necessary)

• Slave Task
  - one of 2-16 members on the bus and receives or transmits data when an appropriate ID is sent by the master.

• Slave waits for Sync Break
• Slave synchronizes on Sync Byte
• 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 2, 4, or 8 Data Bytes & Check-Byte.
- The node serving as a master can be slave.

• Message Frame Header

- Sync Break:

Marks the Beginning of a Message Frame (less than 13 bit)

- Synch Field:

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

- ID-Field:

• Message Identifier: Incorporates Information about the sender, thereceiver(s), the purpose, and the Data field length.
• Length 6 Bit.
• 3 classes of 2/4/8 Data Bytes. The length coding is in the
• 2 MSB of the ID-Field. A total of 64 Message Identifiers ispossible.
• 2 linked Parity Bits protect this highly sensitive ID-Field.

• Message Frame Header

- Data Field:

• 1-8 bytes in length, as determined during system configuration of the message frame ID’s.
• may consist of one or more ‘signals’ appended together.

- Checksum Field:

• consist of single byte.
• defined as the 1’s complement sum of all data bytes.
• LIN 1.3 and Diagnostic message frames: classic checksum.
• LIN 2.0: Extended checksum-all data bytes plus the protected ID byte.

Physical Layer:

• single-wire: ISO 9141 compliant
  - max 20% / min 80% VBAT Low/High transmit level
  - min 40% / max 60 % VBAT Low/High receive threshold
  - controlled slew rate (1-2 V/µs)

LIN Transfer Speed:

• Speed up to 20K bit/sec:
  - Acceptable speed for many application (limited for EMI-reasons)
  - The recommended data rates are 2400bps, 9600bps and 19200 bps.
  - controlled slew rate (1-2 V/µs)

• Data Format:
  UART/SCI base
  - Hardware or software (with standard I/O port)
  - Low cost silicon implementation based upon common UART/SCI interface

Guaranteed signal-transmission latency times:

• Time Triggered Approach

- Message Length is known

• Number of transmitted data bytes is known minimum length can be calculated
• Each Message has length budget of 140% of it's minimum length
  - maximum allowed length is known
  - distance between beginning of two messages

- Message sequence is known

• Master uses scheduling table

- Use of different scheduling tables is possible

 

Network configuration:

• Standard LIN Configuration Language
  - allows nodes to be used for various purposes without jeopardizing the LIN system functionality by message incompatibility or network overload.
  - is useful for debugging LIN clusters or diagnose the traffic. - provides “plug-and-play” capability with any off-the-shelf slave node MCUs.

• Standard LIN API
  - simplifies Application code design.
  - enables to select any controllers that support LIN peripheral

Dynamic configuration:

• Standard LIN Tool
  - LIN Database Manager (LDM):
  The LDM is a standalone offline tool, providing a user-friendly Windows interface for logically describing and configuring LIN systems at a high abstraction level.

  - LIN Configuration Tool (lcfg):
  The LIN API, together with the LIN Configuration Tool and an optimized embedded SW package enables the user to get correctness and quality together with efficiency and reconfiguration flexibility.

  - LINspector:
  a highly flexible tool for testing and verifying communication for compliance with the LIN standard.