Lin protocol description. Automotive body network презентация

LIN protocol description

Automotive Body Network

Typical LIN Applications

MUX Standards (Costs and Speeds)

LIN Consortium Consortium formed in 1998. Five Car manufacturers ONE Semiconductor Supplier (Motorola) One tool Supplier (VCT) Specification finalised on 02/02/00 Official Launch at SAE March ‘00 Open Specification. Motorola Ready to support LIN with extensive device families and new parts already in the discussion/ spec finalization loop. First dedicated LIN part available Q3 ‘00

LIN Standard - Overview

Hierarchical Network Structure

Sub-Network: LIN vs. CAN

SubNets Necessary to reduce Busload on main Bus Solutions CAN Automotive Standard Bus Compatible with Main Bus Expensive (Die Size/ Dual Wire) Serial Sub Bus no standard Bus System not compatible with Main Bus inexpensive SCI-Based: Interface exists even on cheap devices Interface can easily be reconstructed by ASIC or CPLD

Sub Bus Concept Basic Requirements: Satisfy Need for a Standard for Sub Busses Cost driven: The solution must be cheaper than CAN Reliability: Same Level as CAN expected Long Term Solution Logical Extension to CAN Scalable: Capability to extend Systems with additional nodes Lowering Cost of Satellite nodes: No Crystal or Resonator Easy implementation Simple State Machines Low Reaction Time (100 ms max) Predictable Worst Case Timing

Master / Slave Protocol 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 the master. The node serving as a master can be slave, too!

Master / Slave Protocol Master has control over the whole Bus and Protocol The master controls which message at what time is to be transferred over the 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 on consistance 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)

Master/Slave Protocol Slave Is one of 2-16 Members on the Bus and receives or transmits Data when an 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!

LIN protocol offers message timing predictability 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

Data Transmission

Message Frame Synch Byte: Specific Pattern for Determination of Time Base (Determination of the time between two rising edges) A Synch Byte precedes any Message Frame ID-Field: Message Identifier: Incorporates Information about the sender, the receiver(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 the 2 LSB of the ID-Field. Each class has 16 Identifiers. A total of 64 Message Identifiers are possible. 2 Parity Bits protect this highly sensitive ID-Field.

Identifier The identifier field is sent by the master node to all LIN nodes This identifier normally contains one of 64 different values and includes 2 parity bits in the 8 bit data The identifier is normally associated with a collection of signals that are subsequently transmitted on the LIN bus In a specific case this can initiate SLEEP mode in the LIN slave nodes – in this case no further data is transmitted on the LIN bus

LIN Message Frame

LIN Communication - Data from Slave to Master

LIN Communication - Data from Master to Slave(s)

LIN Communication - Data from Slave to Slave

LIN Message Frame

Frame Synchronisation (1)

Frame Synchronisation (2)

Bit-Synchronisation A start bit transition to a low logic level (dominant) indicates a start of a byte, least significiant first and completing with a logic high level (resessive) bit to indicate the STOP bit

Bit Sampling

Bit-Synchronisation

Taking account of Ground-Shift

LIN Physical Interface

Examination of whether the Deadline is met

Message latency

Message latency across a network

Latency optimisation with LIN

Variables Scheduling

Event Triggered Message Problem Specific node communication required but this takes up too much time for all network messages Solution : Event Triggered frame: Header is sent out normal case: no answer Rare response: only one node responds Very rare response : several nodes respond simultaneously Cases 1 and 3 are exceptions that should be addressed at the application design. Event triggered messaging is complementary to the regular signal based messaging scheme

Further information http://www.lin-subbus.org

LIN Development Flow

LIN Configuration Description File Includes all essential information of network signals, latency periods, cycle times, nodes affected Input file serves as a development interface for a node LIN Application Generator LIN-Emulator LIN Analyser

The Workflow Data Input Definition of objects Definition of relations between the objects Data Processing Signal Packing (Frame Editor/Frame Compiler) Timing Analysis Data Output Configuration file generation Various optional customer-defined post-operations