---
title: Linbus
categories: [cheatsheets]
tags: [automotive]
---
# LIN Bus - Local Interconnect Network

* Version 1.0 was published 1999
* Used to connect ECU's
* Master-Slave Principle with up to 16 Slaves
* Transceiver is based on the UART protocol and LIN only has one cable
* Baud rate of about 20kBaud (as defined in the standard)
* Mostly 19.2kBaud are implemented in reality
* maximum of 40m cable


## Basic Connections

* Only the master is able to initiate connections
* Slaves can only answer to master-requests
* Master needs to init. the communication between two slaves
* Messages are send as in the scheduling table defined (in the master)


## LIN-Frame

```
<-----[ Header ]-----> <-----[ Response ]----->
```

#### Header

* Sync-Break - used for Frame Synchronisation
* Sync-Field - used for Bit Synchronisation (mostly 0x55)
* ID         - Unique Identifier (6 bytes + 2 parity bytes)


#### Reponse

* Datafield - contains data
* Checksum  - modulo 256 checksum of the data-field


### Special Frames

* Diagnostic Frames are send via Broadcast
* Event-Triggered Frames: Master asks for a Value, Slave only answers if the value changed.
  -> If two slaves answer: Buscollision
  -> Master requests the message with the higher priority first

### Checksums

* The checksum is calculated via a modulo 256 calculation
* The Carry-Bit is added to the LSB bit of the checksum

#### Example
```
  Data | Checksum
  0x41   0x41
+ 0x55   0x9f
+ 0x93   0x132    // to big, carry bit = 1
         0x33     // added carrt bit to LSB checksum bit
         0x12     // inverted the checksum

The Checksum is 0x12 and gets appended to the data.
```