LIN

The first specification of the standard under the LIN brand was published in 1999 at the initiative of a consortium of European car manufacturers and other well-known companies, including Audi AG, BMW AG, Daimler Chrysler AG, Motorola Inc., Volcano Communications Technologies AB, Volkswagen AG and VolvoCar Corporation. The latest consortium specification (LIN 2.2) was published in 2010. Currently, the documents of the standard are transferred under the control of the International Organization for Standardization ( ISO ), where the standard was given the new name ISO 17987 . Due to the ISO policy, a copy of the standard has become paid.

The LIN protocol is designed to create low-cost, local networks for exchanging data over short distances. It serves to transmit input actions, switch states on control panels, and so on, as well as the response actions of various devices connected to the same system via LIN, occurring in the so-called “human” time range (of the order of hundreds of milliseconds).

The main tasks assigned to LIN by a consortium of European automobile manufacturers are the integration of automotive subsystems and components (such as door locks, wipers, power windows, radio and climate control, electric sunroof, and so on) into a single electronic system. The LIN protocol is approved by the European Automobile Consortium as a cheap addition to the highly reliable CAN protocol.

LIN and CAN complement each other and allow you to combine all electronic automotive devices into a single multifunctional on-board network. Moreover, the scope of CAN - areas where super reliability and speed are required; LIN's field of application is the combination of low-cost nodes that work with low information transfer rates at short distances and at the same time preserve flexibility, versatility, and ease of development and debugging. The LIN standard includes technical requirements for the protocol and for the data medium. As a serial communication protocol, LIN effectively supports the management of electronic components in automotive systems with a Class A bus (bidirectional half-duplex), which implies the presence of one master ( English ) and several slave ( English ) nodes in the system.

The standard defines the network topology , physical layer , signaling, data exchange protocol, network access program interface , bus configuration description method and testing methodology. In the standard of 7 parts:

• ISO 17987-1: General information and definitions.
• ISO 17987-2: Transport layer.
• ISO 17987-3: Protocol specification.
• ISO 17987-4: Physical layer specification 12V / 24V.
• ISO 17987-5: Application Programmer Interface (API).
• ISO 17987-6: Test report.
• ISO 17987-7: Tests for the physical layer.

Network topology of the common bus type. The network has only one master and several slaves (up to 15).

The physical layer is based on the ISO 9141-1 standard, better known as K-Line . It allows connecting up to 16 nodes with one signal wire (of which 1 master) with cable lengths up to 40 meters. Initially, it was envisaged to work only in cars with 12-volt on-board power supply (rated voltages 9 ... 18 V, overload up to 40 V). A number of microelectronic companies produce LIN / ISO 17987 physical driver chips. Some of them are shown in the table.

Signaling is based on an asynchronous interface ( UART ). Allowed speeds are from 1 to 20 ka baud , the sending format is 8N1. To simplify the nodes, the alarm provides a specific synchronization sequence, due to which the initial deviation of the clock source from the slave can reach 14%. This allows you to abandon the quartz or ceramic frequency stabilization and reduce the cost of the device.

Data exchange occurs in packets . Each package has a header . The title is only transmitted by the master. The header consists of a UART Break, a 0x55 sync byte, and a packet identifier byte. UART Break - a special package of 13 zero bits in a row. The standard UART Break contains 11 zero bits in a row, but, due to the permissible non-standard deviation of the synchronization frequencies, it was expanded to 13 bits. The packet identifier encodes the data length (up to 8 bytes) and the type of message. Message types can be predefined by the specification (for example, event or diagnostic frames) or custom (that is, their designation is determined by the device developer). After the header is the data that the master or slave can transmit, depending on the identifier value in the header. The packet ends with a single-byte checksum.

It is possible to put the bus into sleep state (silence on the line> 25000 bit intervals) and wake up the bus (zero by 8 bit intervals).

LIN is an object-oriented protocol. That is, it does not address physical devices on the bus but some functions encoded in the packet identifier. Therefore, the package does not have a formal device address.

• Flexray

• The now defunct LIN Consortium website .