LIN Overview
Local Interconnect Network (LIN) is a low-cost serial communications protocol implemented mostly in automotive networks. It is typically used for mechatronic sub-nodes in automobiles (sensors, actuators), but is also well suited for industrial applications.
The following figure shows an example of an automotive communications architecture with a central gateway. Here, LIN controls the damper motors of the air conditioning system. The LIN specification denotes a LIN sub bus as a LIN Cluster:
Key Features
- Master-Slave medium access control concept
- Low-cost silicon implementation based on common UART/SCI interface hardware, an equivalent in software or as a pure state machine
- Self-synchronization without a quartz or ceramics resonator in the slave nodes
- Deterministic signal transmission with signal propagation time computable in advance
- Low-cost, single-wire implementation
- Speed up to 20 kbit/s
- "Signal" based application interaction
- Predictable behavior
- Reconfigurability
- Transport layer and diagnostic support
There are a variety of LIN node configuration possibilities, however, all nodes contain a LIN transceiver, a Universal Asynchronous Receiver Transmitter (UART) Module and an Application Controller (MCU) as shown:
Microchip offers a variety of LIN transceivers and MCUs with LIN-enhanced UARTs to enable these common LIN node configurations.
LIN Specification
The LIN standard includes the specification of the transmission protocol, the transmission medium, the interface between development tools, and the interfaces for software programming. LIN promotes the interoperability of network nodes from the viewpoint of hardware, software, and predictable Electromagnetic Compatibility (EMC) behavior.
The LIN specification was developed/maintained by the LIN Consortium up until 2010 with the release of the v2.2A specification.
In 2013, the LIN specification was transcribed to the International Organization for Standardization (ISO) as part of the process to be accepted as ISO standard ISO 17987 Part 1-7, which was released in 2016.
LIN Supplier ID maintenance is now handled by the Society of Automotive Engineers (SAE).
Specification Listing
- LIN v2.2A Specification
- ISO/CD 17987-1 Part 1: General information and use case definition
- ISO/CD 17987-2 Part 2: Transport protocol and network layer services
- ISO/CD 17987-3 Part 3: Protocol specification
- ISO/CD 17987-4 Part 4: Electrical physical layer (EPL) specification 12V/24V
- ISO/CD 17987-5 Part 5: Application programmers interface (API)
- ISO/CD 17987-6 Part 6: Protocol conformance test specification
- ISO/CD 17987-7 Part 7: Electrical Physical Layer (EPL) conformance test specification
LIN Workflow
The configuration of the LIN cluster is described in the LIN Description File (LDF). This is an ASCII-text file created by the network designer and is provided to vendors who will be developing the Master/Slave nodes.
From the LDF, ANSI-C driver code and header files are automatically generated using suitable tools such as the IHR LIN Driver Configuration Tool.
LIN Protocol (Overview)
Many network protocols may be described using the seven-layer Open System Interconnection (OSI) Model, as depicted here. LIN is an all-embracing concept according to the OSI model, where the specification covers the Physical, Data Link, Network, and Application layers.