LIN networks meet embedded design challenges
September 3, 2009 by John Day
By Willie Fitzgerald
Director, Product Marketing
Automotive Products Group
Microchip Technology Inc.
The Local Interconnect Network (LIN) is being implemented in vehicles around the world to help embedded system designers meet challenges including lower system cost, lower power consumption, weight reduction, and faster time to market for innovative electronic solutions.
LIN is a low-cost, serial communication system for distributed electronic systems, such as window controls, seat movement, mirror positioning, LED lighting, and other body-oriented applications. It is estimated that by 2010 there will be an average of 20 LIN nodes per vehicle; the second largest number of networked nodes.
The LIN Protocol
LIN is a holistic communication concept for local interconnect networks in vehicles. The specification covers the definition of the protocol and the physical layer, as well as the interfaces for development tools and application software. LIN enables a cost-effective communication network for switches, smart sensors and actuator applications within the vehicle where the bandwidth and versatility of CAN are not required. The communication protocol is based upon the SCI (UART) data format, including a single-master/multiple-slave concept, a single-wire 12V bus, and clock synchronization for nodes without a stabilized time base. This integrated concept of communications and development environment allows the implementation of a seamless chain of development and design tools, while enhancing the speed of development and the reliability of the network.
Body-control electronics improve the comfort and safety of vehicle occupants. Innovative body-control electronics enable car manufacturers to produce smarter vehicles that are pleasing to drive, and are reliable and safer. Body-control electronics improve driver safety by simplifying the operation of the vehicle and releasing the driver from the distractions of secondary activities.
As noted in Figure 1, typical applications for the LIN bus are assembly units, such as doors, steering wheels, seats, motors and sensors used for climate control, lighting, rain, smart wipers, intelligent alternators, switch panels, and RF receivers. LIN nodes are easily connected to the car network and become accessible to all types of diagnostics and services. The commonly used analog coding of signals is being replaced by LIN’s digital signals, leading to an optimized wiring harness.
Generally, actuators and sensors are hard-wired, with one Electronic Control Unit (ECU) utilizing CAN connectivity in a centralized body-control system. One ECU exchanges signals via a CAN link with other main ECUs. Hardwiring is chosen if the local actuators and sensors require high computing performance. In systems where the local performance can be low, an alternative distributed system based upon smart actuators and sensors can be used. This partitioning is chosen in order to achieve a scalable system architecture with universally applicable components. This architecture is cost effective if the additional cost for the local intelligence and networking can be compensated for by cost savings in production and development, due to a lower variety of electronic components. One of the key enablers for this type of architecture is the sub-bus LIN standard.
The key features of LIN are:
- Low-cost single-wire implementation
- Enhanced ISO 9141, VBAT-Based
- Speed up to 20 Kbit/s (limited for EMC reasons)
- Single Master/Multiple Slave Concept
- No arbitration required
- Low-cost Silicon implementation based upon common UART/SCI interface hardware
- Self synchronization in the slave nodes, without a crystal or ceramic resonator
- Significant cost reductions for the hardware platform
- Guaranteed latency times for signal transmission
With LIN residing in low-end applications, the following two factors are extremely critical:
- The communication cost per node must be significantly lower compared to CAN
- The performance, bandwidth and versatility of CAN are not required
The main cost savings of LIN versus CAN are derived from the single-wire transmission, the low cost of implementation as hardware or software in silicon, and the avoidance of crystals or ceramic resonators in slave nodes. These advantages are realized through LIN”s lower bandwidth and the restrictive single-master bus access scheme
At a Glance: LIN in Lighting Applications
Lighting performance and the aesthetics of a vehicle are improved with LEDs. Ambient lighting is one application area that is benefitting from the cost effectiveness of the LIN network. Ambient lighting placed in strategic areas within the vehicle has the ability to create a mood within the car, as well as outside of the car. The lower costs of LEDs and the embedded ICs that control them lead to usage in a variety of areas, such as cup holders, door sills and footwells, because LED technology enables deployment while satisfying space and power budgets.
Microchip Technology’s RGB LED reference design (part # APGRD004) shows how to create an interior ambient lighting module that controls a remote RGB LED device residing on a LIN bus, while supporting communication with a central body-control module. Module features include:
- Multi-color mixing from 7 to 16,383 colors
- 1,023 levels of intensity
- Constant voltage/ current drive
- LIN/J2602 bus slave capability
Additionally, Microchip’s LIN Serial Analyzer (part # APGDT001) serves as a network debug-and-analysis tool.
Over the last seven years, LIN has gained significant global interest beyond its initial roots in the European market. Factors contributing to applications using the LIN Standard include the following:
- LIN is a cost-effective bus concept for sub-networks in cars. LIN helps to optimize system cost and increases system efficiency. An open serial-bus standard for cost-effective and effective communication was developed to ensure the simultaneous availability of a consistent tools concept, and appropriate software interfaces.
- A wide availability of tools are available to support the design, development, simulation, analysis, calibration and testing of distributed networks with their associated electronic control units.
LIN advances basic networking capabilities to subsystems that have historically been considered uneconomical for smart actuators and controls. LIN complements the existing portfolio of automotive multiplex networks, led by CAN. Successfully addressing the needs for lower-cost systems supports the continued expansion of LIN nodes within the vehicle.
Willie Fitzgerald is the Director of Product Marketing for the Automotive Products Group at Microchip Technology Inc. He has been with Microchip since April 1994, when he joined the Company as the North America PIC® Microcontroller Product Marketing Manager. Currently, Fitzgerald is responsible for the global automotive marketing strategy. He has over 20 years of industry experience in embedded solutions for automotive applications.
Fitzgerald holds a BS in electrical engineering from Texas A&M University, College Station, Texas and a MBA with a marketing concentration from the University of Houston, Houston, Texas.