As applications continue to expand, today's and tomorrow's microcontroller proliferation and vehicle networks are continuing. The MCU is the "brain" of various electronic control modules in the vehicle, while the network is the "system interconnection." The Local Interconnect Network (LIN) is the industry's first to propose an in-car ClassA open multiplex protocol standard. It defines a low-cost serial communication system that supports distributed body control electronics in vehicles. LIN complements the existing product line of CAN-guided automotive multiplex networks. Industrial analysts point out that it is estimated that by 2010 each vehicle will have an average of 20 LIN nodes. Body control applications represent an important area of ​​the vehicle, and LIN helps to simplify the simplification of low-cost sub-networks without the need for additional bandwidth or complexity.
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General-purpose microcontrollers, such as Microchip's FlashPIC® microcontrollers, have a unique combination of program memory and peripherals that are ideal for applications that require 8-bit or 16-bit microcontrollers for body control in the CAN and LIN standards.
. Microchip's broad portfolio of products offers embedded control designers a wide range of price and performance options to meet their current design requirements.
Advancing body control electronics is an essential element for car manufacturers to produce more pleasing, more reliable, safer and smarter vehicle capabilities. Body control electronics improve vehicle safety by simplifying vehicle operation and freeing drivers from distracting secondary behavior. Each such electronic control module must address advanced performance and vehicle network connectivity and competitive price issues. The integration of advanced peripherals provided by microcontroller vendors, such as Microchip, gives system designers a competitive edge in the market, and they can create their RISC-based PIC® architecture.
LIN is a communication concept for the vehicle network sub-bus. The specification covers the definition of protocols and physical layers, as well as interface definitions for development tools and application software. LIN enables a cost-effective communication network for applications such as in-vehicle switches, smart sensors and actuators, without the bandwidth and versatility of CAN. The communication protocol is based on the SCI (UART) data format, a single master/slave concept that is a single-wire 12V bus and node clock synchronization that does not require a stable time base. The LIN Alliance developed this standard around serial low-cost communication concepts and development environments, enabling automakers and their suppliers to create ways to implement and process complex hierarchical multiplexing systems in a very cost-effective manner.
LIN's typical body control application body control electronics improves vehicle driver comfort and safety. Typical applications for the LIN bus are assembly units for climate control, lighting, rain sensors, smart wipers, smart generators, switch panels or radio frequency (RF) receivers such as doors, steering wheels, seats, motors and sensors. LIN nodes can easily connect to the car network and have easy access to all types of diagnostics and services. In addition, the commonly used signal analog code can be replaced by a digital signal to obtain an optimized wiring harness.
Roof: rain sensor, light sensor, lighting control, sunroof, etc. Door: mirror, central control ECU, mirror switch, window lift, seat control switch, door lock, etc. Climate: small motor, control panel Steering wheel: navigation control, wiper, lighting adjustment, etc. Options: climate control, radio, telephone, etc. Seat: seat position motor, personnel presence sensor, control panel engine: sensor, small motor
In a centralized body control system, the actuators and sensors are hardwired via an electronic control unit (ECU) with CAN connectivity. The ECU exchanges signals with other main ECUs via CAN links. If local actuators and sensors require high computing performance, you need to choose hardwired. In systems with low local performance, it may be necessary to choose a distributed system based on smart actuators and sensors. This configuration was chosen to implement a scalable system architecture with commonly available components.
This architecture is cost-effective, and because of the variety of electronic components, the additional cost of local intelligence and networking can be offset by savings in production and development costs. The key methods of this architecture are sub-bus LIN standards, low-cost electromechanical and assembly and semiconductor integration.
There are two key factors in LIN's low-end applications: (a) each node must have low communication costs compared to CAN; and (b) no CAN performance, bandwidth, and versatility. The main cost savings of LIN over CAN is driven by: (1) single-wire transmission; (2) low-cost hardware or in-chip software implementation; and (3) no need to use crystal or piezoelectric ceramics at the slave nodes. These advantages include lower bandwidth and a restrictive single-master bus access method. The main features of the LIN and CAN protocols are as follows.
LINCAN
Medium access control single master node multi-master node typical bus speed 2.4 to 19.6kbd62.5 to 500kbd
Multi-point transmission information routing 6-bit identifier 11/29-bit identifier node code NRZ8N1 (USART) bit padding NRZ
Each frame of data bits 2, 4, 8 bytes 0 to 8 bytes required transmission time 20kbd is 3.5ms when 125ms125kbd is 0.8ms
4 data bit error detection 8-bit checksum 15-bit CRC
Physical layer single line, Vbat twisted pair, 5V
Clock generation master node: crystal, slave node: RC/piezoceramic crystal per node related cost 0.51
LIN protocol
LIN is a single-wire serial communication protocol based on the general-purpose SCI (UART) byte word interface. LIN can also be executed with software equivalent code or a pure state machine. Media access in the LIN network is controlled by the master node, which eliminates the need for slave node arbitration or collision management, thereby ensuring that there is no worst case delay for signal transmission (see Figure 2).
The main features of LIN include:
-- low cost single line execution
--VBAT-based enhanced ISO9141
-- Speed ​​up to 20Kbps (due to EMC restrictions)
-- Single master node and multiple slave nodes concept
-- no arbitration needs
-- Low cost silicon implementation based on general purpose UART/SCI interface hardware
-- Self-synchronization from the node, no crystal or piezoceramic
-- Significantly reduced the cost of the hardware platform
-- Guarantee the delay time of signal transmission
-- predictable system
A special feature of LIN is the synchronization mechanism, which allows clock recovery from slave nodes without the need for crystal or piezoceramics. Line driver and receiver specifications follow an enhanced ISO9141 single line standard. The maximum transfer speed is 20kbps, which is due to electromagnetic compatibility (EMC) and clock synchronization requirements.
In addition to the naming of the primary node, the nodes in the LIN network do not use any information related to the system configuration. Nodes can be added to the LIN network without changing the hardware or software of the other slave nodes. The typical size of a LIN network is 12 nodes (although this is unrestricted) due to a small number of 64 identifiers and a relatively low transmission speed. Clock synchronization, simple UART communication, and single-line media are major cost-effective factors for LIN.
Communication Concept A LIN network consists of a master node and one or more slave nodes. All nodes include a slave node communication task divided into sending and receiving tasks, while the master node includes an additional master node to send tasks. Communication in an active LIN network is always initiated by the master node task.
The master node sends an information header consisting of a synchronization interrupt, a sync byte, and a message identifier. Just one of the slave tasks is activated when the identifier is received and filtered, and then begins to transmit the message response. The response includes two, four or eight data bytes and one checksum byte. The header and response sections form an information frame.
The information identifier represents the content of the information, not the destination file. This communication concept enables data exchange of various methods: from the master node (using it from the task) to one or more slave nodes, from one slave node to the master node and/or other slave nodes. It is possible to send a signal directly to the slave node at the slave node without routing through the master node, or to broadcast information from the master node to all nodes in the network. The order of the information frames is controlled by the master node. The number, order, and frequency of information in the master node timing frame are determined along with the baud rate, system response time, and time behavior. The design must be careful, because if the master node misses the information of a slave node, due to the concept of master-slave, this information will arrive at the master node first at the next timing.
The LIN protocol provides a dedicated synchronization mode that initiates each frame of information, allowing the slave node to synchronize its local time base with the time base of the master node without the need for crystal or piezoceramic.
The LIN physical layer LIN bus is a single-wire bus powered by a positive resistor node Vbat termination resistor termination matching resistor. The line transceiver of this bus is an enhanced tool of the ISO9141 standard. The bus can take two complementary logic levels: a dominant value representing a logic '0' with a near grounded electrical voltage, and an electrical voltage recessive value representing the logic '1' with access to the battery supply voltage.
The bus uses a master node's 1Ω pull-up resistor and a 30Ω resistor on the slave for termination. The typical value of the matching capacitance of the slave node is 220pF. The capacitance of the master node is relatively high in order to make the entire line capacitance independent of the number of slave nodes.
The main electrical parameters of the LIN physical layer are listed below:
Parameter typical value communication speed 9.6kbd, 19.2kdb
Voltage level 13.5V
Signal slew rate 2V/μs
Terminal matching resistor master node: 1kΩ
Slave node: 30kΩ
Terminal matching capacitor master node: 220pF
Slave node: 2.2nF
Line capacitance 100?150pF/m
The specification of the LIN physical layer imposes high performance requirements on the transceiver. Transceiver switching should not interfere with other electronic components. Special attention must be paid to the EMC requirements of the car manufacturer.
. With waveform shaping or edge rounding, the conducted emissions of the transceiver can be minimized.
Example of a LIN bus system: The number of electronic functions added to the door of a car door and mirror module is a good example of the use of the LIN bus. When performing maintenance, you can increase or decrease the functionality without affecting the original system design or affecting the hardware and software of the remaining slave nodes. Additional functions or options are required during the development process, and pre-assembled, pre-tested test modules can be integrated at the end of the vehicle's LIN assembly. The door LIN function cluster includes:
· Window lift, with / without anti-pinch control · Motor PWM control, window position monitoring · Door lock actuator control, including motor control (lock) and door switch control · switch panel control · switch lighting mirror function can be More LIN integration from the nodes depends on the flexibility of the OEM's optional feature plan for the user. These mirror functions include mirror up/down, in/out motor control, heating, puddle lights, turn indicators, dimming (electroplating mirrors), electric folding.
Summarizing the continuous advancement of body control functions, as well as microcontroller and LIN protocols are key factors in reducing system cost. Several factors have been promoting LIN as an extension of the "Universal Sub-Bus Network Standard", which includes:
The introduction of LIN occurred at a time when the in-vehicle electronic control module experienced dramatic growth. Many of today's automotive innovations are achieved through the use of advanced electronic concepts. Users pursuing vehicles with more comfort and safety have fueled the development of this market. Regulatory norms promote this trend. At the same time, automakers need to get cost-effective implementations from their suppliers.
LIN is a cost-effective bus concept for in-vehicle subnetworks. It helps optimize system cost and increase system efficiency. The LIN concept continues to find many supporters throughout the global automotive industry. Even though the LIN Alliance was initiated by an OEM, tool builder and semiconductor vendor group, this cost-effective communication open serial bus standard has demonstrated simultaneous availability in terms of ensuring a unified tool concept and appropriate software interfaces.
As one of the driving factors for implementing a hierarchical vehicle network, the LIN standard covers specifications such as transmission protocols, transmission media, interfaces between development tools, and software programming interfaces. From the perspective of hardware and software, LIN guarantees the interoperability of network nodes and predicts EMC behavior. The LIN bus meets the performance and cost requirements of body control applications. It supports standardization and reusability of actuator and sensor designs.
Body control applications benefit from continued advances in flash-based microcontrollers with a broad portfolio of memory, peripherals and packages, and LIN's global support as a low-end multiplexing solution standard. PIC microcontrollers are versatile building blocks that help develop effective solutions to complex vehicle control application challenges and accelerate time-to-market for automotive electronic control module developers.
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