FAQ Local Interconnect Bus (LIN) and SAE J2602

Basics

What is LIN?
Answer:
LIN (Local Interconnect Network) is a low cost serial communication system for distributed electronic systems in vehicles. It complements the existing portfolio of automotive multiplex networks. LIN enables cost-effective communication for smart sensors and actuators where the bandwidth and versatility of CAN is not required.

Does LIN replace CAN?
Answer:
No, LIN and CAN co exist in the automotive market.

LIN addresses an application space that requires less bandwidth and versatility when compared to the CAN application space.

What are the target applications for LIN Bus?
Answer:
Target automotive applications include mirrors, window lift, doors switches, door lock, HVAC motors, control panel, engine sensors, engine cooling fan, seat positioning motors, seat switches, wiper control, light switches, interface switches to radio/navigation/phone, rain sensor, light control, sun roof, RF receivers, body computer/smart junction box, interior lighting and more.

Can LIN be used for non-automotive applications?
Answer:
Although designed for automotive applications, LIN is not limited to automotive applications and has found it’s way already into applications such as appliance and consumer.

What is the latest LIN Bus Specification?
Answer:
In November 2006 LIN 2.1 has been released. No further changes are planned at this moment. Please check LIN home page (www.lin-subbus.de) for the latest status.

What is the compatibility between LIN 2.0 and 2.1?
Answer:
A LIN 2.1 master node may handle a LIN 2.0 slave node if the master node also contains all functionality of a LIN 2.0 master node, e.g. obsolete functions like Assign frame Id.

A LIN 2.1 slave node can be used in a cluster with a LIN 2.0 master node if the LIN 2.1 slave node is pre-configured, i.e. the LIN 2.1 slave node has a valid configuration after reset. A LIN 2.0 slave node shall not use NAD 0x7E since it is reserved as functional address for diagnostics in LIN2.1. The LIN 2.1 slave node will consider NAD 0x7E as a functional NAD and a LIN 2.0 slave node as a NAD.

The LIN physical layer of Revision 2.1 is technically identical to Revision 2.0. Only ambiguous and incorrect specifications have been clarified and missing specifications have been added. For example : A chapter about the physical layer compatibility has been added. The ambiguous term "clock tolerance" has been changed into "bit rate tolerance". The constraint for slave-to-slave communication has been clarified. A chapter has been added, which specifies the bit sample timing of byte fields. The supply voltage reference has become unique. In this context the voltage reference of the battery and ground shift has been changed from the voltage across the vehicle battery connectors to the ECU supply voltage connectors. A chapter about the performance in non-operation range has been added. A chapter about the performance during fault modes has been added. All parameters in this specification are defined for the ambient temperature range.

What is the difference between LIN and J2602?
Answer:
Generally speaking, SAE J2602 is a sub set of LIN Bus Specification Revision 2.0.

SAE J2602 uses LIN experience and LIN standard. Some differences of SAE J2602 to LIN 2.0/2.1 are SAE J2602 has more stringent requirements on Sample Point conformance testing, the configuration process is different and driver status is added to each response providing additional information. On the other hand, SAE J2602 uses one fixed baud rate of 10.4kBaud only.

What is Microchip’s role in the LIN consortium?
Answer:
Microchip Technology is an Associate Member of the LIN Bus Consortium.

Where can I find more information about LIN?
Answer:
Go to www.microchip.com/LIN or go to www.lin-subbus.de

Microchip Solutions

What is Microchip’s experience with LIN/J2602 applications?
Answer:
Microchip Technology is an associate member of the LIN Bus Consortium.

Through early involvement in the LIN Bus Consortium as well as an active role in the SAE J2602 working group Microchip has been early involved during the development of LIN and J2602 specification revisions.

Microchip’s application engineers have already supported a wide range of automotive Tier1s during development of LIN and J2602 applications. Many of these applications are in production cars today. Microchip has been closely working with car makers and independent LIN/J2602 test houses to ensure Microchip solutions meet the car maker’s requirements and latest LIN Bus/J2602 Specifications. Reference designs are available from Microchip on www.microchip.com/LIN.

How does a typical Microchip Solution for LIN/J2602 look like?
Answer:
A typical LIN/J2602 solution from Microchip consists of a MCU or DSC and a Physical Layer Transceiver with built in voltage regulator. Customers can select from a wide range of 8-bit PICmicrocontrollers and 16-bit PICmicrocontrollers or 16-bit dsPIC the most cost efficient solution for their application.

What Microcontrollers/Digital Signal Controllers support LIN/J2602?
Answer:
Microchip demonstrated in application notes how to implement LIN communication on microcontrollers as small as 8-bit/8-pin PICmicrocontrollers using bit-banging.

Also, any PICmicrocontroller with USART on-chip can implement LIN communication using an external resonator.

Most of the newly released 8-bit/16-bit MCU and DSC solutions incorporate one or more Enhanced USARTs (EUSART). These devices allow the most elegant solution with the lowest CPU interference handling the LIN/J2602 communication. Devices with EUSART on-chip can also utilize the on-chip RC oscillator and thus reduce system implementation cost even further.

What LIN hardware support is on-chip of Microchip’s MCUs/DSCs?
Answer:
Enhanced USART (EUSART) and on-chip RC oscillator are key features for LIN/J2602 application support. Examples of further features which are of benefit for many LIN/J2602 applications are: EEPROM for calibration of sensor parameters, fast and high precision AD converters, POR/BOR on-chip eliminate the need of external POR/BOR devices, small packages and high operating temperature specifications.

What is an EUSART?
Answer
The Enhanced USART (EUSART) has been first introduced to the PIC16F Family and since proliferated across all Microchip MCUs and DSCs. The EUSART reduces CPU overhead significantly handling LIN/J2602 communication. It includes the ability to wake-up from Sleep when there is activity on the receive pin, if needed could calculate an incoming baud rate, detect when the receive operation is Idle, and transmit a 13-bit Break character. Also, it is possible to specify the clock polarity in Synchronous mode and transmit polarity in Asynchronous mode. These features make it a much more versatile and easier to use communication peripheral, capable of use in a variety of applications. The EUSART peripheral uses two registers, SPBRG and SPBRGH, to implement a 16-bit Baud Rate Generator (BRG) which supports both the Asynchronous and Synchronous modes. This allows more baud rates while decreasing bit error rates. The 8-bit mode is still possible through the BRG16 control bit in the BAUDCTL register.

To access the new features, the Baud Rate Control Register (BAUDCTL) was added to the EUSART. For more specific information check the datasheet of the device of interest.

Which LIN Bus Revisions does the EUSART support?
Answer:
The EUSART supports all LIN Bus Revisions and J2602. The detail of the LIN Bus Specification Revisions is implemented in the software libraries provided by Microchip and 3^rd parties.

Can I use the on-chip RC oscillator for LIN/J2602 applications?
Answer:
In general the answer is yes. The detail depends on a number of factors, such as the maximum on-chip RC oscillator frequency, the maximum Baudrate which the application must support, the LIN Bus Specification Revision / J2602 and the implementation of the LIN software library. PICmicrocontrollers with an on-chip RC oscillator greater 8 MHz are recommended for LIN 2.1 where 16 clock mode for sampling must be used. Earlier LIN Bus Specification Revisions and where 4 clock mode for sampling 8 MHz internal RC oscillator is recommended although it may work with less than 8 MHz.

In order be able to make use of the internal RC oscillator, frequency deviations must be automatically adjusted and the software driver as well as the underlying hardware must support this. This is done by the EUSART feature and most of Microchip’s software libraries have been written to support this. 3^rd party software libraries may not make use of this feature and then an external resonator may be required.

Where can I get software libraries for LIN Data Link Layer?
Answer:
Microchip provides application notes free of charge for 8-bit MCUs and 16-bit MCUs and DSCs. Several 3^rd party companies also offer software libraries for Microchip MCUs and DSCs, such as Vector Informatik and Mentor Graphics.

For Microchip’s software libraries, please check www.microchip.com/LIN.

How much program memory and other resources does a software library for LIN 2.0 consume?
Answer:
On a PIC16F for example (AN1099A) the software driver typically uses 1636 words of program memory and 89 bytes of data memory. A 16bit Timer interrupt can be used for checking the header and response time-outs. The USART Receive Interrupt is used for receiving and back-to-back transmission bit failure checking. (An external interrupt can be used for end of Sync Break check if auto-baud feature is enabled. Note: This only necessary for older devices which have a notified errata for autobaud enable )

What are the costs for a Microchip LIN software library?
Answer:
The Microchip LIN software libraries are free of charge.

Please contact 3^rd parties to obtain a quotation for their software drivers.

Are the Microchip LIN software libraries conform to LIN/J2602 specification?
Answer:
Application notes AN1009 and AN1099A have been tested by independent 3^rd party test house and are LIN 2.0 compliant. Further testing to LIN 2.1 and J2602 is ongoing. Microchip continues to invest in LIN/J2602 development and plans to release more LIN/J2602 compliant application notes in 2008.

Please contact your local Microchip sales representative for the latest status or check www.microchip.com/LIN.

Where can I get a conformance test report for Microchip LIN software libraries?
Answer:
This information is available on request. Please contact your local Microchip sales representative.

What tools does Microchip offer for LIN bus development?
Answer:
LIN Serial Analyzer (APGDT001)
PICDEM CAN-LIN 3 (DM163015)

What Physical Layer Interface Solution does Microchip Offer?
Answer:
Microchip offers the Product Family MCP202x.

Which version of the LIN Bus specification does MCP202x Family support?
Answer:
MCP202x devices support LIN 1.3, 2.0 and 2.1 as well as J2602.

What is the difference between MCP202x and MCP201?
Answer:
MCP201 was designed to meet LIN 1.2. MCP202x meets LIN 1.3, 2.0, 2.1 and J2602.
MCP202x is a family of 4 devices: MCP2021-500, MCP2021-330, MCP2022-500, MCP2022-330. The MCP2021-500E/SN is the migration path for customers who have been using MCP201. Also, the MCP201 is not recommended for any new designs.

Is the MCP2021 compatible and drop-in compatible with MCP201?
Answer:
MCP2021-500E/SN is pin to pin compatible with MCP201 but not drop in compatible. There are only minor modifications in existing MCP201 systems required. The document “Migrating Designs from MCP201 to MCP2021-500 (DS01075a)” describes the details.

What is the qualification and production status of MCP202x?
Answer:
MCP202x has been released to production by Microchip.

AEC-Q100 qualification report is available on request.

Conformance testing for LIN and J2602 has been completed and reports are available on request. Approvals at car makers throughout the world is ongoing, some have already approved the MCP202x for usage in their cars.

Has MCP202x been conformance tested by 3^rd party and from where can I get the results?
Answer:
Yes, LIN and J2602 conformance testing has been completed and test reports are available on request. Please contact your local Microchip sales representative.

Which car maker approved the MCP202x Family?
Answer:
Some Car makers have approved MCP202x and with some car makers work is still in progress. Microchip cannot disclose at this forum the names of the car makers. Please contact your local Microchip sales representative for more information.

Does Microchip offer Reference Designs for LIN/J2602 applications?
Answer:
Yes, Microchip offers reference designs for LIN/J2602 applications. Some of these applications have already been tested by independent 3^rd party test house (for example: iHr GmbH in Germany, www.ihr.de). An example of such a reference design utilizing PIC16F688+MCP2021+Microchip LIN software library AN1099A can be purchased on-line at www.microchip.com/automotive.

Are Microchip LIN/J2602 Solutions compliant to LIN/J2602 Specifications?
Answer:
Yes. Microchip develops and tests silicon ICs, software libraries and reference designs where applicable to the LIN/J2602 conformance specifications.

Does Microchip guarantee compliance to LIN/J2602 bus specification at application level?
Answer:
No, Microchip cannot guarantee compliance of a customer application. Microchip’s technical field and Headquarter application resources will assist customers’ in achieving this, however, cannot guarantee this. It is recommended to consult independent 3^rd party test houses for system level conformance testing such as iHr GmbH in Germany, www.ihr.de.

Where can I find more information about Microchip LIN/J2602 solutions?
Answer:
Please check out the following links:
www.microchip.com/automotive
www.microchip.com/connectivity
www.microchip.com/LIN