Automotive BusesThe number of sensors, actuators, entertainment and navigation systems and their corresponding electronic control units in the typical automobile has been growing exponentially. These devices and systems must communicate via an electrical or optical signal employing a well defined protocol. These signals and protocols constitute a communications bus. This page provides an overview of the most common communication buses used in cars. CAN (Controller Area Network)Brief Description: Can bus is a serial bus originally developed by Robert Bosch GmbH in 1986 for in-vehicle networks in cars. CAN buses employing twisted wire pairs were specifically designed to be robust in electromagnetically noisy environments. The applications of CAN bus in automobiles include window and seat operation (low speed), engine management (high speed), brake control (high speed) and many other systems. CAN buses can also be found in other embedded control applications such as factory automation, building automation, and aerospace systems. Maximum Data Rates:
1Mbps at 40m, 125Kbps at 500m, 50kbps at
1000m LIN (Local Interconnect Network)Brief Description: LIN specifications are developed by the LIN consortium. Version 1.1 was released in 1999. The current version is 2.0. A primary advantage of this bus is that it can be implemented with a single wire (using the vehicle chassis as a current return path). A small and relatively slow in-vehicle communication and networking serial bus system, LIN bus is used to integrate intelligent sensors and actuators. LIN can also communicate over a vehicle's power distribution system with a DC-LIN transceiver. Maximum Data Rates: 19.2Kbaud at
40m FlexRayBrief Description: FlexRay is a high-speed serial communication bus for in-vehicle networks. It is an extended protocol version of byteflight. The extended FlexRay has the performance features required for active safety, such as redundant transmission channels and a fault-tolerant synchronization mechanism. Applications for FlexRay include steer-by-wire and brake-by-wire systems. Maximum Data Rates: 500
kbps ~ 10 Mbps MOST (Media Oriented Systems Transport)Brief Description: MOST was originally designed by Oasis SiliconSystems AG (now SMSC) in cooperation with BMW, Becker Radio, and DaimlerChrysler for multimedia applications in the automotive environment. It was intended to be implemented on an optical fiber, so the bit rates of this bus system are much higher than previous automotive bus technologies. Since 1997, seventeen international automotive manufacturers and more than fifty key component suppliers including automotive electrical suppliers and audio-video manufacturers have contributed to this technology. MOST buses provide an optical solution for automotive peripherals like car radios, CD and DVD players, and GPS navigation systems. Maximum Data Rates: 23 Mbaud OBDII (On-Board Diagnostics II)Brief Description: OBDII is the second generation of the OBD specification. Since on-board vehicle computers were introduced in the early 1980's, OBD systems have made it possible to give the vehicle owner or a technician access to information on the state of vehicle subsystems. Early implementations of OBD monitored a few emission related components and simply illuminated a malfunction indicator light. OBD II defines a communications protocol to provide a standardized series of diagnostic trouble codes (DTCs) via a standardized fast digital communications port. These codes allow a user to identify and remedy malfunctions within the vehicle. Signal Protocols: There
are 5 signaling protocols currently employed by the
OBD II Interface (J1962 Connector); BYTEFLIGHTBrief Description: BYTEFLIGHT, was developed by BMW together with Motorola, Elmos and Infineon, primarily for safety-critical applications in motor vehicles. The BYTEFLIGHT protocol combines the advantages of the familiar synchronous and asynchronous protocols and guarantees high data integrity. Automotive applications of BYTEFLIGHT include passive and active safety, body applications. Maximum Data Rates: 10
Mbit/s gross, at full bus load > 5 Mbit/s
net MI (Motorola Interconnect)Brief Description: The MI bus is used to control smart switches, motors, sensors, and actuators. Applications include mirror and seat controls, window lifting and head light operation. Physical Layer: Single
Wire SAE J1850Brief Description: The SAE J1850 Bus, developed in 1994, is used for diagnostics and data sharing applications in vehicles. It can be found in OBD II connectors in some older makes of cars. Maximum Data Rates: 41.6
kbps (PWM); 10.4 kbps (VPW) SAE J1708Brief Description: J1708 provides serial data communications between microcomputer systems in heavy-duty vehicle applications. J1708 defines the physical layer only. Maximum Data Rates: 9600
bps IEBus (Inter Equipment Bus)Brief Description: The IEBus, developed by NEC Electronics, is used in car audio systems. Maximum Data Rates: 3.9
kbps (6-MHz Osc) or 4.1 kbps (6.29-MHz Osc) for
Mode 0; 17 kbps (6-MHz Osc) or 18 kbps (6.29-MHz
Osc) for Mode 1; IntellibusBrief Description: Intellibus was originally developed by Boeing for military avionics applications. It can also be used with electronic engine controls, transmission controls, or other vehicle systems. Maximum Data Rates: 12.5 Mbps; D2B (Domestic Digital Bus)Brief Description: D2B is an isochronous TDM network system. It can be used to communicate between in-car multimedia devices such as radio head units, CD changers, navigation systems, telephones, TV and others. Physical Layer: plastic
optical fiber (POF) or unshielded twisted pair
(UTP) SMARTwireXBrief Description: SMARTwireX was initially designed for D2B electrical networks. It is an electrical physical layer solution for automotive networks. Maximum Data Rates:
25 Mbps IDB-1394Brief Description: IDB-1394, an automotive version of IEEE-1394, was developed by the Joint Automotive Working Group, a partnership between the IDB Forum and the 1394 Trade Association. IDB-1394 is being deployed for passenger vehicle applications in Japan and Europe, with automotive OEM introductions expected from several manufacturers as early as model year 2006. Standard: SAE
J2366 DSI Bus (Distributed Systems Interface)Brief Description: DSI Bus was developed by Motorola as a dedicated safety bus. Applications in vehicles include air bags and other safety related sensors and components. Maximum Data Rates:
150 kbps BST (Bosch-Siemens-Temic)Brief Description: BST Bus is another vehicle safety bus used, for example with air bags. Maximum Data Rates:
250 kbps; MML (Mobile Multimedia Link)Brief Description: MML Bus is a multimedia bus that is fault tolerant and handles plug and play. Maximum Data Rates:
100 Mbps; |