Automotive Buses and Vehicle Bus Description

Dovie Salais

Automotive Buses and Vehicle Bus Description Automotive Buses [BST bus] [byteflight] [CAN bus] [D2B] [DSI bus] [FlexRay] [GVIF] [IDB-1394] [IEBus][Intellibus] [J1708 bus] [J185 bus] [LIN bus] [MEC bus] [MI bus] [MML bus] [MOSTbus] [OBDII] [Planet] [SMARTwireX] [Amazon Engine Diagnostic Products] [Bus Info Page][Home] Note: There are six classifications of vehicle […]

Automotive Buses and Vehicle Bus Description

Automotive Buses

[BST bus]
[CAN bus]
[DSI bus]
[J1708 bus]
[J185 bus]
[LIN bus] [MEC bus]
[MI bus]
[MML bus]

[Amazon Engine Diagnostic Products]
[Bus Info Page]

Note: There are six classifications of vehicle Buses:
Class A, Class B, Class C, Emissions/Diagnostics, Mobile Media, and
Many of the buses listed below have a notation defining what
class they reside in.
Class A: A multiplex wiring system which reduces wiring by
transmitting and receiving multiple signals over the same signal bus.
The multi-purpose bus replaces individual wires performing the same function.
Normally Class A defines general purpose UART communication with bit
rates below 10kbps
Class B: A multiplex wiring system which transmits data between
nodes. The nodes replace existing stand-alone modules.
Class B is used as a non-critical 10kbps to 125kbps bus
Class C: A multiplex wiring system which reduces wiring by using
real-time high-data signals. Operating between 125kbps and 1Mbps
Emissions/Diagnostics: handle either Emissions or Diagnostics
Mobile Media: buses handle Mobile Media equipment.
X-by-Wire: is the collective term for the addition of electronic systems into the vehicle to enhance and replace tasks that were
previously accomplished via mechanical and hydraulic systems.
Automotive temperature requirements are -40C to +125C.

In addition, a number of the listed buses define the Electrical Physical
layer and the Optical Physical layer, which is normal for a bus which
defines both interface types.
The Physical interface bus being either
fiber [Optical] or wire [electrical]. The difference here, in some cases,
is that the electrical interface being defined resides just prior to the
optical encoder. So the Physical interface bus from device to device is
optical [fiber], but the specification also defines the Physical
[electrical] interface into the optical transmitter/receiver [which is
not normally done outside of Automotive buses].
Also: … “It is becoming clear that regardless of carmaker, new vehicles
will be made using LIN for the lowest data-rate functions, CAN for medium
speed, MOST for the high-speed data rates and FlexRay, for
safety-critical applications such as steer- and brake-by-wire.” from
Automotive Industries.

MOST bus Description

MOST bus: [Media Oriented Systems Transport],defines a multimedia
fiber-optic (low overhead, low cost) point-to-point network implemented
in a ring, star or daisy-chain topology over Plastic optical fibers
The MOST bus specifications define the Physical [Electrical and Optical parameters] Layer as well as the Application Layer, Network Layer, and Medium Access Control.
The MOST bus provides an optical solution for automotive media [entertainment] networks [Video, CD..].

J1850 bus Description

The SAE J1850 bus is used for
diagnostics and data sharing applications in On and Off road vehicles.
The J1850 interface takes two forms; A 41.6Kbps Pulse Width
Modulated (PWM) two wire differential approach, or a 10.4Kbps Variable
Pulse Width (VPW) single wire approach. The single wire approach may have
a bus length up to 35 meters (with 32 nodes). The J1850 interface was
developed in 1994, J1850 may be phased out for new designs. The J1850 is
a class B protocol. The J1850 protocol uses CSMA/CR
arbitration. The frame consists of a Start Of Frame [SOF], which is high
for 200uS. The Header byte follows the SOF and is one byte long.
The data follows the header byte. The one byte CRC [Cyclical Redundancy Check] follows the data
After the CRC an End Of Data [EOD] symbol is sent. The EOD is sent as a 200uS low pulse.

{Back to Automotive Bus Index}

MI Bus Description

MI Bus (MI Bus [Motorola Interconnect] is
a serial [Single wire] communications protocol with one Master and many
The MI bus may applied to drive Mirrors, Seats, Window lifts or Head light levellers. The Master sends address and data [the Push Field]
to all slaves on the bus.
The slave with the same address responds with the information requested [the Pull Field].
The Push field contains a Start bit [low for 3 bit times], a synchronization bit [bi-phase encoded
0], a data field [5 bits bi-phase encoded], and an address field [3 bits
bi-phase encoded].
The Pull field contains a synchronization bit [bi-phase encoded 1], the data field [3 bits encoded NRZ], and a End of
frame field [~ 3 cycles of a 20KHz square wave].
The single wire line operates between Logic 0 [0.3v maximum], and Logic 1 [+5 volts].)

DSI Bus Description

DSI Bus [Distributed Systems Interface] developed by Motorola
as a dedicated safety bus.
DSI is a two-wire serial bus linking safety-related sensors and components in vehicles.

BST Bus Description

BST Bus [Bosch-Siemens-Temic] is another vehicle safety bus, used
with air-bags (for example).
The BST bus is a 2-wire bus using Manchester encoding and either Parity or CRC for error correction and detection. The BST bus runs up to a maximum of 250Kbps.

MML Bus Description

MML Bus [Mobile Multimedia Link] is multimedia bus.
The MML Bus
uses plastic optical fiber technology in a star architecture via a
Master/Slave communication approach.
MML Bus has an operation speed of
100Mbit/sec with a maximum cable length of 10 meters [that can’t be
right]. Encoding for MML is NRZ.
The MML bus is fault tolerant and
handles plug and play.

byteflight (SI-Bus) Description

byteflight is used for safety-critical applications in motor
vehicles [air-bags]. Byteflight is a TDMA [Time Division Multiple Access]
protocol that runs at 10Mbps over [2-WIRE or 3-WIRE] Plastic optical
fibers [POF] in a bus, Star or Cluster configuration which provides an
information update rate of 250uS. Byteflight is based on a
message-oriented transmission process, with Master/Slave media access
[all messages are made available to all bus subscribers at the same
time]. The frame consists of a 6-bit Message Start sequence, an
8-bit message identifier [ID], one length byte [LEN], up to
12 data bytes can be transmitted in the following data field [D0 to
After the data field a 2-byte [16-bit] CRC-sequence is sent [CRCH/CRCL].

{Automotive Bus Index}

FlexRay Description

FlexRay is a high-speed serial [Synchronous and Asynchronous]
communication system for in-vehicle networks [Control Systems] using
Point-to-Point [Star topology] links, at 10Mbps [Fault-Tolerant] over
Un-shielded Twisted Pair [UTP] or Shielded Twisted Pair [STP] cable.
The FlexRay bus defines the Physical layer [Electrical and Optical] and
FlexRay is an extended protocol version of byteflight.
Applications for FlexRay include; steer-by-wire and brake-by-wire.

{Automotive Bus Index}

domestic digital data bus (D2B)

Domestic Digital Bus [D2B] is an optical data bus system
connecting audio, video, computer peripheral and telephone components in
a single ring structure within the vehicle.
Mercedes-Benz uses a combination ring and Star optical [650nm] topology at a speed of 5.6MBps
[20MBps maximum].
The D2B interface has a maximum fiber distance of 10 meters [1 coupler] or 7 meters [2 couplers].

{Automotive Bus Index}

SMARTwireX Description

SMARTwireX defines an electrical physical layer (PHY) supporting
D2B networks running up to 25Mbps.
SMARTwireX runs over standard low-cost UTP cabling, with full automotive EMC compatibility.
SMARTwireX is an electrical physical layer solution for automotive networks.
Initially designed for D2B electrical networks, but potentially capable of supporting other
networks as well.
SMARTwireX uses a Master/Slave approach connected via twisted pair, encoded as PWM. SMARTwireX has a maximum bus length of 150m [meters].

{Automotive Bus Index}

IDB-1394 Bus Description

The IDB-1394 Bus is the Automotive version of the IEEE
“IDB-C was the first of a family of in-vehicle serial communication
protocol networks. IDB-C is defined in the SAE J2366 – ITS Data Bus
series of specifications.
IDB-C is based on CAN 2.0B (Controller Area Network) silicon and
physical layer, specifically on SAE J2284 – High Speed CAN.”
There are four layers of the IDB protocol stack; J2366-1, Physical Layer, J2366-2,
Link Layer, J2366-4, Thin Transport Layer, J2366-7, Application Message
The IDB is primarily used as a consumer device bus operating over an unshielded Twisted Pair [UTP] multidrop cable.

IEBus Description

Inter Equipment Bus [IEBus] is used as an
In-vehicle bus support using half duplex asynchronous [Multi-Master]
communication with CSMA/CD
for access control.
Two differential lines are used; Data+ / Data-. Two
modes are defined: Mode 0 uses 16 bytes/frame and runs at 3.9kbps [6MHz
Osc.] or 4.1kbps [6.29MHz Osc.].
Mode 1 uses 32 bytes/frame and runs at
17kbps [6MHz Osc.] or 18kbps [6.29MHz Osc.]. The IEbus allows 50 units on
the bus over a maximum length of 50 meters.
The cable capacitance is
rated to have 8000pF max [6MHz] or 7100pF max [6.29MHz]. The bus is
terminated to 120 ohms. Each device on the bus has a 12 bit address.
The IEBus was developed by NEC Electronics. For a detailed description, and circuit Interface
implementation; see the IEbus Interface page

{Automotive Interface Bus Index}

LIN Bus Description

Local Interconnect
[LIN] is used as an in-vehicle communication and
networking serial bus between intelligent sensors and actuators.
specification covers the transmission protocol [Physical Layer and the
Data Link Layer of LIN], and the transmission medium.
The LIN Bus is a
class A protocol operating at a maximum bus speed of 19200 baud over a
maximum cable length of 40 meters.
The specification may be obtained from LIN Consortium.
For a detailed description, Engineering Data, and circuit Interface
implementation; see the LIN Bus page.

{Automotive Interface Bus Index}

CAN Bus Description

CAN Bus Transceiver Circuit
CANbus Transceiver

CAN Bus. A vehicle may have one
or more CANbus implementations. An application for a low speed CANbus may
include operate window and seat controls. A high speed CANbus may be
employed for engine management or brake control, in addition to other
The Controller Area Network (CAN) specification defines the Data Link Layer, ISO 11898 defines the Physical Layer.
The CAN interface is an asynchronous transmission scheme controlled by
start and stop bits at the beginning and end of each character. This
interface is used, employing serial binary interchange. A class B, and
Class C bus. Information is passed from transmitters to receivers in a
data frame. The data frame is composed of an Arbitration field, Control
field, Data field, CRC field, ACK field. The frame begins with a ‘Start
of frame’, and ends with an ‘End of frame’ space. The data field may be
from 0 to 8 bits.
The frame check sequence is derived from a Cyclic Redundancy Code (CRC);
the coefficients are generated modulo-2: X15 + X14 + X10 + X8 + X7 + X4 + X3 + 1
For additional information refer to: CAN Specification; Version 2.0, or ISO 11898/11519

Controller Area Network (CAN); ISO 11898/11519.
For a detailed description, Engineering Data, circuit Interface
implementation and specifications; see the CANbus page.
The CAN bus page also
lists additional protocols based on CAN bus.

{Automotive Interface Buses Index}

Intellibus Description

Intellibus is a multi-drop communications bus developed by Boeing
initially for military avionics applications, but also has an application
in the automotive field. Similar to CAN in concept with similar
limitations and inefficiencies. Intellibus operates at bus speeds of
12.5Mbps. Intellibus is used with electronic engine control,
transmission, and other vehicle systems as another Drive-by-Wire
Intellibus uses a Master/Slave approach with Manchester Bi-Phase bit encoding over a twisted pair wire. The maximum bus length is 30 meters, at 12.5Mbps to a maximum of 64 nodes.
Intellibus provides both parity and CRC error detection. A class B, and Class C bus.

Intellibus Interface Module [IBIM]
Intellibus Network Interface Controller [INIC]
Intellibus Chassis Interface Module [CIM]

{Automotive Buses Index}

OBDII Bus Description

OBD2 [On-Board
Diagnostics II] defines a communications protocol and a standard
connector to acquire data from passenger cars. It was required by U.S.
EPA on all gasoline powered cars and light duty trucks manufactured for
the U.S. after 1996 to help monitor/inspect vehicle emissions.
OBDII will light a lamp called a MIL (malfunction indicator lamp), also known as the
“check engine” light on the dash.
The OBD-II standard allows for multiple electrical interfaces, which complicates the hardware used to interface
with the vehicle. OBDII data as defined by the SAE J1979 standard
For a detailed description, Engineering Data, and circuit Interface
implementation; see the OBDII Bus page.

OBDII to 15-pin Dsub Cable

{Automotive Buses Index}

SAE J1708 Bus Description

Serial Data Communications Between Microcomputer Systems in
Heavy-Duty Vehicle Applications
. J1708 defines the physical layer only.
J1708 uses the RS485 bus as the electrical layer.
The cable is a 2-wire 18 AWG wire with a maximum distance of 40
meters. Class A operating to 9600bps. A message starts with a Message
Identification Character [MID], followed by Data characters and then a
The total message length is 21 or less characters. Each character
is 10 bits, each character begins with a Start bit [logic low].

{Automotive Buses Index}

Vehicle Area Network

VAN An automotive bus developed by Peugeot and Renault [early 1990’s].
The VAN bus is a differential bus with Enhanced Manchester Data Encoding.
The Two-wire data bus consists of ‘Data’ and ‘DataB’.
The VAN network may have one or more Masters and some number of Slaves.
The VAN Networking Topology may be interconnected in a number of different architectures.
VAN may be either a BUS, Ring, Tree or Star style using broadcast or point-to-point communications.

ISO standard 11519-3 [VAN Protocol]. Transmission speed 160kHz [estimate].
IC Interface MTC-30521, Alcatel. VAN Data Link Controller TSS461F, Atmel.
The resistors [R2] shown in the graphic are for impedance balance of the VAN Bus.
Resistors R1 and Capacitors C1 form a low pass filter [Ri / RiB] which then feeds the comparators.
The normal circuit output is from Ro. However is either Data or DataB fail, the output can still be reconstituted.
The Ro can be used with one of the two supplementary comparators [either R1 or R2] to allow communication, even though one line has failed.

VAN Receiver Schematic
VAN Receiver Schematic

{Automotive Buses Index}


Planet [Philips Lite Automotive NETwork] is used as an in-vehicle [Automotive] network designed for safety-critical network concept for dedicated passenger-restraint systems, air bags.
Planet uses two wires for the transmission of power, data and clocking. Planet has its own Protocol.
The Philips Lite Automotive NETwork was developed by Philips [now nxp] and Special Devices Inc.
The first device to interface with the Philips Lite Automotive NETwork was released in 2000.

The only identified device: nxp; AU6101 squib driver IC {air-bag electronic initiator}
Editor note, Philips Semiconductors is now called nxp.

{Automotive Buses Index}

Additional notes for Automotive Buses:
ISO 15765 [CAN] – Controller Area Network, a new
higher speed interface
ISO 9141-2 is a name of the upper protocol for automotive failure
diagnosis using a UART interface.
This communication speed is 9.6kbps. [used by Chrysler and import
ISO 11992 truck/trailer point-to-point interface with a physical
layer over twisted pair (CAN_H and CAN_L) for the transmission of the
differential signals. The signal voltage levels are different from ISO
11898-2. The voltage levels for a dominant bit are specified as
2/3-supply voltage for CAN_H and 1/3-supply voltage for CAN_L. A
recessive bit is represented by 1/3-supply voltage for CAN_H and
2/3-supply voltage for CAN_L.
ISO 14230, or KWP2000 (Keyword Protocol) shares the electrical
portion of ISO9141 standard, but defines it’s own commands.
PWM J1850-41.6 See the J1850 topic listing, (41.6Khz Pulse Width
Modulated) [used by Ford vehicles]
VPW J1850-10.4 See the J1850 topic listing, (10.4Khz Variable
Pulse Width) [used by GM vehicles]
SAE J1587 Joint SAE/TMC Recommended Practices for Electronic Data
Interchange Between Microcomputer Systems in Heavy-Duty Vehicle
E&C Bus [Entertainment & Comfort] bus used in GM vehicles
to control the radio and HVAC controls. E&C Bus is a class A protocol
using 1 wire, with PWM bit encoding at a maximum of 1kbps over a 20 meter
Ford uses a proprietary Standard Corporate Protocol (SCP) for Module
communication, and an audio corporate protocol {ACP) for audio
BEAN bus is a Class A protocol running up to 20kbps over a 40
meter single wire cable.
I2C Bus {listed on it’s own page} is
defined as a class A protocol and was used as a HVAC bus by
USB Bus {listed on it’s own page}.
USB has a Slow-Speed mode of 1.5Mbps is used for devices such as mice.
Full-Speed mode is used by most devices and allows a transfer rate of
12Mbps. High-Speed mode [defined by USB 2.0] allows rates of 480Mbps. Up
to 127 devices may be connected together in a tiered Star topology over a
maximum cable length of 4 meters.
1394 FireWire Bus {listed on it’s own page}.
The differential cable version operates at 100, 200, or 400Mbits/sec,
[800Mbits/sec for 1394b] using half-duplex [full duplex 8B/10B
encoding for 1394b]. Firewire supports up to 63 devices at a maximum
cable distance between devices of 4.5 meters. With a maximum of 16
devices on the bus allows a total maximum cable distance of 72 meters.
Transmitting data over CAT5 cable allows data at 100Mbps to travel 100m
{listed on it’s own page} is defined as a class A protocol.
ACP is a class A protocol running over twisted pair wire at
9600bps for a maximum distance of 40 meters
Safe-by-Wire [SdW] protocol describes the physical Layer, Data
Link Layer, and Application Layer. Safe-by-Wire uses a two wire
differential pair, with three data levels. Normal data level ‘0’ is
transmitted at 6 volts. Normal data level ‘1’ is transmitted at 3 volts.
The power distribution level is at 11 volts, and the safing level is at 0
SINEBUS protocol, a single wire bus used in audio applications
operating up to 200kHz over a cable of 10 meter maximum. SINEBUS is a
class A protocol. SINEBUS uses SAM bit encoding.
GMLAN (General Motors GM) microcontroller network using the CAN
protocol. A Class B bus

Diagnostic Trouble Code Acronyms

APS/IVS; Accelerator Pedal Position Sensor and
Idle Validation Switch
BAP; Barometric Absolute Pressure
CKP; Crankshaft Position
CMP; Camshaft Position
DTC; Diagnostic Trouble Code
EBT; Exhaust Back Pressure
ECI; Engine Crank Inhibit
ECL; Engine Coolant Level
ECT; Engine Coolant Temperature
EFAN; Engine Fan Control
EGR; Exhaust Gas Recirculation
EOP; Engine Oil Pressure
EOT; Engine Oil Temperature
GPC; Glow Plug Control
IAT; Intake Air Temperature
ICP; Injection Control Pressure
IDM; Injection Driver Module Power
IPR; Injection Pressure Regulator
MAP; Manifold Absolute Pressure
MAT; Manifold Air Temperature
PCM; Powertrain Control Module
VGT; Variable Geometry Turbocharger
VSS; Vehicle Speed Sensor

{Top of Automotive Interface Buses}

Modified 6/13/15
Copyright © 1998 – 2016 All rights reserved Larry Davis

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