Toyota training overview of multiplexing

Conventional wiring between components MPX communication line Discrete signals Light Motor Heater Solenoid Switch Light Motor Heater Solenoid Switch ECU ECU In conventional electrical ci

• Why Use Multiplexing?

• How ECUs Communicate

• Communication Protocols

• Multiplex Topology

• Single Wire vs Twisted Pair

Section 2 Topics

Overview of Multiplex

Communication

Why Use Multiplexing?

One multiplex circuit does the work of many conventional circuits.

• Fewer wires

• Lighter wiring harnesses

• Simpler, more reliable wiring

• Fewer components

• Fewer connections

• Lower cost

• Self diagnostics

Multiplexing (or MPX) is a method for communicating between multiple components over a single one-wire or two-wire communication line

Without multiplexing, inter-module communication requires dedicated, point-to-point wiring between all components resulting in bulky, expensive, complex, and difficult-to- install wiring harnesses Using multiplexing reduces the number of wires by combining many signals on a single wire

Control modules use the data received to control functions such as anti-lock braking, turn signals, power windows, dashboard displays, and audio systems

In-vehicle networking provides a number of benefits:

• Each function requires fewer dedicated wires, reducing the size of the

wiring harness This yields improvements in system cost, weight, reliability, serviceability, and installation cost

• Common sensor data, such as vehicle speed, engine temperature, etc

are available on the network, so data can be shared, thus eliminating

the needfor redundant sensors or multiple connecting wires

• Networking allows greater vehicle flexibility because functions can be

added through software changes in the ECU Without multiplexing, systems require an additional module or additional terminals for each function added

Benefits of

Multiplexing

Applications of

Multiplexing

What is Multiplexing (MPX)?

Multiplexing is a way to use one wire to communicate between many devices

Conventional wiring between components

MPX communication line

Discrete signals

Light

Motor

Heater

Solenoid Switch

Light

Motor

Heater

Solenoid Switch

ECU ECU

In conventional electrical circuits, each voltage signal between components requires its own dedicated wire The presence, absence, or amount of voltage on the wire (supplied by a switch or a sensor, for example) controls the operation of a component on the other end

In a multiplex circuit, a computer chip on one end of a single wire can transmit a series of coded voltage signals that can be interpreted by a

computer chip on the other end The computer chips are inside electronic

control units (ECUs), and the coded voltage signals are data packets.

A data packet may instruct the receiving ECU to:

• Turn on a light

• Start a power window motor

• Activate a solenoid Because the data packets are sent in series, multiplexing is also referred to

as serial communication or serial networking, and the communication line

is called a serial data bus.

Multiplexing

How ECUs Communicate

ECU Logic Circuit:

To communication line:

• Supply voltage when transistor is OFF

• Ground voltage when transistor is ON

• Controls the ON/OFF signal

• “Reads” the data on the MPX line

• Performs self diagnosis

ECU

Time

Voltage

0 v

ECUs communicate by sending voltage pulses in a coded sequence.

Supply

In the ECU, a switching transistor in the logic circuit controls the transmitting

of multiplex signals

When the transistor is OFF, no current flows Referring to the diagram above,

if you were to measure the available voltage on the communication line, you would find supplied voltage

When the transistor is turned ON, current flows and all of the available voltage is dropped across the resistor Now the voltage measurement on the communication line (after the resistor) is ground voltage

By turning the transistor ON and OFF in a timed sequence, the ECU can

send a message to another ECU, similar to sending a message in Morse

code Part of the message, called a data packet, indicates which ECU the

message is addressed to Other ECUs listening to these messages ignore the ones not intended for them

The ECU communication line is powered through a resistor that acts as a load in the circuit This is commonly called a pull-up resistor If the circuit is grounded, the resistor protects the ECU from damage

ECU Communication

NOTE

Signaling Between ECUs

Sender Supplies B+

Receiver Supplies B+

Sends signal

ECU ECU

12V

ECU ECU

When one ECU signals another, the one sending the signal is

not necessarily the one supplying the power to the circuit

Sends signal

12V

In diagnosing ECU controlled circuits, don’t make the assumption that the ECU sending a signal is the one supplying the circuit voltage As shown in the illustrations above, it’s possible for the ECU receiving a signal to be the one providing power to the circuit

Signaling

Between ECUs

Protocol BEAN

(TOYOTA Original)

CAN (ISO Standard)

LIN (Consortium)

AVC-LAN (TOYOTA Original)

Application Body Electrical Power Train Body Electrical Audio Communication

Speed 10 kbps

500 kbps (HS)*

250 kbps (MS) 20 kbps 17.8 kbps Communication Wire

AV Single Wire Twisted-pair wire AV Single Wire Twisted-pair wire

Drive Type Single Wire

Voltage Drive

Differential Voltage Drive

Single Wire Voltage Drive

Differential Voltage Drive Voltage 10+ volts 2.5v to 3.5v CANH

2.5v to 1.5v CANL 8 volts

2v to 3v TX+

2v to 3v TX-Configuration Ring/Daisy Chain Bus Star Star Sleep/Wake-up Available Available Available N.A.

Communication Protocols

A “protocol” is the set of rules and standards for communication

between components.

BEAN:Body Electronics Area Network

CAN:Controller Area Network

LIN:Local Interconnect Network

AVC-LAN:Audio Visual Communication - Local Area Network

* Up to 1 Mbps

The rules and standards for transmitting and receiving data packets between

ECUs are called a protocol Some protocols provide faster exchange of

messages between components and more reliable operation than others As speed and reliability increases, so does the cost

The chart above compares some of the characteristics of the different protocols found in Toyota vehicles

• BEAN is the earliest protocol used by Toyota Based on early technology,

it is also one of the slowest protocols BEAN is typically used for body electrical systems such as lights, locks, windows, and air conditioning

• AVC-LAN is another early protocol developed by Toyota as a faster

alternative to BEAN for audio, video, and navigation components

• CAN, the ISO standard for automotive applications, is a high-speed

protocol for critical vehicle systems such as engine control, braking, pre-collision, and SRS systems

• LIN is an alternate, low-speed standard protocol developed in later years

and used by many manufacturers Because it is a common standard, it is slightly lower in cost, and because it is a newer standard, it is slightly

faster than BEAN In later model Toyota vehicles, LIN replaces BEAN

for control of some body electrical systems such as windows and seats

Network speeds are measured in bits per second (bps) A “bit” (represented

as ON or OFF, or 0 or 1) is the smallest unit of the code used in a data

packet Kbps stands for kilobits (1000 bits) per second Mbps stands for

megabits(one million bits) per second

Communication

Protocols

NOTE

Multiplex Topology

Star Style Each ECU is connected directly to a master

ECU with a central control function

Bus Style

All ECUs are connected to a single common communication line

Daisy Chain Style

The ECUs are connected in a combination

ring and bus form

Applies to CAN

Applies to LIN and AVC-LAN

Applies to BEAN

ECU ECU ECU

ECU ECU

ECU

ECU

ECU

ECU ECU

ECU ECU

Master ECU

ECU

ECU

ECU

Topology describes the pattern of physical connections between components on a network This may also be called network architecture.

Multiplex networks can be configured in a variety of designs Toyota networks are arranged using primarily three styles: the bus, the ring, and the star

• Bus In the bus style, multiple ECUs are connected to a single common

communication line, allowing each ECU to transmit or receive signals directly with any other ECU on the network

• Ring ECUs connected in a ring have two network lines to provide a

backup path for communication If one communication line is disconnected, the ECU can still receive network communications on the other line

• Star The star style uses a central ECU called a master to control the other ECUs in the network (slaves) In this configuration, slaves cannot

communicate directly with one another without passing the message through the master

• Daisy Chain Sometimes a multiplex circuit can combine two design

types An example is a BEAN circuit with both ring and bus topologies

Components on a network are referred to as nodes ECUs are not the only

possible nodes Sensors with multiplex communication capability can also be

nodes on a network Examples are steering angle sensors and yaw rate

sensors.

Multiplex

Topology

NOTE

Ring Topology

In a ring network, a single open circuit in the loop does not affect

performance.

Communication lines (bus)

One open wire does not affect network operation

When network components are connected in a ring, every component has

two paths for sending messages to another component The advantage of ring topology is added reliability because the network continues to operate normally in the event of an open wire anywhere in the multiplex circuit

Ring Topology

Ring Topology

Two open connections in a ring network isolates part of the

multiplex circuit and sets a DTC

Communication lines (bus)

When one ECU sends data to another, the receiving ECU typically sends back a message that it received the data

When a ring network experiences two open wires in the ring, one or more of the ECUs in the network become isolated from the others An isolated ECU does not receive messages and cannot acknowledge them The lack of

response from an ECU may cause a diagnostic trouble code (DTC) to be

set

By studying the network topology and identifying the location of the unresponsive ECUs, you can determine which legs of the circuit contain the open wires

Two Opens in a

Ring Network

Star Topology

A single open in a star network isolates only one component.

Master ECU

In a star network, the master ECU has a separate communication line to each

of the other ECUs An open in any connection affects only one ECU and does not affect the entire network

Open in a Star

Network

Bus Topology

The effect of an open in a bus network depends on the location

An open on the main bus line isolates part of the network

An open on a sub bus (branch line) isolates only the component on that branch

In a bus network, each ECU is connected to a common communication line called the main bus An open in the main bus divides the network into two segments The ECUs that are still connected together in one segment can communicate among themselves but cannot communicate with ECUs in the other segment

The connection between an ECU and the main bus is called a sub bus (or branch line) An open in the sub bus isolates only the ECU on that branch

Open in a Bus

Network

Single Wire vs Twisted Pair

Communication Wire Feature

Communication occurs by applying Hi or positive (+) and Lo or negative (-) voltages to the two lines in

order to send a signal (Differential Voltage Drive).

compared with the Twisted-pair Wire.

Voltage is applied to this line in order to drive the

communication (Single Wire Voltage Drive).

for BEAN, LIN, etc.

Differential Voltage Drive Single Wire Voltage Drive

ECU

Hi

Lo

Hi

Lo

Communication over a multiplex line consists of a series of voltage pulses that form a pattern of bits interpreted as data by the receiving ECU In a

typical multiplex system, the voltage pulses are carried over a single wire

In some multiplex systems (CAN and AVC-LAN for example), a pair of twisted wires carry matching pulses—one positive and one negative This method reduces electromagnetic interference or noise and is more reliable in circuits requiring a greater degree of transmission reliability

For additional reliability and protection from voltage being induced by nearby wiring, some systems use twisted-pair wires with added shielding (AVC-LAN, for example)

Single Wire vs

Twisted-Pair

Advantage of Twisted-Pair Wiring

Differential Voltage Drive

3.5 V

2.5 V

1.5 V

0 1 0 1 Data

Noise

Single Wire Voltage Drive

4.0 V

0 V

1 0

Data

1 0

Noise

Abnormality

Cancel Each Other

0 1

0 1

Electromagnetic interferencefrom nearby wiring can induce unexpected

voltage spikes (noise) in a multiplex communication line which alters the

coded data being transmitted The receiving ECU has a way of detecting the data has been altered, but it then has to send a request to the sending ECU

to retransmit the data This slows down communication between the ECUs

To keep high-speed networks operating at high speed, twisted-pair wires provide protection from induced noise When a network that is wired with twisted pair wiring experiences noise, the abnormality affects each wire in the

same way, so the effect of the interference is cancelled out.

Advantage of

Twisted-Pair Wiring

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