Mazda 6. Manual - part 56

MULITIPLE COMMUNICATION SYSTEM 

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OUTLINE

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Due to the simplification of the wiring harness, a controller area network (CAN) system for transmission of 
multiplex input/output signals among electrical modules has been adopted.

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Twisted-pair wiring is used for connections between the following modules (Each electrical module hereafter 
referred to as a CAN system-related module): 
— PCM to ABS (ABS/TCS) HU/CM (with ABS (ABS/TCS) or DSC HU/CM (with DSC) to instrument cluster. 
— Instrument cluster to audio unit. 

• With an on-board diagnostic function included for each multiplex module, display of DTCs using the SST (WDS 

or equivalent) has improved serviceability.

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STRUCTRURAL VIEW

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MULITIPLE COMMUNICATION SYSTEM

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ABS (ABS/TCS) HU/CM (with ABS (ABS/TCS))

DSC HU/CM (with DSC)

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Instrument cluster

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Audio unit

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PCM

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MULITIPLE COMMUNICATION SYSTEM 

SYSTEM WIRING DIAGRAM

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MECHANISM OF CAN SYSTE-RELATED MODULE

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A CAN system-related module is composed of an electrical circuit, CPU, and input/output interface.

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The size of the module has been reduced due to the elimination of the bulky, superfluous, input/output interface 
in the conventional type of electrical module.

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The CPU (multiplex block) controls all signals exchanged on the CAN harness.

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Communication with non-multiplex parts is carried out by conventional input/output interface.

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The functions of each component are shown below.

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PCM

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ABS (ABS/TCS) HU/CM (with ABS (ABS/TCS))

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DSC HU/CM (with DSC)

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Data link connector

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Instrument cluster

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Audio unit

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Twist  pair

Component

Function

Electrical circuit

Supplies power to CPU and vicinity, and to input/output interface.

CPU

Computation processing block Control function has been expanded, and when transmission is necessary, 

transmitted data is stored in a multiplex block. If a multiplex block receives a 
request to read stored data, transmitted data is read from the multiplex block.

Multiplex block

Transmits to computation processing block data received from bus line. In 
addition, sends to bus line transmitted data stored from computation 
processing block.

Input/Output interface

Electrically converts information signals from switches practically input to 
CPU, and signals output from CPU for operating actuator or indicator lights.

MULITIPLE COMMUNICATION SYSTEM 

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TWIST PAIR

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The multichannel use two spirally twisted wires called the twist pair, and each wire, bus line A and bus line B, 
has its own special function.

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Both bus lines are opposite phase voltage. This allows for hardly any noise being emitted and makes if difficult 
for noise interference to be received.

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Input signal

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Output signal

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Connector

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Input interface

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Output interface

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CPU

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Conventional module

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CAN harness

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Conventional wiring harness

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Multiplex block

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Computation processing block

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CAN system-related module

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Bus line A

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Bus line B

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MULITIPLE COMMUNICATION SYSTEM 

CAN SYSTEM OUTLINE

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Time Division Multiplex

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For information exchange between the electrical modules in the conventional system, a wire connection was 
necessary for each information signal. However, by sending the different signal at varying times over one 
channel, it is possible to send a large amount of information via a small harness.

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In the conventional, non-multiplex system, in order to control the illumination of the five bulbs, one switch and 
one channel was necessary for each bulb. For bulbs B and C to illuminate, switches B and C must be ON and 
electricity must flow through the channel. With the time multiplex system, this can be done through one 
channel. The channel is comprised of five data signal transmitters which transmit either “0” or “1” signal to 
indicate for a bulb to turn ON or OFF. For example, to illuminate bulbs B and C, transmitters B and C transmit a 
“1” and transmitters A, D, and E transmit a “0”. When the receiver receives these signal, bulbs B and C 
illuminate.

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VEHICLE CAN SYSTEM

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By rearranging the multiple signal, common information between the CAN system-related modules is 
transmitted and received through the multichannel.

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The signal transmitted by one CAN system-related module is sent through the multichannel to all the CAN 
system-related modules, but only the concerned module(s) receives the signal and performs the appropriate 
operation (ex. light illumination, fan operation).

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Non-multiplex system

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Time division multiplex system

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Data

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Each signal is transmitted one by one through the 
channel as it is received.

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Each signal is output one by one it is received from 
the channel.

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Conventional system

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Electrical module

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CAN system

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CAN system-related module