MULTIPLEX COMMUNICATION SYSTEM CONSTRUCTION/OPERATION[L3]

id0940001004a5


CAN System-Related Module Construction

•  A CAN system-related module is composed of a power circuit, CPU, and input/output interface.
•  Module size has been reduced due to the elimination of redundant parts of the input/output interface used in conventional types of electronic modules.
•  The CPU (multiplex block) controls all signals exchanged via the bus lines (multiplex communication system wiring harnesses).
•  Communication with non-multiplex parts is carried out using conventional input/output interface.
•  The functions of each component are shown below.

Component

Function
Power circuit
Supplies power to CPU and vicinity, and to input/output interface.
CPU
Computation processing block
In addition to conventional CPU function, when transmission is necessary, transmitted data is stored in a multiplex block.
When the multiplex block receives a request to read stored data, transmitted data is read from the multiplex block.
Multiplex block
Transmits data received from bus lines to computation processing block.
In addition, sends transmitted data stored from computation processing block to bus lines.
Input interface circuit
Converts information signals from switches to electrical signals that can be input to CPU.
Output interface circuit
Converts electrical signals output from CPU for operating motors and other parts.

acxuun00000506

Twisted Pair Construction

•  The CAN system uses two spirally twisted wires called a twisted pair, and each wire, bus line A (CAN_L) and bus line B (CAN_H), has unique characteristics.
atraan00000372
•  Both bus lines are opposite phase voltage so that emitted noise is lessened and exterior noise interference is not easily received.

CAN System Outline

•  For information exchange between electronic modules in a conventional system, separate information signals are required. However, with the CAN system, it is possible to send a large amount of information via a small wiring harness by sending multiple signals at varying times over one channel. This is referred to as time division multiplexing.

CAN System Operation


Time Division Multiplex

•  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 connected and electricity must flow through each transmission channel.
•  With the time multiplex system, this can be done through a single wire. The channel is comprised of five data signal transmitters which transmit either a “0” or “1” signal to indicate whether a bulb turns 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 are illuminated.
acxuun00000508


Vehicle CAN System

•  By rearranging the multiple signal, common information between the electronic modules is transmitted and received via the twisted pairs.
•  The signal transmitted by one CAN system-related module is sent via twisted pairs to all the CAN system-related modules, but only the corresponding module(s) receives the signal and performs the appropriate operation.
acxuun00000509


CAN Signal Table

•  Sending/receiving of CAN signals is as follows:

OUT: Output (Sends signal)
IN: Input (Receives signal)

Signal

CAN system-related module

PCM

ABS HU/CM

Instrument cluster
Engine speed
OUT
―
IN
Vehicle speed
OUT
―
IN
Brake system warning light illumination request
―
OUT
IN
ABS warning light illumination request
―
OUT
IN
ECT
OUT
―
IN
Distance travelled
OUT
―
IN
Engine warning light illumination request
OUT
―
IN
O/D OFF indicator light illumination request
OUT
―
IN
Generator warning light illumination request
OUT
―
IN
Wheel speed (LF, RF, LR, RR)
IN
OUT
―
Engine specification
OUT
IN
―


ON-BOARD DIAGNOSTIC SYSTEM OUTLINE

•  CAN system-related modules have an on-board diagnostic function that is able to determine malfunction locations when there is an irregularity in the CAN system.
•  The on-board diagnostic function has a malfunction detection function that detects irregularities in CAN system-related parts, a memory function that stores detected malfunctions, and a display function that displays the location and contents of malfunctions via DTC output.
•  DTCs can be read out and cleared using the Mazda Modular Diagnostic System (M-MDS).
•  The CAN system has a fail-safe function. When a malfunction occurs in the CAN system, the transmission module sends a warning signal, the receiving module illuminates the warning light, and the fail-safe function performs control to safeguard the system.

On-Board Diagnostic System Construction/Operation


Block Diagram

aesffn00000114


Malfunction detection function

•  Detects irregularities in the input/output signals of CAN system-related modules.
•  The DTC for the detected malfunction is output to the DLC-2, and the detected result is also sent to the memory, display, and fail-safe functions.


Fail-safe function

•  When the malfunction detection function determines that there is an irregularity, the fail-safe function illuminates a warning light to advise the driver and controls input and output parts to allow safe driving.


Memory function

•  Stores DTCs for malfunctions of the input/output signal system, as determined by the malfunction detection function.


Display function

•  Outputs the signal for a malfunction determined by the malfunction detection function as a DTC to the DLC-2.
•  DTCs can be read out using the Mazda Modular Diagnostic System (M-MDS).

DTC table

DTC

Malfunction location

DTC Output Unit
U0073
Module communication error
•  PCM
•  Instrument cluster
U0121
Communication error
PCM
U1900
Communication error
•  ABS HU/CM
•  Instrument cluster
U2023
Abnormal data
ABS HU/CM


PID/data monitor function

•  The PID/data monitor function is used for optionally selecting input/output signal monitor items preset in the instrument cluster and reading them out in real-time.
•  PIDs can be read out using the Mazda Modular Diagnostic System (M-MDS).

Mazda Modular Diagnostic System (M-MDS) display

Status

Description

Monitor module

Terminal
ABS_MSG
Present
Communication circuit between ABS HU/CM and monitor module is normal
Instrument cluster
3E, 3C
Not Present
Communication circuit between ABS HU/CM and monitor module is not normal
PCM_MSG
Present
Communication circuit between PCM and monitor module is normal
Not Present
Communication circuit between PCM and monitor module is not normal


Malfunction Location Determination

•  The on-board diagnostic function can determine CAN system malfunction locations by verifying the detected DTC information from each module.
•  Refer to the display function for a detailed explanation of DTCs. (See Display function.)

Flowchart

atraan00000376


Example (PCM-related wiring harness open circuit)

Note
•  This example applies to the PCM, ABS HU/CM, and instrument cluster.

1.  DTCs for CAN system-related modules are verified using the Mazda Modular Diagnostic System (M-MDS).

Module

DTC

Probable malfunction location
PCM
U0073
PCM-related CAN system malfunction
U0121
Communication error
ABS HU/CM
U2523
Communication error
Instrument cluster
U1900
Communication error

2.  Instrument cluster PIDs are verified using the Mazda Modular Diagnostic System (M-MDS).

PID

DTC

Probable malfunction location
PCM_MSG
Not Present
Communication error between the instrument cluster and the PCM
ABS_MSG
Present
Normal communication between instrument cluster and ABS HU/CM

aesffn00000115

3.  If there is a communication error between the instrument cluster and PCM, even if the communication between the ABS HU/CM and the instrument cluster is normal, it is probable that there is a malfunction in the PCM or PCM-related wiring harnesses.