Foreword
Multiplexing consists of sending several pieces of digital information between various items of electrical equipment, on a single transmission channel made up of 2 wires, "CAN high" and "CAN low"
Definition of multiplexing
Multiplexing is a means of operating electrical equipment needing an specially adapted electrical installation
A multiplexed architecture consists of a single circuit, the bus, which connects all of the ECUs
All the messages sent on this circuit comprise an "information" part and a part for identification of the receiver or identification of the transmitter
NoteThese messages are referred to as "data streams"
Multiplexing uses the CAN communication protocol (Controller Area Network)
The associated architecture simplifies the harnesses and makes it possible to offer the customer new functions
Advantage of multiplexing
Multiplexing allows
- Electrical harnesses to be simplified
- Improvement in the number of functions (for the same number of wires)
Electrical structure
Presentation
The vehicle's electrical architecture permits the following services
- Communication and operation of the various components of the system
- ECU diagnostics, configuration or downloading
The electrical architecture consists of the following networks
- IS CAN, connecting all of the ECUs of the power train
- BODY CAN, connecting the safety systems
- COMFORT CAN, creating the vehicle's Man/Machine interface
- CAN DIAG, permitting the downloading of certain ECUs of the CAN
- DIAG ON CAN, permitting vehicle downloading, configuration and diagnostics
Flow chart
Key
- Triple line: multiplexed networks
- Single line: remote-controlled wake-up line (RCD)
| reference | designation |
|---|---|
| BSI1 | built-in systems interface |
| C001 | diagnostic socket |
| A | ECUs of the COMFORT CAN |
| B | ECUs of the BODY CAN |
| C | ECUs of the IS CAN |
| CAN DIAG | CAN DIAG |
| D | ECUs of the IS CAN connected to the remote controlled wake-up line (RCD) |
| E | DIAG ON CAN network |
Is CAN
Presentation
The CAN IS connects all of the power train ECUs
The data transmission speed is 500 KBits/s (High Speed)
The IS CAN is a "multi-master" network on which each ECU continuously transmits information to the entire network
Each ECU processes the information for which it has a use
The transmission of the messages on the network takes place periodically, with the exception of the messages relating to events
The IS CAN has a general acknowledgement system which establishes communication when at least two ECUs are connected to the network
The engine mangement and built-in systems interface (BSI 1) ECUs are the only ECUs which have termination resistors
In order to guarantee the communication on the network, the engine management and built-in systems interface (BSI 1) ECUs must always be present on the network
The remote controlled wake-up (RCD) line permits the early wake-up of the ECUs
NoteThe cutting of an IS CAN High or IS CAN Low wire prevents network communication
General synopsis of the IS CAN
Key
- Triple line: multiplexed networks
- Dotted line: according to option
NoteFor ease of understanding, the remote controlled wake-up (RCD) line is not represented
| reference | designation |
|---|---|
| BSI1 | built-in systems interface |
| 1320 | engine ECU |
| 7122 | Power steering electropump assembly |
| 7715 | suspension ECU |
| 7800 (*) | stability control (ESP) ECU or anti-lock braking system ECU (7020) |
| 7803 | steering wheel's angle sensor |
| 7804 | gyrometer/accelerometer bi-sensor (dynamic stability control) |
Note(*) depending on the versions
Topology of the CAN IS
Key: triple line: multiplexed networks
| reference | designation | connection to the remotely controlled reawakening line (RCD) |
|---|---|---|
| BSI1 | built-in systems interface (BSI1) | yes |
| 1320 | engine ECU (1320) | yes |
| 7126 | electric power steering ECU | no OK |
| 7715 | suspension ECU | yes |
| 7800 | ESP ECU | no OK |
| 7803 | steering wheel's angle sensor | no OK |
| 7804 | gyrometer/accelerometer bi-sensor (dynamic stability control) | no OK |
Location of the ECUs of the IS CAN
| reference | designation |
|---|---|
| (1) | electrohydraulic power steering ECU (7126) |
| (2) | built-in systems interface (BSI1) |
| (3) | gyrometer/accelerometer bi-sensor (dynamic stability control) (7804) |
| (4) | steering wheel's angle sensor (7803) |
| (5) | suspension ECU (7715) |
| (6) | engine ECU (1320) |
| (7) | dynamic stability control (ESP) ECU (7800) or anti-lock braking system ECU (7020) |
Representation of the IS CAN
Key
- F: Udiff: difference in voltage between the two wires IS CAN High - IS CAN Low
- G: Inter System CAN message (status "0" or status "1")
- V: Volts
- T: time
The IS CAN message is determined by the difference in voltage Udiff between the IS CAN High and IS CAN Low wire
- If Udiff is higher than or equal to 2: the bit is at 0
- If Udiff is equal to 0: the bit is at 1
IS CAN voltage level
Key
- H: IS CAN on standby
- J: IS CAN active
- V: Volts
- T: time
The Inter System CAN is characterised by its two average voltages during phases of network activity
- IS CAN High: 2,65V
- IS CAN Low: 2,35V
The IS CAN is active when IS CAN High + IS CAN Low = 5 V
NoteThe voltage values represented are average voltages
CAN IS reference graphs
Key
K: IS CAN High
L: IS CAN Low
Scales (/div.)
- Voltage: 1 Volts
- Time: 100 milliseconds
- Offset: -2
Test conditions
- Engine stopped
- Ignition on
Results
- Observe a continuous component of approximately 2,5 volts and a sequence of variable pulses of amplitude 1 volt representing the information circulating on the CAN IS
- The CAN IS Low signal is inverted in relation to the CAN IS High signal
BODY CAN network
Presentation
The BODY CAN connects all of the safety components
The data transmission speed is 125 KBits/s (Low Speed)
The transmission of the information in permanent on the entire BODY CAN
The BODY CAN is a "multi-master" network on which each ECU continuously transmits information to the entire network
The transmission of the messages on the network takes place periodically and each ECU processes the information for which it has a use
The network communication is managed and the "CAN +" electrical supply is established by the built-in systems interface (BSI1)
The ECUs of the BODY CAN have their own adaptation and are supplied, depending on the case, by the "CAN +", the "BAT+" or the "IGNITION ON" supplied by the engine relay unit
NoteThe cutting of one of the two wires or a short circuit between the "BODY CAN High" or "BODY CAN Low" wires permits network communication, with the returning of fault information
General diagram of the Body CAN network
Key
- Triple line: multiplexed networks
- Dotted line: according to option
| reference | designation |
|---|---|
| BSI1 | built-in systems interface |
| BSM | engine fuse box |
| CV00 | switch module at the steering wheel |
| BSR1 | trailer relay unit (BSR) or conversion unit (BTC) |
| 5007 | brightness/rain sensor |
| 6570 | airbag ECU |
| 8602 | anti-intrusion alarm |
NoteThe trailer relay unit is only fitted as an accessory
NoteThe steering wheel with fixed central controls is on a supplier LIN
Topology of the BODY CAN
Key
- Triple line: multiplexed networks
- Dotted line: according to option
Location of the ECUs of the BODY CAN
| reference | designation |
|---|---|
| (8) | brightness/rain sensor |
| (9) | trailer relay unit (BSR) or conversion unit (BTC) |
| (10) | airbag ECU |
| (11) | switch module at the steering wheel |
| (12) | engine fuse box |
| (13) | anti-intrusion alarm |
Comfort CAN
Presentation
The COMFORT CAN permits creation of the Man/Machine interface
The data transmission speed is 125 KBits/s (Low Speed)
The transmission of the information is continuous on the entire COMFORT CAN
The COMFORT CAN is a "multi-master" network on which each ECU continuously transmits information to the entire network
The transmission of the information is continuous on the entire COMFORT CAN
The transmission of the messages on the network takes place periodically and each ECU processes the information for which it has a use
The network communication is managed and the "CAN +" electrical supply is established by the built-in systems interface (BSI1)
The ECUs of the COMFORT CAN have their own termination resistor and are supplied, depending on the case, by the "CAN +", the "BAT+" or the "IGNITION ON" supplied by the engine relay unit
NoteThe cutting of one of the two wires or a short circuit between the "COMFORT CAN High" or "COMFORT CAN Low" wires permits network communication, with the returning of fault information
General diagram of the Comfort CAN network
Key
- Full line: optical link
- Triple line: multiplexed networks
- Dotted line: according to option
| reference | designation |
|---|---|
| BSI1 | built-in systems interface |
| 0004 | instrument panel |
| 7215 | type A+ and type C- multifunction screen |
| 7215 (*) | multifunction screen (DT) optical connection |
| 7500 | Parking assistance ECU |
| 8080 | air conditioning ECU |
| 8410 | audio RD4 |
| 8415 | compact disc changer |
| 8480 | RT3 telematic unit |
| 8492 | hands-free kit |
(*) according to model: radio RD4 or telematic unit RT3
Topology of the COMFORT CAN
Key
- Full line: optical link
- Triple line: multiplexed networks
- Dotted line: according to option
Location of the ECUs of the COMFORT CAN
| reference | designation |
|---|---|
| (14) | instrument panel |
| (15) | type A+ and type C- multifunction screen |
| multifunction screen (DT) optical connection | |
| (16) | audio RD4 |
| RT3 telematic unit | |
| (17) | compact disc changer |
| (18) | air conditioning ECU |
| (19) | Parking assistance ECU |
| (20) | hands-free kit |
| not shown | additional air conditioning ECU (rear right of the vehicle) |
Representation of the BODY CAN or COMFORT CAN
Key
- V: voltage (in volts)
- T: time
- BODY CAN high - BODY CAN low = 3,6 - 1,4 = + 2,2 V (logic level 0)
COMFORT CAN voltage level
M: comfort CAN High
N: comfort CAN Low
Time scale
- Voltage: 2 Volts
- Time: 1 millisecond
Test conditions
- Engine stopped
- Ignition on
Results: sequences of variable pulses represent the information circulating on the high line (HIGH) of the COMFORT CAN
The COMFORT CAN LOW signal is additional to the COMFORT CAN HIGH signal
The voltage levels of the COMFORT CAN LOW are the following
- Low level: 1 Volts < U < 1,4 Volts
- High level: 4,8 Volts < U < 5,6 Volts
The voltage levels of the COMFORT CAN HIGH are the following
- Low level: 0 Volts < U < 0,2 Volts
- High level: 3,8 Volts < U < 4,2 Volts
BODY CAN voltage level
P: BODY CAN high
Q: BODY CAN low
Time scale
- Voltage: 2 Volts
- Time: 1 millisecond
Test conditions
- Engine stopped
- Ignition on
Results: sequences of variable pulses represent the information circulating on the high line (HIGH) of the BODY CAN
The BODY CAN LOW signal is additional to the BODY CAN HIGH signal
The voltage levels of the BODY CAN LOW are the following
- Low level: 1 Volts < U < 1,4 Volts
- High level: 4,8 Volts < U < 5,6 Volts
The voltage levels of the BODY CAN HIGH are the following
- Low level: 0 Volts < U < 0,2 Volts
- High level: 3,8 Volts < U < 4,2 Volts
Diagnostic socket (C001)
Role
The diagnostic socket (21) permits connection of the diagnostic tool to the vehicle and communication with all of the ECUs on the vehicle
Description
(21) 16 way central diagnostic socket
Connections
| terminal | signal |
|---|---|
| 1 | +APC |
| 2 | not connected |
| 3 | DIAGNOSTIC CAN (High) |
| 4 | tester earth |
| 5 | signal earth |
| 6 | CAN (High) |
| 7 | not connected |
| 8 | DIAGNOSTIC CAN (Low) |
| 9 | not connected |
| 10 | not connected |
| 11 | not connected |
| 12 | not connected |
| 13 | not connected |
| 14 | CAN (Low) |
| 15 | not connected |
| 16 | tester Permanent + |
Diagram of the diagnostic socket networks
Key
- Triple line: multiplexed networks
- Single line: remote-controlled wake-up line (RCD)
| reference | designation |
|---|---|
| BSI1 | built-in systems interface |
| C001 | diagnostic socket |
| CAN DIAG | CAN DIAG |
| C | ECUs of the IS CAN |
| D | ECUs of the IS CAN connected to the remote controlled wake-up line (RCD) |
| E | DIAG ON CAN network |
CAN DIAG
The speed of transmission of the CAN DIAG is 500 Kbits/s
Functions of the CAN DIAG
- Downloading of the software of the ECUs present on the CAN
- Returning of the information necessary for the EOBD (European On Board Diagnosis) standard permitting checking of the emission control information
Downloading
The CAN DIAG is integrated specially into the multiplexed architecture of the vehicle to download the software of the ECUs of the CAN IS
NoteThe CAN DIAG permits downloading of the software of the ECUs in a few minutes
EOBD (European On Board Diagnosis) fault reading
The CAN DIAG permits reading of the information incorporated in the engine ECU, via the statutory "SCANTOOL" tool and fulfils the statutory diagnostic requirements concerning pollutant emissions
DIAG ON CAN network
The speed of transmission of the DIAG ON CAN network is 500 Kbits/s
Functions of the DIAG ON CAN
- ECU diagnostics
- Downloading of the software of the ECUs
- Configuration of the ECUs
Diagnostic
The DIAG ON CAN permits the diagnosis of the various ECUs of the CAN IS, BODY CAN and COMFORT CAN
Downloading
The DIAG ON CAN network downloads the software of the ECUs of the two BODY CAN and COMFORT CAN networks and of the built-in systems interface (BSI1)
Configuration
The configuration function of the DIAG ON CAN network enables the user, via the diagnostic tool, to set the parameters of the various components of the system