Controller Area Network CAN – Multiplexing
CAN Waveform on Oscilloscope
The Range Rover 4.A Vogue 2001 LRn2 had an easily accessible CAN system twisted wires.
A yellow/black and yellow/brown twisted wire pair where located under the bonnet on the driver’s left hand side and connected to the ABS HCU.
The waveform of one of the wires below: (time is small enough so you don’t have “aliasing”.)
Colour of wire: Yellow/brown
Time per division: 200ms
Voltage per division: 1V
The main voltage on the line in the waveform above is 2.3V
The other voltage on the line, when the voltage is pulled down to talk is 1V
Colour of wire: Yellow/black
Time per division: 200ms
Voltage per division: 1V
Aliasing is in signal processing, it refers to an effect that causes different signals to become indistinguishable (or aliases of one another) when sampled. It also refers to the distortion or that result when the signal that is reconstructed from samples is different from the original continuous signal.
These waveforms are not aliasing this is shown by the clear digital wave form that is easily distinguishable and relates well to the original signal
In the waveform above, the main voltage on the line is 2.2V
The voltage on the line, when the voltage is pulled up to “talk” is 3.2V
When comparing it with DC volts or AC volts setting. AC would tell you if the signal is switching. Because it would alternate on and off
However our readings were; Yellow/Brown: 2.63DCV, 0.23AC and Yellow/Black; 0.005ACV, 0.26VDC.
When observing the signals above with a voltmeter it was concluded that a voltmeter was no good for reading
Scan Tool Observations
The vehicle that will show CAN system operation on a scan tool the Range Rover is connected to an AutoBoss scan Tool.
The different functions available on the scan tool to examine the CAN system are the; Multimeter, DSO, Auto DSo, Primary and Secondary Ignition, Engine Analyser.
The different systems that are controlled by CAN
High Speed;
CAN C Chassis ABS, ECU, ESP, TCS, TCU
Low Speed;
CAN B Body, Dash systems Power Distribution
Earth Distribution
Anti-theft Alarm
Engine Immobilization
Central Door Locking
Windows
Sunroof
Door Mirrors
Interior Mirrors
Seats
Steering Wheel
Steering
Diagnostic Socket
Body Control Unit
Charging and Starting
Engine Management System
Fuel Pump
Secondary Air Injection
Cooling Fans
Cruise Control
Electronic Automatic Transmission
Air Suspension
Anti-lock Brake System (ABS)
Supplementary Restraint System (SRS)
Air Conditioning
Fuel Burning Heater
Heated Front Screen
Heated Rear Screen
Wipers and Washers
Exterior Lamps
Interior Lamps
Interior Illumination
Instruments
Rotary Coupler
Clock
Horn (s)
Accessory Socket
Cigar Lighter
Audio Systems
Navigation Systems
Television
Splices and Centre Taps
Communication Data Buses
Tyre Pressure Monitoring
Park Distance Control (PDC)
Telecommunication Systems
Trailer Socket
Wiring Diagram
(left) This is a CAN system wiring diagram for a Kawasaki (KRL650) road bike
Describe how this is helpful in diagnosis: IF i had been supplied a CAN wiring diagram it would have been easy to determine;
Low/high speed parts of the system on the diagram:
CAN A/B
Location of a “Gateway” on the diagram,
The system could be “divided” to aide in diagnosis.
A system that goes to “sleep” after a short time is CAN branch H&L
What voltage do you see when it is “awake”? 1.8V
What voltage do you see when it is “asleep”? 0.1V
On what wire do you see this voltage change? Yellow/Black twisted wire
Current Drain:
Measure the amp drain at the battery when the system is asleep 0.001A
Measure the amp drain at the battery when the system is awake: 0.2A
How long did it take the system to go to sleep? 2min
What made the system “wake up”? Pressing the brake pedal
Notes
CAN or Controller Area Network
Now uses 2 wires to connect ECUs to communicate with each other,
Components controller, Can high - 5V and can low – 0v bidirectional which transfer data
EDL is drive by wire
Bits can have a value of on or off they are the smallest possible unit in computing and data transfer
The Controller Area Network (CAN) is a high-integrity serial data communications bus for;
Real-time control applications it operates at data rates of up to 1 Mega bits per second,
Have excellent error detection and confinement capabilities
Is now being used in many industrial automation and control applications
Has an OSI session layer known as Time Triggered CAN (TTCAN)
Has a sub-bus known as the Local Interconnect Network (LIN)
By having the can wires twisted every 20-30mm prevents capacitance, dampens EMF noise and radio interference.
Resistance, Capacitance, length and resistance must remain the same or the signal will be affected.
ISO 11898-2: Can C - faster high speed Can (256Kbs, 512Kbs up to 1Mbs) is used for important ECUs like the ABS (Antilock Brake System), Power train, Engine control Modules and emission control.
ISO 11898-3:The slower/fault-tolerant Can B (125kbs) is used for body electrics such as door locks and comfort devices also in units where an advanced level of security is needed like the and offer transceivers with fault-tolerant capabilities brake lights, low-speed/fault-tolerant CAN offers a solution.
References
Lesson 11 Can
Can Worksheet
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