Controller area network (can bus)

Controller Area Network (CAN
bus) in the Automotive Industry
An efficient way to establish in-system communication.
By: BESSAAD NASSIM
2016

 Introduction:The needs leeds to innovation.
 First Approach.
 Conception of the CAN bus.
 Details about CAN.
 CAN in cars.
 OBD and CAN.
 Conclusion.
PLAN

In order to understand the birth of the CAN bus
technology, we must go back in time.
After WWII, most of the military application
manufacturers (tanks, jets, …) switched to cars instead
(Wolkswagen, SAAB..).
The market grew exponentially, the automotive industry
became the heart of the economy, that led to big
competition and rivalry and this naturally leads to new
horizons for the automotive industry.
The car electronics became a large part of the car,
naturally the wiring harness became a problem.
Introductions:

 The man of the hour was Robert Bosch
It was 1986, Detroit USA, the annual SAE
Congress, Robert Bosch revealed the
Controller Area Network bus system to support short
messages that circulates between the vehicles embedded
systems.
Solution:

This is a vehicle bus with:
 Serial communication protocole.
 Multi-master message model.
 System flexibility.
 Message anti-collision protection procedure (arbitration).
 Communication speed up to 1 Mb/s.
 Error detection.
 Maximunm network size is limited only by electrical loading.
CAN characteristics:

Bit Rate / Bus Length
1M bit/sec 40 meters (131 feet)
500K bit/sec 100 meters (328 feet)
CAN characteristics:

 BUS : The physical medium that allows data to find its way
from source to desired destination.
Conception:

 The CAN is a gathering of nodes without a limited number
of them, but the electrical loading suggests under 70 node
is best.
 This nodes communicates using messages called frames
which is a common language for all nodes, the frame has
four types:
 DATA FRAME
 REMOTE FRAME
 ERROR FRAME
 OVERLOAD FRAME
Conception

 The stream of bits in CAN bus is coded according to
the non return to zero (NRZ) methode with bit
stuffing.
 after having sending five consecutive bits of identical
value, a stuff bit is added, it’s a bit of inverse value of
the past five. Of course it’s discarded by the receiver.
Conception

Conception
The data frame in 2.0 A has the following format:

 Controller Area Network 2.0A which is the standard frame
and 2.0B is the extended frame.
 The main difference between the A and B is in the message
frame, particularly in the Identifier, the standard CAN 2.0A
uses identification field of 11 bits the extended CAN 2.0B
has a 29 bit Identifier (Arbitration Field).
 PS: We can Implement both CAN frame formats in the
same Network with no problems of compatibility.
 But if two different format nodes has the same 11 first bits
in the arbitration, the one with CAN 2.0A wins regardless of
the remaining bits of node with CAN 2.0B frame format.
Extended Message format:

 The microcontroller or the central processing unit:
The brain of the node, it supervise
the communication, sending and
receiving and treating decisions.
CAN controller: responsible of
storing the received bits until a
complete message is available.
The CAN transceiver: it represents
the physical link between the nodes
core and the wires of a bus, it has the role of a converter,
applies the voltage difference on the wires to create the signal to be
transmitted.
CAN node:

 In CAN we find several error detection procedures:
 Bit Monitoring
 Compares every bit placed on the CAN bus with the actual bus level
 Stuff Check
 Compares arriving bit stream for a sequence of six homogeneous bits.
 Form Check
 Comparison of the arriving bit stream with the message format
 Cyclic Redundancy Check
 Every node compares the received value of the CRC with the
calculated one it has.
 ACK Check
 Acknowledge error (ACK error) is detected if the recessive level
placed by the sender is not overwritten.
CAN data protection:

 Every node has three states:
CAN data protection:

 Multi-master priority based bus access.
 Non-destructive contention based arbitration
 Multicast message transfer by message acceptance filtering
 Remote data request
 Configuration flexibility
 System wide data consistency
 Error detection and error signaling
 Automatic retransmission for message that lost arbitration
 Automatic retransmission for message that were destroyed by errors
 Distinction between temporary errors and permanent failures of
nodes
 Autonomous deactivation of defective nodes
 Low-cost, Lightweight network.
CAN proprieties (Advantage):

 CAN was originally conceived for applications in the
automotive industry, but its grand reliability and flexibility plus
its Baud-rate that generates quick response enabling real-time
application implementation, turn the heads of all area
application designers in order to invest in the efficiency of this
communication protocol.
 So, we find today CAN in military, medical, automation …ETC
 More than five billions integrated CAN chips are cheeped
every year.
 But the automotive industry still the biggest winner for CAN
evolution as we shall see further in this presentation.
CAN applications:

 The Controller Area Network became an essential for
cars, to understand how big its role we must understand
the cars electronics and evaluate the thing that makes
these machines one of the greatest invention of
mankind.
CAN in automotive

 The built-in system interface or “BSI” in a vehicle is a gateway
to the diagnostic tool that can incorporate many electronic
modules such as the interface electronics, the control
electronics because it can directly communicate with the
engine ECU and the petrol pump; also it contains
 the vehicles information
 (VIN code, key code,
 HF remote control code…..).
CAN Built-in System Interface:

 OBD monitors the components that make up the emission
system and key engine components. It can usually detect a
malfunction or deterioration of these components before the
driver becomes aware of the problem.
 Since the 1996 model year all vehicles must comply with OBD II
requirements. OBD II requires the monitoring of virtually every
component that can affect the emission performance of a
vehicle plus store the associated fault code and condition in
memory.
On-Board Diagnostic:

 When the OBD system determines that a problem exists, a
corresponding “Diagnostic Trouble Code” is stored in the
computer memory.
 Trouble codes are how OBDII identifies and communicates to
technicians where and what on-board problems exist. The first
number in the DTC indicates whether the code is an SAE
generic code (applies to all OBDII systems) or is specific to the
vehicle manufacturer. The remaining three numbers provide
information regarding the specific vehicle system and circuit.
 Theses DTCs comes handy for a technician in order to apply the
necessary maintenance for the car because their interpretation
is universal (generic).
ON-Board Diagnostic Trouble Codes

 To be able to extract needed data the SAE J1979 standard
define a method for requesting various diagnostic data and a
list of standard parameters that might be available from the
ECU, the available parameters are called Parameter
identification numbers (PIDs).
 Every manufacturer has the liberty of changing some listed
PIDs in the SAE J199and add others freely.
 The OBD II has (09) nine operation modes.
OBDII:

MODE 1:This mode returns certain current values of vehicles sensors.
MODE 2:This mode returns instant data of a malfunction; when a
malfunction is detected by ECU it registers the sensors data at the
moment of the fail appears.
MODE 03:Returns DTC registered, these codes are standardized for all
brands of vehicles.
Mode 04:This mode Allows clearing the stored trouble codes; and
shutting down the malfunction Indicator.
Mode 05:This mode doesn’t use the CAN bus.
OBD II modes:

Mode 06:This mode returns the test results of a diagnostic for
ECUs using CAN bus only.
Mode 07:This mode shows pending Diagnostic Trouble Codes
(detected during current or last driving cycle).
Mode 08:This mode shows Control operation of on-board
component/system, not used a lot in Europe.
Mode 09:Returns Vehicles information .
OBD II modes:

 The request and response uses functional addresses, the
diagnostic tool uses a CAN ID of 0x7DF to broadcast a query
later it accepts 8 ECUs responses using IDs from 0x7E8 to
0x7EF.
 The ECU response has an ID of their assigned ID plus 8.
 Figure: OBD II query PID on CANbus.
PBD II PIDs:

 ECU response:
OBD II PIDs:

 Many contributions affected the automotive industry in the
last century, but the Controller Area Network and On-Board
Diagnostic had a huge impact for what it brought of
advantage for the car manufacturers and the simple
consumer.
 Therefore, the development of electronic gadgets based on
those technologies is on the run, we now can diagnose the
car and retrieve many informations easily thanks to those
tools.
Conclusion

Controller area network (can bus)

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