CAN BUS

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What is CAN BUS?

Imagine that your car is like a human body and let's see how this is possible;

CAN stands for Controller Area Network.

CAN bus is the nervous system, enabling communication between all parts of the body.

Similarly, ‘nodes’ or electronic control units (ECU) are connected via the CAN bus, which acts as a central networking system.

CAN is designed for communication between microcontrollers and devices.

CAN is used in automotives to allow communication between ECUs and sensors.

What is CAN STANDARDS?

The ISO 11898 standard specifying a high-speed transceiver for CAN-based networks.
CAN is internationally standardized in ISO 11898. Over its lifetime, this standard has seen several 
revisions,resulting in it being broken up into multiple parts. The current CAN protocol standards 
include:

ISO 11898-1:

2015 – Road vehicles – Controller area network (CAN) – Part 1:

Data link layer and physical signalling specifies the characteristics of setting up an interchange of digital information between modules implementing the protocol’s data link layer.

ISO 11898-2:

2016 – Road vehicles – Controller area network (CAN) – Part 2:
High-speed medium access unit specifies the high-speed physical media attachment (HS-PMA),  including HS-PMAs without and with low power mode capability and those with selective wake-up functionality.

ISO 11898-3:

2006 – Road vehicles – Controller area network (CAN) – Part 3:

Low-speed, fault-tolerant, medium-dependent interface specifies characteristics of setting up an interchange of digital information between electronic control units of road vehicles equipped with CAN.

ISO 11898-4:

2004 – Road vehicles – Controller area network (CAN) – Part 4:
Time-triggered communication sets up a time-triggered interchange of digital information between 
electronic control units (ECU) of road vehicles equipped with CAN.
CAN Topology
CAN standard supports several topologies.  Commonly used topologies are:

•Line / Bus Topology

•Star Topology

•Ring Topology
Signalization Characteristic 
•The most common media is a twisted pair 5v differential signal which will allow operations in high
 noise environments and with the right drivers will work even if one of the wires is open circuit.
•Its higher speeds it is necessary to terminate the bus at both ends with 120 Ohms.  The resistors
 are not only there to prevent reflections but also to unload the open collector transceiver drivers. 
We should that you terminate the bus correctly in all circumstances.
•It is also a differential signal ( i.e we have CAN high and CAN low). This leads the CAN bus to be less 
prone to interference. 
In a CAN frame, how many bits the ID field occupy ? How it is changed in CAN versions ?
•There are two CAN standards, CAN2.0A and CAN2.0B.
•The message ID field is 11 bits in CAN 2.0A
•The message ID field is 29 bits in CAN 2.0B..
  The CAN2.0B protocol allows you to define more messages with 29 bits. 
Baud rates ?
•The Baud-rate on a CAN BUS device refers to the rate (speed) at which data is transmitted on 


the network.
•This is typically expressed in kilobits-per-second (kbps).
•Selecting the incorrect Baud-rate can cause erratic behavior on the network.

Supported Baud-rates:
•125 kbps
•250 kbps
•500 kbps (Standard for most automotive applications)
•1000 kbps (1 mbps)


References
•https://www.csselectronics.com/screen/page/simple-intro-to-can-bus/language/en
•http://www.mindsensors.com/content/86-can-and-its-topology

       MK




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