Introduction to CAN bus

Introduction to CAN bus


In this video, we will talk about one of the
most popular communication protocol in the on-board diagnostics (OBD)-II standard, which
is Controller Area Network (CAN). Along with the brief introduction to CAN,
we are also going to take a look at some cool (CAN line inspection) features of our G-scan2. Back in a day when the world was less concerned
about environment, there were fewer sensors and modules in the car. At that time, all sensors and modules were
connected by point to point wires because they did not need to be linked together for
exchanging real time information. However, as the environment regulation gets
stricter, vehicles were required to have more and more sensors and modules to control emission
from the exhaust pipe. They needed to share information in real time
to effectively control emission. This meant more wire harnesses were required
between modules and therefore, much more weight to the car, more complexity of system and
eventually higher cost. In order to optimize efficiency of the network,
Robert Bosch GmbH came up with a new protocol in 1985, called, CAN., Controller Area Network. CAN allowed different modules to communicate
each other using a common cable. As the automotive industry started to adopt
CAN, International Organization for Standardization (ISO) released the CAN standard ‘ISO 11898’
in 1993. Later on ISO added several higher versions,
for example, ISO11898-2 (High speed CAN) and ISO 11898-3 (Low speed, fault-tolerant CAN). There are more types of CAN bus, but for the
sake of simplicity of this video, we are not going to go over all the details of each types. Let’s dive into major
difference between two mostly used types, High speed CAN and Low speed / fault-tolerant
CAN. In automotive industry, High speed CAN (ISO
11898-2) has been the most widely used protocol among others due to its fast transfer rate
and simplicity of wires between modules. High speed CAN allows up to 1 Mbit/sec and
uses a linear bus with 120 ohms termination resistor located at each end. Instead of having two termination resistors
at the end, in Low speed /fault tolerant CAN (ISO 11898-3), termination resistors are located
at each modules and its overall resistance is around 100 ohms. Due to the individual termination at modules,
Low speed/ fault tolerant CAN allows the CAN bus to communicate in case of wire failure. It offers transfer rate (baud rate) from 40
Kbit/s to 125 Kbits/s When there is a problem in CAN line, symptoms
could be ranging from communication error between modules to thoroughly No communication
with a scan tool. You may diagnose it manually with a set of
oscilloscope but probing onto correct pins on OBD port and analyzing the graph can sometimes
be cumbersome. But what if your scan tool can check the CAN
line with just DLC cable connected? G-scan2 offers convenient and simple function
to perform preliminary check for CAN line signals through Data Link Connector. In the utility menu, select Communication
Line inspection. You have options to choose the type of protocol. In this video, I’m going to demonstrate
high speed CAN. You need to set the key ON position and connect
DLC main cable. Hit OK. On the left side, it displays high and low
signal pin numbers. You may switch the pin location in Setting. Default setting for high line is 6 and low
is 14. If CAN line is in properly working order,
these indicators will blink. This is for fast check to see if there is
CAN signal but please keep in mind that it does not represent the correctness of the
signals. What if I want to check the waveform of CAN
signals? For further diagnosis, you can see the live
waveform of high and low CAN signal by selecting this Waveform button Up here represents CAN High signal and below
represents CAN Low signal. It displays voltages at cursor A and B, and
average voltages of entire waveform. G-scan2 offers simple
check of termination resistor value. Without manually probing your multi-meter
to OBD port, you can check the termination resistor of the CAN bus with simply connecting
the DLC cable. This simple preliminary check can also save
you time

28 comments

Add a Comment

Your email address will not be published. Required fields are marked *