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CAN BUS: A Close Look

What is CAN BUS?

Le bus CAN dans l'automobile
CAN BUS in full is a controller Area Network used in most vehicles to connect ECU’s together with corresponding sensors.

Basically, it is a lower cost yet robust way of sending message-based protocols.

In another way, it can be described as the complete version of the human nervous system.

Nodes, therefore, act as the central networking base and can also be inferred to as the electric control units.

A control unit can be in various forms per say.

It could be the engine unit, airbags or even the transmission base.

Most modern vehicles have as many as seventy electronic control units.

To break this further, the CAN BUS enables communications between these electronic units without rapid wiring like previous makes did.

This ease allows for the additional actions like software installations.

The main incentive of CAN BUS, therefore, is to minimize the workload on the controlling computer while still enabling smooth flow of communication between each ECU.

Apart from running connection and signals it also:

  • Gives your vehicle a lower weight
  • Enables the control system easy to operate or regulate
  • Shares a data line lowering the risk of connection errors
  • Has modules which make the diagnostics of the vehicle quite simplified
  • Is also more affordable compared to the ease of use

CAN BUS development History

Recognizing that wires tend to be quite different due to designs, sizes and makes also affects the usage of CAN BUS.

Robert Bosch is mostly accredited with his discovery of the BUS in the late twentieth century.

Pre CAN: In this wake, a theater was only wired connections from one ECU to another.

1986:

Bosch developed the model of CAN BUS in 1986 which later made headlines in an SAE Meeting.

He later published the 11 bit and 29 bit CAN versions in 1999.

1993:

Later on, in 1993, CAN received ISO Certification to begin working and adoption.

2012:

In 2012, Bosch released the CAN FD 1.0 with flexible data rates.

The Future of CAN BUS

There is future for the use of CAN BUS.

This is mostly because of its adoption in the marine industry and another field of electric handling.

The elevation if the flexible data rate version if CAN also brightens the future if adopted.

The major use of the internet is another attributing factor giving CAN a promising future as well.

The future is also rife considering the development of cloud technology and the improvement in cellular networking such as mobile data and Wi-Fi. The continued adoption also ensures it is here to stay.

Almost all cars and ships are being built with this technology in mind and it’s a great repulsion toward its extinction.

Advantages of CAN BUS

Flexible data rates

With a speed rate of about one megabit, this system is regarded as one of the fastest internet connection ever.

This makes it more appealing as compared to other types of BUS.

The support of a larger bandwidth is also good to go.

It also contains a chip which receives all messages, decides how relevant they are before acting accordingly.

Such criteria will allow for the inclusion of any other useful nodes.

Reduced wiring

The reduce running of wires in the body of the vehicle is a plus for this type of BUS.

The less complexity it oozes also increases usage by several companies.

Low cost

ECU’s communicate only through a single CAN interface which therefore minimizes possible errors and charges.

A lot of resources including money and time is saved.

The amount of time spent wiring is lowered a great deal.

This implies that the cost that would be channeled into buying wires is also saved greatly.

You can get ample time, especially for flash programming.

Diversity

The CAN BUS is suited for several electric based environments.

This is a good option considering the several numbers of electric interactions that the industries associated with.

Compatibility

Another way to retract a number of errors, especially for the CAN BUS, savors compatibility.

This can be useful in realizing bit error, CRC error, and even form error.

Efficiency

CAN are normally prioritized through ids in such a way that those with the highest priority are not interrupted.

Such a good example is vehicle systems.

What is a CAN-BUS message and how do you log and covert it?

A CAN BUS message comprises eight components which make it easy to log in with a CAN interface or logger.

CAN message uses a format CAN 2.0B for its messages.

This system has numerous components which work with one another.

They should also be integral. To log any kind of information, a logger is needed.

Components of a CAN-BUS message

  1. SOF: this acts as a tip-off that sends a signal that a message is about to be received.
  2. CAN-ID: usually has the identifier for the message that is on the way
  3. RTR: enables electronic control units to request information from.one another
  4. Control: determines the length of data to be used
  5. Data: contains the actual information from the data sets to be used or presented
  6. CRC: is uses to check how integral the data is
  7. ACK: confirms if the CRC above is working in good condition
  8. EOF: seals the end of the message

Logging in therefore requires three scenarios:

  • The CAN ID
  • Control
  • Data field

Interfaces or loggers, therefore, act as the nodes on the BUS system and will read all the messages.

They are then transferred to a waiting storage in the form of an SD card.

It is prudent to note that applications require various scenes to connect to the logger or interface.

How to log CAN-BUS data and convert into the human-readable form

To be able to read such information, conversion must be done first.

This means you can also decode CAN-BUS data.

To convert a raw data set into readable form, you can reversely engineer the CAN BUS data which is a hard task to partake.

For every ID, you have to be sound of the parameters being used.

For instance, in 64 bits of data in 34d, you are most likely to find CAN data emanating from three parameters.

They all have different bit start as well as bit lengths.

To code CAN information, you should have each CAN signal.

Basically, it will involve the conversion by combining the decimal values of information offered.

It uses the formulae:

(Scaled data value)= (offset) + (scale) multiplied by the raw decimal data value

N/B: For every parameter offset and scale values have to be known.

What is the link between CAN BUS and J1939, OBD-II and CANOPEN?

The comparison is a must for a very complex situation.

There is need to make sure that there are higher protocols to be observed. Some of them include CAN BUS AND J1939, OBD-II and CANopen.

This is why both have to run together.

In this context, therefore, CAN BUS provide the communication criteria.

While more than eight megabits can be hard for the CAN to handle, the higher protocols like the one mentioned are quite useful.

J1939

Also referred to as SAE J1939, is used for higher trucks and buses.

Its messages use the extended version of the 29-bit identifiers.

Its parameters are also identified through a suspect parameter number which in turn is grouped into a larger parameter number.

OBD-II

On-board diagnostics as the full translation of OBD-II is a self-diagnosing technique which reports what actually is wrong with a vehicle.

It specifies the number of diagnostic trouble codes which are easily retrieved through the use of a CAN logger from any vehicle.

It also has support for several real-time parameters like speeds and fuel consumption.

To log data from OBD-II, the logger has to request data by submitting certain CAN frames with specific ids to the CAN BUS.

CANOPEN

Widely used in industrial applications that are automated.

The can is built on physical layers and the data linking layer.

A data logger is used to log data from CANopen apps through the technique as ex-post data conversion varies depending on the specified application.

Conclusion

The CAN BUS is a nice technique to include as part of the systems in most vehicles due to its features and costs.

This actually is a way to save you from numerous expenses that come along especially if you opt for old models.

Such a good way of operation for your vehicle should not be taken lightly.

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Tim MillerFounderOBD Advisor

I knew incidentally what an OBD scanner was by searching on the Internet. Now I have over 10 years of experience in car repair and using OBD scanners. With what I know, I think I should share with everyone. That’s the reason I created this blog.

Web: https://www.obdadvisor.comEmail: [email protected]
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