Yes you CAN ! Understanding the CAN BUS - Part 1
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- Опубликовано: 5 фев 2025
- In this part we look at the bus systems in cars, focus on the CAN bus. What it is , how it works and what it is used for and how to troubleshoot it. Part 1 covers the physical aspects and topology. Part 2 will cover the electrical specifications and Part 3 the protocol itself. I hope that you will enjoy it
Nicely done. I do embedded systems for a living and have worked with the CAN busses on AGCO combines and Cat heavy equipment, and your explanation is very good.
A lot of people don't realize how much copper is saved by using CAN bus. Instead of running individual wires from a flasher unit, light switch, steering column, and brake switch to the back corners of a car, you have the steering column switches and brake switch talk to the body controller. The body controller sends messages to a light controller at the back of the car over a twisted pair. The light controller takes care of clearance lights, licence plate illumination, signal lights, brake lights, emergency flashers, and reversing lights, for the whole rear of the car. Less copper is less failures, less weight, less fuel consumption.
Some will complain of the unrepairability of the system because of the computers taking over, but they also didn't know that these computers are already on their cars, doing their jobs silently for years without even being noticed. They're dead reliable and just do their job.
Yes indeed and that is something I will address in the next video's , when I talk about the arbitration (based on the CAN ID's) and how the entire can bus operates in CSMA/CD (carrier-sense multiple access with collision detection.) amplifying your example. And yes, there will always be people that complain. One thing , I do agree with them is that to much information is held back by manufactures. Open interfaces and standard coding would be great.
Also CAN is really simple when it comes to the processing. You can easily do 100Mbps ethernet with one twisted pair, but the CAN hardware is like 10 times cheaper. If the two-wire ethernet chips would be done at the same scale, I guess the difference would only be something like 2x.
@@rkan2 Also if you are comparing PHY to PHY CAN is cheaper, but I can tell you that a lot of ethernet stacks, along with the TCP/UDP/IP stacks for microcontrollers suck. Plus, ethernet on a micro is a very recent thing unless you were getting some sort of external controller chip. On the automotive side (very wide temperature range chips with big gate sizes for reliability), it's pretty recent that the microcontrollers have built in ethernet.
So, sure, given a time machine, ethernet makes sense where CAN exists. But automotive electronics are mostly put together by mechanical engineers and run on AUTOSAR rather than, say, Linux, so the support is going to be rather patchy (which is why you see it in head units and infotainment rather than body controllers).
For door or seat area networks, LIN is great since it's just one wire.
You are truly a jack of all trades. Great video. Thanks for doing this.
Thanks
Very nice topic to be discussed. Some pretty good comments in the comment section too. CAN bus is not something I know all that much about technically speaking, so it is a good time to learn more about it. Looking forward to the next parts.
Another top video Steve, like others I'm surprised you are skilled in this area but a really good explanation. I'm currently interersted in this environment so this has popped in at a good time. Can't wait for the following parts.
Thanks for the Content. Great Video.😀
Just measured my 20 years old Renault :) 60 Ohm 🎉 so far, so good
Cool
Excellent explanation, well done!
Should be shown in automotive schools, good job 👍
Thanks! 👍
Ai Steve now you retired and have much of the time than before. But this is killing us because you now dive very deep. I listened to this video but I heard almost nothing.
Not that you don't make sense.just because my mind is very small to understand such deep teaching.😮
Moshitoa south Africa
I am sorry, as I was trying to keep it as simple as possible. The next step "electrical can details" will be simular and final step is the communications protocol. The point is that repairs on modern cars require a good understanding of the CAN bus. I seem to remember that you asked me about the `ecu and how to test sensors' , will many sensors today are CAN devices, and as such this is something that will help you. Which part did you not understand ?
@D3Sshooter hahaha you have sharp mind Steve. Am excited to see that you notice who you speak to. Hahaha I want to screen shot this conversation and keep it safe.
Serious I wonder what brains you have. if you may borrow someone your brain for one day we will find him mad tomorrow. Wish to talk to you over phone one day.
Moshitoa south Africa
Question: you said different modules use two wires to communicate at one time. For me it sounds like someone is writing a letter and another person takes the same page and write another letter on top of first writing. I wonder how the signal will look like and how will distinguish one from another.
Learned something new today! Tank you.
Heck yeah this is great!!
Thanks
Hi Steve, great video😊👍🏻
Glad you enjoyed it
It was superb!🤘🤘Thank you!
I hope you are enjoying your retirement. Thanks for posting
Oh yes.. thanks
Cool 😎
What I don't understand is how Ethernet managed to move from a bus to star topology (with a cheap switch) 35 years ago, and cars are still stuck with a bus topology that's likely to break everything whenever any part of it breaks.
Ethernet was not what it is today in the 80's , never the less both ethernet and CAN work on the principle of CSMA/CD.. Common sense multi access with collision detection. However the CAN protocol is better in error detection within the link layer. Where ethernet relies more on the upper protocols. Yes you have a point that a bus topo is less resilient then a star ... however stars suffer from more collisions. Anyhow, the new trend is more car ethernet and I bet that within a few years it will be all ethernet, even at 10G/40G and 100G if need be in cars.
@@D3Sshooter I can't see why star would have more collisions - collisions are caused by two parties simultaneously transmitting, so even with a dumb hub at the center of the star, it'd seem the same? With a real switch (not broadcast), it seems much less likely on a given segment with star than bus, also switches can store and forward to avoid collisions (at the cost of increased latency though).
I remember working on ethernet bus topologies back in the day and they were always a pain in the butt to diagnose. I suppose whether it's worth doing star or not depends on the number of network nodes, which might explain why cars were slower to switch over?
Anyway, thanks very much for the videos, it's all very well theorizing, but we still need to deal with what the manufacturers added ;) Also good to know they're introducing ethernet, I had no idea - I look forward to analyzing traces with wireshark on my car ;-)
Lets forget the hub, that is an issue by itself. So lets look at an etherswitch. The main difference is that a star topology whas long drop cables in a car. Lets say the core switch is the ECU/TCU and all other controllers attach with a drop cable to the core switch. Each of those drops are of different lenghts . Thus propagation delays vary. Especially long drop cables will cause more collision . Why ? Well the NIC will listen for traffic , is there no traffic it will send its frame out. The fact that the time between listening (for quiet state) and the frame arriving at the core switch is subject to Time N ( propagation delay on the wire). Other controllers on a shorter drop cable, also listened to the quiet state and reacted immediate with sending is frame out. This frame will get to the switch sooner then the other who believes that there was no traffic. And thus frames have a collision if send to the same MAC DA. But besides that , there is no arbitration in the LAN protocols , in terms of priority where the can bus has that as part of the CAN ID all in one go. All can transmit at the same time , but the lowest CAN ID wins the priority. That will never work on a LAN. Furthermore LAN's are always MAC SA to MAC DA ( exception is the broadcast MAC address). On a CAN bus its one to all and the all can react on a send frame while the frame is still on the wire if a CRC or other delimiter fault is detected . Without any further special frames that need to be send. On a LAN bus ( which is no longer used ) it used to called thick and think lan, the drop lengts were to be of very specific lenghts. I used to design those things and that was always an issue. Today the best LAN approach is a Core and Edge construct also called Leaf and Spine , where every leaf connects to every Spine. Leaves do not interconnect. The spine does. Running SDA over that physical infra makes it a L3 overlay on a L2 topology avoiding all the issues with routing loops, broadcast storms and unused uplinks. Anyhow, I think I am drifting to far of topic. Thanks for the discussion
@@D3Sshooter I disagree with your prediction that "all will be ethernet". The implementation costs of ethernet is much higher than for a CAN bus (chips, cables, connectors, ...), so I think that ethernet will only be used in those applications where CAN can not fulfil the requirements.
In the early years of CAN bus have car manufacturers intensively analysed all kinds of topologies, their benefits and disadvantages. Bus topologies, star topologies, combination of both, etc. All have been investigated. Most topologies were considered too complicated to implement in mass production, or too expensive. That's why eventually the bus topology became the most common one.
This is only part 1 of can bus. Normal switch can be explained and understood in seconds.
Good video! But what I'm curious about is the story behind that miner's hard hat and light on the cabinet behind you? :)
That is my grandfathers hard hat , who used to be a mining engineer manny moons ago. When he died , he passed it to me as I had a certain interest in mining on how it was done back then. As a child, I used to sit on his lap and listen to his stories from the coal mines.
here is that video ruclips.net/video/EvaRqFlJ9EA/видео.htmlsi=uHGhTGdYAyeeoXcH
@@D3Sshooter That explains a lot about your talents, you owe a lot to your grandfather.
@@D3Sshooter Thanks for the video! I use to produce and co-host a podcast called This Week in Energy. My co-host (in Germany) she and I would interview people on energy topics from around the world. Of course, we covered coal and during the podcast's run the Massey Energy Upper Big Branch Mine in West Virginia disaster happened killing 29 in 2010. It is stunning what coal mine operators were--and are--allowed to get away with. I will never understand why greed and money hoarding are not treated as the mental disease they are. Was that a photo of your grandfather in the video? If so, you two look a lot alike!
@@v2gbob Indeed and thanks for the comments
i am looking a solution to get communicate each other my range classic powered LS chevy engine with Volvo electric steering pump . for now without Canbus is in limp home 70%capacity
@@gokmenturk28 what signals is it expecting? I kind of wanna do the same with an EV conversion, but I'll use a hydraulic pump.
Holy poop, I thought you were a genius with the Weber's and you were just a carb guy.. but teaching advance CanBus.. bravo.. I teach this all the time, but one thing may i suggest you mention, is most manufactures ping the entire canbus system and shows which one is non-communicative.. at that time I tell my techs to save all codes,, clear,, repeat. Then at that time, you can verify 100% which mod is not working by simply having a conversation. Make it do something (pending which mod), or no data. Then that's the only one you have to chase.. if the mains comm, and most aub mods speak, but one does not, then you know who or what happened. From there you focus that section..
Great work and explanation..
Thank you , and yes that is a very good remark