Yes you CAN ! Understanding the CAN BUS Part 2 - Electrical Signals
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- Опубликовано: 10 фев 2025
- This is part 2 in the series of four. In this video we look at the electrical signals on the CAN bus.
Part 1: Covers the physical aspects of the CAN bus ( published)
Part 2: Covers the electrical signals of CAN bus ( published)
Part 3: Covers the CAN bus protocol ( coming soon)
Part 4: Covers CAN messaging. ( coming soon)
Thats the best CAN bus tutorial I have seen on youtube
Thank you
Another great video Steve. I've got to say if there is one thing you are good at it's lots of things!
I've watched a good few videos on CAN bus, some of which have gone into great detail but your presenting style just makes it so much easier to take in. I also like that you have demonstrated it working rather than just the theory of it, for me that makes it all make sense. Unfortunately my 'toy' car is a bit long in the tooth for needing CAN bus although it does get me thinking of what I could do with it.
Well presented, clear and not skipping in anything.
A quick 2 questions please.
1. Where did you get your information (shown at 3:18) of what modules are on what BUS?
2. What is the usual frequency of the CAN bus?
Thanks
Thanks for the comments, for your question 1: That is based on the datasheets and build information on several CAN modules. CAN transceivers come by multiple vendors, but all meet the CAN bus specification.
2. The CAN bus where we are talking about here runs at 1Mbps , others older at 512kbps, and new CAN FD's at higher speeds. As you will have noticed , I have no X-tal on the transceiver as that is only a transceiver. In the next video, we will dig in to the synchronization and the actual CAN frames for 1Mbps CAB bus. You will notice that the frequency /xtal runs at 8Mhz.
Nice overview with basic explanation on how the physical layer works. The shown physical layer is by far the most used one. But there are two other physical layers that are used in some cases by some car manufacturers: Fault Tolerant CAN, and Single Wire CAN. The voltages on the bus wires are different for those physical layers.
Yes indeed, and that is why in the first video , `i did mention that we are looking at the standard ISO 11898-2 A/B ' and that there are different standards such as the ones you listed and the CAN FD...
Master class
Sir, this is an awesome channel. I`m mostly into component level electronics myself , but I also appreciate a lot of mechanical stuff. I own a 1984 camaro sport coupe, so you can imagine that I have to spend a lot of time under it. LOL. Lets make a deal......... If I watch all 13 years of your You Tube portfolio, you will issue me a masters degree, Because it`s worth it goddammit.
Very interesting Steve.
Thanks Tim
The explanation in this video assumes that all connected modules have the same ground (i.e. reference) voltage. In a real car this might not be the case. Due to poor grounding there might be several Volts ground offset between one module and the other. In those cases will the voltage levels on the bus be different. Especially the wave forms in the recessive state may look different. On an oscilloscope this will easily be recognisable, but measuring with a voltmeter might confuse you tremendously.
Thanks for the comment, so lets look at that : First all CAN controllers should have a good ground. If that is not the case it should be fixed. The ground is in essence irrelevant for the Transceivers and the signals on the bus as they measured not towards ground but towards the differential difference between CAN -H and CAN-L. Of course the Vcc and Vss must be within tolerance to power the transceivers and the CAN controller. Remember that the Transceivers are embedded in t he CAN controllers . Thus those must be provided with a good ground and the needed Vcc ( +12V or sub voltage). If they are not having a good ground , there will be potential issues with the CAN controller itself and yes it might be that the CAN-H and CAN-L voltages varying. Pending how that ground behaves. That is why measuring the CAN bus with reference to ground for both CAN-H and CAN-L is indicative only and as you stated can be very misleading . Hence my advice for a scope.
@@D3Sshooter You are correct that the receiver only looks at the differential voltage. However, all transceivers have a limited so-called common mode voltage range. If the grounding is poor it is, in theory, possible that a receiver gets pushed out of its common mode voltage range. Or that a reverse current starts flowing in the output stage of the transmitter. If I remember correctly is a ground offset voltage of 2 Volts no problem for the transceivers to handle (some types can handle more than this).
@@windmill1965 Indeed, that info is available on the datasheets of the specific transceivers.
I see what you did there ;-)
? and that is what ?
CAN and can.
Took me some time to digest that binary 1 is 0V CAN differential.
I know, its kind of the reverse logic and it can take a bit before it sinks in..
That is somewhat counterintuitive but if I remember correctly this becomes an advantage when handling message collisions and which has higher priority. I may be mis-remembering that but I'm sure there is an advantage to it, maybe this will come up in future videos and I don't want to pre-empt Steve.
Is there anything this man doesn't try his hand at!
Oh yes , but thanks a lot
We want a guitar tube amp
Aja... dat gaan we dan eens doen binnenkort , nu dat we op pensioen zijn... tot morgen op de koffie