pt16a4
Junior Member
Posts: 83
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Data Bus
Oct 26, 2020 15:02:56 GMT
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Post by pt16a4 on Oct 26, 2020 15:02:56 GMT
Quick question regarding the various data bus options: can anyone explain when each should be used and any important differences between them?
I have recovered some lost functions by long coding and adaptations, but am unsure if the selected data bus are ideal.
Would appreciate any available insight.
Thanks in advance!
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pt16a4
Junior Member
Posts: 83
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Data Bus
Nov 5, 2020 22:16:55 GMT
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Post by pt16a4 on Nov 5, 2020 22:16:55 GMT
Not the most responsive forum in the world, are we?
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pt16a4
Junior Member
Posts: 83
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Data Bus
Mar 21, 2021 14:35:10 GMT
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Post by pt16a4 on Mar 21, 2021 14:35:10 GMT
Nada.
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Deleted
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Post by Deleted on Mar 21, 2021 15:51:12 GMT
It might help if you told people what car / year / region (eg us europe etc)
Also a bit about what problem you are trying to resolve might help people to help you
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pt16a4
Junior Member
Posts: 83
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Post by pt16a4 on Mar 23, 2021 19:24:01 GMT
I am not asking related to a problem; I am trying to understand the relationship/differences between the data buses.
Comfort data bus, Databus drivetrain, Infotainment, Extended, Terminal 15 etc.
I understood this to be a fairly generic question.
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Deleted
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Post by Deleted on Mar 23, 2021 19:50:24 GMT
My misunderstanding hopefully dv52 (Australia) Can step in here and share his knowledge. |
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Post by dv52 (Australia) on Mar 23, 2021 22:02:04 GMT
@testeronline - thank you for the request. Not the most responsive forum in the world, are we? hmm........ you are probably correct in that there are likely better run forums on the net - BUT with the exception of one forum member, the rest of us "regular" members on this forum are volunteers and guess-what? We all actually have regular lives in which family, friends, paid-work, leisure and the usual pressure of normal life is of far greater importance than being a forum member.
So moral of my rant (without any offense intended); cut-us-some-slack, please - especially since your questions are related to general knowledge about vehicle nomenclature (i.e. your questions are not related specifically to OBD11 as a product)
Anyhow, apropos of your questions: Today's cars are ever-increasing in their sophistication. So, think about how designers have needed to solve the problem of ensuring reliable CAN communications on vehicles with an ever increasing number of control modules. On normal computer networks and in the main, the general solution to greater communications traffic is to increase processing speed and to precisely control internal comms pathways.
However, on vehicles the physical environment is not at all conducive to fast-speed communications because of often severe electrical noise that permeates throughout every part of the car and because the mechanism for sending/receiving CAN messages is via an unshielded pair of twisted wires which is part of the car's loom.
So - that's the problem that problem that engineers needed to solve and they chose a solution that relies on distributed communication's protocol. In this protocol, the message-traffic congestion that would result from every module communicating on one bus is solved by splitting the messaging task over a number of independent CAN "buses" which are defined by broad function types. Generally, the name of the CAN bus is evocative of the module functions that are allocated to that part of the CAN network. For example, the running gear CAN bus will consist of modules for functions like ABS, Parking assist, Power steering,All-wheel drive etc
A picture is probably better to explain the multi-CAN messaging topology on modern cars. On MQB platform vehicles, there are 5 x separate CAN buses like this:
Ignore the LIN bus (it's another topic) but notice the 5 x CAN buses and how they are connected in a type of "spoke" topology via "J533" - which is the module that OBD11 calls "Gateway module" (it lives on the CAN network @ address hex19). The Gateway module's role is like that of the "Fat Controller" on Tomas-The-Tank-Engine - amongst other tasks, the Gateway module co-ordinates messaging within a CAN bus and across multiple CAN buses.
Herein endeth the CAN bus lesson
As for your question about "Terminal 15" - this is a term used in the industry-standard DIN 72552. Read HERE
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pt16a4
Junior Member
Posts: 83
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Post by pt16a4 on Mar 24, 2021 0:26:28 GMT
Gentlemen,
Thank you for responding, as always it is much appreciated.
I did not expect my comment to rub the wrong way, as I assume all members of a forum are "volunteers", posting as they see fit and within their availability. My threads are not demands, but rather requests for information. That is, in my understanding, the purpose of a forum: to share inormation and comment on a topic of interest. Without dialogue, I personally fail to see the point of participating.
That said, thank you for the detailed explanation that goes far beyond what I expected.
I have reviewed a few OBD11 backups of 5F modules, in which varying data buses have been used for the same component within different vehicles (same model/year), which is the origin of my question.
Some of the data buses seem logical - I am indeed talking OBD11 - some I am unsure. The consequences of changing a data bus, via OBD11, I do not know. Perhaps overloading of a particular data bus is possible - yet again, I do not know.
In my experience, recoding a 5F module, functions have been recuperate via MMI regardless of the selected data bus.
Cheers.
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Post by dv52 (Australia) on Mar 24, 2021 2:17:43 GMT
pt16a4 OK - if your primary interest is the hex5F module, then your question relates to the Infotainment CAN bus shown in the top right box in my picture above. Here's the same CAN network diagram as in my first post but this time showing the topology of the separate modules that make-up the Infotainment CAN bus: As discussed in my first response, again J555 is the portal through which the Infotainment bus communicates with the other CAN buses. It's not surprising that the Infotainment CAN bus should need access to ALL the CAN buses in the car given the broad scope of data that can be obtained by the driver via the MIB screen
As shown, the infotainment CAN bus includes a "sub-bus" which is identified in the picture above as the MIB (Modular Infotainment System) CAN bus. The hex5F module is J794 in my picture.
Don
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pt16a4
Junior Member
Posts: 83
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Data Bus
Mar 24, 2021 7:20:26 GMT
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Post by pt16a4 on Mar 24, 2021 7:20:26 GMT
Thanks Don.
This is a massive amount of information, which is far beyond my level, but great to have.
On a basic level - admittedly very basic - can the selection of an incorrect "data bus" limit the functionality or customisation of said feature via the MMI? Ex. Message bus for the Climatic Master (Comfort vs. Terminal vs. Infotainment vs. Extended)
Can the selection of an incorrect data bus render a feature unavailable?
Apologies, this not the easiest question to express efficiently.
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Post by dv52 (Australia) on Mar 24, 2021 21:08:11 GMT
pt16a4 : Using forums like this for training purposes is not ideal - so yes, I always provide too-much data when answering these questions on the assumption that the person asking the question can then use the data to do further research. It's entirely up to you- now !!
Not sure that I understand your question - but in general, ALL of the MIB screens/functions that can be accessed by the driver have very specific pre-conditions to work properly. Amongst these requirements, the screens/functions must access the correct CAN bus (to get the data to correctly populate the MIB display) and sometimes the CAN bus isn't used at all and instead, the correct "Terminal voltage" must be present, which is often "T15" (see my previous response about DIN 72552). If OBD11 is used to select an inappropriate option, the screen/function won't work correctly (if at all)! Don |
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pt16a4
Junior Member
Posts: 83
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Data Bus
Mar 25, 2021 22:31:35 GMT
via mobile
Post by pt16a4 on Mar 25, 2021 22:31:35 GMT
Thank you very much, sir! On all levels, an excellent help.
I believe you have answered my question, and quite possibly why I have a "currently unavailable" speed warning setting in my MMI.
Seems logical to me that specific functions must communicate via dedicated paths, but the variances that I have seen raised doubts.
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pt16a4
Junior Member
Posts: 83
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Data Bus
Apr 5, 2021 12:33:16 GMT
via mobile
Post by pt16a4 on Apr 5, 2021 12:33:16 GMT
Don,
If settings are present via the MMI, but "currently unavailable", is this indicative of an incorrect message bus?
My Speed Warning adjustment and Pre Sense (both found within the driver assistance settings) are both returning this message when selected.
Do I simply have incorrect message paths? Both of these functions were previously available.
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pt16a4
Junior Member
Posts: 83
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Data Bus
Apr 17, 2021 17:38:07 GMT
via mobile
Post by pt16a4 on Apr 17, 2021 17:38:07 GMT
Any thoughts on the correct path for those two settings?
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pt16a4
Junior Member
Posts: 83
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Post by pt16a4 on Nov 30, 2021 20:46:37 GMT
Still trying to figure this one out. Speed Warning & Audi Pre Sense are greyed out and "currently unavailable" via the MMI. Can anyone share their particular database path, or if there are other ideas as to the cause, happy to hear your thoughts.
Thanks.
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