Re: Practical setup of the CAN physical layer in automobiles

It is ok, but may reduce the over-all length possible for the network. The
stars need to limit the length between the star and the node (each stub
length counts approxiametely double in the total length calculation).
Also, the stars tend to look like a cllumped load, and therefore distort
the signal. Cars aren't very big, so it works. May need tweaking to make
it robust.

David
PS: CAN is not a 'linear' bus per se. However, linear systems have been
well-characterized, and are easier to calculate for. An edge has to
propogate to all nodes and back in a set time frame for it to work. Also,
the returned signals need to not interfere with each other too much such
that the edge is distorted beyond the limits.


On Thu, Apr 11, 2013 at 7:50 AM, Dinesh Guleria <[email protected]>wrote:

> >> In fact that's the way it is done.
> But how can a star network be possible with a serial CAN bus protocol ?
>
> Regards,
> Dinesh
>
> On Thu, Apr 11, 2013 at 8:14 PM, Tom <[email protected]> wrote:
>
>> SC> I am currently working with a vehicle prototype where all CAN
>> SC> lines are connected in a star point.  I cannot imagine that this
>> SC> is the way it would be done in a mass production vehicle.
>>
>> In fact that's the way it is done.
>> Some have two stars - one in front other at the back.
>> As many as 8 pairs in one place.
>>
>> Some have mixed connections.
>> Nodes are conected in series - two pairs into one socket, but on
>> some nodes there is more than just two. Junction is made in a plug.
>>
>> I'm talking about cars like those from top from Germany.
>> They have a lot of nodes, but not only on one CAN BUS.
>>
>> "Regular" cars have much less modules.
>>
>> Tom
>>
>>
>> W liście z 11 kwietnia 2013:
>> From: [email protected]
>> To: [email protected]
>> CC:
>>
>> SC> Hello,
>>
>> SC> Literature on the CAN bus usually only explains how the CAN bus
>> SC> should work in theory, but I am wondering how the physical layer
>> SC> of the CAN busses in automobiles is actually implemented in real cars.
>>
>> SC> I am currently working with a vehicle prototype where all CAN
>> SC> lines are connected in a star point.  I cannot imagine that this
>> SC> is the way it would be done in a mass production vehicle.
>>
>> SC> On the other hand, a line structure would require some kind of
>> SC> T-junction connectors. Another possibility would be to place the
>> SC> junction inside of the control units, but that would require two
>> SC> pairs of CAN lines to be fed into the control units.
>> SC> I have never seen neither this nor that in automotive wiring
>> harnesses.
>>
>> SC> Can someone with practical experience tell me, how the CAN wiring
>> SC> in series cars is actually set up?
>>
>> SC> Thank you in advance,
>> SC> Christian
>>
>> --
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>
>