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Absent Address Claim at Startup

 
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smartmt



Joined: 09 Oct 2009
Posts: 3

PostPosted: Fri Oct 30, 2009 5:57 am    Post subject: Absent Address Claim at Startup Reply with quote

I am investigating a truck application that has two nodes, a brake controller and a transmission controller.

Nothing else is connected to the CAN bus.

At startup, neither unit executes an address claim, they just start straight in transmitting on the expected, SAE-defined, SAs.

If I inject an Address Claim request via CANAlyzer neither unit responds.

Is this normal practice or is it possible there is a CAN gateway in the system and these messages are just re-transmitted on a secondary bus?

Many thanks in advance for any suggestions.

Steve.


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jkaufmann



Joined: 12 Mar 2008
Posts: 75

PostPosted: Tue Nov 03, 2009 12:24 pm    Post subject: Reply with quote

I would guess that they just didn't implement this portion of the protocol since it sounds like they have complete control over the bus and never intended for other devices to be connected anyway.

I would just pick a SA that doesn't conflict and start transmitting requests or whatever it is you are trying to accomplish. It is likely that they don't support any requests either unless the devices were specifically programmed for communication between each other or some other diagnostic tool.
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smartmt



Joined: 09 Oct 2009
Posts: 3

PostPosted: Wed Nov 04, 2009 4:17 am    Post subject: Reply with quote

Thanks Jonathan,

I didn't realise that address claim was optional - my interpretation from the standard and from Wilfried's book was that it was mandatory.

I'm still not entirely sure why the ABS controller and TCU need to communicate, unless shifts are inhibited during an ABS event.

There is definitely no response to address claim requests or PGN request from either node.

Diagnostics are on a separate J1587 bus, which is slightly annoying as I shall now have to buy yet another diagnostic tool!

Steve.


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jkaufmann



Joined: 12 Mar 2008
Posts: 75

PostPosted: Wed Nov 04, 2009 10:28 am    Post subject: Reply with quote

I'm not saying its optional, just that I wouldn't be surprised if people deviated.

I'm sure it is "mandatory" per the spec - Wilfred's book is not wrong, but if its a private bus, then maybe they just pulled the bits and pieces they wanted and its not truly J1939 "by the book".
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smartmt



Joined: 09 Oct 2009
Posts: 3

PostPosted: Thu Nov 05, 2009 4:29 am    Post subject: Reply with quote

The brake controller is Wabco and the TCU is Allison so there must have been a degree of collaboration in the design of the system, either that or there is an 'accepted practice' between manufacturers of omitting address claim if your ECU falls into one of the SAE source address categories.


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