address claiming messages and request messages in J1939

[Owen Senmeis]

Hello,

 

I’m a newbie in J1939 and from now on have to develop a diagnostic device so don’t laugh if my questions are too silly.

 

1.       Must every J1939 device send an Address Claiming message after power up? Even a diagnostic device?

2.       I’m reading some code about request messages which was written by an advanced expert. The following words are taken from his comment in the main file:

 

To test this demo application send the following request

messages:

0x18EA3301   0xD6 0xFD 0x00

0x18EA3301   0xD7 0xFD 0x00

            

As result the protocol software will send the following

data messages:

0x18FDD653   Data is changing (length = 8 bytes)

0x18FDD753   0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00

 

Is it correct with the address? The requested address is 0x33 but the responded address is 0x53.

 

Thanks

Senmeis

[Bram Kerkhof]

Some parts of this message have been removed. Learn more about Nabble's security policy.

According to the spec (J1939-81, 4. Technical requirements) each CA must claim an address and must be able to provide its NAME. However, this is not always implemented: there are constructors that have non-configurable addressing for their ECUs, that don’t bother with the address claiming process because it is assumed that there won’t be extra (unknown) nodes that attach to the network.

 

In my opinion you should implement it according to spec, but ensure that your device will operate properly if the other nodes don’t.

If you don’t need to send anything: don’t bother with the address if those AC/CA messages are the only thing you’ll be sending. If you have to send anything, claim an address first as specified. As a failsafe, implement a check when another node is using the address you claimed (because it did not properly reply to your claim) and be able to deal with that situation (e.g.: by claiming a different address).

 

About the request: the addresses are indeed not what they should be for the RQST message. According to the spec the CA with address 0x33 should respond with the requested PGN or with a ACKM.NACK if it isn’t able to provide them.

 

So: the documentation is wrong (even advanced experts are human), or the implementation is not up to spec.

 

cheers,

Bram

 

From: canlist-owner@... [mailto:canlist-owner@...] On Behalf Of Owen Senmeis
Sent: woensdag 7 oktober 2009 13:12
To: canlist@...
Subject: [CANLIST] address claiming messages and request messages in J1939

 

Hello,

 

I’m a newbie in J1939 and from now on have to develop a diagnostic device so don’t laugh if my questions are too silly.

 

1.       Must every J1939 device send an Address Claiming message after power up? Even a diagnostic device?

2.       I’m reading some code about request messages which was written by an advanced expert. The following words are taken from his comment in the main file:

 

To test this demo application send the following request

messages:

0x18EA3301   0xD6 0xFD 0x00

0x18EA3301   0xD7 0xFD 0x00

            

As result the protocol software will send the following

data messages:

0x18FDD653   Data is changing (length = 8 bytes)

0x18FDD753   0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00

 

Is it correct with the address? The requested address is 0x33 but the responded address is 0x53.

 

Thanks

Senmeis

[Funny N.]

Some parts of this message have been removed. Learn more about Nabble's security policy.

If you still try to develop your own device, you can try one of our J1939 simulators(Twelve different editions in the family for the moment, there will be Sixteen editions in the near future).

All Engine Premium and Vehicle Platinum editions can generate DM1, DM2, response to request (e,g, Engine Hour, Engine Clock, DM2, etc.), and multiple packets communication protocol, such as: TP.CM.BAM+TP.DT; TP.CM.RTS+TP.CM.CTS+TP.DT, etc.

 

Funny N.
Au Group Electronics, http://www.AuElectronics.com
http://www.AuElectronics.com/products
http://augroups.blogspot.com/

---

From: Owen Senmeis <senmeis@...>
To: canlist@...
Sent: Wed, October 7, 2009 7:12:17 AM
Subject: [CANLIST] address claiming messages and request messages in J1939

Hello,

 

I’m a newbie in J1939 and from now on have to develop a diagnostic device so don’t laugh if my questions are too silly.

 

1.       Must every J1939 device send an Address Claiming message after power up? Even a diagnostic device?

2.       I’m reading some code about request messages which was written by an advanced expert. The following words are taken from his comment in the main file:

 

To test this demo application send the following request

messages:

0x18EA3301   0xD6 0xFD 0x00

0x18EA3301   0xD7 0xFD 0x00

            

As result the protocol software will send the following

data messages:

0x18FDD653   Data is changing (length = 8 bytes)

0x18FDD753   0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00

 

Is it correct with the address? The requested address is 0x33 but the responded address is 0x53.

 

Thanks

Senmeis

[Funny N.]

Some parts of this message have been removed. Learn more about Nabble's security policy.

SAE recommend address claim as a good practice. And all OEMs have their own requirement and regulation.

The example shows a request to PGN 64982 and PGN 64983, which are the basic joystick message 1 and extended joustick message 1. SAE defined both PGNs as broadcast PGNs (100~200 ms repetition), I don't know why it needs request.

>The requested address is 0x33 but the responded address is 0x53.
The destination address doesn't match the source address response to the request. So if that is not some properitary definition, there must be some inside stories.

 

Funny N.
Au Group Electronics, http://www.AuElectronics.com
http://www.AuElectronics.com/products
http://augroups.blogspot..com/

---

From: Owen Senmeis <senmeis@...>
To: canlist@...
Sent: Wed, October 7, 2009 7:12:17 AM
Subject: [CANLIST] address claiming messages and request messages in J1939

Hello,

 

I’m a newbie in J1939 and from now on have to develop a diagnostic device so don’t laugh if my questions are too silly.

 

1.       Must every J1939 device send an Address Claiming message after power up? Even a diagnostic device?

2.       I’m reading some code about request messages which was written by an advanced expert. The following words are taken from his comment in the main file:

 

To test this demo application send the following request

messages:

0x18EA3301   0xD6 0xFD 0x00

0x18EA3301   0xD7 0xFD 0x00

            

As result the protocol software will send the following

data messages:

0x18FDD653   Data is changing (length = 8 bytes)

0x18FDD753   0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00

 

Is it correct with the address? The requested address is 0x33 but the responded address is 0x53.

 

Thanks

Senmeis

[Allen Pothoof]

Some parts of this message have been removed. Learn more about Nabble's security policy.

When I first got involved with J1939, I also had the question about Address Claim and  I have seen it several times since then.
 
The standard says that if you wish to transmit on the bus, you need to do an Address Claim when you join the bus; if you are in a listen-only mode, you are exempted.  Not all modules implement Address Claim (which is what prompted my original question: I was using one of my company's prior modules as an example and it didn't implement it) but it is required by the standard and should be implemented.
 
Further, if you lose the Address Claim (some other module has the same address and a "higher priority" name), you don't transmit further on the bus (actually, I think the standard says not to transmit further until you win an Address Claim, which would imply that you could send another Address Claim request; don't try it repeatedly with the same address,  you'll "flood" the bus).
 
The assumption that some module doesn't need to do Address Claim because all the modules have fixed addresses and that module's address is unique is, in my opinion, taking a risk in that those assumptions may be wrong, either by design (variable addressing) or because someone (a  maintenance technician, for example) plugged in the wrong module.  The problems caused by multiple modules with the same address can range from minor to catastrophic and can be difficult to debug, particularly if you have a large number of network nodes.  A module which simply doesn't talk is likely to be swapped out quickly.
 
Hope this explanation helps.
 
Regards,
Allen Pothoof
 

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Date: Wed, 7 Oct 2009 19:12:17 +0800
Subject: [CANLIST] address claiming messages and request messages in J1939
From: senmeis@...
To: canlist@...

Hello,

 

I’m a newbie in J1939 and from now on have to develop a diagnostic device so don’t laugh if my questions are too silly.

 

1.       Must every J1939 device send an Address Claiming message after power up? Even a diagnostic device?

2.       I’m reading some code about request messages which was written by an advanced expert. The following words are taken from his comment in the main file:

 

To test this demo application send the following request

messages:

0x18EA3301   0xD6 0xFD 0x00

0x18EA3301   0xD7 0xFD 0x00

            

As result the protocol software will send the following

data messages:

0x18FDD653   Data is changing (length = 8 bytes)

0x18FDD753   0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00

 

Is it correct with the address? The requested address is 0x33 but the responded address is 0x53.

 

Thanks

Senmeis

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