Messages with unknown CAN IDs sent by PDM

[lokmanho]

Hello,

I have two PDM30s in our experimental vehicle and we connect them to a CAN channel on a dSpace Microautobox. When I view the CAN messages using a Vector CANcase, I see that the PDM transmits not only the single output CAN message that it has been configured to send (ID 300 and 310), but also a series of other messages that look as if they have extended CAN identifiers (1CF8FC7Ax and similar). These messages have 7 bytes of data and the CAN identifier also changes every message. I know that they come from the PDM because they are visible on the CAN even if the MicroAutobox is not activated. My question is, what are they, and can I stop the PDM from sending them?

This is what a trace looks like:

Time Chn ID Name Dir DLC Data Diff time
[+] 9.776332 1 310 PDM_R2BNCU_1 Rx 8 10 00 00 00 00 00 00 00 0.010075
[+] 9.787700 1 300 PDM_F2BNCU_1 Rx 8 40 00 00 00 00 00 00 00 0.010003
| 0.300677 1 1CF8FC7Ax Rx 7 02 11 29 5A 3F 3E 8D 0.300677
| 0.306570 1 1CF80760x Rx 7 02 11 29 59 3F 3E 8B 0.306570
| 0.800744 1 1CF8CC19x Rx 7 02 11 29 5A 3F 3E 8E 0.800744
| 0.806594 1 1CF87787x Rx 7 02 11 29 59 3F 3E 8C 0.806594
| 1.300739 1 1CF8DC38x Rx 7 02 11 29 5A 3F 3E 8F 1.300739
| 1.306588 1 1CF867A6x Rx 7 02 11 29 59 3F 3E 8D 1.306588
| 1.800811 1 1CF83FE6x Rx 7 02 11 29 5A 3F 3E 90 1.800811
| 1.806631 1 1CF857C5x Rx 7 02 11 29 59 3F 3E 8E 1.806631
| 2.300858 1 1CF82FC7x Rx 7 02 11 29 5A 3F 3E 91 2.300858
| 2.306660 1 1CF847E4x Rx 7 02 11 29 59 3F 3E 8F 2.306660
| 2.800910 1 1CF81FA4x Rx 7 02 11 29 5A 3F 3E 92 2.800910
| 2.806688 1 1CF8A43Ax Rx 7 02 11 29 59 3F 3E 90 2.806688
| 3.300977 1 1CF80F85x Rx 7 02 11 29 5A 3F 3E 93 3.300977
| 3.306734 1 1CF8B41Bx Rx 7 02 11 29 59 3F 3E 91 3.306734

Thank you in advance.

Lok Man

[YuriK]

Hi,
These are so called discovery messages, they are used to identify the device on the network and they can't be disabled. Why do you want to disable the messages?

Thanks!
YuriK

[lokmanho]

Hello YuriK,

Thank you for your prompt response! We would have preferred to disable them because they are of no use to us on our system (no other Motec devices present), and we want to ensure that they are not interpreted incorrectly by any other devices on the network. These come from other manufacturers and we do not have control over how they react to random CAN messages. So far we have not yet had any errors that we can directly attribute to these messages, but this CAN bus is very sensitive on our car because there are many devices on it over a relatively long length.

Cheers,
Lok Man

[JayDee]

Hi,
I must admit that the extended messages confused us when they appeared after fitting an ADL3 back in 2008/2009. No one has ever given us a decent description of their purpose and since we scrutinize the data on our CAN bus quite a bit its always been a bugging issue. In a very specific case we have had some trouble when running through CAN gateways, I guess it might have been down to them not passing the extended messages correctly. It was quite a while ago but we worked around it. Its just a shame that historically MoTeC have been very open about their datastreams and they have been pretty straightforward to integrate into many different systems, it would appear however that it is becoming more secretive and less flexible. The kit is still pretty good for the price but please don't go the old PI route and make everything 'need to know' because it the end customer never seems to get told. Like the little hidden gem that if you want a VIM to work anywhere near its stated performance update rate you should not have anything (or very little) running on the same BUS, easy once you know but a bit late after being brought in to help a customer who has already build all of their looms.
Rant over... J.