A little Can Bus tutorial

[Knizar]

Clarification on CAN-BUS.

The CAN-BUS protocol is about messages not devices.

That is, every device on the bus broadcasts it's messages with specific identifiers and every device listens to all messages ignoring all but those having the specific identifiers of interest.

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Conceptual explanation of the relationship between CAN-BUS and OBD-II.

CAN-BUS is how the Spyder talks* to itself.

OBD-II is how the Spyder talks* to us.

* talks using CAN-BUS messages.

I must be CAN-BUS because after reading this you have me " Talking to MYSELF ", I'm a bit hard of hearing, but the OBD-II must not be working because I haven't heard a word out of my Spyder! Thanks for the info though. Bill

[UtahPete]

If you understand LAN protocols, each device has an address.
In a packet of data sent from anything it has a address in the header for the destination component.
It's not that the VSS doesn't talk to the radio, the radio actually does see the packet the VSS sent but it just ignores it as the packet is not addresses to it.

Bob

That helps.

[BertRemington]

I was trying be careful in not saying it but now I must: CAN-BUS is not a LAN.

Without over-simplifying too much:

* CAN-BUS carries complete messages; LAN carries packets with complete, incomplete and multiple contents (messages)

* CAN-BUS "addresses" are device-independent message identifiers; LAN "addresses" are content-independent device identifiers (multicast is special "device" address)

* CAN-BUS uses a robust two-wire signalling protocol with simple message prioritization, deconfliction and filtering rules implemented with cheap chips (eg MCP2515 and MCP2551); automotive LAN 10xxBASE-T1 uses a single twisted pair which provides inter-device packet exchange using a variety of line codes (and chip families) and requiring additional chips for device-unique higher-level content (message) processing.

As our vehicles evolve to "software carriers" and MCUs are replaced with CPUs, CAN-BUS will likely remain for "transport-critical" functions while LAN is introduced for non-critical functions. I doubt the Spyder radio will ever move from CAN-BUS to LAN but I'm pretty sure your Mercedes radio already has.

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Adding a note about OBD-II and Spyders. OBD-II requires certain standard messages for specific emission certifications. Spyders aren't required to meet those certifications (note the lack on your under-seat stickers) and therefore is using manufacturer-unique OBD-II messages (allowed by the standard). Which I learned at the cost of $100 in hardware and software.

[IdahoMtnSpyder]

Clarification on CAN-BUS.

The CAN-BUS protocol is about messages not devices.

Thanks for the clarification about the "how" of the network messages. It looks like I did have the "what" reasonably correct. I had completely forgotten I made this post nearly 7 years ago!

Adding a note about OBD-II and Spyders. OBD-II requires certain standard messages for specific emission certifications. Spyders aren't required to meet those certifications (note the lack on your under-seat stickers) and therefore is using manufacturer-unique OBD-II messages (allowed by the standard). Which I learned at the cost of $100 in hardware and software.

When I've looked for additional info on Spyder Error Codes I've noticed that many of them are in fact the same ID and explanation as automotive codes, particularly those related to engine operations that affect emissions.

The Spyder CanBus system is much the same as industrial control systems, right? And there are a bunch of them! https://en.wikipedia.org/wiki/List_o...tion_protocols

[CloverHillCrawler]

Clarification on CAN-BUS.

==========

Conceptual explanation of the relationship between CAN-BUS and OBD-II.

CAN-BUS is how the Spyder talks* to itself.

OBD-II is how the Spyder talks* to us.

* talks using CAN-BUS messages.

I don't know this "update" has me asking questions as this is the first time of me hearing OBDII in relation to the Spyder.

Are you saying that BUDS is using OBD-II as its communication protocol?

[BertRemington]

When gkamer asked about CAN-BUS for Ryker and SportsterDoc cited your 2016 tutorial I took the opportunity to update the community with what I've learned in the last year or so.

Yes the Spyder OBD PIDs match the standard PIDs except ... extracting them using off-the-shelf hardware (OBDlink) and software (OBDwiz) in KWP2000 and CAN-BUS 2.0a (11-bit) message formats didn't work. There is a Service 01 PID 1C - OBD standards this vehicle conforms to but OBDwiz didn't display any helpful information whatsoever. OBDwiz does have a direct command interface to the OBDlink (based on the Hayes AT command set if you can imagine that) but I'm really not that interested* in chasing that rabbit, a chase that began when wlinn1 asked about a HUD and I foolishly thought I can do that. NOT!

I know the PIDs are in there, you just need to know how to ask the Spyder for them. The best approach would be to have a CAN-BUS sniffer listening while a BUDS is requesting and receiving them. And a pre-BUDS2 Spyder (pre-2017) will probably be easier to decode than later Spyders.

If someone wants to use the AT command capability of OBDwiz to decode the OBD PIDs the Spyder is generating, I'll loan them my OBDlink, OBDwiz (I have an unused activation) and the 6-pin Deutsch DT connector. Start by researching the software here https://www.scantool.net/obdwiz and the forum here https://www.scantool.net/forum/index.php

* My interest is specific device-level messages such as LT button pressed, RT button pressed, etc and I've decoded those.

[BertRemington]

CloverHill -- explaining something conceptually is tricky so here's some additional information.

In both cases the "communications protocol" is CAN-BUS.

When talking to itself, the messages are "internal use only" specific to the Spyder.

When talking to us via the BUDS laptop and Spyder console, the messages are defined by the OBD-II standard.

Special qualification: while the BUDS laptop and Spyder console display "OBD-style" B/C/P/U codes, I don't know for sure the messages themselves are in OBD-II format. It just seems to me with an ECM, TCM, etc designed and built by Bosch who is the standard-setter that the messages would be in OBD-II format, just not in the emissions certification OBD-II format off-the-shelf OBD-II software (eg, my OBDwiz) recognizes. But that's a hypothesis not a certainty that I will continue with.

Only the BUDS laptop, Spyder console and certain top-line diagnostic equipment know how to request and decode Spyder OBD-II messages.

The BUDS laptop and the Spyder console are using the Spyder CAN-BUS (accessed by the laptop at the 6-pin Deutsch Data Link Connector) to transmit OBD messages and receive the responses.

For the B/C/P/U DTCs, the Service 03 - Show stored Diagnostic Trouble Codes message is broadcast that when recognized by specific Spyder devices (eg, ECM TCM*) broadcast in response DTC messages that are decoded and presented to us on the laptop and console as B/C/P/U codes.

* I believe each device responds with its own DTCs but there's a possibility the console serves as the central collection and response interface.

Real-time data is requested and returned using the Service 01 - Show current data PID. It was this information I hoped could feed a HUD but I couldn't request/decode it with OBDwiz.

It's easier to understand these interactions by examining CAN-BUS and OBD-II separately. That is, don't think about CAN-BUS when figuring out how OBD-II works and vice versa.

[BertRemington]

IdahoMtnSpyder

The Spyder CanBus system is much the same as industrial control systems, right? And there are a bunch of them! https://en.wikipedia.org/wiki/List_o...tion_protocols

That is a fun list. I bookmarked it. Thanks.

Yep CAN (BUS) is on that list. Although I'm pretty sure my and earlier Spyders use KWP2000 which is also on the list. I surmised this from this service manual picture.
BUDS KWP2000.jpg
And the CAN-BUS does run at 500kbps.

PS I said CAN-BUS was cheap and Wikipedia agreed with me.

[BoatFixx]

I hope this link works.

https://www.roadrunner.travel/articl...kly-newsletter