Hi,
You must be my twin. I am doing the same thing right now. :)
The only "open" spec for the CAN bus is this:
http://www.semiconductors.bosch.de/pdf/can2spec.pdf

>From there, you can decipher the bits in the frame but not the meaning
behind the content...unless it's OBD-II.
The Wikipedia page is fairly comprehensive about the OBD-II CAN
frames. You will NOT find published CAN data frame information as
this is proprietary to the manufacturer. There are some other forums
out there that hint at what's going on but no one is going to tell you
what messages are sent between the headlight controller and the main
ECU. :) (An example...)

With the Bosch spec and your filtering set up correctly you should be
able to read in the OBD-II data frames. You might have to learn how
to issue a request for data in order to receive a response. I would
suggest buying a "T" cable and an OBD-II scanner with CAN. Let your
board sit back and listen and learn with the scanner doing the
messaging. Once you see what's going on you can then write your own
routines to make your own scanner.

HTH
--- In l..., Jean-Sebastien Stoezel
wrote:
>
> Hi,
>
> I understand the OBD adapters come in different flavours. I'm
> interested in OBD2, supporting CAN bus, which is mandatory on al cars
> built after 2008. I built an LPC2368-based datalogger and I want to
> decipher the CAN bus frames I am receiving.
> On 30-Dec-08, at 9:48 PM, Robert Adsett wrote:
>
> > Jean-Sebastien Stoezel wrote:
> > > Thanks for your quick answer from both of you guys. I'm getting
> > > confused now... Is ISO 11898 simply the CAN bus specification??
> >
> > 11898-1 appears to be the CAN protocol
> > 11898-2,-4 and -5 are physical layers (the electrical and wire
> > connections), CAN supports quite a variety.
> > 11898-3 is a higher level protocol (usually referred to as a HLP) that
> > builds on the CAN protocol, just as http builds on TCP/IP .
> >
> > > I'm
> > > looking for information regarding CAN message format specifically
> > used
> > > by ECUs and OBD2. I though this was covered by ISO 11898, but
> > based on
> > > the links you've posted, it looks like ISO 11898 is simply the CAN
> > bus
> > > specification...
> > >
> > > What's the specification for OBD2 using CAN bus? (mandatory in all
> > > vehicles since 2008).
> >
> > I don't think it's as simple as a single protocol. There's a reason
> > the
> > ODB adapters come in different flavours.
> >
> > What are you trying to do? If you just want to read the data you are
> > probably better off getting a commercial adapter.
> >
> > Robert
> >
> >
>

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