Re: [avr-gcc-list] Anyone interface an AVR with a CAN bus?

[Bruce D. Lightner]

Reza Naima wrote:

> > In fact there are both SAE *and* ISO standards which apply to the OBD-II 
> > automotive CAN-bus.  They are in fact "available"...for a fee.  However, 
> > getting everthing you need is pretty expensive.  (One of the ISO standards 
> > is less than 5 pages long, and, as I recall, each ISO standard costs 
> > ~$100...what a rip-off!)
>
> I'm willing to buy them.  I've already gotten the ISO 15765-1 doc which
> just refers to the other relevant docs.  The ISO 15765-4 seems the most
> interesting, but I can't find that for sale anywere.  Do you have any
> references or information availabe.  Or know where I can pick up that
> (or ay related) documents.  

Those damn ISO committees!  It looks like that spec has been in 
"committee" for at least 5 years, and since it is not "approved", it still 
is not for sale.  Somehow Ford, GM, Mercedes and others have managed to 
make it work for OBD-II without a standard!  Welcome to the generic "scan 
tool" business! :-)


> > > I'm looking at going with the MCP2515 controllre IC, though I'm not sure
> > > how fast of an oscillator it needs.
> >
> > For 1 MHz OBD-II CAN, you will need 16 MHz clock with that chip.
>
> Will a ceramic resonator work?  I find them easier to deal with than
> crystals.  And they're cheaper :)

CAN-bus at 1 Mbps has pretty tight timing.  You need to look at the spec 
for the chip and the specs for your resonator.  Me?  I've been using 
"cheap" 16 MHz crystals.


> p.s. I've posted a simple schematic of how I think the AVR should hook
> up to the CAN controler and transiever.  If you wouldn't mind looking at
> it -- am I missing anyhthing?  I'm not sure what resitor values I should
> use for the CAN termination and the slew rate control... I'm picking 120
> and 10, respetctivly, as that's what I've seen used elsewhere...

Posted where?  A 120 ohm termination resistor is correct, but normally the 
vehicle itself supplies this.

Best regards,

Bruce

--
 Bruce D. Lightner
 Lightner Engineering
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