VW, SAE and ISO protocols

Hi,

I have recently started work on a PC based scan tool: I wanted to build a
protocol converter (SAE to RS232) based on a PIC chip. The same could be
done using the Intersil HIP7020, but I wanted to keep the cost down.

I only had access to the SAE documentation, so I was not aware of the
fact that a 'ready made' standard serial mode is already implemented in
VWs. This can make life a whole lot easier - a voltage converter based on
the MAX200 chips would be very easy to make, and I could skip the protocol
converter stage and could start on the data gathering and display software
straight away. The standard status/control/diagnostic code sequence definitions
are in the SAE documents and most of those are likely to apply to VW as well.

What would be helpful though:

> RTS is hooked up (thru a level converter) to the L line & "wakes up" the
> ECU @ 5 baud or something. ISO 9141-2 also says you need to talk @ 5bps
> on the L line to start communication, but VWTool seems to use the VAG
> custom protocol, not ISO otherwise.
Info on the start-up sequence, i.e. how the protocol type is selected. I have
not seen the ISO documents, so I would be interested to know what's in them
regarding this.

Any info on this 9600 bps VW protocol. If nobody has that info I suppose
we will have to find out from the traces...

> unless VW will give us a list of keywords & their numbers
There is probably a bit more to it than just a list of code-description pairs,
but if anyone has any info on VW specific OBD sequences, please share it ;-).

Any other thoughts?

Cheers

John

 
Received on Mon Mar 20 04:56:52 2000