>>>>> "Steve" == Steve <
[email protected]> writes:
Steve> The OBD-II port is RS485 link isn't it ? There was an
Steve> Elektor project recently to provide a OBD-II to 232 link.
There are three difference communications standards that run over
OBD-II. One of them is RS485 or similar; the interface to RS-232 can
be built trivially.
BUT the testbook software doesn't use the serial port - at least not
in the latest revisions. It uses the ETHERNET port to talk to the
HHT. And that's a much more complex proposal - figuring out how the
HHT converts it's ethernet data to something the car can understand.
Alternatively, you could consider getting an old version of Testbook
to run on modern hardware. T4 runs happily under Windows XP until you
try to communicate with the vehicle, when it bitches about the absence
of the HHT. Don't ask how I know. The earlier versions ... are
early. They pre-date Pentium processors for one thing, and are likely
to have lots of hardware dependencies on the specific HP laptop that
was used.
Another approach is to build from existing open knowledge on the
OBD-II protocols and build your own testbook. There's a Yahoo! group
called Open Diag that's populated with people building their own
interfaces to VAG diagnostics, and if you search around you can get
the BMW diagnostic software (which should talk to the engine in a
L322, BTW) off the web along with a diagram of how to build the
interface. As an aside, there's also a group called Hack The I Bus,
which is devoted to interfacing PCs to the I-Bus used in BMWs, the
L322, and possibly other post-BMW Land Rovers so that you can, for
example, surf the web from the in-dash display. Hopefully while
stationary.
But building an interface for a Range Rover isn't just as simple as
building your own OBD-II interface. ODB-II specifies a minimum
communication protocol to communicate with the Engine Management
System (EMS) only. And the P38A has three different "OBD-II"
connections in the same interface - I forget the pinouts now, but the
Engine, BeCM, and EAS all communicate over different wires.
Many ECUs require a specific challenge-response sequence to activate
the manufacturer specific functionality: for example, encrypting a
random number supplied by the EMS. If you can't reverse engineer the
key used, you're stuck. Or, more simply, the EAS ECU in the P38A
requires that you send a specific OBD-II style request with a specifc
interval (measured in microseconds) after resetting power to the
system.
None of this is specified in the OBD-II standard. OBD-II will let you
reset the fault codes on the Engine, but it doesn't address anything
to do with EAS, or the BeCM, or anything else specific to the vehicle.
I'm not trying to put you off the project. I'm just trying to share
the benefit of what I learned two years ago, when I decided that it
wasn't going to be trivial, and went off and bought a Rovacom Lite
instead.
Andy
--
Andy Cunningham --
www.cunningham.me.uk