Can Bus specifications

The official (I think) CANBUS specification can be found at CIA, that stands for Can In Automation. There are both base and extended protocol. They seems to be very clear and intuitive and I think they will be very helpful as soon as we start coding some CAN sniffer or similar. I have to start thinking about how big the sniffed data will be and where to store that so that we can study it easily. Maybe the only choice for this is a database (for which I guess mysql would do pretty well).
We'll see soon. Coding time is approaching!

About CAN BUS

Here I have found a good introduction to the CAN bus.
It is a link level protocol, similar to ethernet, with CDMA (Collision Detect, Multiple Access) policy.
Every CAN bus peripheral can receive and send data on the same bus and has the capabilities to recognize where someone else is using the bus at the same time. A priority mechanism ensures that in this case only one transmission is completed.
Unlike ethernet, this protocol is content oriented, that means the each message does not have destination and source fields, but just an identifier that specifies the meaning of the data associated to the message. The meaning of the identifier is not specified in this standard as it is choosen by higher level applications.

Each message consists of an identifier, some flags and crc and the payload.
The identifier is 11bit wide in CAN bus version 2.0A and 29bits wide in version 2.0B

There are four different message types:

• Data frame: a frame containing node data for transmission
• Remote frame: a frame requesting the transmission of a specific identifier
• Error frame: a frame transmitted by any node detecting an error
• Overload frame: a frame to inject a delay between data and/or remote frames

The arbitration on the bus is based on the identifier. As the bus is AND wired, each time two components send a signal on the bus, the result on the bus is the logical AND between the two signals. This means that when collision happen, only one of the identifiers of the messages gets trasmitted to the bus (the one with most zeros); the transmitter can simultaneously read what is on the bus and if the identifier coincides they proceed to transmit the complete message.

This info on Wikipedia will probably be very useful to get data structures written in C or any other language I might choose for this adventure.

EOBD Connector Pin Layout

According to the info found on this page this should be the pin layout for the EOBD connector:

Pin 1 - Ignition positive
Pin 2 -
Pin 3 - Data Tacho / MUX network Late generation
Pin 4 - Chassis ground
Pin 5 - Chassis ground
Pin 6 - Data Climate control/CAN High ('IS' Late generation)
Pin 7 - K Line Data Engine management / Automatic gearbox management
Pin 8 - Cooling fan control information / MUX network Late generation
Pin 9 - Charge information
Pin 10 -
Pin 11 - Data BSI
Pin 12 - K Line Data ABS/ESP/GEP/Suspension control
Pin 13 - Data Air Bag/Headlight control
Pin 14 - CAN Low('IS'.. Late generation)
Pin 15 - Data Engine management
Pin 16 - Battery positive

The OPEL/Vauxhall Vectra should use the CAN BUS to exchange information between the various components. I wonder how the pin are placed on the actual connector, since it seems a bit different. We will have to attach probably to pins 6 and 14 to get access to the bus.

EOBD on board diagnostic connector on the Vectra

Seems like my 2002 Vauxhall/OPEL Vectra supports the EOBD connector. I have found it near the gear shift lever and I'm now pretty sure about it thanks to this image:

found with Google Images. I'll post a picture of the exact location as soon as I can download photos from my mobile or get a decent camera.
This connector should provide access to all the internal diagnostic informations from the car like tire pressure, engine parameters, temperatures and more.
I have found some more info on it on Wikipedia. Seems like it's a standard for European vehicles since 2001 and should also include the CANBUS interface I'm interested in.
Now that I think about it, it should also be present on the other Vauxhall our family owns. I have to check this sooner or later!