I am working on a large paper that will describe the entire vehicle network in detail. In the process of doing that, I will need lots of diagrams. I thought I would share a few of them as a preview to help understand the network as a whole.

Figure 1. AVC-LAN Network

First some clarification. The term AVC-LAN actually refers to a collection of signals.

• Two wire Differential Serial data based on NEC's IE-Bus protocol
• Video (in our case, it is RGBs, however there is a composite video available)
• Audio (Stereo, or mono in the case of the NAV and Telephone)
• Mute - Used to allow a component in the system to mute other sources of audio

We are mostly interested in the Two Wire Differential Serial Data signals. This by itself is an IE-Bus developed by NEC electronics. The devices are wired in parallel with one device acting as a 'hub' of sorts. In the case of the SC430, the Radio acts as the hub. It is the master in the system and the rest of the components will not operate without its presence. Do note the 60-80 Ohm resistor shown in the diagram within the H/U. From my research it appears that this is really all that makes something a master. If true (need to verify) the radio could be eliminated by a simple box with a resistor.

Take-Away: IE-BUS is connected in parallel in a Star topology.

 Let's the look at the rest.

 Figure 2. Entire Network

Figure 2 is a bit more complex, but accurately represents the entire network in the SC. The Network Gateway is capable of handling 3 BEAN buses, one IE-Bus, and one Debug interface (ISO 9141).

The BEAN bus uses a single wire and all devices are arranged in a ring (in series.) The various devices in the ring use an open-collector signaling in order to prevent interference on the bus when they are quiet. Bus arbitration is handled within the bus by buffering the signal coming in, adding its own frame, and then passing the data out. A priority code inside each message will determine the order of the signals. If the highest priority code is present in a message, the signal is just passed along and the device will add its own message after.

So how do we add on to this network, then? Well, there are two possible methods. The first would be to insert our ECU into the ring in series. The second is to use a buffer circuit to connect to the network in parallel. If you notice in Figure 1, the Mayday transceiver is connected using a buffer.  I am suspecting, but have not yet verified) that this only provides a read-only connection to the network. This should be fairly easy to verify.

I will be receiving the telephone computer and Mayday transceiver today. Included are several other components, one of those I am hoping is the buffer so I can verify the above. If not, I will need to pick one up ($35 on eBay.)

As always, much more to come...

Books and Links - Networks

I'm going to use this post to link to books and reference material that I have located throughout my research. As such, expect this post to be edited as I discover more information.

Books

Multiplexing and Networking (Progress in Technology) (1999) by Ronald K. Jurgen
This one contains 114 SAE papers, including all papers on the BEAN protocol. This book is out-of-print, so you will need to pick it up used.

Multiplexing and Networking Vol. 2 (2006) by Ronald K Jurgen
Contains 63 SAE papers covering networking protocols and technology between 2000-2005

SAE

 

ISO 

 

LINKS

Reverse Engineering the Vehicle's Networks

This is such a complex topic that I expect this category is going to get really messy. I'll do my best to mitigate that by putting together more concentrated information into the Papers section.

Essentially, what we are looking to do here is to take control of the various networks within the car. By why would we want to do that?

Well, let's talks about ECUs. An ECU is a computer inside the car. Your car has tons of them. I will be putting together a list of all the ECUs soon. But anyway, all of these ECUs are able to talk to each other which allows for the integration you experience in the car.

Just an example: When you open your hardtop, the roof ECU commands the door ECUs to roll down the driver and passenger side windows. It does this by sending commands over the BEAN bus (Body Electronics Area network.) The BEAN bus carries tons of information around the car containing sensor, switch, analog, and diagnostics data.

This networking concept reduces the amount of wiring needed in the car. Without out, the roof ECU would need several wires running throughout the car to activate the relays for the windows. With the BEAN bus, just one wire is used.

This network also makes expansion possible. Additional ECUs can be added to the system as 'Dealer Options' to provide more functionality to the car.

Unfortunately this is not very well documented and is going to require quite a bit of work to reverse engineer the system, but the ability to take control of the systems in the car and develop new functionality is a prize worth working for.

In order to do this, I will be building up a little 'test-bench' that involves wiring up some of the original components from the car. It will also require the development of some tools (hardware and software) to monitor and explore the network communications between the components. Once I have something stable, I can then install this in the car and from there, I can work towards unlocking all of it's secrets.

I have some parts I will need coming, so you'll be seeing a flurry of activity in the category.