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...