MIR Nav Bus Format
 

Ok, I appreciate I've probably lost most of you with that thread title.

It appears the MKIII (and MKIV?) have an option to be able to provide sat nav in cars that don't have a Bord Monitor, but rather a small mono LCD on the radio unit (MIR).

http://www.xoutpost.com/attachment.p...chmentid=39161

This is connected to the Nav computer in Connector X1312 at pin 7 (labled in docs I've seen as 'Signal Nav Bus'..

Does anyone know the format of the signals that go down this wire? This LCD appears to be used in my MG ZT within the IKE and I'd quite like to drive it from the CarPC I'm developing.

But I need to know the format of the data on that wire and I can't seem to find any info on it anywhere.

Any help would be greatly appreciated.

I presume that's a no then!

Seriously, no-one has looked into this then?

Not something I've checked personally, and I doubt anyone would, the mk3 and mk4 will work with the mono screen (like in the pics), but requires the bmw HU to do so.

Since most of us have the colour monitor then this has never come up before.

Yeah, I thought it was a bit of a long shot. Damn. Oh well, I'm going to end up replacing the screen anyway with an TFT screen driven by the PC, so it doesn't matter quite so much now.

Just wondered if anyone had been able to get their hands on, what in hindsight would probably be confidential BMW technical information!

Suppose you could reverse engineer it though if you had the right equipment, but then its down to time vs benefits really. As you say, its not much of a point with BMWs as the colour screen replaces it, its only the MG & Rovers that have the screen in a different location and additional to the Sat Nav screen.

Tried simply sniffing it with NavCoder?

Nope, but I wouldn't have thought simply connecting it to a COM port was a very good idea really, never know what's going down the line!

Could really do with a scope and the knowledge to know what I was looking at on the scope!

As I said above, its not really worth the trouble really. If someone knew the format that's fine, but I don't have the electronic skills to reverse engineer it.

What I'm saying is there's a good chance it uses the same protocol as on the ibus and kbus

In that case, protocol is clearly understood, and command structure will be easy to determine

If the line uses ibus protocol, then NavCoder will show the data very easily.

So: Try and See!

I **think** the basic format of the i-bus/nav signal could be csma/cd or a basic form of it.

csma/cd is just a method for handling collision detection

ibus / kbus protocol is based on ISO-9141 but has a few differences....

Not to be pedantic, but that's the /cd part mate,

CSMA/CD = Carrier Sense Multi-Access/Collision Detect.

CSMA is the signal carrier, the cd parts is to detect, pause, clean up and resend signals corrupted by collisions.

It is internationally standardized in IEEE 802.3 and ISO 8802.3.

Looking at the ISO-9141 spec then you are probably right (lol, you are in most things, re the i-bus).

I will bow to your better knowledge mate, It was just a guess, based on the way that the i-bus interface works (and what I've read before).

OP ignore my wild ramblings :) Jochens the man.