Passat 8/98 AFN - CAN-Bus am MSG vorhanden oder nicht? | Posts 16+

Hi.

Quote:

Fundamentally, the baud rate must be correct, otherwise you'll get error frames and you'll damage the CAN bus.

Using incorrect bit rates won't likely damage the hardware on the bus; it will simply prevent communication as long as the problematic control unit is connected.

Best regards, Rainer.

Don't worry, I definitely won't merge the Comfort-CAN and the Powertrain-CAN – that wasn't the purpose of the exercise. The Comfort-CAN remains separate, of course (it probably works plug and play, see Schorni...). I wasn't aware of the voltage differences, but the speed issue shouldn't exist, thanks to the sync bits – at least, that's the specification, which should also apply in the automotive sector. But okay... everyone's just doing their own thing .

- The speed issue shouldn't exist, precisely because of the sync bits - at least, that's the specification, which should also apply in the automotive sector. But well... everyone is cooking up their own thing .

No, the problem lies exactly here.

CAN Bus is a standardized protocol where the physical layer and the protocol are predefined. In this system, no one can implement their own custom solutions.
The synchronization cannot function in this way because the first 5 bits in the data stream are transmitted alternately to synchronize the process. At a data rate of 100 kbps, the first bit lasts as long as 5 bits in the 500 kbps range. However, if the first 5 bits are recessive in sequence, an error is detected, and an error frame is sent.
Therefore, the different combinations of baud rates cannot work.
Synchronizing with the Bourate might theoretically work if you only have two bus participants that exchange Bourate values until they can establish communication.
Is the third one now involved? You no longer have a chance, because there's no defined signal on the bus to indicate a baud rate switch. One of the participants isn't receiving the signal and is sending error frames...
'As far as I know, there's no CAN (Controller Area Network) system where this is done automatically.'

Best regards, Jochen.

Hi Jochen,

I actually understand the term "Schießen" to mean irreversible destruction.
The bitrate and Baudrate on the CAN bus are the same due to the modulation used.
http://de.wikipedia.org/wiki/Baudrate

Best regards, Rainer.

I probably need to review the specifications again. I was actually under the impression that faster bus participants could easily decode slowly transmitted data packets... But never mind - in principle, the use of 3B-Comfort CANs with new KIs works. And the drive-related CAN is anyway not involved in this - that's why I would say: Back To Topic.

So... I didn't feel like it today, I skipped all the measuring, sorry .

'However, reprogramming the MSG to automatic was no problem - I just drove 30km on the highway - it drives like always, with no noticeable changes in performance (which I wouldn't have expected), and: there are no error codes stored.'

Quote:

drives as always

Well, not quite . Try giving it a sudden burst of acceleration while coasting in 2nd gear at 1500 rpm, and you'll notice a difference.

Best regards, Rainer.

Mist[tm] - I haven't quite figured out the thing about accelerating yet (what should I expect?)... but the really dumb thing is that the GRA (presumably a system or component) unfortunately no longer cares about pressing the clutch pedal.

[Edit]
Am I imagining things, or is the car feeling a bit more jerky when I accelerate?
[Edit]

[EDIT again]
I once messed around with some coding stuff.

The gear shift is in '2', which in binary is 10.
Automatic: '1', Binary: 01

According to Adam Riese, the binary number 11 is equal to 3 in decimal. The MSG (presumably a specific organization or entity) has not objected to this encoding method before.

Result: a bit rougher in 2nd gear, like with automatic coding; GRA is working... I finally need to connect to the MSG and take measurements .

[EDIT: Again]

Okay, so it seems that's it... The measuring device (admittedly, a multimeter) shows weak oscillations at 400 Hertz with the engine running... regardless of whether it's automatically coded or not... that's hardly a plausible signal for CAN... I might take a look with an oscilloscope again sometime, but it looks pretty bad.

Quote:

[Edit] Am I imagining things, or is the car feeling a bit more jerky when I accelerate? [/Edit]

Bingo

Okay...

Had a meeting... no CAN CPU or bus driver available *grumbling*.

Well... I'm not giving up yet .

So...

Had a meeting... no CAN CPU or bus driver available *grumbling*.

Well... I'm not giving up yet .

I thought so too, it's exactly the same for me.
That's not surprising, because the ASV is just an AHF.

So, CAN is present in both ASR (Anti-Slip Regulation) and automatic transmissions, but the hardware used for it is different. This is also the case with Seat and VW vehicles.
Were you trying to access the instrument cluster via the comfort CAN bus, or am I mistaken?

My speedometer (see the type in my other post) has both the 'analog' connections for things like the speed signal and RPM, and also CAN. If your hardware is similar, maybe the 'new' combination instrument will work.

Best regards, Jochen.

'Comfort-CAN is an add-on, but for the speed signal and fuel consumption, I absolutely need the drive-train CAN bus – there's no way around it. I came across an idea in another forum, though... I'll let you know if anything new develops on my end.'

Hello!

I installed a speedometer from a 2000 model in my 3B 12/97! (My tachometer isn't working either!)

Now, VW told me that while the engine control unit has CAN connectors, these connectors only start communicating when the data bus control unit in the instrument cluster initiates or triggers them.

The automatic transmission, which I also have, communicates with the engine control unit via a separate (approximate) bus. (Blue with a yellow stripe and blue with a purple stripe).

These are also visible in the wiring diagrams! The CAN (Controller Area Network) is only visible on the wiring diagrams starting in October 1999, and this also applies to the AFN engine!

I'll run the two cables to the speedometer tomorrow and let you know if it works!

By the way, the CAN system also works even if only one wire is connected.

Then the control unit reports: "Corporate Data Bus."
In single-wire operation.

However, you never know which one is interrupted, whether it's the high or the low signal!

If anyone needs help or documents, please reach out!

Greetings.

Olli.

Hello!

'Now, VW told me that while the engine control unit has CAN connectors, these connectors only start communicating when the data bus control unit in the instrument cluster activates or triggers them.'

The automatic transmission, which I also have, communicates with the engine control unit via a separate (approximate) bus. (Blue with a yellow stripe and blue with a purple stripe).



Based on everything I've learned recently about the CAN bus in older TDI models, it's correct that the automatic transmission uses a CAN bus. This isn't just similar to CAN; it is a CAN bus.
At that time, the CAN bus was only between the MSG and the automatic transmission control unit. That's why the colors are different compared to the current powertrain CAN bus.

It is only possible to trigger the CAN bus to a limited extent. There is a 'wake-up' function on the CAN bus where a 12-volt signal is sent for a defined period instead of the normal 5 volts for the CAN High line.
This only applies to newer vehicles, specifically those manufactured after 2002. Your vehicle doesn't have this feature implemented yet. The 'wake-up' function is used, for example, when terminal 15 is connected to the control units via CAN.



I'll run the two cables to the speedometer tomorrow and let you know if it works!


It could definitely work if the CAN function is activated on the combination instrument. However, be absolutely sure not to reverse the CAN High and CAN Low connections.



By the way, the CAN system also works even if only one wire is connected.

Then the control unit reports: 'Corporate Data Bus.'
In single-wire operation.

However, you never know which one is interrupted, whether it's the high or the low signal!


'You're right, that's the emergency mode in the CAN bus. However, this doesn't work with all control units, as it needs to be implemented in the transceiver. Furthermore, the baud rate changes here and is significantly reduced (less than 100 kBd).'
The emergency running mode is not working on the VW drive CAN system!

Best regards, Jochen.

Jochen_145: Do you happen to know what that component is exactly, located near the output of the control unit? I suspect it's some kind of throttle...

Okay, so the missing components are basically the CAN-CPU, the bus driver, and the component at the output... However, I haven't been able to identify them precisely yet.

Okay, one more question - I couldn't really find this information in the datasheets for the CAN controller (Intel 82527): does this component require programming into internal flash memory or something similar? It seems more likely that the CAN data blocks are initialized via software within the MSG (Main System Controller).

[EDIT] Part 2 is no longer relevant. The CAN controller does not have its own program memory and is only initialized via registers. [/EDIT]