CAN-Bus Wakeup

Hello,

I would like to learn more about WakeUp mechanisms in CAN buses, specifically what WakeUp options are available (e.g., voltage applied to the bus, which voltage, when?), and which buses can be woken up. For example, can a diagnostic bus be woken up in the same way as a CAN bus inside the vehicle? It's not specifically about a vehicle, but more about the principle behind it.

Does anyone here have a suggestion for search terms I should use? While CAN and Wakeup provide me with a lot of results, the underlying principle is not clear from them.

Regards,
Rolf.

There is at least one specific procedure for the low-speed comfort/body bus. Is there a detailed description of the CAN bus in any of the VW SSP (Service Information) documents? I believe that, according to my recollection, the on-board voltage (12V) is used as an auxiliary voltage for signaling purposes.
In principle, you can design any bus participant to wake up when the bus enters the active state. Some controllers have this functionality built into the hardware, but otherwise, you can always connect the CAN-Rx line to an interrupt input. Alternatively, you can even connect the CAN bus itself via an additional level shifter if you need to disable the CAN transceiver (to reduce power consumption in sleep mode).
Waka-Up about CAN diagnostics: Well, if the car manufacturer wants it, the suppliers will implement it, but I can hardly imagine that any car currently has that feature. Without the Class 15 module on the OBD connector, usually nothing works anyway.

Best regards,
Ingo

Hello Ingo,

I'm only getting back to you now because I wanted to gather all the information first. Thank you very much, that was valuable information. I found the following passage in a diagnostic interface (J533):

Quote:

Terminal 15 run-on. Certain control units in the CAN data bus need to exchange information even when terminal 15 is off. For this reason, a message is sent to the CAN data bus to activate the keep-alive mode. The control units internally establish a connection from terminal 30 to terminal 15, which allows them to continue communicating. In this way, the power steering control unit, for example, designated J500, can communicate with other control units. The run-on mode can last between ten seconds and fifteen minutes. The duration of the transmission depends on the amount of data being sent. To finish the run-on period, the data bus diagnosis interface initiates the sleep command.

That's also what I naively thought: If I don't have ignition (no terminal 15), then I'll just connect it to constant power (terminal 30). Apparently, in these VW/Audi vehicles (if we stick to the SSPs), only a portion of the control units can be activated. Specifically, only those that have their own connection from terminal 30 to 15, and this connection can be controlled (as shown in the accompanying diagram).

Interestingly, the text also mentions diagnostic control units that apparently activate the other control units (using an additional connection to them). It doesn't seem like 12V is being applied directly to the bus itself (typically between CAN-hi and CAN-lo), but rather that there is a separate switched connection. It's possible that it was only meant to clarify things, and that the "line" actually referred to the voltage on the bus.

If I now follow this SSP (Service Programming Specification), the diagnostic control unit can wake up the others. However, this only makes sense if those units are asleep and the diagnostic control unit itself is not, or if the diagnostic control unit itself has been woken up. What reasons could there be for the diagnostic service to start automatically?

If you have an Audi with a door sensor, it's described that when the door is touched, the car's systems also activate. This makes sense, as it likely indicates that someone is about to get into the car. According to the documentation, it seems to pass through a separate control line again, but does it make sense to additionally wire a car with many control lines?

Overall, I've made significant progress, but I still don't fully understand the system. Is it actually possible to apply 12V to the bus without damaging anything? I do have some concerns about that.

Regards,
Rolf.

Hello,

Quote:

Interestingly, this also mentions diagnostic control units that apparently activate the other control units (using the additional terminal 30 connection to them).

Here: The diagnostic control unit is the gateway.

Quote:

It doesn't seem like 12V is being directly applied to the bus itself (typically between CAN-hi and CAN-lo?), but rather that there's a separate switched line present. It's possible that it only served to clarify something, and that the "line" was actually the voltage on the bus.

I looked it up again; it was in SSP307 (electrical system). Touran, p. 27).
When all sensors are in sleep mode, the "Comfort-CAN-low" line goes to 12V. If one of the sensors pulls the "CAN-low" line down, all sensors wake up.

Quote:

If I now follow this SSP, the diagnostic control unit can wake up the others. However, this only makes sense if these are asleep and the diagnostic control unit itself is not, or if the diagnostic control unit itself has been woken up. What reasons could there be for the diagnostic system itself to wake up?

The diagnostic control unit (gateway) detects, for example, that the vehicle network control unit has become active, and then activates the CAN-based powertrain control unit and the CAN-based infotainment system.


Best regards,
Ingo

Quote:

The Comfort-CAN-low goes to 12V when all SG units are sleeping; pulling one of the SG CAN-low lines wakes up all SG units.

Therefore, would it suffice to simply connect the Can-Low line to ground (possibly through a resistor)?

Regards,
Rolf.

In vehicles with network management systems (OSEK or AUTOSAR), there are both an active and a passive wake-up mechanism for the CAN bus.

"With active WakeUp, the control unit is awakened via a line, which also activates the CAN bus. This is often practiced at the gateway. Passive WakeUp occurs via the CAN bus itself; the transceivers detect a level change while in a sleep state and activate themselves (via the inhibit output). At this point, the transceiver can determine whether it is a valid message and, if so, may wake up the communication controller (CAN controller)."

The first message (which could also be an error frame, since there is no acknowledgment) wakes up the transceiver, and the second message checks whether a valid message is present and, if so, activates the controller.

First of all, thank you very much for the interesting information!
Does connecting the CAN-low line to ground to trigger the WakeUp function also work on BMW F-series vehicles?
'If so, should a resistor be installed to limit the current, and if so, what value should it be?'
Thank you in advance for your reply!

Has anyone figured anything out yet? I would need it for an A3 8P.

I have a Raspberry Pi here with an SPI controller and transceiver.
What voltage or signal would I need to send to an A-class radio for it to turn on?
Baud rate, ID bytes.
There's already some discussion about the Ignition Message for the W211 model on the vehicle forum, but I'm not allowed to post there yet.
The baud rate is not specified, the ID is clear, but I'm unsure about the meaning of the bytes starting with 0x... I don't know how many bytes there are or what they represent.
It will probably work if nothing comes out.
It seems that it's not working for me, even with the power supply turned on, despite having a positive voltage and a ground connection.

'I'm going with the old-school spark plug cable, but I'd prefer to know more about the CAN bus system.'

Ingo.

First, we need to know which A-Class you're referring to, as there are several different models.

Then the question is, what exactly does the radio need? Do you have the ability to measure the CAN bus signals within the vehicle?

It's a W169 from 2010.

Are there not at least some standardized, manufacturer-independent controls, such as the ignition button?
Your question sounds like these basic messages aren't even consistent across different A-class implementations.
They probably don't know for sure at China Radio.
Perhaps the radio station will be satisfied if something happens on the Can.
Without the ACC cable, the radio goes into a deep sleep mode. When plugged into the charger, no power consumption is displayed. However, you wouldn't see anything below 50mA, so I would need to insert the multimeter in between. When it's connected, it's consuming around 500mA.
Perhaps this also works through this 'wake-up' mechanism and doesn't necessarily require a specific message, which is why I'm writing here; I haven't quite understood the 'wake-up' process yet.
Is there not a list somewhere with general CAN messages?

Ingo.

Hi.
I'm just chiming in here. I'm new to this group, my name is Christian, I'm from the lovely town of Horneburg (near Hamburg), and I work for an automotive supplier.
Since I'm not yet very familiar with this forum, I'm just hoping that this thread is in the right place .

Okay, I have a driver's seat from an Audi A8 4E, manufactured in 2007, that I would like to install in my VW T4.
I have already downloaded the relevant wiring diagrams from ELSA. Unfortunately, I have absolutely no understanding of CAN and LIN bus systems.

The seat features electric adjustment, heating, and ventilation. Regarding the heating and ventilation system, I already know that I will need the climate control unit. But it still has a moment to go .
To start with, it would be really great if I could just get the engine running. Unfortunately, he's not responding.
Okay, here are my two hypotheses:
1) The seat control unit has a component protection feature, which means I can't easily operate the seat without the corresponding vehicle 'around' it.
2) The seat control unit waits for a 'wake-up signal.'

Regarding the actual question: What might such a wake-up signal look like for a 2007 Audi? As mentioned above, for example, you might simply need to pull the Low-CAN line to ground. Can it really be that simple?

I am really, really excited to hear your answers .
Thank you very much and best regards.