RCD 300: CAN Bus Testing Environment

Good evening.

'I've been working for a while on building an interface between a PC and a CAN bus using an ATmega microcontroller and an MCP2515. My test board is almost complete, except for a few minor issues. Unfortunately, I'm still missing a CAN bus to test it with. The goal is to send and receive CAN messages through my test board via USART to the PC.'

Here I have an RCD 300 radio, which normally operates in the car via the CAN bus. The problem I have is that I'm not 100% sure if my test board is working correctly, so I need to know for sure if the CAN signal from the radio is okay.

So far, I've connected the radio as follows: 12V to pins 15 and 16, and ground to pin 12. This should provide the correct power supply. I can also turn the radio on.

I connected PIN 9 to Can High and PIN 10 to Can Low on the diagnostic connector of my test board... Could this work? Or do I also need to add two 120 Ohm resistors to the ends of two cables and then tap the signal between the two wires to the diagnostic connector? Does the radio even send messages without a gateway?

Hi subcoder,
I'm just starting to get familiar with this topic. For the test setup, the following points must be correct:
- The transceiver chips must be compatible. In my opinion, the RCD300 uses a low-speed CAN bus. This means that you also need the corresponding transceiver chip on your board.
- You must terminate both sides with 120 ohms each.
- You need to operate your CAN controller in a way that it transmits the acknowledge bit – in other words, don't operate it in listen-only mode.
- I can imagine that the RCD only communicates when it receives messages itself.
For the lab setup, I purchased a CAN-BUS analyzer from Microchip for approximately 100 euros. With the included software, you can send and receive messages. However, it has a high-speed transceiver (ISO 11898) built in.

P.S. In my project, I also want to implement a custom-built circuit (using a PIC32 with an integrated CAN controller), just like you. I'll connect it to the PC via a virtual COM port over USB. To avoid using only my own designs, I also want to connect a 'foreign' device. Later, I plan to tap into the vehicle's CAN bus for experimentation. Since I don't want to make the OBD2 activation too complicated, I'll monitor the powertrain CAN bus at the CAN gateway.

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- The transceiver chips must be compatible. In my opinion, the RCD300 uses a low-speed CAN. This means that you also need the corresponding transceiver chip on your board.

Normally, this isn't a problem. High-speed transceivers like the 82C250 can operate at 20 kbit/s and over 1000 meters of cable without issues.

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- You must terminate both sides with 120 ohms each

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At 100 kbit/s, a few meters might work even without termination, but it's better to use it.

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- You must operate your CAN controller in a way that it sends out the acknowledge bit - so, do not operate it in "listen-only" mode.

Yes, some devices send certain messages repeatedly if they don't receive an acknowledgment, but only once if an acknowledgment is received. Therefore, "listen only" mode can sometimes be useful when experimenting.

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I will be eavesdropping on the drive CAN via the CAN gateway.

You're definitely going to get a lot of news updates on a regular schedule, whether or not you're actively engaged.

Okay, it's me again. So, somehow, none of this is working.
Okay, I want to set up an experimental setup on my desk. I have...
I would like a Skoda Octavia, specifically a model with the RCD 300 radio system (as mentioned in the title), and an ABS control unit added.

Yesterday evening, I tried connecting the ABS control unit. I identified all the positive (4 pins) and ground (2 pins) wires according to the wiring diagram and connected them to 12V. Then, I wanted to measure the CAN high and low signals at pins 15 and 30 using an oscilloscope, but I didn't get any signal.

I don't know what's causing it. It's also not working with the combination system and the radio. What am I doing wrong? Is there something I need to be aware of? Could it be that the control units are in sleep mode?

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Okay, it's me again. So, somehow, none of this is working. Okay, I want to set up an experimental setup on my desk. I have... I would like a Skoda Octavia, specifically a model with the RCD 300 radio system (as mentioned in the title), and an ABS control unit added. Yesterday evening, I tried connecting the ABS control unit. I identified all the positive (4 pins) and ground (2 pins) wires from the wiring diagram and connected them to 12V. Then, I wanted to measure the CAN high and low signals at pin 15 and 30 (I think) using an oscilloscope, but I didn't get any signal. I don't know what's causing it. It's also not working with the combination system and the radio. What am I doing wrong? Is there something I should be aware of? Could it be that the control units are in sleep mode?

I'm not familiar with ABS and RCD, but the combination instrument should start working if terminals 30 and 15 are connected. Do the lights and MFA (Multi-Function Display) actually turn on in the combination instrument?

I've been trying again over the past few days, but I'm still not getting a CAN signal. The last thing I tried was a parking assist control unit, but I'm not getting a signal from that either. Could it be that the control units first need a kind of authorization message from the gateway before they can send any messages?

Regarding the control panel module: When I connect + to pins 15 and 30 and connect pin 31 to ground, the combination instrument turns on. All the lights come on, and it starts beeping. However, when I measure the signals for the CAN-High and CAN-Low pins with an oscilloscope, I see a signal, but no CAN message (see attachment). Why isn't it sending a message?

subcoder wrote:

I've tried again over the last few days, but I'm still not getting a CAN signal. The last thing I tried was a parking assist control unit, but I'm not getting a signal from that either. Could it be that the control units first need a kind of authorization message from the gateway before they send any messages?

I cannot rule out the possibility that the components on the Comfort-CAN require a wake-up condition via CAN. Do they even have a connection to the ignition power supply?

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Regarding the control panel connection: When I apply + voltage to pins 15 and 30 and connect pin 31 to ground, the combination instrument turns on. All the lights come on, and it starts beeping. Now, when I measure the signals for the CAN-combination high and low pins with an oscilloscope, I do get a signal

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It looks good!

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but no CAN message (see attachment).

Why isn't it sending a message?

Baud rate? The CAN-Bus combination is like the CAN-Bus drive, with a speed of 500 kbit/s.