What might prevent the RTC from supplying the actual Time?

We have one Appalis T30 with Ixora Application Board.
We connect a external PCB which has additional circuitry.

Without PCB connected the Time can be supplied by the RTC. ==> Systemtime is correct

With PCB connected the Time can’t be set. ==> System Time is 1.1.2009

An other Appalis T30 with Ixora connected to the PCB has no Problems setting the Time. ==> Systemtime is correct

Is it possible, that the PCB has some Issues?
I’m still able to detect all I2C Devices.

Do you have some Hints?

I assume your external PCB is connected to the extension connector X27? If so, you probably also connect PIN 5 (I2C1_SDA) and 6 (I2C1_SCL). Also you can still get the IDs, may be the communication between the RTC chip and the CPU somehow gets disturbed. What happens if you cut the connection on these pins? Can you communicate with the RTC chip after that? If so, may you have to review the two lines on your PCB and check what could cause the issue there.

Your assumptions are correct. The thing that confused me is that with another Ixora&T30 module and our PCB the RTC can set the System Time. More than 10 similar configurations are working flawless.
Might there be a problem with the Bus capacity?
Since our PCB seems to work fine i don’t want to cut those lines. Do you have an other Proposal what to check?

Best regards, Stefan

Can you once check with the RTC Sync Tool we added in image 2.0 beta 4. There was an issue with the open drain bit, which is documented in the release roadmap. You find the RTCSync in the related Image BSP. I also uploaded it here for you.

Did you once check the signal quality? Check if your signals are more or less square shaped. May be the signal quality is already quite poor, so that it only works on some modules and not on others. Depending on the length of the lines, you may have to lower the pull ups?