PCF2129 RTC I2C communication stuck

[Pares]

Then INT is active its tied low. We know that we have used the alarm before, but we can’t read any register every response is 0xFF.

We use this chip as our RTC source, its critical that we can maintain time and very low power operation, the Device is battery powered and we have a a backup coin cell on the PCF2129.

I’ve tried some I2C recovery routines on the bus, I2C stop +start, manually generate scl clocks  until SDA doesn’t get stuck. Removing main battery. Resetting the mcu, trying these recovery routines doesn’t produce any results. The only options i can think of are:

-We can try the Poro and see if it revives but then we will lose the time and date. Also, any means to repeat this condition and see if we can work around this issue on runtime.

-we can remove the backup coin cell and see if it revives but then we will lose the time and date. Also, any means to repeat this condition and see if we can work around this issue on runtime.

[Pares]

I did some capture on the I2C on oen device thet is working fine and below on the device that is not responding

[Pares]

The Backup battery is in place, also the VDD is present and stable. Yes I have read that if the communication was interrupted by a switch to the backup battery it won't communicate, actually this is the hypothesis that I am following. I tried this many times with no positive result. This happens rarely and we can’t reproduce the conditions to make it happen again. resetting the backup battery and then testing if the RTC works will discard a hardware problem but then I won't be able to solve the problem. I am debugging this pcb , so yes it has a stable VDD and I can change the code to test solutions in order to get the RTC working again.

Thanks for answering,

[TomasVaverka]

Hello Jordi,

Please check if the PCF2129 is not supplied from a backup coin cell because the I2C interface is disabled during the battery backup operation.

BR, Tomas

[TrueBlue]

Hello Tomas,

Can you tell me how long I have to wait when I apply VDD again until I can communicate via i2c again. ( At power-up)

I have the impression that it does not work if I read too early.

(Without battery i should wait 2s. Can it be a problem if i don't do that with battery?)

BR