PCF2129 internal oscillator getting reset

[adityasaini]

We have a #PCF2129 RTC connected to an mcu via i2c. Its been observed that after a certain amount of time and multiple power on/off operations, the oscillator in the RTC is getting reset(last bit of the Seconds register was found to be set) causing reset of the RTC itself and thus loss of time. The datasheet says that issue is more likely to be come due loss of power to RTC. I am adding the circuitry of the RTC for reference. Is there anything that we are missing which might lead to oscillator reset. Although I noticed that SDI should be connected to Vss when using i2c, I don't see how that will cause the resetting of the oscillator.

Also there is an OTPR bit in CLKOUT_ctl register. What is the purpose of that register and do I need to perform that refresh every-time I power on the system?

[david_diaz]

Hello,

Indeed, the PCF2129 has an on-chip oscillator detection circuit which monitors the status of the oscillation: whenever the oscillation stops, a reset occurs and the oscillator stop flag OSF (in register Seconds) is set logic 1.

Are you giving enough time to the oscillator to getting a stable signal?

What is the temperature operation? Please note that the crystal accuracy varies with it.

In general, I recommend to wait 2 seconds before using the RTC device after a power-on reset.

Please let me know if this information is useful for you.

Regards,

David

[adityasaini]

Hello David,

Thanks for the input. A delay of two seconds has already been provided after a power-on reset. TCR register of CLKOUT_ctl register has default values i.e. after every 4 minutes the RTC will perform temperature compensation of the frequency. The issue still persists.

Can you give some insight on how to use OTPR bit of CLKOUT_ctl register? Because till now we haven't used it even once.