STM32F7 interface to DS3231MZ+

[Tp]

Hi,

We are trying to interface STM32F76 custom board to DS3231MZ+ RTC chip ,we are able to set and retrieve time using I2C and it is incrementing properly as long as board is powered up. But Time and date are reset to 0:0 and year 2000 after board is powered off and powered on.RTC chip is provided with coin cell battery which has proper 3v.

Attached is the design of RTC chip.

1)Reset pin is left unconnected .does it have any impact for above error.

2) We are writing 0x00 value to 0x0E(control register) and 0x08 value to 0x0F(status register) in ds3231 initialization in code.

Thanks & Regars,

P Tulasi Krishna

[Tesla DeLorean]

Perhaps the pair of you can work together or find another colleague with some experience debugging hardware?

https://community.st.com/s/question/0D50X0000BVpGiwSQF/ds3231-rtc-reset-pin

Check the battery voltage wrt ground when the primary supply is removed.

Please crop images.

[Tp]

Hi Clive,

Thaks for the response.Yup He is my colleague.

Attached is the battery supply image to ds3231mz+ .R49 is 0 ohm and R47 is open in the attached picture

and voltage when measured at vbat is 3.06v.

[Tp]

Attached more relevant screenshots

[Tesla DeLorean]

Does the RTC flag a loss of primary power, or that it has reset due to no power? Does it need to be unlocked?

I'd be concerned about what rail the reset is pulled too. Perhaps review documentation and reference circuits for the IC. If they have a development/evaluation board look at that, and test also.