PCF8523T register retention during battery switch over

[david_hirst]

I am having a problem with the PCF8523T RTC chip, I occasionally lose time, and when this happens the control registers are back to there default states. Can some one tell me if the 3 control registers settings are retained during battery switch over, or are they returned to default and need to be written again?

[lisettelozano]

Hello David,

During battery switch-over, the device should keep the registers set and only the interface is disabled in battery backup operation. It looks like the RTC resets (a reset is automatically generated at power-on or initiated with the software reset command) and go back to the default values. After a reset, the RTC enters in the following mode:

• 768 kHz CLKOUT active
• 24 hour mode is selected
• Register Offset is set logic 0
• No alarms set
• Timers disabled
• No interrupts enabled
• Battery switch-over is disabled
• Battery low detection is disabled
• 7 pF of internal oscillator capacitor selected

Is this the case?

Also, can you please share your configuration in control bits PM[2:0] in register Control_3 (02h)? What is the voltage level of the battery VBAT and VDD?

Have a great day,

Paulina