PCF8523T register retention during battery switch over

cancel
Showing results for 
Show  only  | Search instead for 
Did you mean: 

PCF8523T register retention during battery switch over

529 Views
david_hirst
Contributor I

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?

Labels (1)
0 Kudos
1 Reply

372 Views
lisettelozano
NXP Employee
NXP Employee

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

0 Kudos