topic Re: Pcf2127t rtc registers are not retaining the values in LPC Microcontrollers

Pcf2127t rtc registers are not retaining the values

Eager0007 — Tue, 12 Nov 2024 13:20:30 GMT

Hi ,

I am using PCF2127T rtc on my personal board for maintaining realt time. Hardware was like insertion mechanism. So, when i remove the card from rack and after again inserting it. RTC register values are going to zero. eventhough i have the battery backup. I am unable to figure out the issue. I am using the i2c communication for my lpc54608 and rtc.you can check below schematic.

Any idea on how to solve it or debug it properly for root cause.

Re: Pcf2127t rtc registers are not retaining the values

TomasVaverka — Tue, 12 Nov 2024 16:55:03 GMT

Hi,

If the RTC registers are resetting to zero upon reinsertion, despite the battery backup, here are some potential causes and debugging steps:

1. Battery Connection Verification:
- Ensure that only one battery is mounted and connected through the jumper. If no battery is connected correctly, the RTC will lose power when the main board power is removed.
- Measure the voltage at the VBAT pin of the PCF2127T while the main power is off, to confirm that the battery voltage is reaching the VBAT pin.

2. Power Path and Battery Voltage:
- Check that VBAT and VDD are not being shorted or connected improperly. Any misconnection could result in the battery backup not functioning correctly.
- Ensure that the battery voltage is within the recommended range, as a low or insufficient voltage could cause RTC reset issues.

3. Battery Connection to VBAT:
- Check the jumper and battery holders for loose or poor connections. Poor contact could cause the battery backup to fail during reinsertion.

4. I2C Communication:
- After reinsertion, check if you can read any status or error flags that could indicate a loss of power or reset condition.

5. Battery Switching Test:
- If you have access to an oscilloscope, monitor the VBAT pin during the insertion process. This can reveal if there is a momentary power loss or glitch when transitioning from the main power to battery power.

By following these steps, you should be able to pinpoint if the issue is related to the hardware setup, power backup or configuration in software.

BRs, Tomas

Re: Pcf2127t rtc registers are not retaining the values

Eager0007 — Wed, 13 Nov 2024 05:20:50 GMT

Hi @TomasVaverka ,

Here i have connected the battery directly to the VBAT pin.then what is the purpose of placing a jumper here.

Re: Pcf2127t rtc registers are not retaining the values

TomasVaverka — Wed, 13 Nov 2024 09:20:47 GMT

Hi,

Looking at your schematic, I have noticed multiple battery options (CR1632, BR3032 or BR1632), so my assumption was that you are using it to choose between these batteries or to enable/disable the battery backup manually. If your battery is already directly connected to VBAT, the jumper may not be necessary unless you plan to use it for one of these purposes.

BRs, Tomas