PCF2129 time errors

[juliancox]

I am using a PCF2129 RTC connected to a MC9S08QE16 via I2C. Normally, on power-up the correct time is shown on the MCU's display, but occasionally it displays a completely different time, which I then have to adjust using the application software. Also - I am employing the RTC's alarm function (only hours, minutes and seconds), and (again occasionally) the alarm triggers early although the alarm registers are correct. I have built 10 samples and only two units display this problem

[guoweisun]

Do you have a cross test with the good PCF2129 and issue board ?if no please try it! 

[juliancox]

This is a bit problematic as the error only occurs every 3 or 4 days on an irregular basis. The las error occurred yesterday evening, after running for 5 days. This time I switched the unit on at 17:40 and the time was displayed as 00:40. I am currently running ten units, testing the time alarm function and power-down, wait, power-up cycling for two weeks - only two faults on one unit.

[guoweisun]

Please share with your schematic.