PCF8563 RTC chip problem

[tdk]

pcf8563 example

I have made a design where I supply my MPU and rest of circuit with 230VAC via
a Capacitor. All logic is supplied with a regulator with 3V.
I experience the following problem. When the power supply cuts off and then
restores the rtc chipo looses 10 minutes or gains 10 minutes. Other times it looses
20 or 25 minutes.

I supplied my project only with dc voltage 12V and again have th same situation.
I left the PCF8563 alone and when I connected it with the MPU I found that the time was off by 15 minutes.

Has anybody worked with this chip from Philips and can give any idea about this problem ?.

My regards

 

[IanP]

pcf8563 problem

I wouldn't blame the RTC but focus on the way your microcontroller is reset (do you use proper supervisory IC or just a capacitor) and what it does immediately after reset (program) ..
Regards,
IanP

 

[tdk]

rtc chip

Dear IanP

I use PIC18F242 to control the RTC chip. Note that RTC chip is backuped with a
3V lithium cell.

I program the time into the RTC via MPU. After this I disconnect the I2C bus.
In this status I cut off the power and give it back again some times. Now I connect again the I2C bus and supply the board. The RTC may have lost it's time
for 10 or 20 minutes. The deiffernece of time is not always the same and it is not
sure that the RTC will loose it's time. I have used the PCF8583 RTC from the sampe company and never had such a problem. both IC's work with I2C bus.

The situation is a bit wear because it does not happen all the time.

I suppose that a a strange behaviour of the RTC chip due to power spikes could lead to this phaianomenon..........., I dont' know.

My regards

 

[AlinaAnderson]

pcf8563

Problems like this may be related to the fact that SDA and SCL are active low and are forced to this state on power down.

You may want to explore www.zangenberg-s.dk - they have a microcontroller/PCF8563 example...