This my first time to deal with RTC. I forget to add the crystal oscillator to the OSCI of the PCF8563 chip (I thought it has an internal oscillator). Therefore, I had to insert a 32.768kHz (sine wave) clock source from an external function generator to my PCB. I am using a 1 meter coaxial cable between OSCI pin and the function generator output. The problem is when I read from the RTC it keeps giving me false and random readings. if I try to read the year for example, the reading is faulty and it changes randomly. I checked the I2C signal and it is correct. I also has an EEPROM connected to the same I2C bus and it works properly.
What could be the cause of this false reading? is it the connection of the OSCI from external clock source?