RTC connections

[Rocky4]

Hi,

I want to use RTC - PCF85263A for my application. I will be connecting a Crystal of 32.768K Hz across OSCI, OSCO pins. 

Here I'm stuck with whether I should just connect only the Crystal to OSCI, OSCO pins? or I should also connect 7pF load capacitances to OSCI, OSCO pins along with the Crystal?

Because in the PCF85263A datasheet, internal capacitance selection option (through the oscillator control register) is provided.

Thank you in advance.

[guoweisun · Accepted solution]

Hi 

The Cload depends on your selection crystal requirement CL value, if it need 7pF which just meet the RTC integrated 7pF that you don't need any external CL component.

[Rocky4]

Hi guoweisun

Thank you for the reply.

I need another clarification here. If I want to change the crystal, which has a load capacitance of 12.5 pF, in this case do I need to JUST CHANGE THE oscillator control register bits to 10 / 11 as shown below image.

                                                                     OR

I need to change the oscillator control register bits along with adding a load capacitors of 12.5 pF externally?

Thank you in advance.

[guoweisun]

Please direct configure the register as 10 or 11.

[Rocky4]

Hi Guo-Wei Sun,

Thank you so much for the reply.

Just wanted to reconfirm that, If I configur the register to 10/11, then "adding a load capacitors of 12.5 pF externally" is not required now? 

[guoweisun]

Yes,after configure 10/11 you don't need add capacitor.

[Rocky4]

Hi guoweisun,

Thank you for the reply.