![](/media/cache/profiles/f0fcf351df4eb6786e9bb6fc4e2dee02.jpg.50x50_q85.jpg)
Check RTC LSE(External Xtal, 32.768kHz) mode
Homepage
Please refer follow links.
My notebook
http://developer.mbed.org/users/kenjiArai/notebook/nucleo-series-clock-structure-and-xtal-oscillation/
Q&A for RTC Xtal
http://developer.mbed.org/questions/4531/RTC-External-Crystal-Nucleo/