Just received my new PCB from the China manufacturer but after soldering the MCU and the bare minimum components (decoup caps, power, reset etc), my scope says that the on chip oscillator wont start.
Reading various thread on line as well the chips datasheet, indicates that this chip is somewhat sensitive to the choice of crystal and the crystal load caps.
I have already tried 3 different 32.768kHz crystals : a small smd one, a through hole axial version and finally the MS1V-T1K ( 32.768KHZ ±20PPM 12.5PF) with different capacitors 12pf,15pf and 22pf , all with no success. The oscillator simply refuses to start.
Needless to say that i have verified correct 3.3v voltage on all supply pins as well as the 1.2V on VddCore pin.
Is there something else am missing? For example does a brand new chip need to be programmed to start an external oscillator?
In my experience with AVR chips with 16MHz crystals, I never experienced anything like this. It was like solder-and-play!
Schematics and PCB layabout below: