I'm putting together a small board that will be an FM radio (Atmega328p, Si470x FM chip and LCD display).
Currently the board has a 16 mhz SMT crystal on it rated at 8pF load capacitance and 100 ohm ESR (click picture to see the part).
I experimented with loading capacitors (18pF, NPO) types and got these (interesting) results (fuses set for full swing osc - Low Fuse = 0xF7):
Cap on XTAL1 only: XTAL1 pin: Vp-p 1.5v XTAL2 pin: Vp-p 3.0v
Cap on XTAL2 only: XTAL1 pin: Vp-p 4.75v XTAL2 pin: Vp-p 2.0v
Cap on both: XTAL1 pin: Vp-p 1.5v XTAL2 pin: Vp-p 1.5v
No cap on either: XTAL1 pin: Vp-p 1.5v XTAL2 pin: Vp-p 1.3v
It's interesting that with a cap on the XTAL2 pin only, the XTAL1 pin has virtually rail-to-rail crystal swing. This leads me to think that this is the best configuration (but the data sheet says that the caps should be EQUAL).
Any ideas why it's acting this way, and suggestions on how to actually do it properly?