I thought I knew how to calculate the coupling caps for crystals. It turned out I probably don't. This formula from ATMEGA328 data sheet is for low-frequency only and I use 16MHz. For 16MHz, spec lists 12-22pF as range. I usually use a larger crystal with 12pF load cap but need to go smaller with this one that has 18pF load cap. Should I still use 22pF caps or use this formula that I shouldn't use and go with 28pF?Low-power oscillator:Crystal I want to use (18pF load cap) The only one at digikey with 13pF load cap is not in stock.https://www.digikey.com/product-detail/en/cts-frequency-controls/406C35D16M00000/CTX856CT-ND/2293037
The datasheet I have for the 328p has a recommended range of 12-22pf for both low power and the full swing mode (which is no longer supported). I use the low power mode, with 27pF capacitors and take my stray to be about 6pF to match the load capacitance of the crystal.
Full swing has been gone for three yearsIn AT15007 it seems to say the full swing is still in place, but the current datasheet shows it is gone. Should I trust the datasheet or the application note. I can tell you that parts with certification follow the datasheet and the application note is treated as gossip. I am not using the full swing, so it is not my problem. http://ww1.microchip.com/downloads/en/AppNotes/Atmel-42559-Differences-between-ATmega328P-and-ATmega328PB_ApplicationNote_AT15007.pdf
you made it seem like full swing is gone everywhere (which, of course, is not true).
(4) You did not mention the approximately 1 megohm required bias resistor across the crystal pins.