Why do all minimal Atmega328 designs have caps on the the 16Mhz crystal? I haven't and it seems to run fine! just power to the pins 7&8 and Crystal between 9&10.
I normally use a 3-terminal ceramic resonator, which has the capacitors built-in.
Ultimately I plan to implement a high speed serial communications network once I have finished experimenting. Currently I'm just sending a few bytes every second or so.My crystals have the following specs:Frequency: 16MHzFrequency Tolerance: ± 30ppmLoad Capacitance: 18pFFrequency Stability: ± 30ppmShould I therefore be using 18pF Caps? I also assume lower is better for Frequency Tolerance and Stability?
QuoteI normally use a 3-terminal ceramic resonator, which has the capacitors built-in.What would specs should I look for in one of these?Is this preferred because of the lower part count?
Without the right load caps the frequency won't be in-spec for that crystal (they are calibrated for a given load capacitance).
Load caps make the oscillation frequency much less sensitive to stray circuit capacitances I believe - not necessarily important.
A particular oscillator design may assume a certain range of load capacitance too - without it there might be no guarantee of oscillator start-up?
The capacitors perform another important function. The combination of capacitors, crystal and the inverting amplifier make up a Colpitts oscillator. Without the capacitors (or sufficient stray and pin capacitance instead), the circuit would not oscillate.