Hi,

Ok, I understand that there is no big differrence between the crystal and the metal case oscillator. Its only that oscillator can drive multiple devices that need clock.

But the question remians then how to achieve the frequency accuracy.

I have tried same crystal (say 12MHz) with different values of stabilizing caps (33pF to 100pF) and counting the time base events over a period of hours. All diffrenet caps give different variations.

Problem: If a software tuning is done with 33pF its Ok for one time or as long as you are using those caps from the same lot.

The moment you use caps from a different lot, you got to retune your timebase. :(

Simon