Is it common to use resonators in high volume production although it is not specified by freescale? Or is it risky? Any experiences? We've done it with a 68HC11, and i know other companies did it too, but...
I presume the reason a ceramic resonator might be chosen over a crystal would be one of cost. I am not aware that the resonator would be substantially less reliable.
I have previously used resonators in old HC705 projects. However, for newer HC908 and HCS08 projects I have generally found the use of the internal oscillator to be adequate for many applications. For those cases where this is not sufficiently accurate and stable, I would then use a crystal.
My production batch quantities are not sufficiently large for small cost differences to be significant, and I generally have more flexibility in the choice of crystal frequency, for example. 4.9152 MHz.
It should be possible for a ceramic resonator to be used in lieu of a crystal. Of course, the accuracy and stability of the resonator will be much degraded, compared with a crystal.
A two-terminal resonator device would simply replace the crystal in a Pierce oscillator configuration, and would also require a pair of suitable value external capacitors, similarly to the crystal. A three-terminal style resonator integrates the capacitors internally within its package.