Can an external clock source be used instead of a crystal?  If so what do I do with the unused XTALOUT pin?

Question: Can an external clock source be used instead of a crystal? If so what do I do with the unused XTALOUT pin?

 

Answer:

An external source can be used to clock the microcontroller.  The external source should be connected to XTALIN while XTALOUT is left floating.  Grounding Xtalout will effectively short the internal clock to ground.