This is actually an interesting question.
Does it have to be a sine wave like a xtal's? Or will a square wave
work?

Description for the OSC1/CLKIN pin is: "Oscillator crystal
input/external clock source input"

Anybody used a squarewave or any other logic clock source?

Quentin

Andre Abelian wrote:
 you can also use your signal generator as well
> make sure you have sign wave or can based oscillator.

> Donald Kihenja wrote:
 Can I
> > use a 4 Mhz signal from a signal generator instead. Any other
> > alternatives?