sampling frequency and frequency deviation of GFSK created by CPMModulator in communication toolbox

Hello everyone, I would like to implement a 2-GFSK using comm.CPMModulator System object but I am not sure how to set the frequency deviation (fdev) of the modulation (or the frequency separation that is the distance between the two main peaks of 2-GFSK). Any ideas about that? Also, I would like to plot the result but I don't know what is the sampling frequency (Fs) in order to see the spectrum as it should. Thank you