For the 48MHz clock input X1 the datasheets say it is a CMOS level. However it does not say which xVDD source the CMOS level is referenced to.
In the cases where DVDD/AVDD and IOVDD are different levels, and XI is an input, which VDD is the CMOS level referred to?
"It is an analog I/O when used as a crystal input. Is it the same when used as a digital external clock input? Or does it refer to IOVDD in that case? In our application IOVDD=1.8V as needed by logic which interfaces to it. AVDD and DVDD can be 2.5V to 3.3V, controlled by an external CPU."