Why does the PLLCON have three selections for "internal 32,768 Hz oscillator" ?
Because it is designed that way - the three different settings doesn't differ, and because 2 bits where reserved for the cock source selection (other derivatives had more options), to avoid undefined states the 3 settings has been dedicated to internal 32kHz osc.
I read your response regarding unused JTAG pins
How about unused ADC pins? And XTALI pin?
Lastly, XTALO is designated as an output, if the internal oscillator is used, what will XTALO read?
For ADC inputs it is recommended, if not used in the final layout to connect to AGND.
The XTAL pin typically show approx. 1/2 AVDD and should be left unconnected.
In very harsh environments they also can be pulled up with 10K to 100K.
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