I may still be missing the point but if you want to measure and display Vdd, ie the PICs supply voltage, you MUST use an external, stable, source for Vref that does NOT "move" with Vdd, otherwise you will simply get the same reading all the time.

Let's say your Vdd is 4.85V and therefor your Vref is 4.85V. A voltage of 4.85V on the analog inputs will now give you a full scale result (1023) from the ADC because 4.85V is what Vref is set to. Whatever you set Vref to is what will give you a full scale reading so as long as Vref=Vdd you can not measure and display Vdd with the ADC.

/Henrik.