I would like to read voltages from 0 to .5 volts (0 to 500 millivolts). To get highest resolution I would like to set the reference just above .5 volts.

I understand that I can use vss, vdd, a couple of the porta pins, or any combination to set the reference.

Is there any way to set the reference very low without giving up one of the porta adc's. I need all 8 of them. The pic is a 16f877a.

Also, I have heard something about capacitors to keep the adc's from interaction error. Information on this will help me too.

Your knowledge will be appreciated.