More accurate resolution from the A/d converters

Hello,

These are not really Picbasic Pro questions, but it's Picbasic Pro I'm using and I don't know where else to ask! Still learning :)

Am I right in thinking that if you supply a + and - ref to the RA2 and RA3 pins that the same return count applies to a smaller voltage range therefore making the measurement a higher resolution one and more accurate?

Can you supply only the RA3+ reference and leave the RA2 nc?

If I wanted a + ref voltage of 2.5v, would the normal way to do this be by a voltage divider (couple of resistors)?

What I'm trying to do is get a high resolution and accurate voltage measurement between around 2-4.8volts on a 16f877

Thanks.

The 16F877 has a 10 Bit ADC (decimal 1024 possible values, 0-1023)
Your Range is 2.8 Volts (4.8-2)
The max resolution you can achieve with this range is about 3 mV (2,8V / 1024 = 2,73mV)

I have not played with different Vref's yet,
but anyway you will need a well tuned and temperature compensated source for Vref
to make your ADC conversion result accurate.

rgds

Ralph