> The input range of the A/D is from Vss (chip ground) to Vref.  If you use Vdd
> (+5V) as the reference, that will set the range to 0 to 5V.  You can use a
 Vref
> lower than Vdd but not higher.  If you use Vref lower than Vdd, be aware that
> some noise components do not scale with the reference and will therefore be
> larger relative to the full scale range than with Vref=Vdd.  These remarks
 apply
> to the 8 bit successive approximation converter used in the 16C7x devices.
 More
> resolution and flexibility is available with the PIC14000 device, at the cost
 of
> slower conversion rate and more money.
>
> - Mark Sullivan -
I notticed that the data book says the minimum Vref is 3.0 volts. Any
idea why. I would like to use 2.5V or even trim it to 2.55 .
**********************************************************
*Mike DeMetz                      SYSCON International   *
*miked@syscon-intl.com            South Bend, IN USA     *
*aka 73165.1230@compuserve.com    using Pegasus Mail     *
**********************************************************