Bob, thanks for your reply.. I vaguely remember something similar - maybe
from the 16C71 datasheet?.. I will have another long hard look tomorrow (bed
time here) if someone else doesn't provide the answer..

Thanks again

Roland

----- Original Message -----
From: "Bob Blick" <bob@TED.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, March 12, 2001 7:55 PM
Subject: Re: Using small(ish) A/D reference voltage


> > I am in a position where I have to input a 0-1 V signal to the A/D of
the
> > 17C756. To get a reading over the full 10 bit range I would like to set
the
> > A/D reference voltage at 0 - 1 V.  The data sheet mentions that accuracy
may
> > be affected when using a reference voltage other than the supply
voltages,
> > but gives no details (that I could find, also none in the various app
> > notes).
> > Has anyone here used small(ish) reference voltages - experiences (not
> > necessarily on the 17C756 - any pic with an A/D)?  Any comments much
> > appreciated!
>
> Hi Roland,
>
> I can't find it(typical of Microchip data sheets, DC data is usually hard
> to find) but I seen to recall that Vref must be within 0.5 volt of supply.
>
> Also I recall that accuracy is spec'ed based on 1 or 2 LSB relative to
> Vsupply not Vref, so if it were possible to have 1 volt vref you would
> have accuracy of +- 5 or 10 LSB.
>
> Cheers,
>
> Bob
>
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