Absolutely, positively, not.

If you need to see negative readings, you might have to bias the input values up
by some requisite amount, and then subtract the artificial bias off in
software.  You can even read the bias voltage on a seperate analog input, so
that it is a real value not a constant.  This is refered to as 'pseudo
differential'.

A less attractive laternative is to make an absolute value circuit in hardware
that also generates a sign bit.  Offset and such will impact your readings.

In general, never ever allow entry of a voltage less than (GND-0.7V) or
(VCC+0.7) or thereabouts, see the datasheet for exact numbers.  I have seen
negatives on one analog channel scramble readings on all of the channels.

Chris Eddy
Pioneer Microsystems, Inc.

Jeffrey Siegel wrote:

> Can a negative voltage be applied to RA2 (when using the Vref- and Vref+
> modes) to force the A/D conversion from that negative supply as the minimum?
> Has anyone actually done it?