PIC development writes:
>
> Has anyone who has used the example code for the A/D convertor
> on the 16c74A noticed "leakage" between channels?
>
> I don't know if it's because I'm not waiting long enough
> for the internal capacitor to settle or what, but I seem
> to get slightly different values read from AN2, depending
> on the voltage on AN1.

I've noticed the exact same result with the 16C71, I found that
the minimum sample time as computed by the equations given in the
data sheet was too short.  After a few tries, I found that
multiplying the sample time by 2 or 3 (your 20us would be 40 or 60us
with my fix) corrects the problem.  I called an application engineer
at Microchip and got no reasonable explanation. (BTW, this was the JW
package.)

I asked some questions about this very subject in December '97 or Jan '98,
you might want to check in the archives to see if there was anything
else posted along this thread ("crosstalk" was in the subject).

Matt


-----------------------------
Matt Bennett                |
mjb@hazmat.com              |
http://www.hazmat.com/~mjb/ |