Re:
>Has anyone out there had experience with using a separate supply for the
>A/D, and if so, did it work well? (and with what precautions?)

I did an automotive design using a 17C756. AVss was fed off one
dedicated leg of a star ground, and AVdd was fed from an AD586KN
5.000V reference. These two lines were bypassed heavily (47uF, 0.1uF,
0.01uF). "Normal" Vdd and Vss came from an LM2931 set to a nominal
+5V.  Years later, the unit still runs fine, no loss of magic smoke.

One problem I did run into was that the PICMASTER 17C756 pod had AVdd
connected directly to Vdd. I don't recall if that was a big or small
problem, but it was a problem nonetheless, as my nice reference
wasn't being used properly. I ended up cutting/lifting that trace on
the pod, and from then on I always got the same A/D results in
emulation or in runtime.

Did they ever fix the 17C756's half-code A/D error? I.e. 511 and 513
were valid codes, but 512 never showed up. I don't know if it'a also
in the 766.

Regards,
--

  ______________________________________
   Andrew E. Kalman, Ph.D.   aek@pumpkininc.com

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