I have a simple device built with a 16C73A.
I read two channels of the A-D, a dual color LED to indicate which channel,
do a table lookup, and write a byte to Ports B and C.
(Resistor ladder D-As)
The whole system works.... mostly.

When the voltage to the A-D gets to 4.06 volts the PIC freezes.
If I lower the input to 4.05V (or lower) it resumes.
This happens on either channel.

I have noise filtered each A-D channel, which helped slightly.
(It used to freeze at 3.9 volts.)
My 1 Ghz scope shown no noise peaks over 1 mv. at 4.06 volts.

I selected VCC (+5) as the reference for the A-D.

All of this suggests I'm sending voltages over the reference limit,
but I'm at a loss to see how.

Does anyone have any ideas?

Did I miss some critical parameter in the specs?

What is the airspeed of an unladen swallow?

ADVthanksANCE
--
Thomas C. Sefranek  WA1RHP
ARRL Instructor, Technical Specialist, VE Contact.
http://www.harvardrepeater.org
http://hamradio.cmcorp.com/inventory/Inventory.html