Dwayne Reid wrote:

And Thank You for replying.

> >> O.K. So no one is using a 16C73A's A-D?
>
> Yep - use it all the time (except I now use the '73B).
>
> I DEFINITELY get readings from 00 thru FE or FF - I have not looked at the
> code for that project for quite some time - we ship several systems each
> month and I have not had to revisit that part of it for a couple of years now.
>
> The fact that you get higher readings when you put a low pass filter on the
> a/d input suggests to me that you have a noise problem either with the
> reference or the input.  I use VDD as my reference - each input prior to the
> MUX has an input filter of 1uF / 10K.

Yes, I too am trying to use VDD as the internal reference.
04h -> ADCON1

I also am using 10 K resistors to a 1 ufd cap on each analog input.

I've used my scope to look for ANY noise on VDD or the analog inputs,
and it is all well below 5 mv.

I tied RA3 to +5 just in case the ref. is not correctly selected.
(Only two options RA3 or VDD.)

> The MUXes feed RA0 and RA1 (I mux 8,
> 16, or 32 inputs each into RA0, RA1 for a total of up to 64 inputs).  This
> is also a decent amount of bypassing right at the '73's GND and VDD pins.

I have a .1 ufd right at the VDD and Vss pins 20,19.
Pin 8 is connected to the ground rail as well as Pin 19.

> Quick thought - do you have BOTH ground pins connected toghether with a real
> short wire or trace?

I could add a jumper.  The proto board has nice wide traces for power and ground
.

> Not sure what else I can add.  I have always found the a/d section to be
> reliable in the 16c71, 16c73A&B, 16c74A, 12c671.  Don't know about the
> others <g>.
>
> dwayne
>
> Dwayne Reid   <dwayner@planet.eon.net>
> Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
> (780) 489-3199 voice          (780) 487-6397 fax
>
> Celebrating 15 years of Engineering Innovation (1984 - 1999)
>
> * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
> Do NOT send unsolicited commercial email to this email address.
> My posting messages to Usenet neither grants consent to receive
> unsolicited commercial email nor is intended to solicit commercial
> email.

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