----- Original Message -----
From: Drew Vassallo <snurple@HOTMAIL.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, March 06, 2002 1:42 PM
Subject: Re: [PIC]: A/D sketchiness on PIC16F877


> >When I do an A/D conversion I get funny results.  If I use right
justified,
> >ADFM = 1 and try and read 5V... I get something like (011-1000111).
>
> You mention that the left justified results are screwy.  Well, the right
> justified result doesn't seem right, either.  Looks like something's wrong
> with your input source or your Vref.  Are you using a really high
impedance
> or capacitance for your input source?  Is your Vref (Vdd) stable?  Is it
the
> right value?

reading 5v (right justified) gives 11-10000011
reading 5v (left justified) gives 11111111-11[111111] - the numbers in []
should be 0...

Vref is Vdd... yep, stable at 5.06v through a 7805

just trying to measure voltages out of a resistor divider network.  ~10k.
no capacitance


> Also, try using ADCON1 values of 0x09 or 0x00 instead of 0x02.  They
should
> be functionally the same, but try them just in case.  (or 0x80 and 0x89
for
> right justified)

I didn't try the values you recommended because I am using a PORTE for my
lcd ctrl lines.
Is there a reason why you suggested those values... (changing PORTE to
analog?)
I tried some other values, 0x0E, 0x8E, 0x03, 0x83..


> I also assume that you're switching to the proper banks to read ADRESH and
> ADRESL?

Yes.
>
> I've never had a problem using the A/D on the 16F87x series chips.
>
> --Andrew
>

It seems to work if I left justify it...  it just bothers me cause I usually
like to try understand why something is acting the way it is..

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