#1 Rule if things act inconsistantly: CHECK TRIS BITS.  I can't begin to
count how many times I've had problems like yours and it's been because
I had an input as an output and vice versa.

nick@veys.com / www.veys.com

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Jai Dhar
> Sent: Tuesday, January 14, 2003 10:09 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [PIC]: 16f877 A/D stability
>
>
> Hello,
>
> Have a question about the A/D on the 16f877. I gave my first
> shot on coding a simple converter that uses a divider from a
> pot as an input to one of the pins. Now I'm pretty sure I
> have my code set right, because when I read the results (I
> did about 5 test cases), they all seem pretty accurate,
> except with a few problems.
>
> Some of the pins had constantly a constantly changing voltage
> that was registering on my DMM. Most of the pins would be
> stable, either ~0 or 5.2V, but some of them, each on
> different tests, would be fluctuating, sometimes from
> 2.5-2.9V, and sometimes other values. Is this normal? Does
> the fact that my program keeps going in a loop affect this
> (even though I'm reading the Go/! Done flag to check when
> it's done)? And it seems to be different pins each time, so
> there doesn't appear to be a definite pattern. On some
> readings, all the pins are perfect. Any ideas?
>
> Thank you,
>
> Jai
>
> PS: Just in case, I have my Code below.
>
> clrf TRISB                 ;Set all of Port B and D to outputs
> clrf TRISD
>
> movlw 0xff
> movwf TRISA
>
> movlw 0x0E           ;Set Justification and set RA0 as the
> only analog input
> movwf ADCON1
>
>
> bcf STATUS, RP0         ;Switch back to Bank 0
>
> movlw 0xC1           ;Select A/D on, Channel 0 and RC Clock
> movwf ADCON0
>
> movlw 0x00
> movwf PORTB    ;initialize the ports to a blank value.
> movwf PORTD
>
> Start1
>
>
> bsf ADCON0, GO           ;Start the A/D.
> Loop1
> btfsc ADCON0, GO
> goto Loop1
>
> ;Finished The A/D conversion
>
> movf ADRESL, 0     ;Move the low byte into Port B (B<7>:B<6>)
> movwf PORTB
>
> movf ADRESH, 0     ;Move the high byte into Port D (D<7>:D<0>)
> movwf PORTD
>
>
> goto Start1   ;Start it all over again.
>
>
>
>
>
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