Paul Duffy wrote:
> Hi
>
> I am using the 16F684 and want to read 2 different A/D inputs to set 2 di=
fferent time delays in my widget.  I have 2 potentiometers, set up as volta=
ge dividers, connected to the A/D inputs.  My attempts to read the A/D are =
failing.  Here is the relevant code snippet:
>   .....
>   .....
>    off =3D 0;
>    on =3D 0;
>    ansel =3D 0b0000011;          //select AN0, AN1 (pins 12, 13) as A/D i=
nputs
>    adcon1 =3D 0b01010000;     //select 16*Tosc clock - gives TAD of 4uS =

>    adcon0 =3D 0b00000001;     //turn on A/D, select AN0 as input, don't s=
tart conversion
>
>    while(1)                            //Main Loop - continuously update =
porta and portc.  =

>         {
>         porta =3D off;                  //display via leds connected to a=
vailable port pins
>         portc =3D on;                  //display via leds connected to av=
ailable port pins
>     =

>         adcon0 =3D 0b00000001;           //turn on A/D, select AN0 as inp=
ut, don't start conversion
>         delay_ms(10);                      //delay each time through loop=
, =

>         set_bit(adcon0,1);                  //start a/d conversion
>         while (!test_bit(adcon0,1));      //wait for completion
>         on =3D adresh;                          //store on_time - AN0
>         if(on=3D=3D0)on =3D on+1;                //ensures on_time !=3D0
>    =

>         adcon0 =3D 0b00000101;           //Change the input to AN1, don't=
 start conversion
>         delay_ms(10);                       //delay each time through loo=
p, =

>         set_bit(adcon0,1);                 //start a/d conversion
>         while (!test_bit(adcon0,1));     //wait for completion
>         off =3D adresh;                         //store off_time - AN1
>         if(off=3D=3D0)off =3D off+1;               //ensures off_time !=
=3D0
>         }
>
> As it is, this does not work at all.  I see no change on the leds connect=
ed to portc or porta when I change the potentiometers.  If I remove one of =
the "adcon0=3D..." statements, then one of the potentiometers is read and d=
isplayed in both ports.  Depending on which of the 2 "adcon0=3D..." stateme=
nts I delete, I can read either potentiometer.  How do I switch between the=
 a/d inputs so that I can read both potentiometers?
>
> Thanks in advance for any help.
>
> Paul Duffy
>
>
>   =

Hi Paul,

I think the TRIS bits also have to be set so the AD channels are read as =

inputs. The PIC16F684 Datasheet has a code snippet in assembly language =

(below). The command to notice is BSF TRISA, 0, in other words, set =

TRISA bit 0 to 1. In your case, I think you'll need to set TRISA bit 1 =

also.
Sorry not to be more help. I'm struggling with the A/D converter of the =

PIC16F684 right now, and can't get it to read any input other than AN0.

Tony Russell

EXAMPLE 9-1: A/D CONVERSION
;This code block configures the ADC
;for polling, Vdd reference, Frc clock
;and AN0 input.
;
;Conversion start & polling for completion
; are included.
;
BANKSEL ADCON1 ;
MOVLW B=9201110000=92 ;ADC Frc clock
MOVWF ADCON1 ;
BANKSEL TRISA ;
BSF TRISA,0 ;Set RA0 to input
BANKSEL ANSEL ;
BSF ANSEL,0 ;Set RA0 to analog
BANKSEL ADCON0 ;
MOVLW B=9210000001=92 ;Right justify,
MOVWF ADCON0 ; Vdd Vref, AN0, On
CALL SampleTime ;Acquisiton delay
BSF ADCON0,GO ;Start conversion
BTFSC ADCON0,GO ;Is conversion done?
GOTO $-1 ;No, test again
BANKSEL ADRESH ;
MOVF ADRESH,W ;Read upper 2 bits
MOVWF RESULTHI ;store in GPR space
BANKSEL ADRESL ;
MOVF ADRESL,W ;Read lower 8 bits
MOVWF RESULTLO ;Store in GPR space
-- =

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