Bits 3-0 (lower nibble?) of adcon1 are the a/d port configuration 
control bits.  Setting it to 011x means they're all digital I/O (D in 
the table).  So adcon1 = 0x06 will correspond to 00000110 which 
satisfies this.  (In the register 11-2 entry as pointed out by the others.)
Mark

On 2/16/2010 9:17 PM, Joseph Bento wrote:
> I have finally enrolled in a continuing education class on midrange PICs.
> We are concentrating on the 16F877A using a QL200 development board to test
> our programs.
>
> I'm having a bit of a brain fart here in comprehending how ADCON1 is
> configured.  I find plenty of references online as well as my study
> materials that state setting ADCON1 to 0x06 sets all PORTA (and E since I
> see they have the same address) pins as digital I/O vice analog.
>
> I'm trying to see how or why this happens.  How does setting bits 1 and 2
> (0x06) high change the I/O to digital?
>
> I'm looking at Table 4-2 (page 43) in the 16F877A datasheet. I am apparently
> missing something in understing WHY 0x06 is used, and what I would choose if
> I wanted an analog I/O.  What configuration chart am I overlooking that
> describes the settings?
>
> This is a portion of my code: (I apologize ahead of time for any formatting
> issues.)
>
> start   bsf    STATUS,RP0                 ;Switch to Bank1 for ADCON1
>            bcf   STATUS,RP1                 ;Make sure in Bank1
>            movlw 0x06                             ;Load value to make ports A
> &  E digital I/O
>            movwf ADCON1                    ;as opposed to Analog inputs
>
> Thanks for any clarification anyone can offer.
>
> Joe
>
>    

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