At 11:06 PM 4/7/03 +0600, David Strickland wrote:
>I'm having a problem with the A/D convertor in the chip.  It seems to
>always return 0x13 no matter if the input voltage is 5V or 0V.
>I've used interrupt driven and polling, both return the same result.
>I'm reading the results from PORTB and PORTD with a multimeter (limited
>parts availability in the lab, ie no leds).
>
>; Set TRISA for analog input.
>        bsf     STATUS, RP0             ; switch to bank1
>        movlw   0x3f                    ; Set bits 5-0 as 1
>        movwf   TRISA                   ; Sets PORTA<5:0> as inputs.
>:
>
>; Set up the A/D convertor.
>        bcf     STATUS, RP0
>        bcf     STATUS, RP1             ; Switch to bank0.
>        clrf    ADCON0                  ; Clear ADCON0.
>                                        ; Selects channel 0 (AN0)
>                                        ; Turns the A/D off.
>                                        ; Clears GO flag.
>        bsf     ADCON0,ADCS1            ; Set ADSC1 and ADSC0 since we
>                                        ; are going to
>        bsf     ADCON0,ADCS0            ; Use A/D's internal RC for its
>                                        ; clock source.
>
>        bsf     STATUS, RP0
>        bcf     STATUS, RP1             ; Switch to bank1.
>        clrf    ADCON1                  ; Clear ADCON1
>        bsf     ADCON1, ADFM            ; Right justify 10 bits in
>                                        ; ADRESH and ADRESL
>        bsf     ADCON1, PCFG1           ; ADCON1<3:0> = 0010
>                                        ; Set AN7-AN5 as Digital.
>                                        ; Set AN4-AN0 as Analog inputs.
>                                        ; Use AVDD/AVSS (internal) as
>                                        ; reference voltages.

You are still in Bank 1 here - wrong!

>; Do a test A/D conversion.
>        bcf     ADCON0, CHS0            ; Select Channel 0 (AN0).
>        bcf     ADCON0, CHS1            ;
>        bcf     ADCON0, CHS2            ;
>        bsf     ADCON0, ADON            ; Turn A/D on.
>
>
>        movlw   d'31'                   ; 23 us/0.25 us = 92 total
>                                        ; clocks
>                                        ; since loop has 3
>                                        ; instructions... 92/3 = 30.67
>                                        ; -> 31
>                                        ; 23 us is worst case, 10k ohm
>                                        ; impedance and 100 deg C.
>                                        ; 1/4MHz = 0.25 us
>        bcf     STATUS, Z               ; Make sure Zero flag is off.
>addaq1
>        addlw   -1                      ; W=W-1
>        btfss   STATUS, Z               ; Is W = 0?
>        goto    addaq1                  ; NO, loop again.
>
>        bsf     ADCON0, GO              ; Begin A/D conversion.
>loop    btfsc   ADCON0, GO
>        goto loop
>
>        bcf     STATUS, RP0
>        bcf     STATUS, RP1             ; switch to bank0 to access
>                                        ; ADRESH.

You had to be in Bank 0 to talk to ADCON0

>        movf    ADRESH, W
>        movwf   adsaveh                 ; copy upper portion of A/D
>                                        ; result.
>        bsf     STATUS, RP0             ; switch to bank1 to access
>                                        ; ADRESL.
>        movf    ADRESL, W

Opps - still in Bank 1

>        movwf   adsavel                 ; copy lower potion of A/D
>                                        ; result.
>
>        bcf     STATUS, RP0
>        bcf     STATUS, RP1             ; switch to bank0 to access
>                                        ; PORTB.
>        movf    adsavel, W
>        movwf   PORTB
>        movf    adsaveh, W
>        movwf   PORTD

Bottom line: appears to be Banking issues.

dwayne

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