Thanks everybody. Got the bug. ADRESL is in Bank1, whereas the temporary
register (TempA_Lo) was in Bank0. So the zeroes in TempA_Lo.

-----Original Message-----
From: pic microcontroller discussion list
Sent: Tuesday, October 07, 2003 7:46 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: [PIC]: ADC trouble


Hello,

In the ADC I'm doing using a PIC16F870, the ADRESL register does not
'work' properly. When I left justify the results, the ADRESH gives me a
proper reading, but there is 0x00 in ADRESL (so 8 bit ADC). Now, when I
right justify the results, the ADRESL has again all zeroes, while the
ADRESH gives a reading (so now 2 bit ADC). The BANKs, ADCON0, ADCON1 are
set properly (because there IS an AD conversion always, 8 bit / 2 bit).
I've used 3 or 4 different PICs (all 16F870s), but they have the same
problem. I've also changed Fosc/32 to Fosc/8, but still same. The ADC
code is inline below. Searching archives has not been fruitful. This may
sound far-fetched, but is it just possible that the PICs are defective?

Please advise.

Thanks,
Mohit.

;=CODE===========================================
; PIC16F870 @ 20 MHz
;Initialisation for ADC

        BANKSEL ADCON1
        movlw   b'00001110'     ; Left justified (ADRESL=xx000000),
AN0=Analog, Rest Digital.
        movwf   ADCON1
        movlw   B'00001111'     ; Initialise PortA
        movwf   TRISA           ; -do-
        BANKSEL PORTA

ADsample
        BANKSEL ADCON1
        clrf    ADRESL
;       movlw   b'10001110'     ; Right justified (ADRESH=000000xx),
AN0=Analog. Gives 8 bit ADC.
        movlw   b'00001110'     ; Left justified (ADRESL=xx000000),
AN0=Analog. Gives 2 bit ADC.
        movwf   ADCON1
        BANKSEL ADCON0
        clrf    ADRESH
        movlw   b'10000000'     ; Fosc/32 clock, Ch0 (PortA,0), AD
module is off
        movwf   ADCON0
        movlw   1               ; Wait a bit (1 msec),
        call    wait_n_msec     ; -do-.

        bsf     ADCON0,ADON     ; Turn ON AD module.
        call    wait_1_msec     ; Acquisition wait, >20 us. We wait 1
msec.
        bsf     ADCON0,GO_DONE  ; Start A/D conversion.
AD_Conv_Wait
        btfsc   ADCON0,GO_DONE  ; Wait for conversion to finish.
        goto    AD_Conv_Wait

        BANKSEL ADRESL  ; Store results in the alloted registers for
later use
        movfw   ADRESL
        movwf   TempA_Lo
        BANKSEL ADRESH
        movfw   ADRESH
        movwf   TempA_Hi
        return
;=============================================

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