I am having problems getting the ADC on a PIC16C74A to work. The
conversion is being done in sleep mode with the ADC using the RC osc. It
wakes up and jumps to the interupt vector, but the data in the ADRES
register is always 255. I am using internal vref and have put every
voltage possible on the pin i am trying to sample. I have that pin set
as annalog in one of the adcon registers, and as Input(TRISA = 0x00). I
am Operating at 4Mhz. I am allowing 2 ms for setteling time after i turn
the ADC on before setting the GO_DONE bit, but I have tried the
recomended minimum of 8us also.
HELP!

here are some code fragments that I am using.


If anyone has any ADC code fragments that are NOT for the 16c71 or 72 I
would appreciate it greatly!

INIT
      ;set up in page 1 first
    BSF     STATUS,RP0             ;PAGE 1


 ;ALL RA PINS ARE ANALOG
   MOVLW 0x00
    MOVWF   ADCON1              ;ADCON1

 ;make port a all inputs - for A/D
 MOVLW 0xFF
 MOVWF TRISA

 ;make b all outputs
    MOVLW   0x00       ;ALL OUTPUT
    MOVWF   TRISB               ;PORT B

 ;make c all outputs
    MOVLW   0x00       ;ALL OUTPUT
    MOVWF   TRISC               ;PORT C

 ;enable intereupts for a/d
 BSF  PIE1, ADIE

 ;go back to page 0
    BCF     STATUS,RP0             ;PAGE 0

 ;done!
 RETURN



;ADC - Analog to digital conversion routine
;      assumptions: port# is a pin set up to be analoge
;      operands : ADCPORT  port# to read
;      returns:   ADCRES   result of the conversion - can be same as
ADCPORT
ADC NOP


 ;enable periferal interupts
    BSF     INTCON, PEIE
 BSF  INTCON, GIE

 ;clear carry bit for upcomming shift
 MOVLW 0x00
 ADDLW 0x00


;ADCPORT's lowest 2 bits contain the 3 bits used for channel select.
 ;set port # up for use with template of ADCON0
    RLF     ADCPORT, F
    RLF     ADCPORT, F
 RLF  ADCPORT, W

 ;mix port# with template of ADCON0
 IORLW 0xC1

 ;place command in ADCON0
 MOVWF ADCON0

 ;adc is now on, wait for signal setteling 8us at 4Mhz
 ;********what the hell, wait for 2 ms, we have time to spare
    MOVLW   0x02
    MOVWF   DLYMSA
    CALL    DLYMS

 CLRF ADRES

 ;start conversion
    BSF      ADCON0, GO_DONE

 ;wait for conversion to complete
 SLEEP

 ;put result in desired register
 MOVF ADRES, W
    MOVWF   ADCRES

 ;turn off A/D for now
; BCF ADCON0, ADON

 ;done
 RETURN




;interupt vector points here
SERVICE_INT

  MOVF ADRES, W
  MOVWF PORTB

  CALL TONE

; wait 2 seconds
        MOVLW   2
        MOVWF   DLYSA
        CALL    DLYS

;  CLRF PORTB

  ;clear a/d interut flag, just incase
  BCF     PIR1, ADIF

  RETFIE