12F683 ADC problems

[andywpg]

Hi all.

I'm having an issue that is driving me crazy. I'm trying to use a potentiometer on GPIO4 (10K linear - wiper on GP4, ends on 5V and ground).

Originally, I tried to use:

duty = adval 'adval is the result of the ADC

It worked, but it appears that I'm only getting part of the way, as the led (on GP2/CCP1) only varies from off to about half brightness. I then discovered that the result is from 0-1025, not 255 as I had assumed.
Then I tried:

duty = adval >> 2

But the led never lights.

After some more reading, here is what I have now. It still results in the led never lighting, no matter the position of the pot.

;pic12f683
#CONFIG
cfg = _INTOSCIO
cfg&= _WDT_ON
cfg&= _PWRTE_OFF
cfg&= _MCLRE_ON
cfg&= _CP_OFF
cfg&= _CPD_OFF
cfg&= _BOD_ON
cfg&= _IESO_ON
cfg&= _FCMEN_ON
  __CONFIG cfg
#ENDCONFIG

DEFINE OSC  8
' Define ADCIN parameters
Define ADC_BITS 8 ' Set number of bits in result
Define ADC_CLOCK 3 ' Set clock source (3=rc)
Define ADC_SAMPLEUS 50 ' Set sampling time in uS

OSCCON=$70
CMCON0    = 7
TRISIO   = %111011      ;gp2= output
ANSEL = %00111000 ' Set AN3 analog, rest digital
CMCON0 = 7 ' Analog comparators off
ADCON0.7 = 1

adval Var word ' Create adval to store result
duty var byte
result var word
 
mainloop:
    ADCIN 3, adval ' Read channel 3 to adval
    pauseus 50 'wait 50us for read to complete 
    result = adval >> 2 'right shift by 2 bits to divide by 4
    if result > 255 then result = 255
    duty = result.BYTE0  
    ' hpwm Channel, Dutycycle, Frequency 
    hpwm     1,duty,600   ; set led brightness at 600hz
    pause 50 ;Pause for 50 milliseconds   
    goto mainloop

Anyone got any ideas what I'm doing wrong? It's getting a little frustrating. I am planning to do a test for the GO/DONE bit in ADCON0 to make the delay after read less, but I want to get this part working first.

I would appreciate any help anyone can offer.