There are two wais (at least) of using the AD module in PIC microcontrollers.
First one is: set the AD channels and device operating frequency, turn
on the AD module, wait 20uS for aquisition time and wait untill the
GO/DONE bit is changing
The second one is: set the AD channels and device operating frequency,
turn ON the AD module, turn ON the interrupt from the PEIE&GIE&ADIE
bits and inside the interrupt routine poll the ADIF.  Maybe is just
because you forgot to turn on the PEIE&GIE see page 62 of the
DS41190C. I don't know your compiler nor C.

regards,
Vasile


On 9/18/06, Shawn Wilton <black9@gmail.com> wrote:
> I'm attempting to use a polling technique to read the a/d converter on this
> 12F675, but I'm having trouble getting the chip to perform the conversion.
>
> I'm using the freeware version of the BoostC compiler.  Latest version.
>
> My code for setting up the A/D:
>
>
>  //Setting up the TriState Register
>  trisio = 010100b;
>  //Enable pull-ups if we want them
>  //set_bit(option_reg, NOT_GPPU);
>
>  /********
>  Setup the ADC
>  ********/
>  //Right justified
>  set_bit(adcon0, ADFM);
>
>  //Voltage reference = Vdd
>  clear_bit(adcon0, VCFG);
>
>  //Set A/D ports 2 and 3 for analog inputs
>  set_bit(ansel, ANS2);
>  set_bit(ansel, ANS3);
>
>  //Use Frc instead
>  set_bit(ansel, ADCS0);
>  set_bit(ansel, ADCS1);
>  clear_bit(ansel, ADCS2);
>
>  //Enable the A/D interrupt
>  set_bit(pie1, ADIE);
>
>  //Turn on the ADC
>  adc_on = 1;
>
>
> Then the code used to poll the ADC:
>
>  unsigned int result = 0;
>  unsigned int high = 0;
>  unsigned int low = 0;
>
>  //Set the ADC Channel
>  adcon0 |= channel << 2;
>
>  //Begin a conversion
>  adc_go = 1;  // bit 1 of adcon0
>
>  //Begin the conversion and block until it's complete
>  //while(test_bit(adcon0, 1))
>  while(!test_bit(pir1, ADIF))
>  {
>    set_bit(gpio, LED_PIN);
>  }
>
>  //Clear the interrupt flag
>  clear_bit(pir1, ADIF);
>
>  //Convert to 16 bit vars so we can shift properly
>  high = ADRESH;
>  low = ADRESL;
>
>  //Shift the upper bits 8 up and append to the lower bits
>  return ((high << 8) | (low));
>
>
> I'm primarily an Atmel man, so I'm scratching my head wondering why the
> conversion never takes place.  According to the d/s, the adcon0, bit 1
> should be cleared when the conversion is complete, and the ADIF bit should
> be set when the conversion is complete.  I have tried both methods and
> neither are working out for me.
>
> If I have failed to include any relevant details, lmk.
>
> --
>
> Shawn Wilton (b9 Systems)
> http://b9Systems.com  <- New web page
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist