adc is not working pic16f887

[ep.hobbyiest]

Hi,
i have configured ADC of pic16f887's PIC but it is not working properly.
I m using XC8 compiler and 4MHz cystal.

void adc_init(void)
{
  ANSEL = 0x03;
    TRISA = 0x03;// 4 channels selected
  ADCON1 = 0x80;// right justified
  ADCON0 = 0x01;//FOSC/2 and ADC Enabled
}

uint16_t read_adc(uint8_t por)
{
  uint16_t dat;
  ADCON0bits.CHS = 0;
  ADCON0bits.CHS = por;
  ADCON0bits.GO = 1;
  __delay_ms(1);
  while(ADCON0bits.GO_DONE == 1);
  ADCON0bits.GO = 0;
  ADCON0bits.CHS = 
  dat = ADRESL;
  dat |= (ADRESH<<8);
  return dat;
}

 

[andre_luis]

The command "ADCON0bits.GO = 0" looks totally unnecessary.
The command "ADCON0bits.CHS =" seems like it was never compiled.

 

[ep.hobbyiest]

i added that part later after checking that ADC part is not working properly. It is giving same reading again and again for both channel.

 

[spudboy488]

Though your comment says "4 channels select", you have only enabled 2 (AN0 and AN1)

I also seem to remember reading (someplace) that you have to disable the ADC to change any configuration parameter. I can't find the reference but I do it, it works, so it can't hurt.

Your code should be:

  ADCON0bits.ADON = 0;     // Disable to change channel
  ADCON0bits.CHS3 = 0;
  ADCON0bits.CHS2 = 0;
  ADCON0bits.CHS1 = 0;
  ADCON0bits.CHS0 = por;  // Por = 0 for AN0, Por = 1 for AN1
  ADCON0bits.ADON = 1;    // Enable

 

[ep.hobbyiest]

yes. i forgot to update comment in code but in code and in post#3 i mentioned as 2 channels.

- - - Updated - - -

ok. i ll try as suggested , is it differ than what i used?

 

[spudboy488]

  ADCON0bits.CHS = 0;
  ADCON0bits.CHS = por;

Was setting ADCON0bits.CHS to 0 then to por. Not sure how it compiled that way, but still....

 

[betwixt]

Use:

ADCON0 &= 0xC7;  // clear the channel select bits
ADCON0 |= por << 3; // select new channel
__delay_ms(1); // allow S&H to settle
 ADCON0bits.GO = 1;
 while(ADCON0bits.GO_DONE == 1);

that allows you to use any 'por' number, solves the problem of readings from one channel influencing another and it might return the result quicker.

Brian.

 

[Okada]

Use MCC it generates the ADC read function.