Electronic Circuits and Projects Forum

Been reading it - both of those sections and more for a long time. I'm missing or misunderstanding something I'm reading. Can you be any more specific to point me in a direction?

I've disabled the comparators...
I've set my tristates on TRSIO2 and TRISIO3 high...
I've set ANSEL for the clock cycle, justification, and set AN2 as analog...
I've sed ADCON0 with what I believe are the proper settings (error seems to indicate I'm asking for the correct channel)...

When I stop the code right before I try to set ADCON0.GO_DONE high, here are the binary values in key registers:

Code :

TRISIO: 00001100
ANSEL: 00010100
ADCON0: 10001001
CMCON0: 00000111

Those are the values I expect to see based on what I'm reading in the datasheet. Just missing something.

4.2.1 ANSEL REGISTER
The ANSEL register is used to configure the Input
mode of an I/O pin to analog. Setting the appropriate
ANSEL bit high will cause all digital reads on the pin to
be read as ‘0’ and allow analog functions on the pin to
operate correctly.

Where did you set ANSEL bit high for this analog input?
What I see is that you keep mentioning two analog ports AN0 and AN2.
Are you using one or two analog ports?

If you are using AN0, as your post suggests, then fix the code so that you are enabling AN0 and not AN2 (and fix the code comments).
If you are using AN2... same story, stick with AN2 - don't mix and match.

Look at page 35 you don't set this to 0 ANSEL = 0;

You want ANSEL =0x74;

I set the ANSEL bits high in config_ADC():

Code :

    /* Set all ports except GP0 to digital (0) */
    ANSEL = 0;
    ANSELbits.ANS = 0b0100;     // set AN2 to analog
    ANSELbits.ADCS = 0b001;     // set freq to fosc/8

I did it this way because I read somewhere that it's good to explicitly clear the register before I start plugging stuff into it. Plus, being new to this and in a constant troubleshooting mode, it's easier for me to look at it long-hand for now so I know what I'm doing - right or wrong.

@Burt - Tried setting to 0x74 per your suggestion (only clock selection was different from what I had) and identical result.

Originally Posted by MikahB

I set the ANSEL bits high in config_ADC():

Code :

    /* Set all ports except GP0 to digital (0) */
    ANSEL = 0;
    ANSELbits.ANS = 0b0100;     // set AN2 to analog <<<<NOTE What is THIS?  Why AN2 when you want to use AN0?
    ANSELbits.ADCS = 0b001;     // set freq to fosc/8

.

NOTE: What is THIS? Why AN2 when you want to use AN0?

for AN0 you should set

Code :

    ...
     ANSELbits.ANS = 0b0001;     // set AN0 to analog
    ...

or configuration byte should be 0x11 (or 0xX1)

Switched from AN0 to AN2 during troubleshooting - forgot to change the comment but I"ve changed everything else (and now fixed the comment as well). I made a couple other minor changes to the code while troubleshooting also, here is a "fresh" new version that works equally poorly:

Code :

#include <htc.h>
#include <stdio.h>
 
#define _XTAL_FREQ 4000000
#define _ADCBITS 10;
#define _ADC_CLOCK3;
#define _ADC_SAMPLEUS 50;
 
__CONFIG(FCMEN_OFF & WDTE_OFF & PWRTE_OFF & MCLRE_OFF & IESO_OFF & CP_OFF & BOREN_OFF & FOSC_INTOSCIO);
 
void config_ADC(void);
int read_ADC(void);
 
bit on_state = 0;
unsigned char delay;
volatile unsigned int count = 0;
 
void main()
{
    config_ADC();
 
    while(1)
    {
        on_state = ~on_state;
        GPIObits.GP4 = on_state;
 
        count = read_ADC();
 
        while(count>0)
        {
        __delay_ms(10);
        count--;
        }
    }
}
 
void config_ADC(void) {
    /* Turn off all comparators */
    CMCON0 = 7;
 
    /* Set all ports to digital then un-set the ones we need */
    ANSEL = 0;
    ANSELbits.ANS = 0b0100;     // set AN2 to analog
    ANSELbits.ADCS = 0b001;     // set freq to fosc/8
 
    /* Set the ADC Control register per Data sheet */
    ADCON0 = 0;             //initialize to zero
    ADCON0bits.ADFM = 1;    // right-justify for 10-bit ADC
    ADCON0bits.VCFG = 0;    // reference Vdd
    ADCON0bits.CHS = 0b010; // read AN2
    ADCON0bits.ADON = 1;    // turn ADC on
 
    /* Set all pins to output except GP0 (to be used as ADC input)*/
    TRISIO = 0;
    TRISIObits.TRISIO2 = 1;     // set AN2/GPIO2 to input
    TRISIObits.TRISIO3 = 1;     // set MCLR/GPIO3 to input
 
//    __delay_ms(10);
 
}
 
int read_ADC(void)
{ // start an ADC conversion and return the 8 most-significant bits of the result
	int ret = 0;
	ADCON0bits.GO_DONE = 1;	//start conversion <<<NOTE: This is the line that produces the error I mentioned in the 1st post
	__delay_ms(5);
        while(ADCON0bits.GO_DONE);		// wait for conversion
   	ret = ADRESL + (ADRESH & 0x3) << 8;		// get result
	return ret;
}