pic24 ADC converter making me crazier

[snarkysparky]

Values coming back mid scale.  Changing slightly as input goes from zero to Vdd.


setup

Code: [Select]

    TRISA = 0xffbf;   //  1111 1111 1011 1111     // RA6  output  (pwm)
    TRISB = 0x0f7f;   //  0000 1111 0111 1111     //  RB12,13,14,15,7  output   
    ANSA =  0x000d;   //  0000 0000 0000 1101     RA0 RA2 RA3  analog inputs
    ANSB =  0x0003;   //  0000 0000 0000 0011     RB0 RB1  analog inputs
    AD1CON2 = 0x0800; //  0000 1000 0000 0000
    AD1CON1 = 0x0400; //  0000 0100 0000 0000   conv starts with samp bit clear, 12 bit operation
                      //                        abs decimal result unsigned right justified
                      //    AD1CON2 ,AD1CON3  default 0 values OK
    AD1CON3 - 0x0000;
    bit_set(AD1CON1,15);  //  turn on converter       


// Call
unsigned int read_AD(unsigned int channel)
{

   bit_clear(AD1CON1,15);  //  turn off converter 
   AD1CHS = 14;  // channel & 0x000f;
   bit_set(AD1CON1,15);  //  turn on converter 
   AD_SampStart();            // #define AD_SampStart() bit_set(AD1CON1,1)
   delay_cycles(10);
   AD_ConvStart();            // #define AD_ConvStart() bit_clear(AD1CON1,1)
   delay_cycles(3);
   do{}while(AD_Converting);  // #define AD_Converting (!bit_test(AD1CON1,0))

   return ADC1BUF14;

}





Thanks

[mikeselectricstuff]

Sounds like ADC is not sampling the input you want it to.
 
You don't say which PIC - might it be the case that the ANx pin numbers don't map 1:1 with the RAx numbers? - I think this is the case with some PICs.

Also, check you haven't accidentally pin-mapped something else onto the pin - mapping an input might override the analogue input, in the same way that pin-mapped functions can override TRIS settings.
 

[snarkysparky]

Well I fixed it.  It was a pic24F32KA301

The pin I was trying to read was setup in the configuration as OSCOUT.

From the data sheet for the configuration bits.

bit 2 OSCIOFNC: CLKO Enable Configuration bit
1 = CLKO output signal is active on the OSCO pin; primary oscillator must be disabled or configured
for the External Clock mode (EC) for the CLKO to be active (POSCMD<1:0> = 11 or 00)
0 = CLKO output is disabled


So the lesson here is that CLKO overrides the TRIS register.  Pin was set to input but still had the clock on it.

It's converting OK now. 

Thanks

I will delete this topic in a little while

[Buriedcode]

Why delete?  The forum is full of little 'gotchas' like this, and not all of them have a solution/reason.  I say leave it, someone might be doing something similar, google, and find your post helpful!

[MrBungle]

^ exactly.
This is way more usefull than threads like "Have you seen a room messier?", and yet stuff like that sticks around 
Keep it, it will eventually help someone.

[AndyC_772]

Agreed. I always try to remember to post the solutions to questions I've asked, for this very reason. Just because nobody else cares today doesn't mean nobody will care tomorrow.