How to configure ADC sampling rate?

Hi!

I am using dsPIC Starter Kit which has a dsPIC33fj256gp506. I am trying to modify the ADC sampling rate using the example from Microchip.

Here is the code:

Code:

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#ifndef __ADCCHANNELDRV_H__
#define __ADCCHANNELDRV_H__
 #define ADC_CHANNEL_FCY  40000000
#define ADC_FSAMP    8000 /* Sampling Frequency */
#define ADC_BUFFER_SIZE  128    /* This is the size of each buffer */
#define ADC_CHANNEL_DMA_BUFSIZE (ADC_BUFFER_SIZE*2) 
 
 #include "..\h\p33FJ256GP506.h"
 typedef struct sADCChannelHandle {
 int * buffer1;
 int * buffer2;
 volatile int bufferIndicator;
 volatile int isReadBusy;
 
}ADCChannelHandle;
 void ADCChannelInit (ADCChannelHandle * pHandle,int * pBufferInDMA);
void ADCChannelStart (ADCChannelHandle * pHandle);
void ADCChannelRead (ADCChannelHandle * pHandle,int *buffer,int size);
int ADCChannelIsBusy (ADCChannelHandle * pHandle);
void ADCChannelStop (ADCChannelHandle * pHandle);
#define ADCON1VAL  0x0744    /* 12 bit ADC with signed fractional format
                                            * Triggered by Timer 3 and auto start
                                                    * sampling after conversion complete. */
#define ADCON2VAL  0x0000      /* AVdd and AVss voltage reference, 
                                                      * use channel 0 with no scan */
#define ADCON3VAL  0x0010     /* Tad is 16 Tcy    */   
#define ADCHSVAL  0x0000  /* AN0 input on channel 0  */   
#define ADPCFGVAL  0xFFFE  /* AN0 input is Analog  */
#define ADCSSLVAL  0x0000  /* No channel scanning  */
 #endif
 
 
 #include "..\h\ADCChannelDrv.h"
 static ADCChannelHandle * thisADCChannel;
 void ADCChannelInit (ADCChannelHandle * pHandle,int * pBufferInDMA)
{
 /* This function will intialize the DMA  */
 /* DMA0 is used to read from the ADC  */
 
  thisADCChannel = pHandle;
 pHandle->buffer1  = pBufferInDMA; /* Assign the ping pong buffers for the ADC DMA*/
 pHandle->buffer2  = (int *)((int)pBufferInDMA + ADC_BUFFER_SIZE);
 
 DMA0CONbits.SIZE  = 0;  /* Word transfers      */
 DMA0CONbits.DIR  = 0;  /* From ADC1BUF to DMA    */
 DMA0CONbits.HALF  = 0;  /* Interrupt when all the data has been moved */
 DMA0CONbits.NULLW  = 0;  /* No NULL writes - Normal Operation  */
 DMA0CONbits.AMODE  = 0;  /* Register Indirect with post-increment mode */
 DMA0CONbits.MODE  = 2;  /* Continuous  ping pong mode enabled  */
 
 DMA0REQbits.FORCE  = 0;  /* Automatic transfer    */
 DMA0REQbits.IRQSEL = 0xD; /* ADC conversion complete  */
 
 DMA0STA = (int)(pHandle->buffer1) - (int)&_DMA_BASE;
 DMA0STB  = (int)(pHandle->buffer2) - (int)&_DMA_BASE;
 
  DMA0PAD = (int )&ADC1BUF0;
 DMA0CNT = ADC_BUFFER_SIZE - 1;
  AD1CON1  = ADCON1VAL;    /* Load the ADC registers with  value  */                           
 AD1CON2  = ADCON2VAL;    /* specified in 12bitADCDriver.h */ 
 AD1CON3  = ADCON3VAL;                             
 AD1CHS0  = ADCHSVAL;                             
 AD1PCFGLbits.PCFG0 = 0;
 AD1CSSL  = ADCSSLVAL;
TMR3  = 0;
 PR3  = (ADC_CHANNEL_FCY/ADC_FSAMP) - 1;
 }
 
 void ADCChannelStart (ADCChannelHandle * pHandle)
{
 pHandle->bufferIndicator  = 0;
 pHandle->isReadBusy  = 1;
 _DMA0IF = 0;
 _DMA0IE = 1;
 DMA0CONbits.CHEN = 1;  /* Enable the DMA Channel */
 AD1CON1bits.ADON = 1;  /* Enable ADC module  */
 T3CONbits.TON  = 1;  /* Enable Timer 3        */
 }
 void ADCChannelStop(ADCChannelHandle * pHandle)
{
 _DMA0IE = 0;    /* Disable the DMA interrupt */
 DMA0CONbits.CHEN = 0;  /* Disable the DMA Channel */
 AD1CON1bits.ADON = 0;  /* Disable ADC module  */
 T3CONbits.TON  = 0;  /* Disable Timer 3        */
} 
 void ADCChannelRead (ADCChannelHandle * pHandle,int *data,int size)
{
 int *source;
 int  i;
 
 /* if the buffer indicator bit is 1, then use buffer 1 else use buffer2 */
 /* Since the DMA ping pongs between these buffer, you must know */
 /* which one to read. The bufferIndicators keep track of this  */
 
 source = (pHandle->bufferIndicator) ? pHandle->buffer1 : pHandle->buffer2;
 if (size > ADC_BUFFER_SIZE) size = ADC_BUFFER_SIZE;
 
 for(i = 0;i < size;i++)
 {
  data[i] = source[i];
 }
 __asm__ volatile("disi #0x4"); /* disable interrupts */
 pHandle->isReadBusy = 1;
 __asm__ volatile("disi #0x0"); /* enable interrupts */
 }
 int ADCChannelIsBusy (ADCChannelHandle * pHandle)
{
 return(pHandle->isReadBusy);
}
 void __attribute__((__interrupt__,no_auto_psv)) _DMA0Interrupt(void)
{
 
 _DMA0IF = 0;
 thisADCChannel->bufferIndicator  ^= 1;  /* Flip the indicator bit  */
 thisADCChannel->isReadBusy  = 0;  /* New frame is available */
}

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I want to set it to 60kHz. I set ADC_FSAMP = 60000, and calculate ADCS.

Tcy = 25ns (@40MHz)
Tc = 1/60000 = 16.66us = 16666ns (aprox.)
Tad = Tc/14 = 1190ns (aprox.)
ADC Conversion Clock: Tad=Tcy*(ADCS+1) => ADCS = (Tad/Tcy) - 1 = 46,61 = 47 (aprox.).
I set ADCS = 47, so I write:

Code:

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#define ADCON3VAL 0x002F

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To test if the ADC is working correctly, I generate a 10kHz signal for the board using my PC sound card (using Visual Analyser 2011). But the ADC won't finish sampling (I use a LED to signal when 128 samples have been acquired - when finished, the LED switches off). Also, if I generate a DC signal, the ADC won't finish sampling. More interesting is the fact that when I generate a 1kHz signal, the ADC works fine!! I used debug to view the samples, exported the values in a file and plotted them in Matlab.Please help in solving this problem. I really need to get this ADC running for a project I am working on.

Maybe you should try a C forum. Here we do Basic only.

Ioannis

OK. I will try another forum. Thanks!