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Forum: µC & Digital Electronics MSP-EXP5438 ADC12 Sample Code


Author: Vidya Sagar (Guest)
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Dear all,

I am implementing a very small code to read sample from ADC on Msp430 
experimenter board EXP5438A. However I read very false samples (it is 
either a 6 or a 7).I dont really understand where the problem is.

Here is my code. This code is sample code from TI for continuous 
sampling on single channel. I am able to build and successfully debug 
the code. Board works fine. Can anyone please suggest where the problem 
can be? Thank you for the same.

#include "msp430x54xA.h"

#define   Num_of_Results   8

volatile unsigned int results[Num_of_Results];

void main(void)
{
  WDTCTL = WDTPW+WDTHOLD;                   // Stop watchdog timer

  P7SEL |= 0x20;                            // Enable A/D channel A13

  /* Initialize ADC12_A */
  ADC12CTL0 = ADC12ON+ADC12SHT0_8+ADC12MSC; // Turn on ADC12, set 
sampling time
                                            // set multiple sample 
conversion
  ADC12CTL1 = ADC12SHP+ADC12CONSEQ_2;       // Use sampling timer, set 
mode
  ADC12IE = 0x01;                           // Enable ADC12IFG.0
  ADC12CTL0 |= ADC12ENC;                    // Enable conversions
  ADC12CTL0 |= ADC12SC;                     // Start conversion

  __bis_SR_register(LPM4_bits + GIE);       // Enter LPM4, Enable 
interrupts
  __no_operation();                         // For debugger
}


#pragma vector=ADC12_VECTOR
__interrupt void ADC12ISR (void)
{
  static unsigned char index = 0;

  switch(__even_in_range(ADC12IV,34))
  {
  case  0: break;                           // Vector  0:  No interrupt
  case  2: break;                           // Vector  2:  ADC overflow
  case  4: break;                           // Vector  4:  ADC timing 
overflow
  case  6:                                  // Vector  6:  ADC12IFG0
    results[index] = ADC12MEM0;             // Move results
    index++;                                // Increment results index, 
modulo; Set Breakpoint1 here

    if (index == 8)
      index = 0;                            // Reset the index; Set 
Breakpoint here

  case  8: break;                           // Vector  8:  ADC12IFG1
  case 10: break;                           // Vector 10:  ADC12IFG2
  case 12: break;                           // Vector 12:  ADC12IFG3
  case 14: break;                           // Vector 14:  ADC12IFG4
  case 16: break;                           // Vector 16:  ADC12IFG5
  case 18: break;                           // Vector 18:  ADC12IFG6
  case 20: break;                           // Vector 20:  ADC12IFG7
  case 22: break;                           // Vector 22:  ADC12IFG8
  case 24: break;                           // Vector 24:  ADC12IFG9
  case 26: break;                           // Vector 26:  ADC12IFG10
  case 28: break;                           // Vector 28:  ADC12IFG11
  case 30: break;                           // Vector 30:  ADC12IFG12
  case 32: break;                           // Vector 32:  ADC12IFG13
  case 34: break;                           // Vector 34:  ADC12IFG14
  default: break;
  }
}

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