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I'm working on integrating an accelerometer(ADXL335) into my project. So I'm doing three single channel conversions, on the three axes. The first conversion I do gives me a normal reading for horizontal, ~450. The other ones give me ~880 and ~1020. I have switched the axes and the first one always gives me the correct value the others don't. The following code shows my ADC function.

int Acc(char channel)
{
  
  int res, ch;
  
  ch = channel * 0x1000;
  
  ADC10CTL0 &= ~ENC;
  ADC10CTL0 |= ADC10ON;
  ADC10CTL1 = ch + ADC10SSEL_3;
  
  ADC10CTL0 |= ENC + ADC10SC;
  
  while(ADC10CTL1&ADC10BUSY);
 
  res = ADC10MEM;
  ADC10CTL0 &= ~(ADC10ON + ENC);
  
  return res;
}

And my main code,

#include "msp430g2553.h"
#include "central.h"

void main(void)
{
  WDTCTL = WDTPW + WDTHOLD;                                                     //Watchdog Timer Disabled
  
  P1DIR =0xf8;                                                                  //Initialise Pins and Special Functions
  P1SEL=0x00;
  P1IE=0x00;
  
  DCOCTL= CALDCO_1MHZ;
  BCSCTL1=CALBC1_1MHZ; 
  
  int x, y, z, temp;
  
  P1OUT=0x00;

  
  
  while(1)
  {
    x=Acc(0);
    y=Acc(1);
    z=Acc(2);
    temp = Temp();
    if (x>=400) P1OUT = BIT6;
    else if(y>=400) P1OUT = BIT5;
    else if(z>=400) P1OUT = BIT4;
    else {};
    
    if(temp>=300) P1OUT= BIT3;
    else{};
    __delay_cycles(1000);
  }
}

I'm not doing anything with the outputs so ignore them.

 

Has anyone any ideas why one axis gives a sensible result but the other two don't?

 

PS when the accelerometer is powered and the axis pins are not connected, the voltages read with a multimeter are correct. 

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Thanks nemetila,

 

I actually tried that shortly after posting here, doesn't make any difference. I read somewhere else that that register is only needed when doing sequence conversions whereas I am doing three single channel conversions.

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