f2272 ADC error

Michael Owndries

Other Parts Discussed in Thread: MSP430F2272

Hi, have a problem with the ADC 10 of the MSP430F2272,

I want to enable the external 1.5V reference, and after the conversion i want to disable the external reference.

I can't use the REFBURST node because the device has to wait for a charge transient.(The out reference is used to supply the voltage of a NTC).

the trouble observed is that when the REFOUT is enabled , is impossible to disable it.

the code i use is wrotten below:

#include "msp430x22x4.h"

char cnt = 0;

void main(void)
{
WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT
ADC10AE1 = 0x10;       // P4.3 A12 analogic input
ADC10CTL1 = INCH_12;                      // ch12
ADC10CTL0 = SREF_0 + ADC10SHT_2 + REFON + ADC10ON;
TACCR0 = 3000;                              // Delay to allow Ref to settle
TACCTL0 |= CCIE;                          // Compare-mode interrupt
TACTL = TASSEL_1 + MC_1 + ID_3;                  // TACLK = SMCLK, Up mode
__bis_SR_register(CPUOFF + GIE);          // LPM0, TA0_ISR will force exit
TACCTL0 &= ~CCIE;                         // Disable timer Interrupt
P1DIR |= 0x01;                            // Set P1.0 to output direction
//P2DIR |= 0x10;
for (;;)
{
//P2OUT = 0x10;
P2REN &= ~0x10;

////////   abilito la tensione di rigerimento esterna
//enable REFOUT

    ADC10CTL0 |= SREF_0 + ADC10SHT_2 + REFON + ADC10ON + REFOUT;             //

   //aspetto che il transitorio di carica finisca

//wait for transient
   while(cnt < 33)
   cnt++;
   cnt = 0;

    //comincio la conversione

//start conversion
    ADC10CTL0 |= ENC + ADC10SC;

    while (ADC10CTL1 & ADC10BUSY);          // ADC10BUSY?


    //disable REFOUT
    //disabilito il riferimento esterno e interno di tensione per motivi di energy saving
   //ADC10CTL0 &= ~(REFON + REFOUT);
   ADC10CTL0 = 0x0000;
   ADC10CTL0 &= ~ADC10IFG;
   ADC10CTL0 &= ~REFON;
   ADC10CTL0 &= ~ REFOUT;

   /*i can't put REFON and REFOUT = 0
    *perchè non riesco a disabilitare il riferimento di tensione?
    *
    *
    * ADC10CTL0 &= ~(REFON + REFOUT);
    * questa istruzione non funziona!!....i bit REFON e REFOUT di ADC10CTL0 non vanno a 0.
    * come mai?
    *
    *
    * //i try with all these instruction, but REFOUT remains always = 1
    * //
    *    ADC10CTL0 = 0x0000;
     ADC10CTL0 &= ~ADC10IFG;
     ADC10CTL0 &= ~REFON;
     ADC10CTL0 &= ~ REFOUT;
     ma non riesco a portare a 0 i bit del registro.
   *
   *
   * In piu non posso usare ref burst perchè il riferimento esterno (che ha come carico una res da 15k e un C da 22nF)
   * non raggiunge la tensione 1.5V durante la conversione
   *

   */

   //attivo pull down per bloccare a 0 la tensione nel pin VREF+ (P2.4).
   P2REN |= 0x10;

    if (ADC10MEM < 0x311)                   // ADC10MEM = A11 > 1.15V?
      P1OUT &= ~0x01;                        // Set P1.0 LED on
    else
      P1OUT = 0x01;                       // Clear P1.0 LED off
      //P2OUT= 0;

   while(cnt < 250)
   cnt++;