利用单片机自带的AD采集电源电压时利用内部参考源的问题

1万 · 2013-3-5 17:51

该问题就是我用MSP430F5310单片机的自带AD的A0通道采集系统电源电压，附件中为我的电压采集电路，参考源悬起的为单片机的内部参考电压2.5V。R2、R4原来均为10M，当VBAT =4.10V时，得到Vad=1.35V ,此时利用单片机的程序来采集该电压的时候，发现选取的内部电压2.5V使用不成，AD采集的结果十分不稳定也不准确，当选取外部的参考电压3.0V的时候，就可以得到稳定的采集值。
后来当将R2、R4 的阻值均换成附件中的47k 的时候，同样的程序选用内部参考电源就OK啦，值得一提的是此时VBAT=4.10V时，Vad=2.05V。
所以当时就想着是参考源的问题，后来试验的时候就变成了分压电阻的问题，有些不太明白的，请教各位大虾了啊。。。。

1万 · 2013-3-5 17:53

#include <msp430f5310.h>

signed int ADC_Result;
void delay(void);
void int_clk()
{
  WDTCTL = WDTPW+WDTHOLD;                //关闭看门狗
  PMAPPWD = 0x02D52;                      // Enable Write-access to modify port mapping registers
  P4MAP7 = PM_MCLK;
  PMAPPWD = 0;                                  // Disable Write-Access to modify port mapping registers
UCSCTL3 |= SELREF_2;                   // Set DCO FLL reference = REFO
  UCSCTL4 |= SELA_2;                      // Set ACLK = REFO

  // Increase Vcore setting to level1 to support fsystem=12MHz
  // NOTE: Change core voltage one level at a time..
  //SetVcoreUp (0x01);

  // Initialize DCO to 12MHz
  __bis_SR_register(SCG0);                // Disable the FLL control loop
  UCSCTL0 = 0x0000;                      // Set lowest possible DCOx, MODx
  UCSCTL1 = DCORSEL_5;                   // Select DCO range 24MHz operation
  UCSCTL2 = FLLD_1 + 374;                // Set DCO Multiplier for 12MHz
                                          // (N + 1) * FLLRef = Fdco
                                          // (374 + 1) * 32768 = 12MHz
                                          // Set FLL Div = fDCOCLK/2
  __bic_SR_register(SCG0);                // Enable the FLL control loop

  // Worst-case settling time for the DCO when the DCO range bits have been
  // changed is n x 32 x 32 x f_MCLK / f_FLL_reference. See UCS chapter in 5xx
  // UG for optimization.
  // 32 x 32 x 12 MHz / 32,768 Hz = 375000 = MCLK cycles for DCO to settle
  __delay_cycles(375000);

  // Loop until XT1,XT2 & DCO fault flag is cleared
  do
  {
UCSCTL7 &= ~(XT2OFFG + XT1LFOFFG + DCOFFG);
                                          // Clear XT2,XT1,DCO fault flags
SFRIFG1 &= ~OFIFG;                   // Clear fault flags
  }while (SFRIFG1&OFIFG);                // Test oscillator fault flag
// UCSCTL4 =0x0233;
}

void main(void)
{
  WDTCTL = WDTPW + WDTHOLD;                // Stop WDT
P1DIR |= BIT0;                         // Set P1.0 to output direction
  int_clk();
  // Configure ADC
  while(REFCTL0 & REFGENBUSY);             // If ref generator busy, WAIT
  REFCTL0 |= REFVSEL_2+REFON;             // Select internal ref = 2.5V
  ADC10CTL0 |= ADC10SHT_2 + ADC10ON;       // ADC10ON, S&H=16 ADC clks
  ADC10CTL1 |= ADC10SHP+ ADC10CONSEQ_0;                   // ADCCLK = MODOSC; sampling timer
  ADC10CTL2 |= ADC10RES; // + ADC10DF    // 10-bit conv result; signed format
  ADC10MCTL0 |= ADC10INCH_0+ADC10SREF_1;    // A0 ADC input select; Vref=AVCC

// ADC10IE |= ADC10IE0;                   // Enable ADC conv complete interrupt
__bis_SR_register(GIE);
  for (;;)
  {
__delay_cycles(5000);
ADC10CTL0 |= ADC10ENC + ADC10SC;       // Sampling and conversion start
//__bis_SR_register(CPUOFF + GIE);       // LPM0, ADC10_ISR will force exit
while (ADC10CTL1 & ADC10BUSY);
ADC_Result = (int)ADC10MEM0;
__no_operation();                      // For debug only
if (ADC_Result  < 0)
   P1OUT &= ~BIT0;                      // Clear P1.0 LED off
else
   P1OUT |= BIT0;                      // Set P1.0 LED on
  }

1万 · 2013-3-5 17:53

void delay(void)
{
  volatile unsigned long i;
  for (i = 0x7FFF; i > 0; i--);
}

// ADC10 interrupt service routine
#pragma vector=ADC10_VECTOR
__interrupt void ADC10_ISR(void)
{
  switch(__even_in_range(ADC10IV,12))
  {
case  0: break;                         // No interrupt
case  2: break;                         // conversion result overflow
case  4: break;                         // conversion time overflow
case  6: break;                         // ADC10HI
case  8: break;                         // ADC10LO
case 10: break;                         // ADC10IN
case 12: ADC_Result = (int)ADC10MEM0;
//          __bic_SR_register_on_exit(CPUOFF);
         break;                         // Clear CPUOFF bit from 0(SR)
default: break;
  }
}