#include "msp430x22x4.h"
//OA0工作在模式2(unity gain)
//p2.0為正端輸入
//p2.1輸出(最大輸AVCC)
//將輸入電壓的地接到芯片的AVss
//用OAFBR來選擇反饋電阻值
//將直流電源正端接入p2.0,調節電壓值,觀參輸出是否跟輸入保持一致
//                 MSP430F2274
//             -----------------
//         /|\|              XIN|-  
//          | |                 |
//          --|RST          XOUT|-
//            |                 |
//            |             P2.0|<--OA0I0
//            |             AVss|<--GND
//            |             p2.1|-->OA0O     
int main( void )
{
  WDTCTL=WDTPW+WDTHOLD;                   //關看門狗
  BCSCTL1 =CALBC1_1MHZ;                   //設定DCO為1MHZ
  DCOCTL =CALBC1_1MHZ;
  P2SEL |=BIT0+BIT1;                      //P2.0,2.1第二功能選擇
  P2OUT |=BIT1;                           //p2.1,OA0輸出端(不加也沒關系)                         
  
  OA0CTL0=OAP_0+OAPM_3+OAADC1;            //OAP選擇OA0I0輸入,反饋速度為fast,輸出為A1,A3或者A5
  OA0CTL1=OAFBR_1+OAFC_2;                 //R2/R1=4R/16R,反饋電阻為4R
  //OA0CTL1=OAFBR_2+OAFC_2;               //R2/R1=8R/8R,反饋電阻為8R
  //OA0CTL1=OAFBR_3+OAFC_2;               //R2/R1=10R/6R,反饋電阻為10R
  //OA0CTL1=OAFBR_4+OAFC_2;               //R2/R1=12R/4R,反饋電阻為12R
  //OA0CTL1=OAFBR_5+OAFC_2;               //R2/R1=13R/3R,反饋電阻為13R
  //OA0CTL1=OAFBR_6+OAFC_2;               //R2/R1=14R/2R,反饋電阻為14R
  //OA0CTL1=OAFBR_7+OAFC_2;               //R2/R1=15R/1R,反饋電阻為15R
  _NOP();
  _BIS_SR(LPM3_bits);                     //進入低功耗3   
  _NOP();
  return 0;  
}