MSP430之频率测量，误差1Hz

 #include "timerHz.h"
 #include "msp430g2553.h"

 #define _DEBUG_TIMERHZ_

 unsigned int capArray[] = {};
 unsigned char index = , flag = ;
 float hz = ;

 /*
  * 绝对值
  */
 int abs(int x)
 {
     return x>?x:-x;
 }

 /*
  * 系统初始化
  */
 void HZ_Init()
 {
     P1SEL |= BIT1;        //P1.1复用
     P1DIR &= ~BIT1;        //P1.1输入
 //    P1SEL |= BIT2;        //P1.2复用
 //    P1DIR &= ~BIT2;        //P1.2输入

     CCTL0 = CM_1 + SCS + CCIS_0 + CAP + CCIE;             //上升沿捕获,同步,信号源设置,捕获功能,允许捕获中断
     TACTL = TASSEL_2 + MC_2;                        //定时器的时钟源选择SMCLK(16M)，连续计数
 }

 /******************中断服务程序*****************************/
 #pragma vector=TIMER0_A0_VECTOR
 __interrupt void TIME0_A0_ISR(void)
 {
     capArray[index--] = TA0CCR0;
     if(index == )
     {
         index = ;
         TA0CCR0 = ;        // 清零计数器
         flag = ;
     }
 }

 #ifdef _DEBUG_TIMERHZ_
 #include "12864.h"
 #include "sys.h"

 void main()
 {
     double temp = 213.456;
 //    unsigned char i;

     System_Init();
     LCD_Init();
     HZ_Init();

     LCD_Show_String("Measure freq:");
     LCD_Set_Pos(,);
     LCD_Show_Deci(temp);
     LCD_Set_Pos(,);
     LCD_Show_String("Hz");
     LCD_Set_Pos(,);

     _EINT();
     while()
     {
         if (flag == )
         {
 //            for (i = 0; i<=2; i += 2)
 //                temp += abs(capArray[i+1] - capArray[i]);
             temp = abs(capArray[] - capArray[]);
             hz = ((double )())/temp;            //1MHZ,1/1000000s = 1us
             LCD_Set_Pos(,);
             LCD_Show_Deci(hz);        //显示
             flag = ;
         }
     }
 }
 #endif