51AD 采样正弦波是一条直线！频率不对？

只看该作者 · 2012-3-19 11:03

上次问的问题关于 f350的采样慢的问题解决了~ 谢谢ayb_ice等几位大神~跟输出字的速度也有关系最近又遇到了新问题
正弦波的周期是20ms！我想把他采样下来，显示波形。但是不管我如何设置采样周期始终是一条直线~最奇怪的是 ad输入引脚如果接电压用滑动变阻器调节  采样的ad或者电压是对的。这是什么原因呢  ？？？
部分程序
#define MDCLK       128000          // Modulator Clock (Hz)

int ADC_Buffered(void)
{

unsigned int i, Sampling_times=1000;
  float average;

      for (i = 0; i < Sampling_times; i++)
      {
      while(!AD0INT);
      AD0INT = 0;
ADC_OutputVal = ADC0H;
      ADC_OutputVal =ADC_OutputVal<< 16;
      ADC_OutputVal += (long)ADC0L + ((long)ADC0M << 8);
      sample_array = ADC_OutputVal;
      }
   for(i=0;i<Sampling_times;i++)
{
   average=(float)sample_array;
average=average/256/256/256;
average=average*VREF;
average=average*2;
average=average;
ADC_VIN= (int)average;
Uart0_Send232(ADC_VIN);
Uart0_SendString("\n");
}
}

ADC_VIN采样出的波形如下

void SYSCLK_Init (void)
{
   unsigned i;
   OSCICN = 0x80;                      // enable intosc
   CLKSEL = 0x00;                      // select intosc as sysclk source
// INTOSC configure
   OSCICN = 0x83;
// PLL configure
   CLKMUL = 0x00;                      // Reset Clock Multiplier
   CLKMUL &= ~0x03;                      // select INTOSC / 2 as PLL source
   CLKMUL |= 0x80;                      // Enable 4x Multipler (MULEN = 1)
   for (i = 0; i < 125; i++);          // Delay for at least 5us
   CLKMUL |= 0xC0;                      // Initialize Multiplier
   while (!(CLKMUL & 0x20));             // Poll for Multiply Ready
// SYSCLK configure
   VDM0CN = 0x80;                      // enable VDD monitor
   RSTSRC = 0x06;                      // enable missing clock detector
                                       // and VDD monitor reset sources
   CLKSEL = 0x02;                      // select PLL as clock source
}
//-----------------------------------------------------------------------------
// PORT_Init
//-----------------------------------------------------------------------------
//
// Configure the Crossbar and GPIO ports.
// P0.4 - TX0 (push-pull)
// P0.5 - RX0
void PORT7_Init (void)
{
   XBR0 |= 0x01;                      // UART0 Selected
   XBR1 |= 0x40;                      // Enable crossbar and weak pull-ups
   P0MDOUT |= 0xD0;                      // TX, LEDs = Push-pull
  P1MDOUT |= 0xFF;
}
//-----------------------------------------------------------------------------
// ADC0_Init extVREF Bipolar AIN0.1-AIN0.0
//-----------------------------------------------------------------------------
//
// This function initializes the ADC to measure across AIN0.1 and AIN0.0
// on the Target Board (Differential measurements, Bipolar codes)
void ADC0_Init (void)
{
   unsigned ADC0_decimation;
   REF0CN &= ~0x01;                      // disable internal vref
   // REF0CN |= 0x01;                      // (enable if using internal vref)

   // ADC0CN = 0x00;                      // unipolar output codes, GAIN=1
ADC0CN = 0x10;                      // Bipolar output codes, GAIN=1
   //ADC0CF = 0x00;                      // interrupts upon SINC3 filter output
                                       // and uses internal VREF
   ADC0CF = 0x04;                      // interrupts upon SINC3 filter output
                                       // and Ê¹ÓÃÍâ²¿VREF

   ADC0CLK = (SYSCLK/MDCLK)-1;    // Ideally, MDCLK = 2.4576 MHz
                                       // Generate MDCLK for modulator.
// program decimation rate for desired OWR
   ADC0_decimation = (unsigned long) SYSCLK/ (unsigned long) OWR /
                  (unsigned long) (ADC0CLK+1)/(unsigned long)128;
   ADC0_decimation--;

   ADC0DEC = ADC0_decimation;
   ADC0BUF = 0x00;                      // ¹Ø±ÕÊäÈë»º³å

   ADC0MUX = 0x0b;
                                       // AIN+ => AIN0.0
      ADC0DAC = 0x00;

      ADC0STA = 0x00;                               // AIN- => AIN0.1


// ADC0MUX = 0x08;
      ADC0MD |= 0x80;                   // Ê¹ÄÜ(IDLE Mode)
}