问 相关的函数是这样写的：
void init_adc(void)
{
// ADC12 Initialization
//+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
P6SEL = 0x1F;
ADC12CTL0 &=~ ENC; ADC12CTL0 = ADC12ON + MSC + REFON + REF2_5V + SHT0_0;
ADC12CTL1 = SHP + ADC12SSEL_2 + CONSEQ_0;
ADC12MCTL0 = INCH_1 + SREF_0 + EOS;

ADC12CTL0 |= ENC; // Enable conversion
//+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
}


void con_adc_data(void)
{
// Sampling and conversion;
ADC12CTL0 |= ADC12SC; // Sampling open;
ADC12CTL0 &= ~ADC12SC; // Sampling closed, start conversion;

while((ADC12CTL1 & ADC12BUSY) == 1) // Check up if the adc is busy;
{
_NOP();
}
}
//*************************************************************************************
// Adc data transmitting functions by USB port;
//*************************************************************************************

void adc_data_trans(unsigned int length)
{
unsigned int i = 0x00;
unsigned int j = 0x00;
for(j=0; j<length; j++)
{
for(i=0; i<0x08; i++)
{
con_adc_data();
EpBuf[i*8+0] = (ADC12MEM0 & 0x00FF);
EpBuf[i*8+1] = (ADC12MEM0 & 0x0F00) >> 8;
EpBuf[i*8+2] = (ADC12MEM1 & 0x00FF);
EpBuf[i*8+3] = (ADC12MEM1 & 0x0F00) >> 8;
EpBuf[i*8+4] = (ADC12MEM2 & 0x00FF);
EpBuf[i*8+5] = (ADC12MEM2 & 0x0F00) >> 8;
EpBuf[i*8+6] = (ADC12MEM3 & 0x00FF);
EpBuf[i*8+7] = (ADC12MEM3 & 0x0F00) >> 8;
}
D12_WriteEndpoint(0x05, 0x40, EpBuf);
}
}

我用它来对一个40Hz的正弦波采样，结果得到这样的结果：
附图：
请问这可能是什么原因？
谢谢！