ADC工作不对

你好，我正在尝试使用我的DSIC33 FJ128GP802上的ADC来转换4条输入线。我现在想避免DMA。我已经尽可能地建立了ADC系统，而且我被中断了，但是结果并不如预期。这是我的代码：输入线是AN2-4。我用AD1PCFGL将这些线路设置为ADC输入。我需要做点别的吗？提前感谢。



      以下为原文

    Hi,
I am trying to use the ADC on my DSPIC33FJ128GP802 to convert 4 input lines. I am trying to avoid DMA for now. I've set up the ADC system as best I can and I am getting interrupts but the results are not as expected. Here is my code:
void init_adc()
{
    AD1CON1bits.FORM = 0; // Data Output Format: integer
    AD1CON1bits.SSRC = 7; // Sample Clock Source: counter starts conversion
    AD1CON1bits.ASAM = 0; // ADC Sample Control: Sampling begins when samp bit is set
    AD1CON1bits.AD12B = 1; // 12-bit ADC operation
    AD1CON1bits.SIMSAM = 0; // Unimplemented in 12 bit mode
    AD1CON2bits.BUFM = 0;
    AD1CON2bits.CHPS = 0; // Converts CH0
    AD1CON3bits.ADRC = 0; // ADC Clock is derived from Systems Clock
    AD1CON3bits.ADCS = 63; // ADC Conversion Clock
    //AD1CHS0: A/D Input Select Register
    adc_chan=2;
    AD1CHS0bits.CH0SA = adc_chan; // Select the channel to convert
    AD1CHS0bits.CH0NA = 0; // MUXA -ve input selection (Vref-) for CH0
    //AD1PCFGL: Port configuration bits
    AD1PCFGL = 0xFFE3; // AN2-4 as analog inputs, rest is digital
   
    IFS0bits.AD1IF = 0; // Clear the A/D interrupt flag bit
    IEC0bits.AD1IE = 1; // Enable A/D interrupt
    AD1CON1bits.ADON = 1; // Turn on the A/D converter

    // start 1st conversion
    AD1CON1bits.DONE=0; // Clear Done Flag
AD1CON1bits.SAMP=1; // Start sampling
}

void __attribute__((__interrupt__, no_auto_psv))_ADC1Interrupt(void)
{
    // Deal the results
    switch(adc_chan) {
        case 2:
            fmRaw = ADC1BUF0;
            break;
        case 3:
            voRaw = ADC1BUF0;
            break;
        case 4:
            ofsRaw = ADC1BUF0;
            break;
    }
   
    // select next channel
    adc_chan+=1;
    if(adc_chan>4) adc_chan=2;
AD1CHS0bits.CH0SA = adc_chan; // Select the channel to convert
    //start next conversion
IFS0bits.AD1IF = 0; // Clear ADC interrupt flag
AD1CON1bits.DONE=0; // Clear Done Flag
AD1CON1bits.SAMP=1; // Start sampling
}
The input lines are AN2-4. I have set up those lines as ADC inputs using AD1PCFGL. Do I need to do something else?

Thanks in advance.