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PIC16F1773的DA问题

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bingol_jxy|  楼主 | 2018-4-2 15:35 | 显示全部楼层 |阅读模式
用PIC16F1773实现DA时,参考电压选择的是VDD和VSS,即5V和0V,实际出来的值在2.5V和3.78V之间。这是为什么?
DA初始化如下:
   //OE1: DAC Voltage Output Enable bit
    //1 = DACx voltage level is also an output on the DACxOUT1 pin
    //0 = DACx voltage level is disconnected from the DACxOUT1 pin
    DAC1CON0bits.OE1 = 1;

    //OE2: DAC Voltage Output Enable bit
    //1 = DACx voltage level is also an output on the DACxOUT2 pin
    //0 = DACx voltage level is disconnected from the DACxOUT2 pin
    DAC1CON0bits.OE2 = 0;

    //PSS<1:0>: DAC Positive Source Select bits
    //11 = Reserved. Do not use.
    //10 = FVR_buffer2
    //01 =VREF+ pin
    //00 =VDD
    DAC1CON0bits.PSS = 0b00;

    //NSS<1:0>: DAC Negative Source Select bit
    //1 = VREF-
    //0 =VSS
    DAC1CON0bits.NSS = 0b0;
   
    DAC1CON1 = 0;
    DAC1CON0bits.EN = 1; //DAC1 enable,RA2

在1毫米中断执行:
   u8 temp = 255;

    DAC1CON1 = temp;

    DACLDbits.DAC1LD = 1;


结果:
temp=0,da输出2.5V
temp=255.da输出3.78V

为什么不是0~5V?
bingol_jxy|  楼主 | 2018-4-2 15:51 | 显示全部楼层
请高手指教

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