可能使用内部带隙电压基准作为ADC正电压基准吗？

你好，还没有解决问题的办法，但有一个想法：1。配置ADC参考电压为AVdd。2。将ADC输入通道配置为Vbg（内部带隙基准电压源）并测量它。比我独立于AVDD振荡，可以安全地测量。但是现在面对VBG错误测量的问题，用AVdd（AVDD＝3.6V）的参考电压和12位模式I测量VBG并获得2416，当3.6V为4095时。这意味着VBG＝2.12V，我认为这是不对的吗？我认为VBG＝1.2V或1.8V，对吗？PIC18F8J94ADC文档似乎没有完全描述。请给我一些引导线。



      以下为原文

       Hello, still have not a solution to the problem but have an idea :)
 
   1. Configure the ADC reference voltage to be AVdd.
   2. Configure the ADC input channel to be Vbg (The internal band gap voltage reference) and measure it. Than I am independent from the AVdd oscillations and can measure safely. But now face the problem with wrong measurement of Vbg.
 
With reference voltage taken from AVdd (AVdd = 3.6V) and 12 bit mode I measure the Vbg and get 2416, when 3.6V is 4095. This means that Vbg = 2.12V which I suppose is not correct? I think that Vbg=1.2V or 1.8V, am I right?
 
   The PIC18F85J94 ADC documentation seems not fully described. Please, give me some guide lines.
 
#include
#include

#include "../inc/main.h"

#define ADC_T 500UL // The period of the A/D conversion clock in nano seconds.
#define ADCS_VALUE (ADC_T * F_OSC / 1000 / 2 - 1) // From the device data-sheet, equation 22-1.

// Configure the MUX A positive channel only.
#define ADC_CONF_MUXA(value) (ADCHS0Lbits.CH0SA = value)

typedef enum
{ // Describe the available options for the MUX A positive input.
    // ADC_MUXA_CHANNEL_VDD_CORE = 0b,
    ADC_MUXA_CHANNEL_AVDD = 0b11110, // The voltage present on the AVdd pin.
    ADC_MUXA_CHANNEL_VBG = 0b11100, // The internal precision voltage reference.
    ADC_MUXA_CHANNEL_AN7 = 0b00111, // AN7 - the ADC input to measure the battery voltage.
} adc_muxa_channel_t;

void adc_init(void)
{
    ADCON1Hbits.ADON = 0; // If previously was ON, because at some kind of resets the register is not cleared!
    ADCON1Hbits.FORM = 0b00; // Absolute decimal result, unsigned, right-justified.
    ADCON1Hbits.MODE12 = 1; // 12 bits conversion mode select.
    
    ADCON1Lbits.ASAM = 0; // Sampling begins when SAMP bit is manually set.
    ADCON1Lbits.SAMP = 0; // A/D Sample-and-Hold amplifiers are holding.
    // The SAMP bit is cleared after SAMC<4:0> number of TAD clocks following the SAMP bit being set (Auto-Convert mode)
    ADCON1Lbits.SSRC = 0b0111;

    // Select the AVdd pin for positive voltage reference and AVss for negative voltage reference.
    // Inputs are not scanned.
    ADCON2H = 0x00;
    
    // Always uses channel input selects for Sample A.
    // The conversion results will always be written to the ADCBUF0 because SMPI<4:0> = 0.
    ADCON2L = 0x00;

    ADCON3Hbits.ADRC = 0; // A/D Conversion Clock Source is the system clock.
    ADCON3Hbits.SAMC = 0b11111; // After 31 * Tad, the sampling is stopped and conversion begins automatically.

    ADCON3Lbits.ADCS = ADCS_VALUE; // Set the prescaler for appropriate ADC period clock.

    ADC_CONF_MUXA(ADC_MUXA_CHANNEL_VBG); // Initially measure the band gap reference voltage.
    
    ANCFGbits.VBGEN = 1; // Reference voltage on.
    
    while (!HLVDCONbits.BGVST)
        ;
    
    ADCON1Hbits.ADON = 1; // Enable the module.
}

uint16_t adc_measure()
{
    ADCON1Lbits.SAMP = 1; // Start the ADC sampling process. The conversion is started automatically after.
    
    while (!ADCON1Lbits.DONE)
        ;
    
    return ADCBUF0;
}