在18F4680上的A/D转换上遇到奇怪的问题

大家好，我在18F4680上的A/D转换上遇到了一个奇怪的问题：使用xc8 1 34和MPLAP 3.35。他分配给“VAL”，我得到完全不同（错误）的值（0x03FF字节组成）！！我附了一个调试会话的截图。有什么想法吗？提前感谢任何帮助



      以下为原文

    Hello all,
I'm facing a really odd issue on A/D conversion on a 18F4680; using xc8 1.34 and MPLAP 3.35.
This is the code:

void ADC_Init(unsigned char PCFG)
{
    // Setup ADC
    ADCON0 = 0b00000001; // ADON (0): A/D converter is enabled
    ADCON0 |= 0b00000000; // GO_nDONE (1): A/D idle NOTE: he GO/DONE bit should NOT be set in the same instruction that turns on the A/D.
    // ADCON0 CHS(5:2): Analog Channel Select bits - dynamically used

    ADCON1 = PCFG; // PCFG(3:0): A/D Port Configuration Control bits
    ADCON1 |= 0b00000000; // VCFG0(4): V+ ref is AVDD
    ADCON1 |= 0b00000000; // VCFG0(5): V- ref is AVSS

    ADCON2 = 0b00000010; // ADCS (2:0): Fosc/32 (A/D conversion clock for 40MHz)
    ADCON2 |= 0b00010000; // ACQT4 (5:3): TAD (010 = 4 TAD)
    ADCON2 |= 0b10000000; // ADFM (7): Right justified
}

unsigned int ADC_Read(unsigned char channel)
{
    if (channel > 7) // Channel range must be within 0 ~ 7
      return 0;

    ADCON0 &= 0b11000001; // Clear channel selection bits - CHS(5:2) & the GO_nDONE bit
    ADCON0 |= (channel << 3); // Set channel selection bits

    // Since we programmed the Automatic Acquisition Time (ACQT4 in ADC_Init()), we don't need to wait for the capacitor to charge
    //__delay_ms(2); // Acquisition time to charge hold capacitor
    DELAY_mS(2);

    GO_nDONE = 1; // Start the A/D conversion

    while (GO_nDONE); // Wait for conversion to complete

    // test code
BREAKPOINT>>> unsigned int val = (((unsigned int)ADRESH) << 8) + ADRESL;
    return val;
   
    //return (((unsigned int)ADRESH) << 8) + ADRESL; // Return result
}

void main()
{
PIE1 = 0; // Disable TMR1/TMR2/CCP1/MSSP/ESUART txrx/AD/PSP peripheral interrupts
PIE2 = 0; // Disable ECCP1IE/TMR3IE/HLVDIE/BCLIE/EEIE/CMIE/OSCFIE peripheral interrupts
INTCONbits.PEIE = 0; // When RCON.IPEN = 0 disables all Peripheral interrupts
    INTCONbits.GIE = 0; // When RCON.IPEN = 0 disables all Global interrupts

// Setup ADC
    ADC_Init(0b00001010); // PCFG(3:0): AN0->4 = Analog, all other digital

while (1)
{
  DELAY_mS(800);
  unsigned int val = ADC_Read(1);
}
}

The issue is simple: eventhough I can see that ADRESH:ADRESL (0x19:0x36) have correct values (if I set a breakpoint on where I wrote "BREAKPOINT>>>"), when I step trough the assignment to "val", I get completely different (wrong) values (0x03FF after byte composition)!!
I attached a screenshot of a debugging session.

Any ideas on why?

Thanks in advance for any help
Gianni
   Attached Image(s)