我很难让ADC与我的设备配合使用。我正在使用dsPIC33FJ128GP802并试图通过手动采样和转换开始慢速。
我的代码发布在下面，我已经设置了ADC的每个寄存器，然后尝试仅采样一次以获得来自我附加的传感器的电压。我应该看到的值约为0.7V，但我得到的是-17408（10111100 00000000）。这可能会达到-2000左右，但首先不应该是负值。
#include <p33Fxxxx.h>
_FOSCSEL(FNOSC_FRCPLL) // select internal 7.37MHz osc with PPL
_FOSC(OSCIOFNC_OFF & POSCMD_XT) // no clock output, external OSC disabled
_FWDT(FWDTEN_OFF) // disable the watchdog timer
_FPOR(FPWRT_PWR1) // Turn off the power-up timers.
int ADCValue;
void DELAY(unsigned ms) {
unsigned j;
unsigned i;
for (j = 0; j < ms; j++) {
for (i = 0; i < 0x1F40; i++);
}
}
int main(void) {
// set up clock to 80MHz
PLLFBD = 41; // sets M = 41+2 = 43
CLKDIVbits.PLLPRE = 0; // sets N1 = 2
CLKDIVbits.PLLPOST = 0; // sets N2 = 2
while (!OSCCONbits.LOCK); // wait for PLL ready
AD1CON1 = 0; // set everything to zero to start with.
AD1CON1bits.ADON = 0; // turn ADC off.
AD1CON1bits.ADSIDL = 0; // continue module operation in idle mode.
AD1CON1bits.ADDMABM = 1; // DMA buffers are written in the order of conversion.
AD1CON1bits.AD12B = 0; // set to 10bit mode.
AD1CON1bits.FORM = 3; // set data output to signed fractional.
AD1CON1bits.SSRC = 0; // manual conversion. clearing sample bit manually.
AD1CON1bits.SIMSAM = 1; // collect samples from channels 0, 1, 2, 3 simultaneously.
AD1CON1bits.ASAM = 0; // manual sample. samples when SAMP bit is set.
AD1CON1bits.SAMP = 0; // sample enable bit.
AD1CON1bits.DONE = 0; // ADC conversion status bit.
AD1CON2 = 0; // set everything to zero to start with.
AD1CON2bits.VCFG = 0; // converter voltage ref. set to AVdd and AVss.
AD1CON2bits.CSCNA = 0; // input scan select bit. set to do not scan.
AD1CON2bits.CHPS = 0; // channel select bits. set to just channel 0;
AD1CON2bits.BUFS = 0; // buffer fill status (invalid as BUFM is 0);
AD1CON2bits.SMPI = 0; // ADC interrupt is generated after every sample/conversion.
AD1CON2bits.BUFM = 0; // buffer fill mode. set to always start filling from start address.
AD1CON2bits.ALTS = 0; // Alternate input sample mode. set to always uses channel input from sample A.
AD1CON3 = 0; // set everything to zero to start with.
AD1CON3bits.ADRC = 0; // ADC conversion clock derived from system clock.
AD1CON3bits.SAMC = 0; // auto sample time bits, TAD, set to 0.
AD1CON3bits.ADCS = 0; // ADC conversion clock set to 0. 1 * TCY = TAD.
AD1CON4 = 0; // set everything to zero to start with.
AD1CON4bits.DMABL = 0; // allocates 1 word of buffer to each analogue input.
AD1CHS123 = 0; // everything set to zero as not using channels 1, 2, or 3.
AD1CHS0 = 0; // set everything to zero to start with.
AD1CHS0bits.CH0NB = 0; // channel 0 negative input, set by CH0NA. sample B.
AD1CHS0bits.CH0SB = 0; // channel 0 positive input, set by CH0SA. sample B.
AD1CHS0bits.CH0NA = 0; // channel 0 negative input, for sample A. set to VREFL.
AD1CHS0bits.CH0SA = 0; // channel 0 positive input is AN0.
AD1CSSL = 0; // input scan register set to zero as not using it.
AD1PCFGL = 0; // port configuration, set to analogue mode, ADC samples voltage.
AD1CON1bits.ADON = 1; // turn on ADC
AD1CON1bits.SAMP = 1; // Start sampling
DELAY(1); // Wait for sampling time (1ms)
AD1CON1bits.SAMP = 0; // Start the conversion
while (!AD1CON1bits.DONE); // Wait for the conversion to complete
ADCValue = ADC1BUF0; // Read the conversion result
while (1);
}
我使用PIC正在使用的相同轨道为传感器供电，并且我将传感器的输出连接到AN0（引脚2），因为我在代码中设置了它。 PIC通过标准Vss和Vdd（引脚8和13），模拟电源引脚AVdd和AVss（引脚28和27）以及Vcap和Vss（引脚20和19）上的33uF电容供电。还有什么我需要做硬件方面的事情吗？我对AD1CHS0bits.CH0NA寄存器有点困惑，因为我不知道是否必须将地连接到VREFL或在该实例中做什么。
对于我应该采取的纠正这个问题的任何帮助都将非常感谢！此外，任何正确接收后如何转换价值的帮助都会非常有用。
答案 0 :(得分：1)
如果该值不应为负值，则不应使用此设置：
AD1CON1bits.FORM = 3; // set data output to signed fractional.
我希望你的价值是（用Python评估）：
int((2**10) * # 10-bit operation
(0.7/3.3) # 0.7 volts on a 3.3 volt system
- (2**9) # Center at VDD / 2 because of signed operation
) << 6 # Fractional output left-shifted the 10-bit up by 6 to fill 16-bits
= -18816
关于您的代码输出的内容。
改为使用：
AD1CON1bits.FORM = 0; // set data output to integer.
使用此设置以及10位模式，我希望您的值为
int((2**10) * # 10-bit operation
(0.7/3.3)) # 0.7 volts on a 3.3 volt system
= 217