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目前我们的产品设计中正在使用MSP430F5529这款芯片，使用了其ADC12_a片内外设，实际采样过程中模拟输入A0对应的转换结果是最稳定、可信的，但A14，A15不稳定的概率很大。并不是所有芯片都表现为模拟A14，A15对应的转换结果不正确。A14，A15输入的信号可认为是直流稳压信号。参考samplecodes做了一些修改，在IAR中观察ADC12MEMx中的值。附上修改后的samplecode。
#include <msp430f5529.h>
volatile unsigned int results[16]; // Needs to be global in this example
// Otherwise, the compiler removes it
// because it is not used for anything.
void main(void)
{
WDTCTL = WDTPW+WDTHOLD; // Stop watchdog timer
P6SEL = 0x0F; // Enable A/D channel inputs
P7SEL |= (BIT2+BIT3);
ADC12CTL0 = ADC12ON+ADC12MSC+ADC12SHT0_2+ADC12SHT1_2; // Turn on ADC12, set sampling time
ADC12CTL1 = ADC12SHP+ADC12CONSEQ_1; // Use sampling timer, single sequence
ADC12MCTL0 = ADC12INCH_0; // ref+=AVcc, channel = A0
ADC12MCTL1 = ADC12INCH_1; // ref+=AVcc, channel = A1
ADC12MCTL2 = ADC12INCH_14; // ref+=AVcc, channel = A2
ADC12MCTL3 = ADC12INCH_15+ADC12EOS; // ref+=AVcc, channel = A3, end seq.
ADC12IE = 0x08; // Enable ADC12IFG.3
ADC12CTL0 |= ADC12ENC; // Enable conversions
_EINT();
while(1)
{
ADC12CTL0 |= ADC12SC; // Start convn – software trigger
// __bis_SR_register(LPM4_bits + GIE); // Enter LPM4, Enable interrupts
__no_operation(); // For debugger
}
}
#pragma vector=ADC12_VECTOR
__interrupt void ADC12ISR (void)
{
switch(__even_in_range(ADC12IV,34))
{
case 0: break; // Vector 0: No interrupt
case 2: break; // Vector 2: ADC overflow
case 4: break; // Vector 4: ADC timing overflow
case 6: break; // Vector 6: ADC12IFG0
case 8: break; // Vector 8: ADC12IFG1
case 10: break; // Vector 10: ADC12IFG2
case 12: // Vector 12: ADC12IFG3
results[0] = ADC12MEM0; // Move results, IFG is cleared
results[1] = ADC12MEM1; // Move results, IFG is cleared
results[2] = ADC12MEM2; // Move results, IFG is cleared
results[3] = ADC12MEM3; // Move results, IFG is cleared
// __bic_SR_register_on_exit(LPM4_bits); // Exit active CPU, SET BREAKPOINT HERE
case 14: break; // Vector 14: ADC12IFG4
case 16: break; // Vector 16: ADC12IFG5
case 18: break; // Vector 18: ADC12IFG6
case 20: break; // Vector 20: ADC12IFG7
case 22: break; // Vector 22: ADC12IFG8
case 24: break; // Vector 24: ADC12IFG9
case 26: break; // Vector 26: ADC12IFG10
case 28: break; // Vector 28: ADC12IFG11
case 30: break; // Vector 30: ADC12IFG12
case 32: break; // Vector 32: ADC12IFG13
case 34: break; // Vector 34: ADC12IFG14
default: break; }
}
请问出现上述问题可能原因是什么？
灰小子：
不稳定，是差异有多大？略有波动是正常的。
灰小子：
一般ADC转换完，要进行求平均等操作的。
如果波动比较大，就要查找原因了。
可能的原因：1）电路干扰；2）信号源纹波
Mingjun Xing：
回复 灰小子:
波动很大，AD值呈现随机状，12位的ADC可以出现8000或9000以上的值
Mingjun Xing：
回复 灰小子:
信号源纹波甚至不超过20mV
