S32K142_AD

hanchengyu — Wed, 22 May 2019 09:50:10 GMT

I am using the AD function of S32k142,start AD function every 50us,and collect 5 channels every time.Now, I find that the voltage of the port being collected will be pulled down.

Inside the red box,The high level voltage is pulled down to 4.1v,Under normal circumstances, the high level voltage should be 4.8v.I want to know why the voltage is pulled down and how to solve this problem.

The code：

void ADC_init(void)
{
PCC->PCCn[PCC_ADC0_INDEX] &=~ PCC_PCCn_CGC_MASK; /* Disable clock to change PCS */
PCC->PCCn[PCC_ADC0_INDEX] |= PCC_PCCn_PCS(1); /* PCS=1: Select SOSCDIV2 */
PCC->PCCn[PCC_ADC0_INDEX] |= PCC_PCCn_CGC_MASK; /* Enable bus clock in ADC */

ADC0->SC1[0] |= ADC_SC1_ADCH_MASK; /* ADCH=1F: Module is disabled for conversions */
/* AIEN=0: Interrupts are disabled */
ADC0->CFG1 |= ADC_CFG1_ADIV_MASK
|ADC_CFG1_MODE(1); /* ADICLK=0: Input clk=ALTCLK1=SOSCDIV2 */
/* ADIV=0: Prescaler=1 */
/* MODE=1: 12-bit conversion */

ADC0->CFG2 = ADC_CFG2_SMPLTS(12); /* SMPLTS=12(default): sample time is 13 ADC clks */
ADC0->SC2 = 0x00000000; /* ADTRG=0: SW trigger */
/* ACFE,ACFGT,ACREN=0: Compare func disabled */
/* DMAEN=0: DMA disabled */
/* REFSEL=0: Voltage reference pins= VREFH, VREEFL */
ADC0->SC3 = 0x00000000; /* CAL=0: Do not start calibration sequence */
/* ADCO=0: One conversion performed */
/* AVGE,AVGS=0: HW average function disabled */
}

void adc_test()
{
ADC0->SC1[0]&=~ADC_SC1_ADCH_MASK; /* Clear prior ADCH bits */
ADC0->SC1[0] = ADC_SC1_ADCH(9); /* Initiate Conversion */
while(((ADC0->SC1[0] & ADC_SC1_COCO_MASK)>>ADC_SC1_COCO_SHIFT)==0){}
adc_result=ADC0->R[0];

ADC0->SC1[0]&=~ADC_SC1_ADCH_MASK; /* Clear prior ADCH bits */
ADC0->SC1[0] = ADC_SC1_ADCH(8); /* Initiate Conversion */
while(((ADC0->SC1[0] & ADC_SC1_COCO_MASK)>>ADC_SC1_COCO_SHIFT)==0){}
adc_result=ADC0->R[0];

ADC0->SC1[0]&=~ADC_SC1_ADCH_MASK; /* Clear prior ADCH bits */
ADC0->SC1[0] = ADC_SC1_ADCH(0x0A); /* Initiate Conversion */
while(((ADC0->SC1[0] & ADC_SC1_COCO_MASK)>>ADC_SC1_COCO_SHIFT)==0){}
adc_result=ADC0->R[0];

ADC0->SC1[0]&=~ADC_SC1_ADCH_MASK; /* Clear prior ADCH bits */
ADC0->SC1[0] = ADC_SC1_ADCH(0x0C); /* Initiate Conversion */
while(((ADC0->SC1[0] & ADC_SC1_COCO_MASK)>>ADC_SC1_COCO_SHIFT)==0){}
adc_result=ADC0->R[0];

ADC0->SC1[0]&=~ADC_SC1_ADCH_MASK; /* Clear prior ADCH bits */
ADC0->SC1[0] = ADC_SC1_ADCH(0x0B); /* Initiate Conversion */
while(((ADC0->SC1[0] & ADC_SC1_COCO_MASK)>>ADC_SC1_COCO_SHIFT)==0){}
adc_result=ADC0->R[0];
}

Re: S32K142_AD

danielmartynek — Tue, 28 May 2019 10:15:36 GMT

Hi,

What is the source resistance of the measured signal?

Please see Section 6.4.1 ADC electrical specifications in the S32K1xx Datasheet rev.9.

And AN12217, S32K1xx ADC guidelines, spec and configuration, Section 2.2. Sources of error in ADC measurements

Thanks,

BR, Daniel

S32KのトピックS32K142_AD

S32K142_AD

Re: S32K142_AD