ADC

vinkar — Fri, 18 Jul 2014 16:49:23 GMT

Hello ,

I am using the KL04 (24 pin package). The issue I am having is with the ADC of this chip. I am driving a motor and trying to measure the BEMF. The issue is with the ADC read of the BEMF. The voltage supplied is 8.5V. The VEFHH and VREFL are connected to the Vcc and GND in the 24 pin package. Also I have a LPF of 3K and 10K. So, effectively, the 8.5V is stepped down to 1.96V.

So, VREFH = 3.3V and hence-forth for 10bit ADC will show 3FF for 3.3V. Which implies for 1.96V I shld get 260(hex). but end up getting 118. I don't think I am having too much impedance loaded up in my pi. The schematic is shown below

The code for ADC initialisation and read is as shown below -

static void adcInit(void){

uint8_t roughReg;

uint16_t varRough;

uint8_t calibStatus;

SIM_SCGC6 |= SIM_SCGC6_ADC0_MASK;

ADC0_SC1A = 0;

ADC0_SC1A |= 0x80;

adcConfig();

calibStatus = adcCalib();

if(calibStatus == 1){ // calibration successful //

varRough =(ADC0_CLP0+ADC0_CLP1+ADC0_CLP2+ADC0_CLP3+ADC0_CLP4+ADC0_CLPS)/2;

varRough |=0x8000;

ADC0_PG = varRough;

}

else while(1);

adcConfig();

}

static void adcConfig(void){

ADC0_CFG1 |= 8; // 10 bit ADC mode //

//ADC0_CFG1 |= ADC_CFG1_MODE(2);

}

static uint8_t adcCalib(void){

uint16_t varRough;

uint8_t status;

ADC0_SC2 &=~ADC_SC2_ADTRG_MASK;

ADC0_SC3 &= ~ADC_SC3_CAL_MASK;

ADC0_SC3 |= ADC_SC3_CAL_MASK;

while((ADC0_SC1A & 0x00000080) != 0x00000080);

// COCO flag is set //

ADC0_SC1A &= ~ADC_SC1_COCO_MASK;

status = 1;

return(status);

}

and the adc read -

static uint16_t adcRead(uint8_t adcChannel){

switch(adcChannelRead){

case 'W':

PORTB_PCR1 &= ~PORT_PCR_MUX_MASK; // --- W ad

ADC0_SC1A = 0x05;

break;

case 'V':

PORTB_PCR0 &= ~PORT_PCR_MUX_MASK; // --- V adc

ADC0_SC1A = 0x06;

break;

case 'U':

PORTA_PCR7 &= ~PORT_PCR_MUX_MASK; // --- U adc

ADC0_SC1A = 0x07;

break;

default:

asm("nop");

break;

}

//ADC0_SC1A |= 0x07;

while((ADC0_SC1A & 0x00000080) != 0x00000080);

adcDataObt = ADC0_RA;

return(adcDataObt);

}

why is this happening. Am I doing something wrong here.

Re: ADC

RuiFaria — Wed, 15 Apr 2015 14:19:03 GMT

Hi,

You forgot to show adcConfig() function, are you reading always 0xFFFF from the ADC?

I am using KL15 and i am having problems with the ADC.

Do you have some answers or help from FREESCALE support?

Best Regards,

Rui Faria

Re: ADC

vinkar — Wed, 15 Apr 2015 19:47:15 GMT

Hello Rui,

I solved the issue. I can can assist you if you have some issues with your ADC.

R u from Lisbon ?

Vinod

Re: ADC

RuiFaria — Thu, 16 Apr 2015 09:35:11 GMT

Hi,

Thanks for your attention. No, i am from Oporto.

Yesterday, i got different values from ADC but they don't make sense to me yet. I am keep trying to developed a simple unit test with the help of Process Expert.

Process Expert ADC Properties

A/D resolution: 16 bits

Conversion Time: 27 us

Low-power mode: off

High-speed conversion mode: on

Asynchro clock output: off

Sample time: 0 = short

Number of converfsions: 1

Interrupt service/event: off

A/D Channels

0 - ADC0_SE8 - Single Ended

1 - ADC0_SE13 - Single Ended

2 - TempSensor - Single Ended

VREF = 3.284V

...in the inputs i suppose to have these voltages:

ADC CH 0 = 2.579V

ADC CH 1 = 1.638V

...and i read from ADC the following values:

ADC CH 0 0xfbf8

ADC CH 1 0xbcf8

ADC CH 2 0x7df8

Best Regards,

Rui Faria

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