ADC setup and use problem on K20 twr board

yvesb — Thu, 20 Mar 2014 13:23:15 GMT

Hi all,

I've been writing a little code to try the ADC with the K20 tower dev board.

it is using ADC0 with pins ADC0_SE6b(PTD5 / 98) & ADC0_SE7b(PTD6 / 99).

I need to read the voltage on each pin as a single ADC input.

here is my init code:

void adc0_init(void)

{

/* enable ADC0 clock */

SIM_SCGC6 |= SIM_SCGC6_ADC0_MASK;

/* set pin as adc input */

PORTD_PCR5 = PORT_PCR_MUX(0); /* ADC0_SE6b */

PORTD_PCR6 = PORT_PCR_MUX(0); /* ADC0_SE7b */

/* init registers */

ADC0_CFG1 = ADLPC_NORMAL

| ADC_CFG1_ADIV(ADIV_1)

| ADLSMP_LONG

| ADC_CFG1_MODE(MODE_8)

| ADC_CFG1_ADICLK(ADICLK_BUS);

ADC0_CFG2 = MUXSEL_ADCB

| ADACKEN_DISABLED

| ADHSC_NORMAL

| ADC_CFG2_ADLSTS(ADLSTS_20);

ADC0_SC2 = ADTRG_SW

| ACFE_DISABLED

| ACFGT_LESS

| ACREN_DISABLED

| DMAEN_DISABLED

| ADC_SC2_REFSEL(REFSEL_EXT);

ADC0_SC3 = CAL_OFF

| ADCO_SINGLE

| AVGE_ENABLED

| ADC_SC3_AVGS(AVGS_32);

ADC0_SC1A = AIEN_OFF

| DIFF_SINGLE

| ADC_SC1_ADCH(31);

ADC0_SC1B = AIEN_OFF

| DIFF_SINGLE

| ADC_SC1_ADCH(31);

}

then my adc read function:

unsigned int adc0_convert(char channel_number)

{

ADC0_SC1A = AIEN_OFF

| DIFF_SINGLE

| ADC_SC1_ADCH(channel_number);

while (!(ADC0_SC1A && ADC_SC1_COCO_MASK));

return ADC0_RA;

}

now I call it from the main:

unsigned int val;

	PORTC_ISFR=0xFFFFFFFF; //Clear ISR flags
	printf("AD conversion start\n");

	val = adc0_convert(6);
	printf("ADC0_SE6b=%6d\n",val);

	val = adc0_convert(7);
	printf("ADC0_SE7b=%6d\n",val);

In order to test it, I set a voltage on pins 98 & 99 of the chip, but I have a problem: voltage on PTD5 seems to be detected in channel AD7b instead of channel AD6b and voltage on PTD6 not really well detected on channel AD6b onstead of channel AD7b.

Have I misunderstood the manual? Am I missing something?

thanks for your help :smileyhappy:

Yves

Re: ADC setup and use problem on K20 twr board

yvesb — Thu, 20 Mar 2014 14:21:31 GMT

oops...

you might have noticed the mistake was here:

while (!(ADC0_SC1A && ADC_SC1_COCO_MASK));

there should be only one &:

while (!(ADC0_SC1A & ADC_SC1_COCO_MASK));

regards :smileyhappy:

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ADC setup and use problem on K20 twr board

Re: ADC setup and use problem on K20 twr board