CONFIGURATION OF ADC CHANNEL IN STELLARIS EK-LM4F120XL DEVELOPMENT BOARD

GEORGE DAVIS C said:

i also give same input to channel 0 (PE3 pin)

Perhaps because, "ADCSequenceStepConfigure(ADC0_BASE, 3, 0,ADC_CTL_CH10 | ADC_CTL_IE | ADC_CTL_END);" is not channel 0 !  (we helpers must work w/the data you provide...)

Devil in the details...  (should your post be typed in error - check that suspect ADC channel is not one of the 2 pins "cross connected" - your board.  Schematic will reveal)

Use of full-scale input level (3V3) is not, "best practice."  Suggest instead 10%, 50%, 90% (of full scale 3V3) as a better input level.  Use of such "in range" levels will prove more meaningful & useful...

Thank you for your response and guidance.

clarifications of the above question

  code mentioned was  "ADCSequenceStepConfigure(ADC0_BASE, 3, 0,ADC_CTL_CH11 | ADC_CTL_IE | ADC_CTL_END);"

Didn't selected channel 0 at all, even then while giving i/p to it, it is responding,expecting it to not to respond.

I  tested all the 12 channels like this.In most of the channels, found channel 0 responding like this.

Is channel 0(PE3 PIN) is enabled by default?  While channel 0 is selected it shows correct reading 4095 for 3.3V and very low value when shorting to ground.

I will definitely check this by giving different i/p levels.

Couldn't able to find PE3 & PB5 pins cross connected in the schematics(spmu289a)

Could you please give further help, it will be grateful.

Have neither that board nor recent read - that MCU's data.

Perhaps brief posting of your ADC code - especially set-up & config. of ADC - will aid. 

Usually - the GPIO chapter of MCU manual details any "special handling" of GPIO Ports/Pins.  I cannot recall PE3 nor PB5 falling under that category - but ours is different MCU (still Stellaris) M4.

I do note that PE3 & PE2 - on our Stellaris M4 - are reasonably unique in that they include no, "alternate functions."  (thus they may serve as GPIO or ADC - only)

Always wise to check that unexpected/unwanted "other signal routings" do not "spoil" your ADC inputs.  Appears that you've checked for GPIO "loop-back" - but I'd carefully review schematic (and board) on any "misbehaved" channel.   Fact that most channels perform to expectation - points to your proper set-up/config - however a single misplaced parameter may wreak havoc...

Brief (only ADC essentials) code post seems worthwhile...  (you may copy the relevant ADC set-up/config code first into Notepad - subsequent "paste" here will then display nicely.)

hai

ADC code used is given below

#include "inc/hw_memmap.h"
#include "inc/hw_types.h"
#include "driverlib/adc.h"
#include "driverlib/gpio.h"
#include "driverlib/sysctl.h"
#include "utils/uartstdio.h"

void
InitConsole(void)
{
//

SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);

GPIOPinConfigure(GPIO_PA0_U0RX);
GPIOPinConfigure(GPIO_PA1_U0TX);

//

//
GPIOPinTypeUART(GPIO_PORTA_BASE, GPIO_PIN_0 | GPIO_PIN_1);

//

//
UARTStdioInit(0);
}

int
main(void)
{
//

unsigned long ulADC0_Value[1];

SysCtlClockSet(SYSCTL_SYSDIV_10| SYSCTL_USE_PLL| SYSCTL_OSC_MAIN |
SYSCTL_XTAL_16MHZ);

//

//
InitConsole();

//

//
UARTprintf("ADC ->\n");
UARTprintf(" Type: Single Ended\n");
UARTprintf(" Samples: One\n");
UARTprintf(" Update Rate: 250ms\n");
UARTprintf(" Input Pin: AIN0/PE7\n\n");


//
SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);

SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOB);

GPIOPinTypeADC(GPIO_PORTB_BASE, GPIO_PIN_5);

ADCSequenceConfigure(ADC0_BASE, 3, ADC_TRIGGER_PROCESSOR, 0);

ADCSequenceStepConfigure(ADC0_BASE, 3, 0,ADC_CTL_CH11 | ADC_CTL_IE |
ADC_CTL_END);

//
ADCSequenceEnable(ADC0_BASE, 3);

//
ADCIntClear(ADC0_BASE, 3);

while(1)
{
//

ADCProcessorTrigger(ADC0_BASE, 3);

//

//
while(!ADCIntStatus(ADC0_BASE, 3, false))
{
}

ADCIntClear(ADC0_BASE, 3);

//

ADCSequenceDataGet(ADC0_BASE, 3, ulADC0_Value);


UARTprintf("AIN0 = %4d\r", ulADC0_Value[0]);

SysCtlDelay(SysCtlClockGet() / 12);
}
}

I find nothing seriously wrong with code listed.  Would be safer to:

ADCSequenceDisable(ADC0_BASE, 3);  prior to...

ADCSequenceConfigure(ADC0_BASE, 3, ADC_TRIGGER_PROCESSOR, 0);

And you UARTprintf "AIN0" - when PB5 is - and remains - ADC_CTL_CH11.  While sloppy - should not impact your code.

Is it possible - or likely - that you provided an input signal beyond the 3V3 rating of this single, problematic ADC channel?

I HAVE GIVEN I/P SIGNAL OF 5.2V(VBUS+) FROM THE BOARD TO ALL CHANNELS, BUT CHANNEL 0 ONLY RESPONDED LIKE THIS.

NO SIGNAL GREATER THAN 5.2 V GIVEN.

Hi,

Before doing something with unwanted consequences it is recommended to read, understand and memorize at least the electrical characteristics - for ADC it is mandatory the input is less than VDDA (3.3V on your board). Although the ADC input has some internal circuitry to protect it against over/under-voltages, it is recommended to use a small .5...1k resistor in series with the ADC pin, just to protect the micro (at least in testing phase -  did you done such thing?).

Please follow cb1 advise to  apply a much smaller voltage - use a potentiometer - the code looks OK - maybe what I suggest is to add this line

ADCReferenceSet(ADC0_BASE, ADC_REF_EXT_3V);

Your micro starts with external reference set - but it is wise to check the ADCCTL register to see that - anyway this line will not harm.

Petrei