AM335x ADC question

Hi,

Your understanding is correct i.e. AIN terminal is analog input pin where one can connect a analog signal and process its digital output using ADC.

In the StarterWare example no external analog signal is connected to AIN terminal but the transistors connected to the AIN lines are pulled up/down and the corresponding voltage is measured. The transistors are required for touchscreen functionality. This was done since there was no dedicated analog signal connected to the AIN pins of the board.

AIN pin can be configured to not drive the voltage by disabling the transistors. 

Regards,

Jeethan

Hi, Jeethan

Thank you for your reply.

I have been to disable the transistor(Touch_Screen_Enable = 0), but AIN pin has low-voltage drive.

   - AIN0 is 400mV

   - AIN1 is 200mV

Of course I was removed the touch panel on AM335xSK.

Do I have to also set other registers?

Best Regards,

Chi

Hi,

Can you please check by disabling the values for XPPSW, XNNSW, YPPSW, YNNSW, XNPSW, YPNSW, WPNSW present in the STEPCONFIG register?

Regards,

Jeethan

Hi,  Jeethan

I checked by disabling these registers that you have pointed out.

Please check the following code.

~~~~

/* ADC is configured */

static void ADCConfigure(void)

{    

/* Enable the clock for touch screen */    

    TSCADCModuleClkConfig();

    TSCADCPinMuxSetUp();

    /* Configures ADC to 3Mhz */    

    TSCADCConfigureAFEClock(TSC_ADC_INSTANCE, 24000000, 3000000);

    /* Disable Transistor bias */  // <--- modified    

    TSCADCTSTransistorConfig(TSC_ADC_INSTANCE, TSCADC_TRANSISTOR_DISABLE);  

    TSCADCStepIDTagConfig(TSC_ADC_INSTANCE, 1);

    /* Disable Write Protection of Step Configuration regs*/

    TSCADCStepConfigProtectionDisable(TSC_ADC_INSTANCE);

    /* Configure step 1 for channel 1(AN0)*/

    StepConfigure(0, TSCADC_FIFO_0, TSCADC_POSITIVE_INP_CHANNEL1);

    /* Configure step 2 for channel 2(AN1)*/

    StepConfigure(1, TSCADC_FIFO_1, TSCADC_POSITIVE_INP_CHANNEL2);

    /* General purpose inputs */

    TSCADCTSModeConfig(TSC_ADC_INSTANCE, TSCADC_GENERAL_PURPOSE_MODE);

    /* Enable step 1 */

    TSCADCConfigureStepEnable(TSC_ADC_INSTANCE, 1, 1);

    /* Enable step 2 */

    TSCADCConfigureStepEnable(TSC_ADC_INSTANCE, 2, 1);

    /* Clear the status of all interrupts */

    CleanUpInterrupts();

    /* End of sequence interrupt is enable */

    TSCADCEventInterruptEnable(TSC_ADC_INSTANCE, TSCADC_END_OF_SEQUENCE_INT);

    /* Enable the TSC_ADC_SS module*/

    TSCADCModuleStateSet(TSC_ADC_INSTANCE, TSCADC_MODULE_ENABLE);

}

/* Configures the step */

void StepConfigure(unsigned int stepSel, unsigned int fifo, unsigned int positiveInpChannel)

{    

/* Configure ADC to Single ended operation mode */

    TSCADCTSStepOperationModeControl(TSC_ADC_INSTANCE, TSCADC_SINGLE_ENDED_OPER_MODE, stepSel);

    /* Configure step to select Channel, refernce voltages */

    TSCADCTSStepConfig(TSC_ADC_INSTANCE, stepSel, TSCADC_NEGATIVE_REF_VSSA,                     positiveInpChannel, TSCADC_NEGATIVE_INP_CHANNEL1, TSCADC_POSITIVE_REF_VDDA);

    /* XPPSW Pin is off, Which pull up the AN0 line*/ // <--- modified

    TSCADCTSStepAnalogSupplyConfig(TSC_ADC_INSTANCE, TSCADC_XPPSW_PIN_OFF, TSCADC_XNPSW_PIN_OFF, TSCADC_YPPSW_PIN_OFF, stepSel);

    /* XNNSW Pin is off, Which pull down the AN1 line*/ // <--- modified

    TSCADCTSStepAnalogGroundConfig(TSC_ADC_INSTANCE, TSCADC_XNNSW_PIN_OFF, TSCADC_YPNSW_PIN_OFF, TSCADC_YNNSW_PIN_OFF,  TSCADC_WPNSW_PIN_OFF, stepSel);

    /* select fifo 0 or 1*/

    TSCADCTSStepFIFOSelConfig(TSC_ADC_INSTANCE, stepSel, fifo);

    /* Configure ADC to one short mode */

    TSCADCTSStepModeConfig(TSC_ADC_INSTANCE, stepSel, TSCADC_ONE_SHOT_SOFTWARE_ENABLED);

}

~~~~

However, Low voltage is observed.

   - AIN0 is 400mV

   - AIN1 is 200mV

Best regards,

Chi

Hi, Anant

Thank you for your reply.

However, I am a little confused by your answer.

Do we would not be able to use the AN0 to AN4 as genaral ADC input because of this lines are supplied Vref voltage ?

I'll try to make sure about that whether driving low voltage at AN7 and AN8.

Best regards,

H.U

Hi, Anant

I change the questions above.

If AN0 to AN4 have connected as AD converters,
Does some voltage that observed on those line affect the input result of the ADC?

Best regards,
H.U

H.U

Can you provide a register dump when this is happening?

Thanks,

Tyler

Hi, Tyler

I am sorry for the delay in my response.
I  lists the ADC_TSC registers information of the phenomenon during reproduction below.

Best regards,
H.U