TM4C1233E6PM: Incorrect reading on ADC

Hi,

  I try AIN11 on the LaunchPad and I cannot reproduce your result. Why don't you try my code first on a LaunchPad and then on your custom board. I tie PB5 (AIN11) to either GND or 3.3V and I can see the ADC value equal to either 0 or 4095. 

#include <stdbool.h>
#include <stdint.h>
#include "inc/hw_memmap.h"
#include "driverlib/adc.h"
#include "driverlib/gpio.h"
#include "driverlib/pin_map.h"
#include "driverlib/sysctl.h"
#include "driverlib/uart.h"
#include "utils/uartstdio.h"

//*****************************************************************************
//
//! \addtogroup adc_examples_list
//! <h1>Single Ended ADC (single_ended)</h1>
//!
//! This example shows how to setup ADC0 as a single ended input and take a
//! single sample on AIN11/PE3.
//!
//! This example uses the following peripherals and I/O signals.  You must
//! review these and change as needed for your own board:
//! - ADC0 peripheral
//! - GPIO Port E peripheral (for AIN11 pin)
//! - AIN11 - PE3
//!
//! The following UART signals are configured only for displaying console
//! messages for this example.  These are not required for operation of the
//! ADC.
//! - UART0 peripheral
//! - GPIO Port A peripheral (for UART0 pins)
//! - UART0RX - PA0
//! - UART0TX - PA1
//!
//! This example uses the following interrupt handlers.  To use this example
//! in your own application you must add these interrupt handlers to your
//! vector table.
//! - None.
//
//*****************************************************************************

//*****************************************************************************
//
// This function sets up UART0 to be used for a console to display information
// as the example is running.
//
//*****************************************************************************
void
InitConsole(void)
{
    //
    // Enable GPIO port A which is used for UART0 pins.
    // TODO: change this to whichever GPIO port you are using.
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);

    //
    // Configure the pin muxing for UART0 functions on port A0 and A1.
    // This step is not necessary if your part does not support pin muxing.
    // TODO: change this to select the port/pin you are using.
    //
    GPIOPinConfigure(GPIO_PA0_U0RX);
    GPIOPinConfigure(GPIO_PA1_U0TX);

    //
    // Enable UART0 so that we can configure the clock.
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_UART0);

    //
    // Use the internal 16MHz oscillator as the UART clock source.
    //
    UARTClockSourceSet(UART0_BASE, UART_CLOCK_PIOSC);

    //
    // Select the alternate (UART) function for these pins.
    // TODO: change this to select the port/pin you are using.
    //
    GPIOPinTypeUART(GPIO_PORTA_BASE, GPIO_PIN_0 | GPIO_PIN_1);

    //
    // Initialize the UART for console I/O.
    //
    UARTStdioConfig(0, 115200, 16000000);
}

//*****************************************************************************
//
// Configure ADC0 for a single-ended input and a single sample.  Once the
// sample is ready, an interrupt flag will be set.  Using a polling method,
// the data will be read then displayed on the console via UART0.
//
//*****************************************************************************
int
main(void)
{
#if defined(TARGET_IS_TM4C129_RA0) ||                                         \
    defined(TARGET_IS_TM4C129_RA1) ||                                         \
    defined(TARGET_IS_TM4C129_RA2)
    uint32_t ui32SysClock;
#endif

    //
    // This array is used for storing the data read from the ADC FIFO. It
    // must be as large as the FIFO for the sequencer in use.  This example
    // uses sequence 3 which has a FIFO depth of 1.  If another sequence
    // was used with a deeper FIFO, then the array size must be changed.
    //
    uint32_t pui32ADC0Value[1];

    //
    // Set the clocking to run at 20 MHz (200 MHz / 10) using the PLL.  When
    // using the ADC, you must either use the PLL or supply a 16 MHz clock
    // source.
    // TODO: The SYSCTL_XTAL_ value must be changed to match the value of the
    // crystal on your board.
    //
#if defined(TARGET_IS_TM4C129_RA0) ||                                         \
    defined(TARGET_IS_TM4C129_RA1) ||                                         \
    defined(TARGET_IS_TM4C129_RA2)
    //
    // Note: SYSCTL_CFG_VCO_240 is a new setting provided in TivaWare 2.2.x and
    // later to better reflect the actual VCO speed due to SYSCTL#22.
    //
    ui32SysClock = SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ |
                                       SYSCTL_OSC_MAIN |
                                       SYSCTL_USE_PLL |
                                       SYSCTL_CFG_VCO_240), 20000000);
#else
    SysCtlClockSet(SYSCTL_SYSDIV_10 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN |
                   SYSCTL_XTAL_16MHZ);
#endif

    //
    // Set up the serial console to use for displaying messages.  This is
    // just for this example program and is not needed for ADC operation.
    //
    InitConsole();

    //
    // Display the setup on the console.
    //
    UARTprintf("ADC ->\n");
    UARTprintf("  Type: Single Ended\n");
    UARTprintf("  Samples: One\n");
    UARTprintf("  Update Rate: 250ms\n");
    UARTprintf("  Input Pin: AIN11/PE3\n\n");

    //
    // The ADC0 peripheral must be enabled for use.
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);

    //
    // For this example ADC0 is used with AIN11 on port B5.
    // The actual port and pins used may be different on your part, consult
    // the data sheet for more information.  GPIO port E needs to be enabled
    // so these pins can be used.
    // TODO: change this to whichever GPIO port you are using.
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOB);

    //
    // Select the analog ADC function for these pins.
    // Consult the data sheet to see which functions are allocated per pin.
    // TODO: change this to select the port/pin you are using.
    //
    GPIOPinTypeADC(GPIO_PORTB_BASE, GPIO_PIN_5);

    //
    // Enable sample sequence 3 with a processor signal trigger.  Sequence 3
    // will do a single sample when the processor sends a signal to start the
    // conversion.  Each ADC module has 4 programmable sequences, sequence 0
    // to sequence 3.  This example is arbitrarily using sequence 3.
    //
    ADCSequenceConfigure(ADC0_BASE, 3, ADC_TRIGGER_PROCESSOR, 0);

    //
    // Configure step 0 on sequence 3.  Sample channel 0 (ADC_CTL_CH0) in
    // single-ended mode (default) and configure the interrupt flag
    // (ADC_CTL_IE) to be set when the sample is done.  Tell the ADC logic
    // that this is the last conversion on sequence 3 (ADC_CTL_END).  Sequence
    // 3 has only one programmable step.  Sequence 1 and 2 have 4 steps, and
    // sequence 0 has 8 programmable steps.  Since we are only doing a single
    // conversion using sequence 3 we will only configure step 0.  For more
    // information on the ADC sequences and steps, reference the datasheet.
    //
    ADCSequenceStepConfigure(ADC0_BASE, 3, 0, ADC_CTL_CH11 | ADC_CTL_IE |
                             ADC_CTL_END);

    //
    // Since sample sequence 3 is now configured, it must be enabled.
    //
    ADCSequenceEnable(ADC0_BASE, 3);

    //
    // Clear the interrupt status flag.  This is done to make sure the
    // interrupt flag is cleared before we sample.
    //
    ADCIntClear(ADC0_BASE, 3);

    //
    // Sample AIN11 forever.  Display the value on the console.
    //
    while(1)
    {
        //
        // Trigger the ADC conversion.
        //
        ADCProcessorTrigger(ADC0_BASE, 3);

        //
        // Wait for conversion to be completed.
        //
        while(!ADCIntStatus(ADC0_BASE, 3, false))
        {
        }

        //
        // Clear the ADC interrupt flag.
        //
        ADCIntClear(ADC0_BASE, 3);

        //
        // Read ADC Value.
        //
        ADCSequenceDataGet(ADC0_BASE, 3, pui32ADC0Value);

        //
        // Display the AIN11 (PE3) digital value on the console.
        //
        UARTprintf("AIN11 = %4d\r", pui32ADC0Value[0]);

        //
        // This function provides a means of generating a constant length
        // delay.  The function delay (in cycles) = 3 * parameter.  Delay
        // 250ms arbitrarily.
        //
#if defined(TARGET_IS_TM4C129_RA0) ||                                         \
    defined(TARGET_IS_TM4C129_RA1) ||                                         \
    defined(TARGET_IS_TM4C129_RA2)
        SysCtlDelay(ui32SysClock / 12);
#else
        SysCtlDelay(SysCtlClockGet() / 12);
#endif
    }
}