[参考译文] TM4C123GH6PM：简单的 ADC 读数

https://e2e.ti.com/support/microcontrollers/arm-based-microcontrollers-group/arm-based-microcontrollers/f/arm-based-microcontrollers-forum/1115436/tm4c123gh6pm-simple-adc-reading

大家好、

我尝试使用 Tiva 芯片上的 PE2来读取模拟输入。  我找到了下面的示例、并尝试对其进行编辑以读取该端口、但我只得到大约287的值。

奇怪的是、无论输入电压是多少、读入的第一个值的值仍然为+/- 3。  但是、如果我复位程序、我会看到大约20个跳变 (例如、如果我将输入电压降低0.2V。)

我忘记设置或重置某个内容了吗？  我应该使用其他示例吗？

(我不想使用 uDMA 例程、该示例看起来过于复杂、每隔几秒只需简单读取一次。)

//*****************************************************************************
//
// single_ended.c - Example demonstrating how to configure the ADC for
//                  single ended operation.
//
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// 
// This is part of revision 2.2.0.295 of the Tiva Firmware Development Package.
//
//*****************************************************************************

#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"

//*****************************************************************************
//
//! \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 AIN0/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 AIN0 pin)
//! - AIN0 - 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.
//
//*****************************************************************************


//*****************************************************************************
//
// 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_adc(void)
{
    //
    // 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.
    //
    SysCtlClockSet(SYSCTL_SYSDIV_10 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN |
                   SYSCTL_XTAL_16MHZ);

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

    //
    // For this example ADC0 is used with AIN0 on port E7.
    // 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_GPIOE);

    //
    // 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_PORTE_BASE, GPIO_PIN_2);
//    ADCSequenceStepConfigure(ADC0_BASE, 0, 0, ADC_CTL_CH0); // PE3
    ADCSequenceStepConfigure(ADC0_BASE, 0, 0, ADC_CTL_CH2); // PE3
    //
    // 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_CH0 | ADC_CTL_IE |
//                             ADC_CTL_END);
    ADCSequenceStepConfigure(ADC0_BASE, 3, 0, ADC_CTL_CH2 | 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 AIN0 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);

        //
        // This function provides a means of generating a constant length
        // delay.  The function delay (in cycles) = 3 * parameter.  Delay
        // 250ms arbitrarily.
        //
        SysCtlDelay(SysCtlClockGet() / 12);
    }
}

感谢您提供任何指导。  我知道我缺少一些简单的东西。

Bob