DAC示例问题

DAC是数字转模拟转换器（Digital-to-Analog Converter）的缩写，是将数字信号转换为模拟信号的重要设备。在实际开发中，我们有时需要使用DAC进行模拟信号的输出。下面我们来看几个关于DAC的示例问题。

问题一：如何使用DAC输出正弦波？

我们可以使用DAC输出正弦波的离散值，然后用低通滤波器对其进行平滑处理，得到连续的正弦波信号。下面是一个基于STM32的DAC输出正弦波的示例代码：

#include "stm32f10x.h"

float sine_table[256] = {
    0.000000, 0.024541, 0.049068, 0.073565, 0.098017, 0.122411, ..., 0.998795
}

int main()
{
    GPIO_InitTypeDef GPIO_InitStructure;
    DAC_InitTypeDef  DAC_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC, ENABLE);

    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4 | GPIO_Pin_5;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AIN;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    DAC_InitStructure.DAC_Trigger = DAC_Trigger_None;
    DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_None;
    DAC_InitStructure.DAC_LFSRUnmask_TriangleAmplitude = DAC_TriangleAmplitude_4095;
    DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Enable;
    DAC_Init(DAC_Channel_1, &DAC_InitStructure);
    DAC_Init(DAC_Channel_2, &DAC_InitStructure);

    DAC_Cmd(DAC_Channel_1, ENABLE);
    DAC_Cmd(DAC_Channel_2, ENABLE);

    while (1) {
        for (int i = 0; i < 256; i++) {
            DAC_SetChannel1Data(DAC_Align_12b_R, (uint16_t)(4095 * sine_table[i]));
            DAC_SetChannel2Data(DAC_Align_12b_R, (uint16_t)(4095 * sine_table[i]));
            for (int j = 0; j < 10000; j++);
        }
    }
}

问题二：如何使用DMA输出DAC信号？

使用DMA可以大大降低CPU的使用率，提高系统的效率。下面是一个基于STM32的DMA输出DAC信号的示例代码：

#include "stm32f10x.h"

uint16_t sine_table[256] = {
    2048, 2098, 2149, 2200, 2250, 2300, ..., 1997
};

void DMA1_Channel3_IRQHandler()
{
    if (DMA_GetITStatus(DMA1_FLAG_TC3)) {
        DMA_Cmd(DMA1_Channel3, DISABLE);
        DMA_ClearITPendingBit(DMA1_IT_TC3);

        DAC_Cmd(DAC_Channel_1, DISABLE);
        DAC_SetChannel1Data(DAC_Align_12b_R, 0);
    }
}

int main()
{
    GPIO_InitTypeDef GPIO_InitStructure;
    DMA_InitTypeDef  DMA_InitStructure;
    DAC_InitTypeDef  DAC_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
    RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA1, ENABLE);
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC, ENABLE);

    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AIN;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    DMA_DeInit(DMA1_Channel3);
    DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)&DAC->DHR12R1;
    DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)sine_table;
    DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;
    DMA_InitStructure.DMA_BufferSize = 256;
    DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
    DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
    DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord;
    DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;
    DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;
    DMA_InitStructure.DMA_Priority = DMA_Priority_High;
    DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
    DMA_Init(DMA1_Channel3, &DMA_InitStructure);

    DAC_InitStructure.DAC_Trigger = DAC_Trigger_None;
    DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_None;
    DAC_InitStructure.DAC_LFSRUnmask_TriangleAmplitude = DAC_TriangleAmplitude_4095;
    DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Enable;
    DAC_Init(DAC_Channel_1, &DAC_InitStructure);

    DMA_ITConfig(DMA1_Channel3, DMA_IT_TC, ENABLE);
    DAC_DMACmd(DAC_Channel_1, ENABLE);
    DMA_Cmd(DMA1_Channel3, ENABLE);
    DAC_Cmd(DAC_Channel_1, ENABLE);

    while (1) {}
}

问题三：如何使用中断更新DAC输出？

使用中断可以实现同步更新多个DAC通道的输出。下面是一个基于STM32的DAC中断更新输出的示例代码：

#include "stm32f10x.h"

float sine_table[256] = {
    0.000000, 0.024541, 0.049068, 0.073565, 0.098017, 0.122411, ..., 0.998795
}

void TIM6_DAC_IRQHandler()
{
    DAC_SetChannel1Data(DAC_Align_12b_R, (uint16_t)(4095 * sine_table[TIM_GetCounter(TIM6)]));
    DAC_SetChannel2Data(DAC_Align_12b_R, (uint16_t)(4095 * sine_table[TIM_GetCounter(TIM6)]));
    TIM_ClearITPendingBit(TIM6, TIM_IT_Update);
}

int main()
{
    GPIO_InitTypeDef GPIO_InitStructure;
    DAC_InitTypeDef  DAC_InitStructure;
    TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStruct;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC, ENABLE);
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM6, ENABLE);

    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4 | GPIO_Pin_5;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AIN;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    DAC_InitStructure.DAC_Trigger = DAC_Trigger_T6_TRGO;
    DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_None;
    DAC_InitStructure.DAC_LFSRUnmask_TriangleAmplitude = DAC_TriangleAmplitude_4095;
    DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Enable;
    DAC_Init(DAC_Channel_1, &DAC_InitStructure);
    DAC_Init(DAC_Channel_2, &DAC_InitStructure);

    TIM_TimeBaseInitStruct.TIM_Period = 255;
    TIM_TimeBaseInitStruct.TIM_Prescaler = 0;
    TIM_TimeBaseInitStruct.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseInitStruct.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM6, &TIM_TimeBaseInitStruct);
    TIM_SelectOutputTrigger(TIM6, TIM_TRGOSource_Update);

    NVIC_EnableIRQ(TIM6_DAC_IRQn);

    TIM_Cmd(TIM6, ENABLE);
    DAC_Cmd(DAC_Channel_1, ENABLE);
    DAC_Cmd(DAC_Channel_2, ENABLE);

    while (1) {}
}

以上就是关于DAC示例问题的介绍，希望对大家有所帮助！