stm32dac输出方波

要在STM32上使用DAC输出方波，可以按照以下步骤进行：

1. 配置DAC通道，选择使用哪个DAC通道并设置输出精度。
2. 配置GPIO引脚，将DAC通道与GPIO引脚连接。
3. 使用定时器来生成方波信号，可以选择定时器的时钟源和预分频器，以及定时器的计数值和重载值。
4. 在定时器的中断处理函数中更新DAC的输出值，使其跟随方波信号的变化。

下面是一份示例代码，它使用DAC1通道输出方波信号：

#include "stm32f4xx.h"

#define DAC_OUT_GPIO_PORT    GPIOA
#define DAC_OUT_GPIO_PIN     GPIO_Pin_4
#define DAC_OUT_GPIO_SOURCE  GPIO_PinSource4

#define DAC_DMA_STREAM       DMA1_Stream5
#define DAC_DMA_CHANNEL      DMA_Channel_7
#define DAC_DMA_IRQ          DMA1_Stream5_IRQn
#define DAC_DMA_IRQ_HANDLER  DMA1_Stream5_IRQHandler

#define TIM_CLOCK_FREQ       84000000
#define TIM_PERIOD           100
#define TIM_PRESCALER        839

#define WAVEFORM_SAMPLES     100
#define WAVEFORM_AMPLITUDE   2047

static uint16_t waveform[WAVEFORM_SAMPLES];

void generate_waveform(void)
{
    int i;
    for (i = 0; i < WAVEFORM_SAMPLES / 2; i++) {
        waveform[i] = WAVEFORM_AMPLITUDE;
    }
    for (i = WAVEFORM_SAMPLES / 2; i < WAVEFORM_SAMPLES; i++) {
        waveform[i] = 0;
    }
}

void configure_dac(void)
{
    GPIO_InitTypeDef GPIO_InitStruct;
    DAC_InitTypeDef DAC_InitStruct;
    DMA_InitTypeDef DMA_InitStruct;

    /* Enable GPIOA clock */
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);

    /* Configure DAC_OUT pin */
    GPIO_InitStruct.GPIO_Pin = DAC_OUT_GPIO_PIN;
    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AN;
    GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_NOPULL;
    GPIO_Init(DAC_OUT_GPIO_PORT, &GPIO_InitStruct);

    /* Enable DAC clock */
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC, ENABLE);

    /* Configure DAC channel */
    DAC_InitStruct.DAC_Trigger = DAC_Trigger_T6_TRGO;
    DAC_InitStruct.DAC_OutputBuffer = DAC_OutputBuffer_Disable;
    DAC_Init(DAC_Channel_1, &DAC_InitStruct);

    /* Enable DMA clock */
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA1, ENABLE);

    /* Configure DMA stream */
    DMA_InitStruct.DMA_Channel = DAC_DMA_CHANNEL;
    DMA_InitStruct.DMA_PeripheralBaseAddr = (uint32_t)&DAC->DHR12R1;
    DMA_InitStruct.DMA_Memory0BaseAddr = (uint32_t)waveform;
    DMA_InitStruct.DMA_DIR = DMA_DIR_MemoryToPeripheral;
    DMA_InitStruct.DMA_BufferSize = WAVEFORM_SAMPLES;
    DMA_InitStruct.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
    DMA_InitStruct.DMA_MemoryInc = DMA_MemoryInc_Enable;
    DMA_InitStruct.DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord;
    DMA_InitStruct.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;
    DMA_InitStruct.DMA_Mode = DMA_Mode_Circular;
    DMA_InitStruct.DMA_Priority = DMA_Priority_High;
    DMA_InitStruct.DMA_FIFOMode = DMA_FIFOMode_Disable;
    DMA_InitStruct.DMA_FIFOThreshold = DMA_FIFOThreshold_HalfFull;
    DMA_InitStruct.DMA_MemoryBurst = DMA_MemoryBurst_Single;
    DMA_InitStruct.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;
    DMA_Init(DAC_DMA_STREAM, &DMA_InitStruct);

    /* Enable DMA */
    DMA_Cmd(DAC_DMA_STREAM, ENABLE);

    /* Enable DAC */
    DAC_Cmd(DAC_Channel_1, ENABLE);

    /* Enable DMA for DAC channel */
    DAC_DMACmd(DAC_Channel_1, ENABLE);
}

void configure_timer(void)
{
    TIM_TimeBaseInitTypeDef TIM_InitStruct;
    NVIC_InitTypeDef NVIC_InitStruct;

    /* Enable TIM6 clock */
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM6, ENABLE);

    /* Configure TIM6 */
    TIM_InitStruct.TIM_Prescaler = TIM_PRESCALER;
    TIM_InitStruct.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_InitStruct.TIM_Period = TIM_PERIOD;
    TIM_InitStruct.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseInit(TIM6, &TIM_InitStruct);

    /* Enable TIM6 interrupt */
    TIM_ITConfig(TIM6, TIM_IT_Update, ENABLE);

    /* Enable TIM6 */
    TIM_Cmd(TIM6, ENABLE);

    /* Configure TIM6 interrupt */
    NVIC_InitStruct.NVIC_IRQChannel = TIM6_DAC_IRQn;
    NVIC_InitStruct.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStruct.NVIC_IRQChannelSubPriority = 0;
    NVIC_InitStruct.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStruct);
}

void TIM6_DAC_IRQHandler(void)
{
    if (TIM_GetITStatus(TIM6, TIM_IT_Update) != RESET) {
        TIM_ClearITPendingBit(TIM6, TIM_IT_Update);
        DMA_Cmd(DAC_DMA_STREAM, DISABLE);
        DMA_SetCurrDataCounter(DAC_DMA_STREAM, WAVEFORM_SAMPLES);
        DMA_Cmd(DAC_DMA_STREAM, ENABLE);
    }
}

int main(void)
{
    generate_waveform();
    configure_dac();
    configure_timer();
    while (1)
        ;
}

在这个示例代码中，我们使用了DAC1通道和GPIOA4引脚，并且使用了TIM6定时器来生成方波信号。我们使用了DMA来更新DAC的输出值，以避免在中断处理函数中频繁更新DAC值导致的性能问题。在TIM6中断处理函数中，我们禁用DMA流并重新配置DMA缓冲区的长度，然后重新启用DMA流以更新DAC的输出值。