1.首先一定要保证硬件正确，包括接线，工具正常；

2.其次基本配置一定要正确，例如此次配置485的时候，可以实现DMA发送，却不能实现接收。而同样的串口参数配置使用中断方式和232接口都能实现发送接收，个人判断是是接收DMA部分配置有问题，结果卡了很久才发现是基本的管脚配置有误。485的三根引脚要配置成推挽输出，复用，复用模式。

3.最后，还是要多总结经验，多看看源代码。

硬件如下：

其实本质上还是串口通信，只不过多了一个开关控制（485-DIR），用来控制是发送数据还是接收数据，因此是半双工模式。

配置流程：时钟使能，引脚配置，串口配置（波特率，校验位等），DMA配置（需要配置串口中断）。

void USART2_UART_Init(uint32_t bound)

{

  __HAL_RCC_GPIOD_CLK_ENABLE();

  __HAL_RCC_USART2_CLK_ENABLE();

  GPIO_InitTypeDef GPIO_Init2;

  GPIO_Init2.Pin = GPIO_PIN_4;              //485_RTS

  GPIO_Init2.Mode =GPIO_MODE_OUTPUT_PP;

  GPIO_Init2.Pull = GPIO_NOPULL;

  GPIO_Init2.Speed = GPIO_SPEED_FREQ_HIGH;

  GPIO_Init2.Alternate = GPIO_AF7_USART2;

  HAL_GPIO_Init(GPIOD,&GPIO_Init2);

  GPIO_Init2.Pin = GPIO_PIN_5;              //485 TX config

  GPIO_Init2.Mode = GPIO_MODE_AF_PP;

  GPIO_Init2.Pull = GPIO_NOPULL;

  GPIO_Init2.Speed = GPIO_SPEED_FREQ_HIGH;

  GPIO_Init2.Alternate = GPIO_AF7_USART2;

  HAL_GPIO_Init(GPIOD,&GPIO_Init2);

  GPIO_Init2.Pin = GPIO_PIN_6;            //485 RX config

  GPIO_Init2.Mode = GPIO_MODE_AF_PP;

  GPIO_Init2.Pull = GPIO_NOPULL;

  GPIO_Init2.Speed = GPIO_SPEED_FREQ_HIGH;

  GPIO_Init2.Alternate = GPIO_AF7_USART2;

  HAL_GPIO_Init(GPIOD,&GPIO_Init2);        //USART2_GPIO配置

  __HAL_RCC_DMA1_CLK_ENABLE();

  huart2_dma_rx.Instance=DMA1_Stream5;  //USART2RX_ DMA1数据流5，通道4

  huart2_dma_rx.Init.Channel=DMA_CHANNEL_4;

  huart2_dma_rx.Init.Direction=DMA_PERIPH_TO_MEMORY;

  huart2_dma_rx.Init.PeriphInc=DMA_PINC_DISABLE;

  huart2_dma_rx.Init.MemInc=DMA_MINC_ENABLE;

  huart2_dma_rx.Init.MemDataAlignment= DMA_MDATAALIGN_BYTE;

  huart2_dma_rx.Init.PeriphDataAlignment=DMA_PDATAALIGN_BYTE;

  huart2_dma_rx.Init.Mode=DMA_NORMAL;

  huart2_dma_rx.Init.Priority=DMA_PRIORITY_LOW;

  huart2_dma_rx.Init.FIFOMode=DMA_FIFOMODE_DISABLE;

  HAL_DMA_Init(&huart2_dma_rx);

       huart2_dma_tx.Instance=DMA1_Stream6;            //USART2TX_ DMA1数据流6，通道4

huart2_dma_tx.Init.Channel=DMA_CHANNEL_4;

huart2_dma_tx.Init.Direction=DMA_MEMORY_TO_PERIPH;

huart2_dma_tx.Init.PeriphInc=DMA_PINC_DISABLE;

huart2_dma_tx.Init.MemInc=DMA_MINC_ENABLE;

huart2_dma_tx.Init.MemDataAlignment= DMA_MDATAALIGN_BYTE;

huart2_dma_tx.Init.PeriphDataAlignment=DMA_PDATAALIGN_BYTE;

huart2_dma_tx.Init.Mode=DMA_NORMAL;

huart2_dma_tx.Init.Priority=DMA_PRIORITY_HIGH;

huart2_dma_tx.Init.FIFOMode=DMA_FIFOMODE_DISABLE;

HAL_DMA_Init(&huart2_dma_tx);

   __HAL_LINKDMA(&huart2,hdmarx,huart2_dma_rx); //关联USART2和DMA

   __HAL_LINKDMA(&huart2,hdmatx,huart2_dma_tx);  

  HAL_NVIC_SetPriority(DMA1_Stream5_IRQn,1,1);  //配置DMA通道的中断并使能

  HAL_NVIC_EnableIRQ(DMA1_Stream5_IRQn);

  HAL_NVIC_SetPriority(DMA1_Stream6_IRQn,1,1); 

  HAL_NVIC_EnableIRQ(DMA1_Stream6_IRQn);

  huart2.Instance =USART2; 

  huart2.Init.BaudRate =bound;

  huart2.Init.WordLength =UART_WORDLENGTH_8B;

  huart2.Init.StopBits =UART_STOPBITS_1;

  huart2.Init.Parity =UART_PARITY_NONE;

  huart2.Init.Mode = UART_MODE_TX_RX;

  huart2.Init.HwFlowCtl=UART_HWCONTROL_NONE;

  huart2.Init.OverSampling = UART_OVERSAMPLING_16;

  huart2.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE; 

  huart2.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;

  HAL_UART_Init(&huart2);    //串口2配置

  HAL_NVIC_SetPriority(USART2_IRQn,1,1);            //配置USART2的中断并使能

  HAL_NVIC_EnableIRQ(USART2_IRQn);               

RS485_R;

}

void delay485(uint32_t num)

{

while(num--);

}

void RS485_Send_data(uint8_t *pdata,uint16_t data_size)

{

RS485_T;

delay485(4);

while(HAL_UART_GetState(&huart2)!=HAL_UART_STATE_READY);

HAL_UART_Transmit_DMA(&huart2,pdata,data_size);

while(HAL_UART_GetState(&huart2)!=HAL_UART_STATE_READY);

RS485_R;

delay485(4);

}

void RS485_Receive_data(uint8_t *pdata,uint16_t data_size)

{

while(HAL_UART_GetState(&huart2)!=HAL_UART_STATE_READY);

HAL_UART_Receive_DMA(&huart2,pdata,data_size);

}

主程序测试：

int main(void)    

{

  HAL_Init();

  Sysclk_config();

USART2_UART_Init(38400);

RS485_Send_data(buffer1,data_length);

HAL_UART_Receive_DMA(&huart2,buffer2,data_length); //打开DMA接收

  while(1)

  { 

   if(flag==1)

  {

HAL_Delay(200);

   RS485_Send_data(buffer2,data_length);

flag=0;

HAL_UART_Receive_DMA(&huart2,buffer2,data_length);//打开DMA接收 

  }

 }

}

void USART2_IRQHandler(void)

{

HAL_UART_IRQHandler(&huart2);

}

void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart)

{

if(huart==&huart2)

{

  flag=1;

}

}

void DMA1_Stream6_IRQHandler(void)

{

  HAL_DMA_IRQHandler(&huart2_dma_tx);

}

void DMA1_Stream5_IRQHandler(void)

{

  HAL_DMA_IRQHandler(&huart2_dma_rx);

}