使用PD5/PD6重映射为usart2，输出到MAX3232，带1k的上拉电阻，示波器测到的单片机输出波形最小值在800mV左右，改成下拉电阻之后串口时好时坏。
void HAL_UART_MspInit(UART_HandleTypeDef* huart)
{
GPIO_InitTypeDef GPIO_InitStruct = {0};
if(huart->Instance==USART2)
{
/* USER CODE BEGIN USART2_MspInit 0 /
__HAL_RCC_AFIO_CLK_ENABLE();
/ USER CODE END USART2_MspInit 0 /
/ Peripheral clock enable */
__HAL_RCC_USART2_CLK_ENABLE();
__HAL_AFIO_REMAP_USART2_ENABLE();
__HAL_RCC_GPIOD_CLK_ENABLE();
/**USART2 GPIO Configuration
PD5 ——> USART2_TX
PD6 ——> USART2_RX
*/
GPIO_InitStruct.Pin = GPIO_PIN_5;
GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;//GPIO_MODE_OUTPUT_PP;//GPIO_MODE_AF_PP;
GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;//GPIO_SPEED_FREQ_HIGH;
// GPIO_InitStruct.Pull = GPIO_PULLDOWN;
HAL_GPIO_Init(GPIOD, &GPIO_InitStruct);
GPIO_InitStruct.Pin = GPIO_PIN_6;
GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
GPIO_InitStruct.Pull = GPIO_PULLUP;
HAL_GPIO_Init(GPIOD, &GPIO_InitStruct);
__HAL_AFIO_REMAP_USART2_ENABLE();
/* USART2 interrupt Init */
HAL_NVIC_SetPriority(USART2_IRQn, 3, 0);
HAL_NVIC_EnableIRQ(USART2_IRQn);
/* USER CODE BEGIN USART2_MspInit 1 */
/* USER CODE END USART2_MspInit 1 */
}
}
static void MX_USART2_UART_Init(void)
{
/* USER CODE BEGIN USART2_Init 0 */
/* USER CODE END USART2_Init 0 */
/* USER CODE BEGIN USART2_Init 1 */
/* USER CODE END USART2_Init 1 /
huart2.Instance = USART2;
huart2.Init.BaudRate = 115200;
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;
if (HAL_UART_Init(&huart2) != HAL_OK)
{
Error_Handler();
}
/ USER CODE BEGIN USART2_Init 2 */
/* USER CODE END USART2_Init 2 */
}
