HAL_UART_Transmit的注释如下
/**
* @brief Sends an amount of data in blocking mode.
* @note When UART parity is not enabled (PCE = 0), and Word Length is configured to 9 bits (M1-M0 = 01),
* the sent data is handled as a set of u16. In this case, Size must indicate the number
* of u16 provided through pData.
* @param huart Pointer to a UART_HandleTypeDef structure that contains
* the configuration information for the specified UART module.
* @param pData Pointer to data buffer (u8 or u16 data elements).
* @param Size Amount of data elements (u8 or u16) to be sent
* @param Timeout Timeout duration
* @retval HAL status
*/
HAL_StatusTypeDef HAL_UART_Transmit(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size, uint32_t Timeout)
uint8_t TxData[10]= "123456";
HAL_UART_Transmit(&huart2,TxData,100,0xFFFFFFFFU);//把TxData的内容通过uart2发送出去
这里的长度100是发送数据的最大长度，超过这个长度后面的数据不再发送，0xFFFFFFFFU是超时时间，设为最大即可
HAL_UART_Transmit(&huart2,"123456789",5,0xFFFFFFFFU);
如果长度设为5，则串口只发送12345，后面的6789不会发送，
HAL_UART_Transmit(&huart2,"123456789",100,0xFFFFFFFFU);
如果把长度设为100，则串口发送123456789.