STM32F4 串口收发程序，已经通过测试，可以加入自己的要发送的数据就可用；-STM32F4 serial port to send and receive procedures, has passed the test, you can join her to send the data is available

配置STM32串口并接收和播发数据，需自己注意STM32的引脚连接(Configuring STM32 serial port and receiving and transmitting data)

stm32F4的串口利用DMA收发数据,串口的空闲中断接收不定长数据(The serial port of stm32F4 uses DMA to send and receive data, and the free interruption of serial ports receives indefinite long data.)