说明：  在STM32的参考手册中，串口被描述成通用同步异步收发器(USART)，它提供了一种灵活的方法与使用工业标准NRZ异步串行数据格式的外部设备之间进行全双工数据交换。USART利用分数波特率发生器提供宽范围的波特率选择。它支持同步单向通信和半双工单线通信，也支持LIN（局部互联网），智能卡协议和IrDA（红外数据组织）SIR ENDEC规范，以及调制解调器(CTS/RTS)操作。它还允许多处理器通信。还可以使用DMA方式，实现高速数据通信。
(In the reference manual of STM32, a serial port is described as universal synchronous asynchronous transceiver (USART), which provides a flexible method and using industry standard NRZ asynchronous serial data format of full-duplex data exchange between external devices. USART using scores baud rate generator provides wide range of baud rate. It supports synchronous one-way communication and half duplex single wire communication, also supports LIN (local Internet), smart card agreement and IrDA infrared data (organization) SIR ENDEC specification, and modems (CTS/RTS) operation. It also allows a multiprocessor communication. You can also use the DMA mode, realize high speed data communication.)