uart串口协议
/* USART Word Length ---------------------------------------------------------*/
USART_WordLength_8b
USART_WordLength_9b
/* USART Stop Bits -----------------------------------------------------------*/
USART_StopBits_1
USART_StopBits_0_5
USART_StopBits_2
USART_StopBits_1_5
/* USART Parity --------------------------------------------------------------*/
USART_Parity_No
USART_Parity_Even
USART_Parity_Odd
示例：（stm32）
基本配置：
USART_InitStructure.USART_BaudRate = 115200;
USART_InitStructure.USART_WordLength = USART_WordLength_8b;
USART_InitStructure.USART_StopBits = USART_StopBits_1;
USART_InitStructure.USART_Parity = USART_Parity_No;
更改设置，用逻辑分析仪观察不同配置下波形。
（1）总长8位，8位数据位，无校验
（2）总长9位，8位数据位，偶校验
（3）总长8位，7位数据位偶校验