STM32F103RCT6 封装是LQFP64,有5个串口
PIN16 ==PA2 ==USART2.TX,
PIN17 ==PA3 ==USART2.X,
PIN29 ==PB10 ==USART3.TX,
PIN30 ==PB11 ==USART3.TX,
PIN42 ==PA9 ==USART1.TX,
PIN43 ==PA10 ==USART1.TX,
PIN51 ==PC10 ==UART4.TX,
PIN52 ==PC11 ==UART4.TX,
PIN53 ==PC12 ==UART5.TX,
PIN54 ==PD2 ==UART5.TX,