串口发送程序，用无数设备验证过的，可靠，波特率2M，系统时钟40M-Serial transmission program, verified by numerous equipment, reliable baud 2M, the system clock 40M

收发端都采用2M波特率发送串口数据，通过PIN口直接输入输出串口数据，目的是为了跟外围高速器件完成高速的串口数据的收发，普通USB转串口的都只能支持不到1M的波特率，内部采用乒乓FIFO进行时钟域切换以及缓存(The transmitter and receiver are used 2M baud rate serial data transmission, directly through the PIN port serial i