该实验主要实现一个串口发送器功能， 该发送器的数据是从FIFO中读取的。也就是说，只要FIFO中有数据，串口发送器就会启动，将数据发送出去。 -The main experimental realization of a serial transmitter function, which sends the data is read the FIFO. In other words, as long as there is data in the FIFO, serial transmitt