最简单的UART发送程序，vhdl编写，系统时钟40M，波特率9600，外Load有效（一个高脉冲）即向PC发送一个字节0X-UART to send the simplest procedures, vhdl prepared, the system clock 40M, baud rate 9600, outside the Load effective (a high-pulse) to the PC sends a byte 0X55