URAT VHDL程序与仿真，包括顶层程序与仿真，波特率发生器VHDL程序， UART发送器程序与仿真，UART接收器程序与仿真-URAT VHDL procedures and simulation, including the top-level procedures and simulation, VHDL program baud rate generator, UART transmitter and simulation program, UART receiver and simu