说明：   利用8051单片机串行口，实现与PC机通讯。 本实验实现以下功能，将从实验板键盘上键入的字符或数字显示到PC机显示器上，再将PC机所接收的字符发送回单片机，并在实验板的LED上显示出来。
(Using 8051 serial port communication with the PC. The experimental realization of the following functions from the experimental board characters typed on the keyboard or digital display to a PC monitor, and then sent back to the microcontroller characters received by the PC, and on the the experiment board of LED display.)