说明：  1、ps/2键盘输入，通过led显示ascii码 2、稍等1s可以在lcd上显示输入的字符 3、其中键盘上的backspce键是用来清屏的 4、当lcd上显示满字符时，在按下按键自动清屏，从第一行显示。
(1, ps/2 keyboard input, through the led display ascii code 2, wait for 1s in the input character lcd display 3, in which key on the keyboard is used to clear the screen backspce 4, when the lcd display full of character, automatically clear the screen press the button, from the first line.)