通过并口实现2台计算机通讯，程序使用轮询方式-Realize through the parallel port 2 computer communications, procedures for the use of polling mode

采用并行口实现数字0~9、A~F、L、U、P、n总共20个键盘 并将按键的结果用7段数码管显示出来-Using the parallel port for digital 0 ~ 9, A ~ F, L, U, P, n total 20 keyboard The results and key with 7-segment displays