可实现输入的2个一位十进制数的加、减运算。要求：输入提供十个数字键，先转化为8421码，再运算，输入的数据和输出结果都要以七段显示译码器显示出来（仿真波形）。输入模块、运算模块、数据转换模块要求用不同的模块分别实现。-Can be one of the input of two decimal addition, subtraction operations. Requirements: Enter the ten numeric keys provided, the first transformed into 8,421 yards, and then computing, input and output data to seven segment display decoder to be displayed (simulation waveform). Input module, operation module, data conversion module requires a different module were achieved.