设计一个串行的8421BCD码转换成串行余3码的逻辑系统。基本要求如下：8421码作为串行输入，余三码作为串行输出。每四个时钟周期完成一位十进制的转换；提示：从8421码到余三码的转换过程中寻找规律，继而完成状态设计过程；-Design a serial 8421BCD code to convert the serial logic systems of more than three yards. The basic requirements are as follows: 8421 yards as a serial input, more than three yards as a serial output. Every four clock cycles to complete the conversion of a decimal　Tip: to find the law from 8421 yards to more than three yards of the conversion process, then the completion status of the design process