hdlc设计，包括flag检测，插0、串并转换等设计，采用verilog编程。-hdlc design, using verilog

文件中有两种方法实现并串转换模块代码的编写，可以在modelsim软件中正确仿真(There are two methods in the file to achieve the serial conversion module code writing, can be correctly simulated in Modelsim software)