上传的几个VHDL程序：分别是各种功能计数器；使用列举类型的状态机，四D触发器，通用寄存器，伪随机比特发生器，简单的状态机。-Upload several VHDL program: are the various functions of the counter using the enumerated type state machine, four D flip-flop, the general-purpose registers, pseudo-random bit generato