说明：  在开发板FPGA：Spartan-3E 系列，型号：XC3S500E，封装：FGT320，速度-4，利用Xilinx ISE软件，利用VHDL软件编写可逆计数器，包含实验说明以及代码实现VHDL.doc文件,UCF管脚绑定文件
(In the FPGA:Spartan-3E development board series, XC3S500E, package: FGT320, speed -4, using Xilinx ISE software, written in a reversible counter by using VHDL software, including experimental description and code to achieve the VHDL.doc file, the UCF pin binding file)