数字秒表，用VHDL语言描述，用层次设计概念，将设计任务分成七个子模块，规定每一模块的功能和各模块之间的接口，然后再将各模块合起来形成顶层文件联试。-Digital stopwatch, using VHDL descr iption, level design concept, the design task is divided into seven sub-module to provide the interface between each module functions and m