VHDL主要用于描述数字系统的结构、行为、功能和接口。除了许多具有硬件特性的句子外，VHDL语言形式、描述风格和语法与一般计算机高级语言非常相似。VHDL的程序结构是一个工程设计，或设计实体（可以是一个组件，一个电路模块或一个系统）被划分为外部（或可见部分，和端口）和内部（或不可视）-VHDL is used primarily to describe the structure, behavior, function, and interface of digital systems. In addition to many sentences with hardware features, VHDL s language form, descr iption style, and syntax are very similar to general computer high-level languages. The program structure of VHDL is an engineering design, or design entity (can be a component, a circuit module or a system) is divided into external (or visible part, and port) and internal (or not visual)