说明：  本程序的开发环境是VHDL语言环境。本程序采用双进程即双process的方式，实现按键防止抖动编码电路的功能。具体是采用行和列双向选中控制的方式，来判断哪个按键被按下。本程序共有三个状态。 本程序是VHDL课程的状态机的典型应用实例！
(This procedure is the VHDL language development environment environment. The program uses two-way process that double process to achieve key function to prevent jitter encoding circuit. Specific way is the use of selected rows and columns in a controlled manner, to determine which key is pressed. This program consists of three states. This program is a state machine VHDL course typical application!)