[第五章VHDL状体机.ppt

有限状态机及其设计技术是实用数字系统设计中的重要组成部分，它对应于数字电路基础学习里面的电路状态转换图分析。 有限状态机在EDA和VHDL语言工具下，它的具体的设计技术和实现方法有许多新的内容 本章介绍用VHDL设计不同类型有限状态机的方法。 本章结束！！！ Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 再比较两图的输出波形情况，图5-8输出信号Q3，Q2，Q1，Q0的波形良好，没有毛刺现象。而图5-9的输出存在毛刺。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Mealy型状态机的输出变化要领先一个周期，即一旦输入信号或状态发生变化，输出信号即刻发生变化，Moore状态机和Mealy的设计大体相同，稍有不同的是，Mealy型状态机的组合进程中的输出信号是当前状态和当前输入的函数。 下面的例子5-5是一个两进程Mealy型状态机，进程COMREG是时序与组合混合型进程，它将状态机的主控时序电路和主控状态译码电路同时用一个进程来表达；进程COM1负责根据状态和输入信号给出不同的输出信号。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 由于输出信号Q是由组合电路直接产生，所以可以从该状态机的工作时序图5-10上看到输出信号有毛刺。为了解决这个问题可以将输出信号Q的值锁存后输出。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 在例5-5的基础上在COM1的进程中增加一个IF语句，由此产生一个锁存器，将Q锁存后输出。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 与前面图5-10相比，Q的输出序列是一致的，没有发生锁存后延时一个时钟周期的现象，这是由于同步锁存的缘故。 Evaluation only. C