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2、组合逻辑设计.md
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2、组合逻辑设计.md
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# 组合逻辑设计
**单元框图**
* CU 外特性
<img src="https://img-blog.csdnimg.cn/20201219152447662.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzkzNDYwNw==,size_16,color_FFFFFF,t_70" width="30%" height="50%" >
* 节拍信号
<img src="https://img-blog.csdnimg.cn/20201219152513692.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzkzNDYwNw==,size_16,color_FFFFFF,t_70" width="40%" height="50%" />
**微操作的节拍安排**
假定：采用 同步控制方式，一个 机器周期 内有 3 个节拍（时钟周期），CPU 内部结构采用非总线方式
<img src="https://img-blog.csdnimg.cn/20201219152533741.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzkzNDYwNw==,size_16,color_FFFFFF,t_7" width="40%" height="50%" />
* 安排微操作时序的原则
* 原则一： 微操作的先后顺序不得随意更改
* 原则二：被控对象不同的微操作尽量安排在 一个节拍内完成
* 原则三：占用 时间较短 的微操作尽量 安排在 一个节拍 内完成并允许有先后顺序
* 取指周期微操作的节拍安排
<img src="https://img-blog.csdnimg.cn/20201219152554150.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzkzNDYwNw==,size_16,color_FFFFFF,t_70" width="30%" height="50%" />
* 间址周期 微操作的 节拍安排
<img src="https://img-blog.csdnimg.cn/20201219152612859.png" width="25%" height="50%" />
* 执行周期 微操作的 节拍安排
<img src="https://img-blog.csdnimg.cn/20201219152637708.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzkzNDYwNw==,size_16,color_FFFFFF,t_7" width="30%" height="50%" />
* 中断周期 微操作的 节拍安排
<img src="https://img-blog.csdnimg.cn/20201219152701328.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzkzNDYwNw==,size_16,color_FFFFFF,t_70" width="40%" height="50%" />
**组合逻辑设计步骤**
* 1、列出操作时间表
<img src="https://img-blog.csdnimg.cn/20201219152722696.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzkzNDYwNw==,size_16,color_FFFFFF,t_70" width="50%" height="50%" />
<img src="https://img-blog.csdnimg.cn/20201219152741520.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzkzNDYwNw==,size_16,color_FFFFFF,t_70" width="50%" height="50%" />
<img src="https://img-blog.csdnimg.cn/20201219152803787.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzkzNDYwNw==,size_16,color_FFFFFF,t_70" width="50%" height="50%" />
* 2、对每条指令进行选择
<img src="https://img-blog.csdnimg.cn/20201219152829429.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzkzNDYwNw==,size_16,color_FFFFFF,t_70" width="50%" height="50%" />
<img src="https://img-blog.csdnimg.cn/20201219152851847.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzkzNDYwNw==,size_16,color_FFFFFF,t_70" width="50%" height="50%" />
<img src="https://img-blog.csdnimg.cn/20201219152915450.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzkzNDYwNw==,size_16,color_FFFFFF,t_70" width="50%" height="50%" />
* 3、写出微操作命令的最简表达式（如 M (MAR) -> MDR）
<img src="https://img-blog.csdnimg.cn/20201219152937467.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzkzNDYwNw==,size_16,color_FFFFFF,t_70" width="50%" height="50%" />
* 4、画出逻辑图
<img src="https://img-blog.csdnimg.cn/20201219152956602.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzkzNDYwNw==,size_16,color_FFFFFF,t_70" width="50%" height="50%" />
**特点**
* 思路清晰，简单明了
* 庞杂，调试困难，修改困难
* 速度快（RISC）