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📁 这是一本关于verilog编程语言的教程,对学习verilog语言有帮助
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<a href="00875.html" target="topic">第五章 数据声明</a></div>
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<a href="#" onmousedown="showPopup(this, 'popup00108');"><img src="seealsolink.png" border="0" alt="" title=""></a> SystemVerilog 3.1a语言参考手册</div>
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5.6 线网、reg、与logic</div>
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Verilog-2001指出，线网可以使用一个或多个连续赋值语句、原语输出或模块端口写入。多驱动的结果值由线网类型的解析函数确定。线网不能使用过程赋值语句。如果端口一侧的线网被端口另一侧的变量所驱动，那么隐含是连续赋值。<span style="color: #0000FF">force</span>语句可以覆盖线网的值。当其被释放以后，线网返回到解析的值。&nbsp;</p>
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Verilog-2001还指出，一个或多个过程语句可以对变量执行写操作，包括过程连续赋值。最后一次执行的写入操作确定变量的值。变量不能被连续赋值。<span style="color: #0000FF">force</span>语句覆盖过程赋值语句，它轮流覆盖正常的赋值。变量不能通过端口写入，它必须通过一个隐含的由连续赋值驱动的线网写入。&nbsp;</p>
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在SystemVerilog中，所有变量现在都可以通过连续赋值写入，或者通过一个或多个过程语句写入，包括过程连续赋值。在一个被写入的逻辑变量的最长静态前缀扩展中（关于一个最长静态前缀扩展的定义，参见<a href="00598.html" target="topic">9.2.1节</a>），对其中任何项使用连续赋值或过程赋值与连续赋值的混合来执行写入操作都是错误的。所有数据类型都可以通过一个端口写入。&nbsp;</p>
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SystemVerilog变量可以是其它数据类型的压缩或非压缩集合。对变量中独立元素的多个赋值被单独地检查。左侧包含了一个分片的赋值被看作是对整个分片的单一赋值。使用过程赋值与连续赋值的混合形式写入一个压缩结构体或压缩数组类型是错误的。因此，一个非压缩结构体或非压缩数组中的一个元素可以过程化赋值，而另一个元素可以进行连续赋值。并且，一个压缩结构体或压缩数组的每一个元素都可以使用单一的连续赋值。例如，对于下面的结构体声明： </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00192');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00192"><pre class="Element12"><span style="color: #0000FF">struct</span> <span style="color: #800080">{</span>
    <span style="color: #0000FF">bit</span> <span style="color: #800080">[</span><span style="color: #FF0000">7</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">]</span> A<span style="color: #800080">;</span>
    <span style="color: #0000FF">bit</span> <span style="color: #800080">[</span><span style="color: #FF0000">7</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">]</span> B<span style="color: #800080">;</span>
    <span style="color: #0000FF">byte</span> C<span style="color: #800080">;</span>
<span style="color: #800080">}</span> abc<span style="color: #800080">;</span></pre></div></div>
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下列的语句对于结构体<i>abc</i>来说都是合法的赋值： </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00193');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00193"><pre class="Element12"><span style="color: #0000FF">assign</span> abc<span style="color: #800080">.</span>C <span style="color: #800080">=</span> sel <span style="color: #800080">?</span> <span style="color: #FF0000">8</span><span style="color: #800080">'</span><span style="color: #0000FF">h</span><span style="color: #FF0000">BE</span> <span style="color: #800080">:</span> <span style="color: #FF0000">8</span><span style="color: #800080">'</span><span style="color: #0000FF">h</span><span style="color: #FF0000">EF</span><span style="color: #800080">;</span>

<span style="color: #0000FF">not</span> <span style="color: #800080">(</span>abc<span style="color: #800080">.</span>A<span style="color: #800080">[</span><span style="color: #FF0000">0</span><span style="color: #800080">],</span>abc<span style="color: #800080">.</span>B<span style="color: #800080">[</span><span style="color: #FF0000">0</span><span style="color: #800080">]),</span>
    <span style="color: #800080">(</span>abc<span style="color: #800080">.</span>A<span style="color: #800080">[</span><span style="color: #FF0000">1</span><span style="color: #800080">],</span>abc<span style="color: #800080">.</span>B<span style="color: #800080">[</span><span style="color: #FF0000">1</span><span style="color: #800080">]),</span>
    <span style="color: #800080">(</span>abc<span style="color: #800080">.</span>A<span style="color: #800080">[</span><span style="color: #FF0000">2</span><span style="color: #800080">],</span>abc<span style="color: #800080">.</span>B<span style="color: #800080">[</span><span style="color: #FF0000">2</span><span style="color: #800080">]),</span>
    <span style="color: #800080">(</span>abc<span style="color: #800080">.</span>A<span style="color: #800080">[</span><span style="color: #FF0000">3</span><span style="color: #800080">],</span>abc<span style="color: #800080">.</span>B<span style="color: #800080">[</span><span style="color: #FF0000">3</span><span style="color: #800080">]);</span>

<span style="color: #0000FF">always</span> <span style="color: #800080">@(</span><span style="color: #0000FF">posedge</span> clk<span style="color: #800080">)</span>
    abc<span style="color: #800080">.</span>B <span style="color: #800080">&lt;=</span> abc<span style="color: #800080">.</span>B <span style="color: #800080">+</span> <span style="color: #FF0000">1</span><span style="color: #800080">;</span></pre></div></div>
<p class="Element10">
下列的语句对于结构体abc来说都是非法的赋值： </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00194');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00194"><pre class="Element12"><span style="color: #008000">// 对abc.C的多个连续赋值</span>
<span style="color: #0000FF">assign</span> abc<span style="color: #800080">.</span>C <span style="color: #800080">=</span> sel <span style="color: #800080">?</span> <span style="color: #FF0000">8</span><span style="color: #800080">'</span><span style="color: #0000FF">h</span><span style="color: #FF0000">hDE</span> <span style="color: #800080">:</span> <span style="color: #FF0000">8</span><span style="color: #800080">'</span><span style="color: #0000FF">h</span><span style="color: #FF0000">ED</span><span style="color: #800080">;</span> <strong><i><span style="color: #008000">// ？？？</span></i></strong>

<span style="color: #008000">// 对abc.A的连续和过程赋值的混合</span>
<span style="color: #0000FF">always</span> <span style="color: #800080">@(</span><span style="color: #0000FF">posedge</span> clk<span style="color: #800080">)</span>
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