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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

    <span style="color: #800080">@(</span><span style="color: #0000FF">negedge</span> clk<span style="color: #800080">)</span> g <span style="color: #800080">##</span><span style="color: #FF0000">1</span> h <span style="color: #800080">##</span><span style="color: #FF0000">1</span> i<span style="color: #800080">;</span>
<span style="color: #0000FF">endsequence</span></pre></div></div>
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&nbsp;</p>
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在这个例子中，序列<i><span class="Element146">s1</span></i>和<i><span class="Element146">s2</span></i>在连续的<i><span class="Element146">clk</span></i>上升沿事件上被计算。序列<i><span class="Element146">s3</span></i>在连续的<i><span class="Element146">clk</span></i>下降沿事件上被计算。&nbsp;</p>
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&nbsp;</p>
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下面是序列声明的另外的一个例子，它包含了参数： </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00589');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00589"><pre class="Element12"><span style="color: #0000FF">sequence</span> s20_1<span style="color: #800080">(</span>data<span style="color: #800080">,</span> en<span style="color: #800080">);</span>
    <span style="color: #800080">(!</span>frame <span style="color: #800080">&amp;&amp; (</span>data <span style="color: #800080">== </span>data_bus<span style="color: #800080">)) ##</span><span style="color: #FF0000">1</span> <span style="color: #800080">(</span>c_be<span style="color: #800080">[</span><span style="color: #FF0000">0</span><span style="color: #800080">:</span><span style="color: #FF0000">3</span><span style="color: #800080">] ==</span> en<span style="color: #800080">);</span>
<span style="color: #0000FF">endsequence</span></pre></div></div>
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&nbsp;</p>
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序列<i><span class="Element146">s20_1</span></i>没有指定一个时钟。在这个例子中，一个时钟会从某个外部源（例如一个特性或一个断言语句）继承而来。一个序列可以通过它的名字引用。与SystemVerilig命名约定相一致，我们可以使用一个层次化的名字。一个序列可以在一个特性、一条断言语句或者一条覆盖语句中被引用。&nbsp;</p>
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为了将一个命名序列当作另外一个序列的子序列使用，我们只需简单地引用它的名字。对于引用一个命名序列的序列的计算来讲，它在执行的时候就好像这个命名序列被包含成引用序列的词法组成部分一样，这个命名序列的形式参数被实形参数所替代并且这个命名序列中剩余的变量根据命名序列声明的作用域来解析。一个例子如下所示： </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00590');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00590"><pre class="Element12"><span style="color: #0000FF">sequence</span> s<span style="color: #800080">;</span>
    a <span style="color: #800080">##</span><span style="color: #FF0000">1</span> b <span style="color: #800080">##</span><span style="color: #FF0000">1</span> c<span style="color: #800080">;</span>
<span style="color: #0000FF">endsequence</span>

<span style="color: #0000FF">sequence</span> rule<span style="color: #800080">;</span>
    <span style="color: #800080">@(</span><span style="color: #0000FF">posedge</span> sysclk<span style="color: #800080">)</span>
        trans <span style="color: #800080">##</span><span style="color: #FF0000">1</span> start_trans <span style="color: #800080">##</span><span style="color: #FF0000">1</span> s <span style="color: #800080">##</span><span style="color: #FF0000">1</span> end_trans<span style="color: #800080">;</span>
<span style="color: #0000FF">endsequence</span></pre></div></div>
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&nbsp;</p>
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前一个例子中的序列规则等价于： </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00591');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00591"><pre class="Element12"><span style="color: #0000FF">sequence</span> rule<span style="color: #800080">;</span>
    <span style="color: #800080">@(</span><span style="color: #0000FF">posedge</span> sysclk<span style="color: #800080">)</span>
        trans <span style="color: #800080">##</span><span style="color: #FF0000">1</span> start_trans <span style="color: #800080">##</span><span style="color: #FF0000">1</span> a <span style="color: #800080">##</span><span style="color: #FF0000">1</span> b <span style="color: #800080">##</span><span style="color: #FF0000">1</span> c <span style="color: #800080">##</span><span style="color: #FF0000">1</span> end_trans<span style="color: #800080">;</span>
<span style="color: #0000FF">endsequence</span></pre></div></div>
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&nbsp;</p>
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序列名字的任何形式的循环依赖都是不允许的。下面的例子演示了一个<i><span class="Element146">s1</span></i>对<i><span class="Element146">s2</span></i>以及<i><span class="Element146">s2</span></i>对<i><span class="Element146">s1</span></i>的非法的依赖性，因为这个例子产生了一个循环依赖。 </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00592');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00592"><pre class="Element12"><span style="color: #0000FF">sequence</span> s1<span style="color: #800080">;</span>
    <span style="color: #800080">@(</span><span style="color: #0000FF">posedge</span> sysclk<span style="color: #800080">)</span> <span style="color: #800080">(</span>x <span style="color: #800080">##</span><span style="color: #FF0000">1</span> s2<span style="color: #800080">);</span>
<span style="color: #0000FF">endsequence</span>

<span style="color: #0000FF">sequence</span> s2<span style="color: #800080">;</span>
    <span style="color: #800080">@(</span><span style="color: #0000FF">posedge</span> sysclk<span style="color: #800080">)</span> <span style="color: #800080">(</span>y <span style="color: #800080">##</span><span style="color: #FF0000">1</span> s1<span style="color: #800080">);</span>
<span style="color: #0000FF">endsequence</span></pre></div></div>
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