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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML EXPERIMENTAL 970324//EN"><HTML><HEAD><META NAME="GENERATOR" CONTENT="Adobe FrameMaker 5.5/HTML Export Filter"><LINK REL="STYLESHEET" HREF="ch13.css"><TITLE> 13.2 Declaring parameters in specify blocks</TITLE></HEAD><BODY BGCOLOR="#ffffff"><DIV><HR><P><A HREF="ch13.htm">Chapter start</A> <A HREF="ch13.1.htm">Previous page</A> <A HREF="ch13.3.htm">Next page</A></P></DIV><H1 CLASS="Section"><A NAME="pgfId=422"> </A>13.2 <A NAME="61845"> </A><A NAME="marker=55"> </A>Declaring <A NAME="marker=56"> </A>parameters in specify blocks</H1><P CLASS="Body"><A NAME="pgfId=424"> </A>The keyword <B CLASS="Keyword">specparam</B> declares parameters within specify blocks--called <I CLASS="Emphasis">specify parameters</I><A NAME="marker=57"> </A> or <I CLASS="Emphasis">specparams</I>, to distinguish them from <I CLASS="Emphasis">module parameters</I><A NAME="marker=58"> </A>. The<A NAME="marker=62"> </A> syntax <A NAME="marker=63"> </A>for<A NAME="marker=64"> </A> declaring specify parameters is shown below:</P><P CLASS="Body"><A NAME="pgfId=426"> </A></P><DIV><IMG SRC="ch13-3.gif"></DIV><P CLASS="BNFCapBody"><A NAME="pgfId=427"> </A>Syntax 13-2<A NAME="80827"> </A>: Syntax of the specparam declaration</P><P CLASS="Body"><A NAME="pgfId=327"> </A>A specify parameter shall be declared and used only within the specify block. The value assigned to a specify parameter can be any constant expression. A specify parameter declared in the specify block can be used to construct a constant expression for a subsequent specify parameter declaration. A specify parameter shall not be visible outside the specify block it is declared in. </P><P CLASS="Body"><A NAME="pgfId=421"> </A>The specify parameters and module parameters shall not be interchangeable. <A HREF="ch13.2.htm#52443" CLASS="XRef">See : Differences between specparams and parameters</A> summarizes the differences between the two types of parameter declarations. </P><TABLE><CAPTION><P CLASS="TableTitle"><A NAME="pgfId=328"> </A>Table 13-1<A NAME="52443"> </A>: Differences between specparams and parameters</P></CAPTION><TR><TH ROWSPAN="1" COLSPAN="1"><P CLASS="CellHeading"><A NAME="pgfId=386"> </A>SPECPARAMS</P><P CLASS="CellHeading"><A NAME="pgfId=387"> </A>(Specify parameter)</P></TH><TH ROWSPAN="1" COLSPAN="1"><P CLASS="CellHeading"><A NAME="pgfId=388"> </A>PARAMETERS</P><P CLASS="CellHeading"><A NAME="pgfId=389"> </A>(Module parameter)</P></TH></TR><TR><TD ROWSPAN="1" COLSPAN="1"><P CLASS="CellBody"><A NAME="pgfId=390"> </A>use keyword <B CLASS="Keyword">specparam</B></P></TD><TD ROWSPAN="1" COLSPAN="1"><P CLASS="CellBody"><A NAME="pgfId=391"> </A>use keyword <B CLASS="Keyword">parameter</B></P></TD></TR><TR><TD ROWSPAN="1" COLSPAN="1"><P CLASS="CellBody"><A NAME="pgfId=393"> </A>must be declared <I CLASS="Emphasis">inside</I> specify blocks</P></TD><TD ROWSPAN="1" COLSPAN="1"><P CLASS="CellBody"><A NAME="pgfId=394"> </A>must be declared <I CLASS="Emphasis">outside</I> specify blocks</P></TD></TR><TR><TD ROWSPAN="1" COLSPAN="1"><P CLASS="CellBody"><A NAME="pgfId=395"> </A>may only be used inside specify blocks</P></TD><TD ROWSPAN="1" COLSPAN="1"><P CLASS="CellBody"><A NAME="pgfId=398"> </A>may not be used inside specify blocks</P></TD></TR><TR><TD ROWSPAN="1" COLSPAN="1"><P CLASS="CellBody"><A NAME="pgfId=399"> </A>cannot use <B CLASS="Keyword">defparam</B> to override values</P></TD><TD ROWSPAN="1" COLSPAN="1"><P CLASS="CellBody"><A NAME="pgfId=419"> </A>use <B CLASS="Keyword">defparam</B> to override values</P></TD></TR></TABLE><DIV><H3 CLASS="Example"><A NAME="pgfId=428"> </A></H3><P CLASS="Body"><A NAME="pgfId=734"> </A></P><DIV><IMG SRC="ch13-4.gif"></DIV><P CLASS="Body"><A NAME="pgfId=311"> </A>The lines between the keywords <B CLASS="Keyword">specify</B> and <B CLASS="Keyword">endspecify</B> declare four specify parameters. The first line declares specify parameters called <CODE CLASS="code">tRise_clk_q</CODE> and <CODE CLASS="code">tFall_clk_q</CODE> with values <CODE CLASS="code">150</CODE> and <CODE CLASS="code">200</CODE> respectively; the second line declares <CODE CLASS="code">tRise_control</CODE> and <CODE CLASS="code">tFall_control</CODE> specify parameters with values <CODE CLASS="code">40</CODE> and <CODE CLASS="code">50</CODE> respectively. <A NAME="marker=46"> </A><A NAME="marker=52"> </A><A NAME="marker=60"> </A></P></DIV><HR><P><A HREF="ch13.htm">Chapter start</A> <A HREF="ch13.1.htm">Previous page</A> <A HREF="ch13.3.htm">Next page</A></P></BODY></HTML>?? 快捷鍵說明
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