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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="ch06.css"><TITLE> Section 6</TITLE></HEAD><BODY BGCOLOR="#ffffff"><DIV><HR><P><A HREF="none">Chapter start</A> <A HREF="ch06.1.htm">Next page</A></P></DIV><DIV><H1 CLASS="Chapter"><A NAME="pgfId=114"> </A>Section 6<A NAME="26312"> </A></H1><H1 CLASS="ChapterTitle"><A NAME="pgfId=108"> </A><A NAME="marker=17"> </A>Assignments</H1><P CLASS="Body"><A NAME="pgfId=109"> </A>The assignment is the basic mechanism for getting values into nets and registers. There are two basic forms of the assignments:</P><UL><LI CLASS="DashedList"><A NAME="pgfId=110"> </A>the continuous assignment, which assigns values to nets</LI><LI CLASS="DashedList"><A NAME="pgfId=111"> </A>the procedural assignment, which assigns values to registers</LI></UL><P CLASS="Body"><A NAME="pgfId=169"> </A>There are two additional forms of assignments, called <I CLASS="Emphasis">procedural continuous assignments</I>, described in <A HREF="/Humuhumu/Files/Prof_Smith/Academic/ASICs/Web/ASICs/HTML/Verilog/LRM/HTML/06/ch09.htm#43159" CLASS="XRef"></A>.</P><P CLASS="Body"><A NAME="pgfId=112"> </A>An assignment consists of two parts, a left-hand side<A NAME="marker=18"> </A> and a right-hand side<A NAME="marker=19"> </A>, separated by the equal (<A NAME="marker=20"> </A><A NAME="marker=21"> </A>=) character. The right-hand side can be any expression that evaluates to a value. The left-hand side indicates the variable that the right-hand side is to be assigned to. <A NAME="marker=22"> </A>The left-hand side can take one of the following forms, depending on whether the assignment is a continuous assignment or a <A NAME="marker=23"> </A>procedural assignment.</P><P CLASS="Body"><A NAME="pgfId=171"> </A></P><TABLE BORDER="1"><CAPTION><P CLASS="TableTitle"><A NAME="pgfId=187"> </A>Table 6-1Legal left-hand side forms in assignment statements</P></CAPTION><TR><TH ROWSPAN="1" COLSPAN="1"><P CLASS="CellHeading"><A NAME="pgfId=176"> </A>Statement Type</P></TH><TH ROWSPAN="1" COLSPAN="1"><P CLASS="CellHeading"><A NAME="pgfId=177"> </A>Left-hand Side (LHS)</P></TH></TR><TR><TD ROWSPAN="1" COLSPAN="1"><P CLASS="CellBody"><A NAME="pgfId=178"> </A>continuous assignment</P></TD><TD ROWSPAN="1" COLSPAN="1"><P CLASS="CellBody"><A NAME="pgfId=179"> </A>net (vector or scalar)</P><P CLASS="CellBody"><A NAME="pgfId=175"> </A>constant bit select of a vector net</P><P CLASS="CellBody"><A NAME="pgfId=174"> </A>constant part select of a vector net</P><P CLASS="CellBody"><A NAME="pgfId=183"> </A>concatenation of any of the above three lhs</P></TD></TR><TR><TD ROWSPAN="1" COLSPAN="1"><P CLASS="CellBody"><A NAME="pgfId=180"> </A>procedural assignment</P></TD><TD ROWSPAN="1" COLSPAN="1"><P CLASS="CellBody"><A NAME="pgfId=181"> </A>register (vector or scalar)</P><P CLASS="CellBody"><A NAME="pgfId=184"> </A>bit select of a vector register</P><P CLASS="CellBody"><A NAME="pgfId=185"> </A>constant part select of a vector register</P><P CLASS="CellBody"><A NAME="pgfId=186"> </A>memory element</P><P CLASS="CellBody"><A NAME="pgfId=101"> </A>concatenation of any of the above four lhs</P></TD></TR></TABLE><H2 CLASS="SectionTOC"><A HREF="ch06.1.htm#pgfId=116" CLASS="Hypertext">6.1 Continuous assignments </A></H2><H2 CLASS="SectionTOC"><A HREF="ch06.2.htm#pgfId=165" CLASS="Hypertext">6.2 Procedural assignments </A></H2></DIV><HR><P><A HREF="none">Chapter start</A> <A HREF="ch06.1.htm">Next page</A></P></BODY></HTML>⌨️ 快捷键说明
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