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<HTML><HEAD> <META NAME="GENERATOR" CONTENT="Adobe PageMill 2.0 Mac"> <TITLE>1.3 Syntactic description</TITLE></HEAD><BODY><P><A NAME="anchor640956"></A><HR ALIGN=LEFT></P><P><A HREF="ch01.htm">Chapter start</A> <A HREF="ch01.2.htm">Previous page</A> <A HREF="ch01.4.htm">Next page</A></P><H2>1.3 Syntactic description</H2><P><P CLASS="Body"><A NAME="pgfId=72"></A>The formal syntax of Verilog HDLis described using Backus-Naur Form (BNF). The following conventions areused:</P><OL> <P><P CLASS="NumberedLista"><A NAME="pgfId=84"></A>a) Lower case words, some containing embedded underscores, are used to denote syntactic categories, for example:</OL><PRE><A NAME="pgfId=85"></A> module_declaration</PRE><OL> <P><P CLASS="NumberedListb"><A NAME="pgfId=86"></A>b) Bold face words are used to denote reserved keywords, operators and punctuation marks as required part of the syntax. These words appear in larger font for distinction. For example:</OL><PRE><A NAME="pgfId=87"></A> <B>module</B> <B>=></B> <B>; </B></PRE><OL> <P><P CLASS="NumberedListb"><A NAME="pgfId=67"></A>c) A vertical bar separates alternative items unless it appears in bold face, in which case it stands for itself. For example:</OL><PRE><A NAME="pgfId=68"></A> port_expression ::= port_reference | <B>{</B> port_reference {<B> ,</B> port_reference } <B>}</B><A NAME="pgfId=73"></A> unary_operator ::= <B>+ </B>| <B> - </B>| <B> ! </B>| <B> ~ </B>| <B> & </B>| <B> ~& </B>| <B> | </B>| <B> ~| </B>| <B> ^ </B>| <B> ~^ </B>| <B> ^~</B></PRE><OL> <P><P CLASS="NumberedListb"><A NAME="pgfId=90"></A>d) Square brackets enclose optional items. For example:</OL><PRE><A NAME="pgfId=91"></A> input_declaration ::= <B>input</B> [range] list_of_variables <EM>;</EM></PRE><OL> <P><P CLASS="NumberedListb"><A NAME="pgfId=92"></A>e) Braces enclose a repeated item. The item may appear zero or more times; the repetitions occur from left to right as with an equivalent left-recursive rule. Thus, the following two rules are equivalent:</OL><PRE><A NAME="pgfId=111"></A> list_of_param_assignments ::= param_assignment<B> </B>{ <B>,</B><EM> </EM>param_assignment }<A NAME="pgfId=117"></A> list_of_param_assignments ::= param_assignment| param_assignment <B>,</B> list_of_param_assignment</PRE><OL> <P><P CLASS="NumberedListb"><A NAME="pgfId=103"></A>f) If the name of any category starts with an italicized part, it is equivalent to the category name without the italicized part. The italicized part is intended to convey some semantic information. For example, <I>msb_</I> constant_expression and <I>lsb_</I> constant_expression are equivalent to constant_expression.</OL><P><P CLASS="Body"><A NAME="pgfId=80"></A>The main text uses <I>italicized</I>font when a term is being defined, and <CODE>constant-width</CODE> fontfor examples, file names, and while referring to constants, especially <CODE>0</CODE>, <CODE>1</CODE> , <CODE>x</CODE> , and <CODE>z</CODE> values.</P><P><A HREF="ch01.htm">Chapter start</A> <A HREF="ch01.2.htm">Previous page</A> <A HREF="ch01.4.htm">Next page</A></BODY></HTML>⌨️ 快捷键说明
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