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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="ch08.css"><TITLE> Section 8</TITLE></HEAD><BODY BGCOLOR="#ffffff"><DIV><HR><P><A HREF="none">Chapter start</A> <A HREF="ch08.1.htm">Next page</A></P></DIV><DIV><H1 CLASS="Chapter"><A NAME="pgfId=257"> </A>Section 8<A NAME="68347"> </A></H1><H1 CLASS="ChapterTitle"><A NAME="pgfId=299"> </A><A NAME="marker=22"> </A><A NAME="marker=23"> </A>User-Defined Primitives (UDPs)</H1><P CLASS="Body"><A NAME="pgfId=300"> </A>This section describes a modeling technique to augment the set of predefined gate primitives by designing and specifying new primitive elements called user-defined primitives (UDPs). Instances of these new UDPs can be used in exactly the same manner as the gate primitives to represent the circuit being modeled. </P><P CLASS="Body"><A NAME="pgfId=301"> </A>The following two types of behavior can be represented in a user-defined primitive:</P><UL><LI CLASS="DashedList"><A NAME="pgfId=302"> </A><A NAME="marker=25"> </A>combinational--modeled by a combinational UDP</LI><LI CLASS="DashedList"><A NAME="pgfId=303"> </A>sequential--modeled by a sequential UDP</LI></UL><P CLASS="Body"><A NAME="pgfId=304"> </A>A combinational UDP uses the value of its inputs to determine the next value of its output. A sequential UDP uses the value of its inputs and the current value of its output to determine the next value of its output. Sequential UDPs provide a way to model sequential circuits such as flip-flops and latches. A sequential UDP can model both level-sensitive and edge-sensitive behavior.</P><P CLASS="Body"><A NAME="pgfId=306"> </A>Each UDP has exactly one output, which can be in one of three states: <CODE CLASS="code">0</CODE>, <CODE CLASS="code">1</CODE>, or <CODE CLASS="code">x</CODE>. The tri-state value <CODE CLASS="code">z</CODE> is not supported. In sequential UDPs, the output always has the same value as the internal state. </P><P CLASS="Body"><A NAME="pgfId=438"> </A>The <CODE CLASS="code">z</CODE> values passed to UDP inputs shall be treated the same as <CODE CLASS="code">x</CODE> values.</P><H2 CLASS="SectionTOC"><A HREF="ch08.1.htm#pgfId=316" CLASS="Hypertext">8.1 UDP definition </A></H2><H2 CLASS="SectionTOC"><A HREF="ch08.2.htm#pgfId=342" CLASS="Hypertext">8.2 Combinational UDPs</A></H2><H2 CLASS="SectionTOC"><A HREF="ch08.3.htm#pgfId=348" CLASS="Hypertext">8.3 Level-sensitive sequential UDPs </A></H2><H2 CLASS="SectionTOC"><A HREF="ch08.4.htm#pgfId=353" CLASS="Hypertext">8.4 Edge-sensitive sequential UDPs </A></H2><H2 CLASS="SectionTOC"><A HREF="ch08.5.htm#pgfId=361" CLASS="Hypertext">8.5 Sequential UDP initialization</A></H2><H2 CLASS="SectionTOC"><A HREF="ch08.6.htm#pgfId=371" CLASS="Hypertext">8.6 UDP instances </A></H2><H2 CLASS="SectionTOC"><A HREF="ch08.7.htm#pgfId=378" CLASS="Hypertext">8.7 Mixing level and edge-sensitive descriptions </A></H2><H2 CLASS="SectionTOC"><A HREF="ch08.8.htm#pgfId=386" CLASS="Hypertext">8.8 Level-sensitive dominance </A></H2></DIV><HR><P><A HREF="none">Chapter start</A> <A HREF="ch08.1.htm">Next page</A></P></BODY></HTML>?? 快捷鍵說明
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