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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="ch07.css"><TITLE> 7.8 Pullup and pulldown sources</TITLE></HEAD><BODY BGCOLOR="#ffffff"><DIV><HR><P><A HREF="ch07.htm">Chapter start</A> <A HREF="ch07.7.htm">Previous page</A> <A HREF="ch07.9.htm">Next page</A></P></DIV><H1 CLASS="Section"><A NAME="pgfId=1519"> </A>7.8 <A NAME="gate descriptions end"> </A>P<A NAME="marker=315"> </A><A NAME="marker=316"> </A><A NAME="marker=317"> </A>ullup and <A NAME="marker=318"> </A>p<A NAME="marker=319"> </A><A NAME="marker=320"> </A>ulldown <A NAME="marker=321"> </A><A NAME="marker=322"> </A>sources</H1><P CLASS="Body"><A NAME="pgfId=1024"> </A>The instance declaration of a pullup or a pulldown source shall begin with one of the following keywords: </P><PRE CLASS="CodeIndent"><A NAME="pgfId=1520"> </A><B CLASS="Keyword">pullup</B> <B CLASS="Keyword">pulldown</B></PRE><P CLASS="Body"><A NAME="pgfId=1521"> </A>A <B CLASS="Keyword">pullup</B> source shall place a logic value <CODE CLASS="code">1</CODE> on the nets connected in its terminal list. A <B CLASS="Keyword">pulldown</B> source shall place a logic value <CODE CLASS="code">0</CODE> on the nets connected in its terminal list. The signals that these sources place on nets shall have <B CLASS="Keyword">pull</B> strength in the absence of a strength specification. There shall be no delay specifications for these sources. </P><DIV><H2 CLASS="Example"><A NAME="pgfId=1522"> </A></H2><P CLASS="Body"><A NAME="pgfId=1032"> </A>The following example declares two <B CLASS="Keyword">pullup</B> instances:</P><PRE CLASS="CodeIndent"><A NAME="pgfId=1523"> </A><B CLASS="Keyword">pullup</B> <B CLASS="Keyword">(strong1)</B> p1 (neta), p2 (netb);</PRE><P CLASS="Body"><A NAME="pgfId=1524"> </A>In this example, <CODE CLASS="code">p1</CODE> instance drives <CODE CLASS="code">neta</CODE> and the other <CODE CLASS="code">p2</CODE> instance drives <CODE CLASS="code">netb</CODE>.</P></DIV><HR><P><A HREF="ch07.htm">Chapter start</A> <A HREF="ch07.7.htm">Previous page</A> <A HREF="ch07.9.htm">Next page</A></P></BODY></HTML>?? 快捷鍵說明
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