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Subject: Counters - Introduction
Date: Sat, 1 Jan 2011 15:22:46 +0200
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD><TITLE>Counters - Introduction</TITLE>
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<P align=3Dcenter><A name=3DTOC><IMG border=3D0 alt=3DCounters=20
src=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/pics/counter01=
s.gif"=20
width=3D200 height=3D60></A>=20
<H1 align=3Dcenter><FONT color=3Dteal><I>Table of Contents</I></FONT> =
</H1>
<BLOCKQUOTE>
  <H3>&nbsp;&nbsp;&nbsp;<IMG border=3D0=20
  =
src=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/pics/perlred.g=
if"=20
  width=3D13 height=3D13>&nbsp;<A=20
  =
href=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/counter01.htm=
l#Introduction"><B>Introduction</B></A><BR>&nbsp;&nbsp;&nbsp;<IMG=20
  border=3D0=20
  =
src=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/pics/perlyell.=
gif"=20
  width=3D13 height=3D13>&nbsp;<A=20
  =
href=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/counter02.htm=
l"><B>Asynchronous=20
  (Ripple) Counters</B></A><BR>&nbsp;&nbsp;&nbsp;<IMG border=3D0=20
  =
src=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/pics/perloran.=
gif"=20
  width=3D13 height=3D13>&nbsp;<A=20
  =
href=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/counter03.htm=
l"><B>Asynchronous=20
  Decade Counters</B></A><BR>&nbsp;&nbsp;&nbsp;<IMG border=3D0=20
  =
src=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/pics/perlgree.=
gif"=20
  width=3D13 height=3D13>&nbsp;<A=20
  =
href=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/counter04.htm=
l"><B>Asynchronous=20
  Up-Down Counters</B></A><BR>&nbsp;&nbsp;&nbsp;<IMG border=3D0=20
  =
src=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/pics/perlgree.=
gif"=20
  width=3D13 height=3D13>&nbsp;<A=20
  =
href=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/counter05.htm=
l"><B>Synchronous=20
  Counters</B></A><BR>&nbsp;&nbsp;&nbsp;<IMG border=3D0=20
  =
src=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/pics/perloran.=
gif"=20
  width=3D13 height=3D13>&nbsp;<A=20
  =
href=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/counter06.htm=
l"><B>Synchronous=20
  Decade Counters</B></A><BR>&nbsp;&nbsp;&nbsp;<IMG border=3D0=20
  =
src=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/pics/perlyell.=
gif"=20
  width=3D13 height=3D13>&nbsp;<A=20
  =
href=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/counter07.htm=
l"><B>Synchronous=20
  Up-Down Counters</B></A><BR>&nbsp;&nbsp;&nbsp;<IMG border=3D0=20
  =
src=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/pics/perlred.g=
if"=20
  width=3D13 height=3D13>&nbsp;<A=20
  =
href=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/counter08.htm=
l"><B>Applications</B></A><BR></H3></BLOCKQUOTE>
<P><BR><IMG border=3D0=20
src=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/pics/anibar.gi=
f"=20
width=3D600 height=3D1><BR>
<H1 align=3Dcenter><FONT color=3Dpurple><I><A=20
name=3DIntroduction>Introduction</A></I></FONT> </H1>
<BLOCKQUOTE>
  <P align=3Dleft><B>Circuits for counting events are frequently used in =
computers=20
  and other digital systems. &nbsp;Since a counter circuit must remember =
its=20
  past states, it has to possess memory. &nbsp;The chapter about =
flip-flops=20
  introduced how flip-flops are connected to make a counter. &nbsp;The =
number of=20
  flip-flops used and how they are connected determine the number of =
states and=20
  the sequence of the states that the counter goes through in each =
complete=20
  cycle.</B>=20
  <P align=3Dleft><FONT =
color=3D#f4b67d><B><BIG><I>Counters</I></BIG></B></FONT><B>=20
  can be classified into two broad categories according to the way they =
are=20
  clocked:</B><BR>
  <OL>
    <LI>
    <P align=3Dleft><B><FONT color=3D#0080ff>Asynchronous (Ripple) =
Counters</FONT> -=20
    the first flip-flop is clocked by the external clock pulse, and then =
each=20
    successive flip-flop is clocked by the Q or Q' output of the =
previous=20
    flip-flop.</B> </P>
    <LI>
    <P align=3Dleft><B><FONT color=3D#0080ff>Synchronous Counters</FONT> =
- all=20
    memory elements are simultaneously triggered by the same clock.</B>=20
  </P></LI></OL>
  <P align=3Dleft><B>In this tutorial, pure binary, decade and up-down =
counters=20
  within the two categories will be introduced.</B> </P></BLOCKQUOTE>
<P><BR>
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