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Subject: Asynchronous Decade Counters
Date: Sat, 1 Jan 2011 15:23:17 +0200
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<HTML><HEAD><TITLE>Asynchronous Decade Counters</TITLE>
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s.gif"=20
width=3D200 height=3D60>=20
<H1 align=3Dcenter><FONT color=3Dpurple><I>Asynchronous<BR>Decade=20
Counters</I></FONT> </H1>
<BLOCKQUOTE><B>The binary counters previously introduced have two to the =
power=20
  <I>n</I> states. &nbsp;But counters with states less than this number =
are also=20
  possible. &nbsp;They are designed to have the number of states in =
their=20
  sequences, which are called <FONT color=3D#0080ff>truncated =
sequences</FONT>.=20
  &nbsp;These sequences are achieved by forcing the counter to recycle =
before=20
  going through all of its normal states.</B>=20
  <P><B>A common modulus for counters with truncated sequences is ten. =
&nbsp;A=20
  counter with ten states in its sequence is called a&nbsp;<FONT=20
  color=3D#ff00ff><I><BIG>decade counter</BIG></I></FONT>. &nbsp;The =
circuit below=20
  is an implementation of a decade counter.</B> </P></BLOCKQUOTE>
<P align=3Dcenter><IMG border=3D0 alt=3D"Decade Counter"=20
src=3D"http://www.eelab.usyd.edu.au/digital_tutorial/part2/pics/count03.j=
pg"=20
width=3D540 height=3D184>=20
<BLOCKQUOTE><B><BR>Once the counter counts to ten (1010), all the =
flip-flops=20
  are being cleared. &nbsp;Notice that only Q1 and Q3 are used to decode =
the=20
  count of ten. &nbsp;This is called <FONT color=3D#0080ff>partial=20
  decoding</FONT>, as none of the other states (zero to nine) have both =
Q1 and=20
  Q3 HIGH at the same time.</B>=20
  <P><B>The sequence of the decade counter is shown in the table =
below:</B>=20
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