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<P>[ <A HREF="CH06.htm">Chapter start</A> ] [ <A HREF="CH06.8.htm">Previous page</A> ] [ <A HREF="CH06.a.htm">Next page</A> ]</P><!--#include file="AmazonAsic.html"--><HR></DIV>
<H1 CLASS="Heading1">
<A NAME="pgfId=34992">
</A>
6.9 <A NAME="13053">
</A>
Summary</H1>
<P CLASS="BodyAfterHead">
<A NAME="pgfId=34993">
</A>
Among the options available in I/O cells are: different drive strengths, TTL-compatibility, registered or direct inputs, registered or direct outputs, pull-up resistors, over-voltage protection, slew-rate control, and boundary-scan. <A HREF="CH06.9.htm#26448" CLASS="XRef">
Table 6.4</A>
shows a list of features. Interfacing an ASIC with a system starts at the outputs where you check the voltage levels first, then the current levels. <A HREF="CH06.a.htm#15005" CLASS="XRef">
Table 6.5</A>
is a look-up table for Tables <A HREF="CH06.a.htm#30436" CLASS="XRef">
6.6</A>
and <A HREF="CH06.a.htm#23383" CLASS="XRef">
6.7</A>
, which show the I/O resources present in each type of programmable ASIC (using the abbreviations of <A HREF="CH06.9.htm#26448" CLASS="XRef">
Table 6.4</A>
). </P>
<TABLE>
<TR>
<TD ROWSPAN="1" COLSPAN="3">
<P CLASS="TableTitle">
<A NAME="pgfId=43124">
</A>
TABLE 6.4 <A NAME="26448">
</A>
I/O options for programmable ASICs.</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43914">
</A>
<SPAN CLASS="TableHeads">
Code</SPAN>
<SUP CLASS="Superscript">
<A HREF="#pgfId=59090" CLASS="footnote">
1</A>
</SUP>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43128">
</A>
<SPAN CLASS="TableHeads">
I/O Option</SPAN>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43130">
</A>
<SPAN CLASS="TableHeads">
Function</SPAN>
</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43916">
</A>
IT/C</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43132">
</A>
TTL/CMOS input</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43134">
</A>
Programmable input buffer threshold</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43918">
</A>
OT/C</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43136">
</A>
TTL/CMOS output</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43138">
</A>
Complementary or totem-pole output</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=44148">
</A>
nSNK</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=44150">
</A>
Sink capability</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=44152">
</A>
Maximum current sink ability (e.g., 12SNK is I <SUB CLASS="Subscript">
0</SUB>
= 12 mA sink)</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=44142">
</A>
nSRC</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=44144">
</A>
Source capability</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=45359">
</A>
Maximum current source ability (e.g., 12SRC is I <SUB CLASS="Subscript">
0</SUB>
= –12 mA source)</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43920">
</A>
5/3</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43140">
</A>
5V/3V</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43142">
</A>
Separate I/O and core voltage supplies</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43922">
</A>
OD</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43144">
</A>
Open drain/collector</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43146">
</A>
Programmable open-drain at the output buffer</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43924">
</A>
TS</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43148">
</A>
Three-state</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43150">
</A>
Output buffer with three-state control</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43926">
</A>
SR</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43152">
</A>
Slew-rate control</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43154">
</A>
Fast or slew-rate limited output buffer to reduce ground bounce</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43928">
</A>
PD</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43156">
</A>
Pull-down</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43158">
</A>
Programmable pull-down device or resistor at the I/O pad</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43968">
</A>
PU</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43970">
</A>
Pull-up</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43974">
</A>
Programmable pull-up device or resistor at the I/O pad</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43930">
</A>
EP</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43160">
</A>
Enable polarity</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43162">
</A>
Driver control can be positive (three-state) or negative (enable).</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43932">
</A>
RI</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43164">
</A>
Registered input</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43166">
</A>
Inputs may be registered in I/O cell.</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43949">
</A>
RO</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43951">
</A>
Registered output</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43953">
</A>
Outputs may be registered in I/O cell.</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43943">
</A>
RIO</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43945">
</A>
Registered I/O</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43955">
</A>
Both inputs and outputs may be registered in I/O cell.</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43934">
</A>
ID</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43168">
</A>
Input delay</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43170">
</A>
Input delay to eliminate input hold time</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43936">
</A>
JTAG</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43172">
</A>
JTAG</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=43174">
</A>
Boundary-scan test</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=44101">
</A>
SCH</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=44103">
</A>
Schmitt trigger </P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=44105">
</A>
Schmitt trigger or input hysteresis</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=44128">
</A>
HOT</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=44130">
</A>
Hot insertion</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=44132">
</A>
Inputs protected from hot insertion</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=44122">
</A>
PCI</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=44124">
</A>
PCI compliant</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=44126">
</A>
Output buffer characteristics comply with PCI specifications.</P>
</TD>
</TR>
</TABLE>
<P CLASS="Body">
<A NAME="pgfId=42867">
</A>
Important points that we covered in this chapter are the following:</P>
<UL>
<LI CLASS="BulletFirst">
<A NAME="pgfId=32657">
</A>
Outputs can typically source or sink 5–10 mA continuously into a DC load, and 50–200 mA transiently into an AC load.</LI>
<LI CLASS="BulletList">
<A NAME="pgfId=27319">
</A>
Input buffers can be CMOS (threshold at 0.5 <SPAN CLASS="EquationVariables">
V</SPAN>
<SUB CLASS="SubscriptVariable">
DD</SUB>
) or TTL (1.4 V).</LI>
<LI CLASS="BulletList">
<A NAME="pgfId=27320">
</A>
Input buffers normally have a small hysteresis (100–200 mV).</LI>
<LI CLASS="BulletList">
<A NAME="pgfId=43112">
</A>
CMOS inputs must never be left floating.</LI>
<LI CLASS="BulletList">
<A NAME="pgfId=43115">
</A>
Clamp diodes to GND and VDD are present on every pin.</LI>
<LI CLASS="BulletList">
<A NAME="pgfId=27325">
</A>
Inputs and outputs can be registered or direct.</LI>
<LI CLASS="BulletList">
<A NAME="pgfId=43178">
</A>
I/O registers can be in the I/O cell or in the core.</LI>
<LI CLASS="BulletLast">
<A NAME="pgfId=30844">
</A>
Metastability is a problem when working with asynchronous inputs.</LI>
</UL>
<HR>
<DIV CLASS="footnotes">
<DIV CLASS="footnote">
<P CLASS="TableFootLast">
<SPAN CLASS="footnoteNumber">
1.</SPAN>
<A NAME="pgfId=59090">
</A>
These codes are used in Tables <A HREF="CH06.a.htm#30436" CLASS="XRef">
6.6</A>
and <A HREF="CH06.a.htm#23383" CLASS="XRef">
6.7</A>
.</P>
</DIV>
</DIV>
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