Sophie: howto-html-en-20080722-2mdv2010.1 noarch

howto-html-en-20080722-2mdv2010.1.noarch.rpm

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NAME="SERIAL-DISTANCE"
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>11.4. Lengths of serial cables</H1
><P
>The <SPAN
CLASS="ACRONYM"
>RS-232</SPAN
> standard 9600bps port will
   drive 15 metres of shielded cable.  More precisely, an
   <SPAN
CLASS="ACRONYM"
>RS-232</SPAN
> line driver will operate against a
   capacitance of up to 2500 picoFarad with low enough skew to allow a
   9600bps signal to be recovered.</P
><P
>If you select a cable with lower capacitance you can drive
   further distances.  For example,
   <I
CLASS="CITETITLE"
><SPAN
CLASS="ACRONYM"
>ANSI/TIA/EIA-568-A</SPAN
></I
>
   unshielded twisted pair category 5 cable has a maximum capacitiance
   of 55<SPAN
CLASS="ACRONYM"
>pF</SPAN
> per metre, so this popular
   <SPAN
CLASS="QUOTE"
>"<SPAN
CLASS="ACRONYM"
>UTP</SPAN
> cat 5"</SPAN
> cable can be safely
   driven up to 45m.  Beyond that you should check the cable
   manufacturers specifications for the actual <SPAN
CLASS="QUOTE"
>"shunt
   capacitance"</SPAN
> (a common figure is 47.5
   <SPAN
CLASS="ACRONYM"
>pF/m</SPAN
>, giving a maximum cable length of about
   50<SPAN
CLASS="ACRONYM"
>m</SPAN
>).  However long runs of unshielded cable
   will pick up noise easily, as the <SPAN
CLASS="ACRONYM"
>RS-232</SPAN
> signals
   are not balanced.  Some cable manufacturers offer shielded low
   capacitance cables which can be driven up to
   100<SPAN
CLASS="ACRONYM"
>m</SPAN
>.</P
><P
>Similarly, if you select a lower data rate you can drive
   further distances.  <A
HREF="serial-distance.html#SERIAL-MANUFACTURE-DISTANCE"
>Table 11-1</A
>
   shows the maximum distances over standard shielded cable at
   differing data rates.</P
><DIV
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><A
NAME="SERIAL-MANUFACTURE-DISTANCE"
></A
><P
><B
>Table 11-1. Data rates and the maximum distances recommended in
    <I
CLASS="CITETITLE"
>RS-232</I
></B
></P
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><THEAD
><TR
><TH
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>Data rate (bps)</TH
><TH
WIDTH="50%"
ALIGN="CENTER"
VALIGN="TOP"
>Distance (m)</TH
></TR
></THEAD
><TBODY
><TR
><TD
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><P
>2400</P
></TD
><TD
WIDTH="50%"
ALIGN="CENTER"
VALIGN="TOP"
><P
>60</P
></TD
></TR
><TR
><TD
WIDTH="50%"
ALIGN="CENTER"
VALIGN="TOP"
><P
>4800</P
></TD
><TD
WIDTH="50%"
ALIGN="CENTER"
VALIGN="TOP"
><P
>30</P
></TD
></TR
><TR
><TD
WIDTH="50%"
ALIGN="CENTER"
VALIGN="TOP"
><P
>9600</P
></TD
><TD
WIDTH="50%"
ALIGN="CENTER"
VALIGN="TOP"
><P
>15</P
></TD
></TR
><TR
><TD
WIDTH="50%"
ALIGN="CENTER"
VALIGN="TOP"
><P
>19200</P
></TD
><TD
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><P
>7.6</P
></TD
></TR
><TR
><TD
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><P
>38400</P
></TD
><TD
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><P
>3.7</P
></TD
></TR
><TR
><TD
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><P
>56000</P
></TD
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><P
>2.6</P
></TD
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><P
>If you are comfortable in working beyond specifications then
   you might note that the experience of enterprise network operators
   has been that structured cabling layout in buildings is limited by
   the 100m distance limitation of fast ethernet over category 5
   cable, not by the practical distances achieved by RS-232
   asynchronous signals at 9600bps over category 5 cable.</P
><P
>For longer distances use an <SPAN
CLASS="ACRONYM"
>RS-232</SPAN
> line
   driver; these will typically drive up to 2000 meters over category
   3 <SPAN
CLASS="ACRONYM"
>UTP</SPAN
> cable.  For greater distances consider
   using fiber optical modems, the global telephony system, the mobile
   telephony system, satellite or radio.</P
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