358 lines
5.4 KiB
HTML
358 lines
5.4 KiB
HTML
<HTML
|
|
><HEAD
|
|
><TITLE
|
|
>Lengths of serial cables</TITLE
|
|
><META
|
|
NAME="GENERATOR"
|
|
CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
|
|
REL="HOME"
|
|
TITLE="Remote Serial Console HOWTO"
|
|
HREF="index.html"><LINK
|
|
REL="UP"
|
|
TITLE="Serial cabling"
|
|
HREF="serial.html"><LINK
|
|
REL="PREVIOUS"
|
|
TITLE="Cable from console port to terminal (or another PC)"
|
|
HREF="serial-pc-terminal.html"><LINK
|
|
REL="NEXT"
|
|
TITLE="Making serial cables"
|
|
HREF="serial-manufacture.html"></HEAD
|
|
><BODY
|
|
CLASS="SECTION"
|
|
BGCOLOR="#FFFFFF"
|
|
TEXT="#000000"
|
|
LINK="#0000FF"
|
|
VLINK="#840084"
|
|
ALINK="#0000FF"
|
|
><DIV
|
|
CLASS="NAVHEADER"
|
|
><TABLE
|
|
SUMMARY="Header navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TH
|
|
COLSPAN="3"
|
|
ALIGN="center"
|
|
>Remote Serial Console HOWTO</TH
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="left"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="serial-pc-terminal.html"
|
|
ACCESSKEY="P"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="80%"
|
|
ALIGN="center"
|
|
VALIGN="bottom"
|
|
>Chapter 11. Serial cabling</TD
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="right"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="serial-manufacture.html"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"></DIV
|
|
><DIV
|
|
CLASS="SECTION"
|
|
><H1
|
|
CLASS="SECTION"
|
|
><A
|
|
NAME="SERIAL-DISTANCE"
|
|
></A
|
|
>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
|
|
CLASS="TABLE"
|
|
><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
|
|
><TABLE
|
|
BORDER="1"
|
|
CLASS="CALSTABLE"
|
|
><THEAD
|
|
><TR
|
|
><TH
|
|
WIDTH="50%"
|
|
ALIGN="CENTER"
|
|
VALIGN="TOP"
|
|
>Data rate (bps)</TH
|
|
><TH
|
|
WIDTH="50%"
|
|
ALIGN="CENTER"
|
|
VALIGN="TOP"
|
|
>Distance (m)</TH
|
|
></TR
|
|
></THEAD
|
|
><TBODY
|
|
><TR
|
|
><TD
|
|
WIDTH="50%"
|
|
ALIGN="CENTER"
|
|
VALIGN="TOP"
|
|
><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
|
|
WIDTH="50%"
|
|
ALIGN="CENTER"
|
|
VALIGN="TOP"
|
|
><P
|
|
>7.6</P
|
|
></TD
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="50%"
|
|
ALIGN="CENTER"
|
|
VALIGN="TOP"
|
|
><P
|
|
>38400</P
|
|
></TD
|
|
><TD
|
|
WIDTH="50%"
|
|
ALIGN="CENTER"
|
|
VALIGN="TOP"
|
|
><P
|
|
>3.7</P
|
|
></TD
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="50%"
|
|
ALIGN="CENTER"
|
|
VALIGN="TOP"
|
|
><P
|
|
>56000</P
|
|
></TD
|
|
><TD
|
|
WIDTH="50%"
|
|
ALIGN="CENTER"
|
|
VALIGN="TOP"
|
|
><P
|
|
>2.6</P
|
|
></TD
|
|
></TR
|
|
></TBODY
|
|
></TABLE
|
|
></DIV
|
|
><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
|
|
></DIV
|
|
><DIV
|
|
CLASS="NAVFOOTER"
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"><TABLE
|
|
SUMMARY="Footer navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="serial-pc-terminal.html"
|
|
ACCESSKEY="P"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="index.html"
|
|
ACCESSKEY="H"
|
|
>Home</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="serial-manufacture.html"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
>Cable from console port to terminal (or another PC)</TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="serial.html"
|
|
ACCESSKEY="U"
|
|
>Up</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
>Making serial cables</TD
|
|
></TR
|
|
></TABLE
|
|
></DIV
|
|
></BODY
|
|
></HTML
|
|
> |