83 lines
3.8 KiB
HTML
83 lines
3.8 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<HEAD>
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<META NAME="GENERATOR" CONTENT="LinuxDoc-Tools 0.9.21">
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<TITLE>: Appendix A: Very Obsolete Hardware/Software</TITLE>
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<LINK HREF="Serial-HOWTO-23.html" REL=previous>
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<LINK HREF="Serial-HOWTO.html#toc24" REL=contents>
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</HEAD>
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<BODY>
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Next
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<A HREF="Serial-HOWTO-23.html">Previous</A>
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<A HREF="Serial-HOWTO.html#toc24">Contents</A>
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<HR>
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<H2><A NAME="s24">24.</A> <A HREF="Serial-HOWTO.html#toc24">Appendix A: Very Obsolete Hardware/Software</A></H2>
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<H2><A NAME="ss24.1">24.1</A> <A HREF="Serial-HOWTO.html#toc24.1">Replacing pre 1990 UARTS</A>
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</H2>
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<P> Many 486 PCs (old) and all Pentiums (or the like) should have
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modern 16550As (usually called just 16550's) with FIFOs. If you have
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something really old (pre 1990), the chip may unplug so that you may
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be able to upgrade by finding a plug-in 16550A chip and replacing your
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existing 16450 UART. If the functionality has been built into another
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type of chip, you are out of luck. If the UART is socketed, then
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upgrading would be easy if you could find a replacement. The new and
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old are pin-to-pin compatible. It may be more feasible to just buy a
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new serial card on the Internet (few retail stores stock them today)
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or find a used one.</P>
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<H2><A NAME="ss24.2">24.2</A> <A HREF="Serial-HOWTO.html#toc24.2">Two Ports with the Same IO address</A>
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</H2>
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<P>Modern kernels should not allow the opening of ports with the same
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IO address. But one may probe for ports even though they are not
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open. If two ports have the same IO address then old fashioned
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probing by sending commands to the address will erroneously indicate
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only one port. But modem device detection at boot-time should
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discover both ports and report the conflict. In olden days, all sorts
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of errors were reported/observed for devices illegally attempting to
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use the same IO address. See
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<A HREF="Serial-HOWTO-12.html#probing_ss">Probing</A>.</P>
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<H2><A NAME="ss24.3">24.3</A> <A HREF="Serial-HOWTO.html#toc24.3">Configuring by modifying source code</A>
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</H2>
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<P>In the past, to get a certain serial port supported, one might need
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to modify the C source code, perhaps by adding a #define to it.
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Today, the use of parameters for modules or the kernel, or the use of
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configuration options should handle all cases (except possible for
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antique hardware ??).</P>
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<H2><A NAME="ss24.4">24.4</A> <A HREF="Serial-HOWTO.html#toc24.4">Modems on Multiport Cards Obsolete for Sending at 56k</A>
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</H2>
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<P>For a modem to transmit at nearly 56k requires that it be a special
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digital modem and have a digital connection to a digital phone line
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(such as a T1 line). Modems used with serial cards (the modems may
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either be on the serial card or on another card) normally have no such
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digital connection so they can't be used at the 56k speed, and thus
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are obsolete unless one doesn't need to send at 56k. In other words
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they are obsolete for ISP servers but might be OK for small business
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or home use.</P>
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<P>A partial exception to the above are modem banks that connect to
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multiport serial cards where the modem bank can access multiplexed
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digital phone lines. Thus one could use a multiport serial card with
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a few 56k digital modems for sending at 56k. For both analog and
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digital modems there is one modem on each serial port so there needs
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to be an external cable (modem bank to multiport) for each modem.
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This can lead to a large number of cables. So it's less clutter (and
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cheaper) to use internal modems without a multiport card. This makes
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even this "exception" obsolete for high volume work. It's somewhat
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analogous to the lower cost of an internal modem for a desktop PC as
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compared to the higher cost (and more cabling) for an external modem.
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See Modem-HOWTO: Modem Pools, Digital Modems.</P>
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<P> END OF Serial-HOWTO </P>
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<HR>
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Next
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<A HREF="Serial-HOWTO-23.html">Previous</A>
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<A HREF="Serial-HOWTO.html#toc24">Contents</A>
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