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The Answer Guy 32:
High Speed Serial (RS422) under Linux
"Linux Gazette...making Linux just a little more fun!"
 High Speed Serial (RS422) under Linux
From Sujeetharan Sivasubramaniyam on 18 Aug 1998
Hi I want to use RS422 card under linux. I am not sure whether this
is suppored by linux already. Also I would like to see some
documentation on this. Any pointers will be greatly appreciated!
Thanks
Since you don't mention which specific card you are
hoping to use, I'll assume that you are willing to
buy a new/supported card if necessary.
Naturally, with any question about supported hardware,
the first place to check is the Hardware-HOWTO
(http://sunsite.unc.edu/LDP/HOWTO/Hardware-HOWTO.html).
At first we might be led astray (searching on serial
gets us to section 26.6: "Modems and Serial Cards"
--- but that's in reference to PCMCIA cards). However,
we don't find any references to 422 under "Controllers, I/O"
and "Controllers, Multiport" nor anywhere else in the HOWTO.
Running the Excite search on the LDP site using the string
"422" doesn't net any useful results either.
So, we have to dig a bit deeper. A Yahoo search using the
string "+rs422 +linux" nets about 53 hits. The first
of these is from NTLUG (North Texas Linux User's Group)
which lists a company called Vikom, in Irving, TX with
the note:
- "manufactures RS232 and RS422 multiport cards
for Linux"
- (http://www.ntlug.org/lint/index.html).
... No URL or contact information is provided.
Another result of this Yahoo! search is for GTek Inc.
(a long-time manufacturer of serial hardware for PC's).
They list a Cyclone 6 and note that there are "RS422 and
RS485 interfaces available" and separately they say:
- "Drivers are available for all popular operating
systems: WindowsNT, Windows95, Linux, OS/2 and DOS."
- http://www.gtek.com/news.html.
(Granted, this second lead is buried under about a
dozen unlikely results that I didn't follow).
You might also search the Equinox, Digi, Specialix,
and other web pages for manufacturers of specialized
and multi-port serial hardware to see if they have
something that suits your needs.
Presumably there is some RS422 support built into the
Kernel --- at least in the PPC (PowerPC) port. As far
as I know most Mac's and Mac clones shipped with built-in
RS-422 (a.k.a. EIA-422) ports for their modems (and
printers?).
I also found a note that seems to confirm my own experience
--- that is is possible to interface RS-422 connectors to
most RS-232 devices using the proper cabling (the classic
"Mac to PC Modem" cable). There is even one message
about using a special cable to connect an Apple printer
to a PC's serial port. This suggests that some RS-422 devices
can be interfaced to RS-232, as well. (I mention this since
your requirements aren't clear from your message --- potentially
you don't need an RS-422 interface at all).
Obviously if you already have a specific device and
you are interested in details about that RS-422 card
you'll have to provide details about it. Since I don't
have any first-hand experience with any RS-422 hardware on
PC's and I've shown exactly how I did my searches, it would
make sense to do your own searches for support on your
card. If you can't find a manufacturers label or any
docs on the card (i.e. you inherited it in "used" condition)
then you're probably out of luck.
Copyright © 1998, James T. Dennis
Published in Linux Gazette Issue 32 September 1998
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