On Mon, May 05, 2008 at 03:34:45PM -0700, Fred Cisin wrote:
When Joe Campbell was writing his serial books, he was
running 9600
through a SPOOL (~1000 feet) of wire. Apparently the cable lengths in the
RS232 specs are somewhat conservative in their "limits".
We used to run CAT3 (telco) wire across a 5000 sq ft building from user
terminals to our machine room (via the Nevada Western RJ-11 modular gear
I mentioned earlier this year). We couldn't get reliable 19200 comms,
but we were solid at 9600 for interactive sessions or Kermit transfers
and the like.
There was only one thing that we noticed that was strange - typically to
log in, you'd tap the return key a couple of times to get the host port
to lock onto your current baud rate. We usually saw one lowercase 'u'
echoed per press of the return key prior to getting the login prompt.
Once we got characters from the host, we didn't see the strange echo.
We always attributed that to an unloaded line from the host and
crosstalk between the Tx and RX pair between the terminal and the
host, but perhaps someone else has a theory.
In any case, we were well past the normally accepted cable length and
had probably millions of keystrokes go through intact.
For a single point-to-point extra-long serial cable, one can explore
expensive, low-capacitance transmission cable, or perhaps RS-422/RS-232
converters, but I think Tony was less interested in long cables to
trip unwary mammals anyway (or else short-haul fiber modems could be
a possibility).
I have some of the same requirements as Tony for interconnecting older
devices, but my solution was to blow a hole in the computer room wall
and run fiber, 10Base2, CAT5, and 25-pr Telco cable between the second
floor and the basement, reducing the trip hazard.
-ethan
--
Ethan Dicks, A-333-S Current South Pole Weather at 5-May-2008 at 23:00 Z
South Pole Station
PSC 468 Box 400 Temp -65.7 F (-54.3 C) Windchill -97.8 F (-72.1 C)
APO AP 96598 Wind 8.9 kts Grid 55 Barometer 697.0 mb (9993 ft )
Ethan.Dicks at
usap.gov http://penguincentral.com/penguincentral.html