10 Nov
2010
10 Nov
'10
11:37 a.m.
On 2010 Nov 9, at 5:41 AM, Shoppa, Tim wrote:
I suspect there are some dubious cases, and that the LDS120 is one of them...
Some things are clearly modems by any sensible defintion. I don;t think
anyone would try to claim that the think I downloaded this message with
(an old US Robotics Sportster 14K4) is not a modem. Similarly, the
RS232-RS422 interface I have one the shelf is a line driveer by most
definitions. It does, indeed, 'drive a line'.
The LDS120 is in the middle. Yes, it drives a farily long cable. But it
also IMHO changes the incoming date into a pulse train and one end and
changes it back again at the other. That could certainly be considered to
be a form of modulation and demodulation.
De writes:
Yet Another Terminology Debate. In common parlance, I think "modem" has
frequently been used where "line driver" would be more technically
correct. > I am looking for info on a Gandalf LDS120
modem, specifically the
> serial port pinout.
In the division of irrelevant to the original
question, I thought
these
things were line drivers, not modems.
I always thought they got lumped into "short haul 4-wire modems". At ubc, in the
mainframe/MTS/centralised-computing-service days of the
70s/80s, the terminals spread around the campus had ubiquitous little
white plastic utility boxes with a couple of leds on the front sitting
by the terminal. They were RS-232<->4-wire line-drivers, built in-house
by the computing centre. I think they started building them out of
necessity before manufacturers entered the market in a big way.
I extracted one from a junk pile some years ago for nostalgia/history's
sake.
What's inside?
The LDS120 seems ot bave been fairly common in UK Universities. They were
used to link up the Cambridge University Data Network when I was an
undergraduate in the 1980s (I beleive they carried X25 signals from the
JNT-PADs). The first one I bought (at a radio rally) had a label on it
indicating it came from The Other Place. And I got more in a clearout at
Bristol University some years later.
-tony