9 Nov
2010
9 Nov
'10
2:07 p.m.
On 2010 Nov 9, at 5:41 AM, Shoppa, Tim wrote:
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". They do have "DCD" lights on the front. I
seem to recall that it's just
a light and doesn't actually assert any RS-232 pins. But they could
just
be differential line drivers probably with isolation.
20+ years ago I'm sure I looked inside to see what's in there but I
can't recall. I always thought they did some simplistic and almost
certainly
not Bell-standard FSK or PSK but
that was just my impression, no actual evidence to back that up.
Did the 4-wire screws on the back have labels of "+" and "-"?
That would be a point in favor of them being line drivers and not
modems
(although some simple modems were in fact phase-sensitive).
We used them between serial concentrators on different floors or
between serial concentrators between nearby buildings.
I note that there's no Gandalf directory at bitsavers. Gandalf
certainly has a unique heritage not really being a "computer"
company in the usual sense but for so many of us it was the
gateway from terminal to the computer or between computers. I
get the impression they were far more common at large academic
institutions than at any commercial site.
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.
TMR, Gandalf and Develcon were the major competitors for the
terminal-switch / line-driver market in the late-70's/80's.