Brent Hilpert hilpert at
Tue Nov 9 16:07:08 CST 2010

On 2010 Nov 9, at 5:41 AM, Shoppa, Tim wrote:

> De writes:
>>> 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".

Yet Another Terminology Debate. In common parlance, I think "modem" has 
frequently been used where "line driver" would be more technically 

> 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 

TMR, Gandalf and Develcon were the major competitors for the 
terminal-switch / line-driver market in the late-70's/80's.

More information about the cctech mailing list