On Fri, 06 Dec 2002 07:07:57 -0500, "Gan Uesli Starling"
<alias@starling.us> wrote:
> James K. Lowden writes: 
> 
> > I think this would work for two machines.  In terms of RS-232,
> > assuming these machines are within 100 feet of each other, I don't see
> > any reason you couldn't tie their DTRs together and their CDs
> > together, and bridge them both with the same close-on-battery curcuit.
> >   
> 
> This seems is a good idea...except for one tiny thing...
> the part about multiple machines on a single contact. 
> 
> I am a little fuzzy on this...but I do not think you should
> wire a pair of DTR lines together. If memory serves, DTR
> supplies a tone, yes? 

No, ixna on the oneta.  

RS-232 is well documented.  No modulation, no phase, just simple voltages
relative to signal ground on pin 7.  "Tone" happens on the other side of
the modem, where the modulation and demodulation takes place, when your
nice clean bits encounter the legacy of Mr. Bell.  

(It's a good thing he was Alexander Graham Bell, eh?  I mean, imagine if
his last name had been Gong, or Siren, or Car Alarm, or
Fingernails-on-Blackboard.  What kind of noise would your phone make? 
Funny, these little quirks in history that shape our society.)

The liability of tying the two machines' DTRs together is that they might
not agree on what "ground" is.  I think that could be safely solved by
tying the signal (and maybe chassis for good measure) grounds together,
too.  But hey, I was getting a BA when the wireheads were getting their
EEs and I wouldn't use a soldering iron except in self defense.  

I just bought a null modem at Radio Shack yesterday, $6.  My first one
(still in use) I made myself for $70 in parts (that's not a typo).  There
are things to like about the new good days.  

--jkl

> PS - Hi James. 

Hi Gan!