1964 Antique MODEM Live Demo

[Brent Hilpert]

Dave McGuire wrote:
> 
> On May 30, 2009, at 6:46 PM, Chris Elmquist wrote:
> >> So, you can't see a possible set of circumstances where having the
> >> wrong
> >> voltage coming in the serial port could cause the frequency shift
> >> to be
> >> wrong?
> >>
> >> How clever do you think the tone generator side is?
> >
> > Well, as Tony replied-- I think that the RS232 input is a logic level.
> > It's not an analog level.  So, you are going to get either the mark
> > tone
> > or the space tone and not something in between.
> >
> > I think this situation was just a poor explaination of what went
> > wrong.
> > Whatever miscable situation he had caused him to generate the opposite
> > tone of what he was expecting but not a tone that was off frequency
> > from
> > one of the two possibilities.
> 
>    Was it in fact the opposite tones (i.e., mark/space reversed) or
> could it have been an originate mode vs. answer mode issue?  Many
> (most?) modems could be switched between the two sets of tones.

It's a very primitive originate-only modem, I beleive my previous post
explained the mark-space tone behaviour the fellow was observing when he
plugged the cable in. I don't see any unexpected behaviour from (my instance
of) the modem. One would have to go through hoops to get mark/space reversed.
If there was some other problem I think it must have been a configuration issue
on the DTE/terminal-emulation end. As Chris says, his explanation was a little off.