[Coco] Coco Modem phone line connection

[Joel Rees]

Thanks for the correction, Dave.

2019年12月3日(火) 5:39 Dave Philipsen <dave at davebiz.com>:

> You can look here at how TDM fits in with the telephone system:
> https://en.wikipedia.org/wiki/Time-division_multiplexing
>
> ...
> Joel replied that he thought the ability to do full duplex on a
> telephone line was related to the fact that the telephone system (PSTN -
> Public Switched Telephone Network) uses time multiplexing. And the fact
> is that the PSTN *does* use time multiplexing but the ability to do full
> duplex analog voice conversations on a single pair of wires is not due
> to this fact. It is due to the inherent design of the telephone itself.
> A telephone (or a modem for that matter) will work just as well if not
> better (in full duplex) *without* time multiplexing. All you have to do
> to prove that is to hook up two telephones over a two wire link with a
> few nine-volt batteries and a resistor and you will have a two-way full
> duplex link over a single pair of wires, no multiplexing required.
>
> Alex replied that phones don't use TDM and that is technically correct.
> The phones themselves do not use it but the PSTN (phone system) that
> they are connected to does. A classic 300 baud modem achieves full
> duplex in much the same way as a telephone handset where two people can
> both be talking at the same time and both can hear each other
> simultaneously.
>
> Dave
>
>
> On 12/1/2019 11:35 AM, Alex Evans wrote:
> > Phones don't use time division multiplexing, and neither do classic
> > analog modems. If we look at the simple case of a 300 baud modem, it
> > manages full duplex because it uses four different tones, two for the
> > answer side and two for the originate side with one tone one each side
> > for 0 and a different one for each side for a 1. Originate uses 1070
> > and 1270 Hz while answer uses 2025 and 2225 Hz. You could call it
> > frequency division multiplexing.
> >
> > On Sun, Dec 1, 2019 at 9:42 AM Dave Philipsen <dave at davebiz.com> wrote:
> >> Actually you can talk full duplex on two telephones by simply connecting
> >> them both to the same relatively high impedance power supply. I think
> >> time division multiplexing is what allows multiple signals
> >> (conversations) to share the same path or pair of wires.
> >>
> >> Dave
> >>
> >>
> >> On 11/30/2019 8:43 PM, Joel Rees wrote:
> >>> Time multiplexing, as I understand it.
> >>>
> >>>
> >>> 2019年11月20日(水) 13:39 Dave Philipsen <dave at davebiz.com>:
> >>>
> >>>> Yes, in much the same way in which one line allows you to both speak
> and
> >>>> listen at the same time (full duplex) using a standard voice
> telephone.
> >>>>
> >>>> Dave
> >>>>
> >>>>> On Nov 19, 2019, at 10:43 AM, rietveld rietveld <
> rietveldh at hotmail.com>
> >>>> wrote:
> >>>>> Does one line do both receive and send of the data?
> >>>>>
> >>>>> Sent from my BlackBerry
> >>>>>    Original Message
> >>>>> From: Gene Heskett
> >>>>> Sent: Tuesday, November 19, 2019 11:25 AM
> >>>>> To: coco at maltedmedia.com
> >>>>> Reply To: CoCoList for Color Computer Enthusiasts
> >>>>> Subject: Re: [Coco] Coco Modem phone line connection
> >>>>>
> >>>>>
> >>>>>> On Tuesday 19 November 2019 11:17:10 rietveld rietveld wrote:
> >>>>>>
> >>>>>> It looks like the coco only uses the middle two wires(red and green)
> >>>>>> on a four line phone cord.   Is this correct?
> >>>>>>
> >>>>> Probably, since thats all it takes to run a telephone.
> >>>>>
> >>>>>> Sent from my BlackBerry
> >>>>> Cheers, Gene Heskett
> >>>>> --
> >>>>> "There are four boxes to be used in defense of liberty:
> >>>>> soap, ballot, jury, and ammo. Please use in that order."
> >>>>> -Ed Howdershelt (Author)
> >>>>> If we desire respect for the law, we must first make the law
> respectable.
> >>>>> - Louis D. Brandeis
> >>>>> Genes Web page <http://geneslinuxbox.net:6309/gene>
> >>>>>
> >>>>> --
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> >>
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