From: Marcus Andree S. Magalhaes (marcus.magalhaes_at_vlinfo.com.br)
Date: Fri Mar 26 2004 - 12:32:20 PST
You're right on this, but we're getting a bit too far from where we
started. We were talking about serial connections.
When I say "modem", in this context, I'm refering to the common
device we all were using a few years ago, to dial up a phone
number, negotiate a serial connection and, say, start a SLIP or
PPP session.
We could have detailed the paragraph above with some letter soup
acronyms like DCE, DTE and other who-cares-what-they-mean words.
In this interim, a 'modem', as you said, auto senses the speed
of connection and, based on a good old Hayes command (the init
string), configures itself to the speed and parameters set on
the computer side of the link.
Now, take this part of the modem and plug it on the serial output
port of a MP2k. Replace the modulator/demodulator, A/D converion with
a centronics port and what do we have? a device that can (or at least
try) to convert a serial comm port to a parallel one.
Remember that, a long time ago, parallel ports were just one-way
data paths. No need to check those bits telling "paper jam" or stuff
like that.
Now, someone might say "Oh, this won't work with my HP Deskjet XYZ
printer because it needs an extra push and two kicks in the butt
to load the sheet of paper".
I say, that's ok. The main goal of the device is to get the two sides
in communication with each other. Now, if something 'additional' needs
to be in place, so things can work flawlessly, that's another question.
The PrintPack cable can be smart enough to, say, using EPP ports, sense
the type of printer it is attached to, check an internal database, and,
finally, do the house keeping job, but, from a technical point of view,
a "serial-to-parallel" converter isn't the rocket science I'm feeling
some people are talking about.
On the other side, I may be seeing things that just are'n there. ;)
>
>>Well, there's a simple serial device that is as "compatible" and
>> "universal" as possible: a modem. Did we _ever_ had to configure _the
>> modem_ to connect to a computer using a serial port? You simply
>>plug it in, turn it on, configure all serial settings from _the
>> computer_ and do _nothing_ to configure the modem itself (except init
>> strings for performance). Do you know why?
>>
>>Well, it's just because the modem _can_ sense the serial line and react
>> correctly to the changes. OK, it's not a printer, but I guess it serves
>> to the simpler purpose of illustrating my point of view... ;)
>
> I'll call BS on this one. A modem is not a modem is not a modem. Take an
> RS232 modem and try to plug it into a PCMCIA slot or into an X25 cable
> or onto the bus of a Motorola MC68332. It won't go.
>
> All that a modem does is modulate and demodulate. The external physical
> connections are a design decision. The conversation between the
> host/modem/modem/terminal is not set by standards. The AT command set
> was invented by a defunct company called Hayes. You can send AT
> commands to sierra wireless CDPD modems but they are not the Hayes
> commands. You can send AT commands to embedded modems that implement
> the TCP/IP stack, once again they are not the Hayes commands.
>
> RS-232 was defined as a 25 pin serial connection. Most PCs/Macs/Modems
> do not implement a great deal of RS-232. A PC cannot handle the
> external baud rate clocks that synchronous modems can generate. But
> it's all RS-232.
>
> A modem cannot necessarily sense the serial line. That is something
> known as autobaud, I haven't seen an implementation of that since the
> 80s. If you are assuming that a modem is a PCI card, that is a
> completely different ball of wax altogether.
>
> If you take a modem to be a parallel to serial converter with an audio
> converter following that, you have a better view of what a modem is. If
> you take a modem to be made by 3Com and it makes your computer talk on
> the phone, you are assuming a huge number of things.
>
> Andrei (don't get me started on WinModems)
>
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-- This is the NewtonTalk list - http://www.newtontalk.net/ for all inquiries Official Newton FAQ: http://www.chuma.org/newton/faq/ WikiWikiNewt for all kinds of articles: http://tools.unna.org/wikiwikinewt/
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