Re: [TECH] Modem-to-Modem wire connection

From: Michele Andreoli (
Date: Sun Apr 23 2000 - 22:28:06 CEST

On Sun, Apr 23, 2000 at 07:39:58PM +0100, Clive Wright nicely wrote:
> Michele Andreoli wrote:
> >
> <snip>
> >
> > Do not worry about that: I know AT command. My only doubt is about
> > cable, because usually crossover is needed: transmit pin connected
> > to receiving pin, on the other side, and so on.
> >
> Unlike RS232 the connection to a modem is a wire loop there
> is no separate rx and tx line and a zero volt (ground plane)
> connection is not required.
> A crossover is not needed but if one is present it will not
> make any difference as long as the loop is intact. Telephone
> instruments usually receive their power from a (voltage
> limited) constant current source at the telephone exchange;
> but as modems do not depend on the line for power, the lack
> of a DC power source should not present a problem.

This seems very raisonable: from physical point of view, this is
a AC current over two wire. What is missing in my harddisk, is a
tools to track what modem is really receiving (a part LED).


I'd like to conclude with a positive statement, but I can't 
remember any. Would two negative ones do?       -- Woody Allen
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