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From: Michael A. Terrell on 3 Jan 2010 00:49

David Nebenzahl wrote:
>
> On 1/2/2010 4:37 PM Adrian C spake thus:
>
> > David Nebenzahl wrote:
> >>
> >> Everything seems configured correctly: I've set the speed at both ends
> >> to 56K and disabled waiting for dial tone.
> >>
> >> So what am I doing wrong here?
> >
> > The maximun speed you should set for is 33.6 kbps analogue.
> >
> > Above that, the communication relies on connection to an ISP's modem
> > rack port supporting digital network signalling, something that is
> > missing on your back-to-back attempt.
>
> Thanks. I bumped the speed down to 19,200 (I think*); the sounds were
> different, but still no success.
>
> Couple questions:
>
> 1. Are the sounds one hears on the RX side those of the sending modem,
> the RX one or both?
>
> 2. * Hard to tell with HyperTerminal what speed is actually being used.
> I configured to modem to use a maximum speed of 19,200, but HT still
> said "112xxx" (forget the exact #s) until I went and re-configured the
> modem, at which time it then said 19200.
>
> This really should work.


Both modems are set for the same mode. One has to be switched so you
have 'Answer' & 'Originate' modes.

http://hw-server.com/docs/atcommset.html lists some of the commands
in the old Hayes compatible series.

Some early terminal programs set up the modem for you. Some people
just used a freeware 'Bulletin Board' program to get around the problem.

As far as the DC voltage, some modems don't have the telephone line
transformer. They use a set of diodes instead. These need enough
voltage to forward bias them, but it has to be current limited to a few
mA to prevent damage. The DC voltage on a phone line is listed as -48
volts nominal and referenced to ground, but if you were close to the
older type central office it was in the low to mid 50 volt range.

You can also use 'Direct Cable Connection' for serial or parallel
connection of two computers. The cables are easy to make, and a lot
faster than using modems.

Open 'help' in the windows start menu and type cable into the search
box for information. I used to use the parallel port version in Dos and
Win 3.1 days to install software on some computers. That way I didn't
have to install, then remove a CD-ROM drive to install the OS and
drivers. It was also useful to run OEM drive software to repair screwed
up drives after people tried to do Win 95 installs and messed up the low
level format.

Another approach is an external drive enclosure with a USB
interface. Pull the one drive and slave it to the other computer.


The simplest though, is a pair of $10 network cards and a ethernet
cable.

--
Greed is the root of all eBay.
From: JR North on 3 Jan 2010 01:26
There are a number of pc-pc connection programs; I use PCanywhere:
http://www.symantec.com/norton/symantec-pcanywhere
Much cheaper if you shop around.
JR


On Sat, 02 Jan 2010 16:20:44 -0800, David Nebenzahl
<nobody(a)but.us.chickens> wrote:

>I know it can be done, but am having trouble making it work.
>
>The idea is to connect 2 PCs directly through their modems. Not cable
>modems, ordinary 56K modems. I call it my "Poor Man's Network".
>
>I've found the following pages that describe this operation:
>
>http://phorums.com.au/archive/index.php/t-120530.html
>http://www.jagshouse.com/modem.html
>
>That second link suggests powering the connecting line with ~24 VDC, but
>I don't think that's actually necessary. (The first link describes
>connecting two computeri via modem with no extra hardware needed.)
>
>So when I set this up--2 computeri with connected modems, using
>HyperTerminal at each end, with the following commands:
>
>o sending computer: ATX3D
>o receiving computer: ATA
>
>I hear stuff through the speaker on the RX end, typical modem connect
>tones to start, but I don't hear all that "chirping" usually associated
>with dial-up connections; just a steady, low tone that lasts for, say,
>30 seconds or so, then the connection goes dead and I get "NO CARRIER"
>at both ends.
>
>Everything seems configured correctly: I've set the speed at both ends
>to 56K and disabled waiting for dial tone.
>
>So what am I doing wrong here?
>
>Please don't suggest using Ethernet or something else instead. I'm
>trying to use what's at hand here.
>
>Thanks for any help.
HOME PAGE:
http://www.seanet.com/~jasonrnorth
--------------------------------------------------
From: Franc Zabkar on 3 Jan 2010 04:16
On Sat, 02 Jan 2010 16:20:44 -0800, David Nebenzahl
<nobody(a)but.us.chickens> put finger to keyboard and composed:

>I know it can be done, but am having trouble making it work.
>
>The idea is to connect 2 PCs directly through their modems. Not cable
>modems, ordinary 56K modems. I call it my "Poor Man's Network".
>
>I've found the following pages that describe this operation:
>
>http://phorums.com.au/archive/index.php/t-120530.html
>http://www.jagshouse.com/modem.html
>
>That second link suggests powering the connecting line with ~24 VDC, but
>I don't think that's actually necessary. (The first link describes
>connecting two computeri via modem with no extra hardware needed.)
>
>So when I set this up--2 computeri with connected modems, using
>HyperTerminal at each end, with the following commands:
>
>o sending computer: ATX3D
>o receiving computer: ATA
>
>I hear stuff through the speaker on the RX end, typical modem connect
>tones to start, but I don't hear all that "chirping" usually associated
>with dial-up connections; just a steady, low tone that lasts for, say,
>30 seconds or so, then the connection goes dead and I get "NO CARRIER"
>at both ends.
>
>Everything seems configured correctly: I've set the speed at both ends
>to 56K and disabled waiting for dial tone.
>
>So what am I doing wrong here?

Some modems have a transformer based DAA and electromechanical relay,
others have a silicon DAA. The latter consists of a host side chip and
a line side chip. The line side chip requires loop current to operate.

You can tell whether you have an DAA with a electromechanical relay by
muting the modem's speaker and commanding it to pulse dial (while
disconnected from the phone line).

ATL0M0DP00000000 (all zeros, no "ohs")

Listen for the clicking of relay contacts.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
From: William Sommerwerck on 3 Jan 2010 04:34
Sorry for coming in late, but if the computers are in the same room, there's
no need for modems, as there is no need to modulate/demodulate. A simple
serial-port-to-serial-port connection is enough -- with the right software.


From: Jeroni Paul on 3 Jan 2010 15:31
On 3 Gen, 01:20, David Nebenzahl <nob...(a)but.us.chickens> wrote:
> o sending computer: ATX3D
> o receiving computer: ATA

I've done this and it worked for me with two internal winmodems. If
you can see the modem board (as in internal modems) watch for a small
transformer, if the modem does not have one it may not work without
line voltage.

I think it only worked if you issued ATX3D first in one computer and
then ATA in the other within a timeout period.

> Everything seems configured correctly: I've set the speed at both ends
> to 56K and disabled waiting for dial tone.

I think you mean the serial port speed here, you can set it to 115000
and it will work. To limit the real modem speed you must use an AT
command but if you don't it will negotiate 33.6k.
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