Maybe OT modem question.

wrote:


I have not been able to use the onboard serial port. It needs a
proprietary cable I do not have. I have some serial port to header
cables but the pin outs are different.

I made one, using a cable intended for some other interface
on one of my retail motherboards.

https://s10.postimg.org/aa45oad4p/serial_DB9.jpg

Whatever that cable came off, the blocking pin was in the wrong position.
And the blocking pin wasn't the type that pries out with an Xacto knife.
I drilled it out, being careful to not remove so much plastic
that the pin underneath would escape.

The blocking pin would belong underneath that one, if needed.
The alignment tab happens to fit nicely in the mating location
on the socket, so it can't be inserted incorrectly anyway.

There are two pinouts for serial computer motherboards.

DTK

AT-Everex

And that wiring pattern is one of the two :-)

I can tell you that pattern is Asus-Compatible, and might
well work with some Gigabyte boards as well. Asus has been
reasonably consistent, since maybe the year 2000 or so.

When wiring the back of the DB9, the first five wires of the
ribbon, go across the five pins on the bottom row.

The next four wires go across the top pins from left to right
(as viewed from the back of the connector).

The last wire ("pin 10") is a no connect. And that should correspond
to the hole on the connector, just below the "blocking pin cover" I
removed with a drill.

There are several different patterns for 2x5 connectors. The blocking
pin scheme is intended to prevent RS232, USB, and Firewire 400
ribbons from getting confused. Whatever purpose that scrap of ribbon
originally served, it wasn't intended for serial.

Some blocking pins, you can pull them out with an Xacto knife, and
then you could do a nice job on the cable. Mine is a little bit hacked
up, as you can see in the photo.

Paul

In message , Paul
writes:
[]
But since you're not getting dial tone, I don't think
the dialing string makes any difference to that.

Paul

1. Does the MoDem work (not report "no dial tone") if you open the line
with something else (e. g. a 'phone on the same line)?
2. I have vague memories of there being an AT (or similar) command that
would make MoDems "dial" regardless of whether they could sense a dial
tone (I think others here have mentioned this); probably worth a try, to
get you going, though doesn't explain why this has started to not work
where it was working before. I can't remember whether the "ignore
absence of dial tone" was part of the official standard, or was only
implemented on some MoDems.
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

A perfectionist takes infinite pains and often gives them to others

In microsoft.public.windowsxp.general, on Sat, 26 Aug 2017 01:39:06
-0400, wrote:

I have a dual core XP machine and my dial up connection stopped
working. I have tried 3 different Win Modems. The modems install OK
and the diagnostics say it is connecting OK but when I try dialing
out, I get the message that there is no dial tone. That phone wire
works in a phone (same wire that plugs into the modem) I can also plug
a phone into the other port on the modem and dial out through it. I
tried swapping ports to be sure it wasn't just labeled wrong.
There is no activity on the line when I listen from another phone.
Any ideas?

Ihaven't read the whole thread, but is there any chance the red and
green are reversed in the phone jack.

And that even though nowadays phones will still dial when it's
backwards, your modem is different and it won't dial?

(Actuallly, I thought it was the phone exchange that had changed and
made it possible to dial when the L1 and L2 were reversed, but it's a
thought anyhow.)

micky wrote:
In microsoft.public.windowsxp.general, on Sat, 26 Aug 2017 01:39:06
-0400, wrote:

I have a dual core XP machine and my dial up connection stopped
working. I have tried 3 different Win Modems. The modems install OK
and the diagnostics say it is connecting OK but when I try dialing
out, I get the message that there is no dial tone. That phone wire
works in a phone (same wire that plugs into the modem) I can also plug
a phone into the other port on the modem and dial out through it. I
tried swapping ports to be sure it wasn't just labeled wrong.
There is no activity on the line when I listen from another phone.
Any ideas?

Ihaven't read the whole thread, but is there any chance the red and
green are reversed in the phone jack.

And that even though nowadays phones will still dial when it's
backwards, your modem is different and it won't dial?

(Actuallly, I thought it was the phone exchange that had changed and
made it possible to dial when the L1 and L2 were reversed, but it's a
thought anyhow.)

https://en.wikipedia.org/wiki/Tip_and_ring

"...the dual-tone multi-frequency signaling (DTMF) tone generator
also required correct polarity as it depended on the line D.C.
voltage for operation.

Later Touch-Tone telephones included a diode bridge that eliminated
the polarity sensitivity, so that consumer telephone service is
essentially immune to reversal today.

However, some special circuits, such as some direct inward dialing
(DID) trunks, T-1 lines, and ground start lines connected to
field side (terminal) equipment, e.g., a corporate PBX switch,
correctly operate only with proper tip and ring polarity.
"

So it sounds like the issue was "power extraction". An ADSL modem relies
on the wall adapter for power, and doesn't need power from CO battery.

The DAA provides some isolation between the line and the customer equipment.
If you open your ADSL modem, you will see some carefully laid out tracks
on the surface of the PCB, which carry the very-low-level ADSL slgnal
to the big chip for processing. But there is still some sort of DAA
in there. It physically isn't as large as the DAA in your dialup modem.
Even if you don't understand every detail of what's in here, you can
see they're separating things for some reason. Almost like the
wires coming in from the outside world, "are dangerous or something".

https://web.archive.org/web/20071008...em-designs.pdf

Some of the capacitors involved, have a high withstanding voltage. I think
the idea is, the customer equipment is supposed to survive if a high tension
line falls on the phone line. Like maybe 1100V or something. It's not intended
to survive if a 55kV transmission line falls on your house.

A dialup modem needs some protection like that too. I don't know
if there are any dialup modem schematics kicking around or not.

Paul

On Thu, 31 Aug 2017 01:50:48 -0400, micky
wrote:

Ihaven't read the whole thread, but is there any chance the red and
green are reversed in the phone jack.

Phones have not cared about that since the original Western Electric
touch tone designs and modems never cared.
Even if the modem dialer was line powered like the touch tone phone,
it would still "see" dial tone.

On Thu, 31 Aug 2017 03:10:32 -0400, Paul
wrote:

https://en.wikipedia.org/wiki/Tip_and_ring

"...the dual-tone multi-frequency signaling (DTMF) tone generator
also required correct polarity as it depended on the line D.C.
voltage for operation.

I have put this problem on the shelf for now but my next step is to
actually swap out the whole machine and cut the problem in half.
I have another PC sitting here as we speak but I have a couple "honey
do" jobs that have bumped the priority level down. Thanks for all of
the suggestions. When I figure this out I will report back.