Seeking modem pinouts (3b1)

Thaddeus P. Floryan thad at public.BTR.COM
Thu Feb 21 18:47:40 AEST 1991

bruce at balilly.UUCP (Bruce Lilly) in <1991Feb20.023929.24345 at blilly.UUCP> writes:

	Unless CD is asserted, a write to/read from a tty port will fail. So
	something like:

	echo ATZ >/dev/tty001

	will not work, if a modem connected to the port has not asserted CD.
	The connection I gave will work, as DTR is asserted when the port is

Oh?  Then perhaps you'd like to explain why HDB UUCP, Kermit, Pcomm, etc.
all can "talk" to a modem whose CD signal is not asserted TRUE at the 3B1's
RS-232 interface port?

Has everyone so quickly forgotten the anecdote posted last month about a
person who called the US Naval Observatory time service number in Washington,
DC, only to later find a humongous phone bill because the modem wasn't strapped
to properly drop CD when the connection was to be terminated?

Seems people have forgotten my posting two years ago when I brought up HDB
UUCP on my 3B1 and I claimed that HDB was brain-damaged and "... would put
even Mother Theresa on a killing rampage...".  The docs for HDB UUCP in this
regards are truly bad for the "stock" SVR3.2 version (but are OK in the docs
for the 386 SVR3.2 manual set).  Some of the docs do appears in the SVR3.2
Utilities Release Notes in obscure places.

Remember: the "stock" version 2 uucp worked correctly talking to a modem when
CD wasn't asserted, but the HDB did NOT work correctly until one used the
very poorly documented "\M" (for CLOCAL) in Dialers and ",M" in Devices.

	Nothing in any of the HDB UUCP files will affect the example given
	above.  I've been using the connection above with no problems

I just one paragraph above mentioned the "\M" and the ",M" ... those options
ONLY work for HDB and for precisely the reasons I've described time and time

	Thad, why do you feel that ``it is MOST important for the 3B1...''?

	1) What will break given the connection I posted?
	2) How would you be able to write to the modem (simply) from the shell?

1) If some data connection terminates abnormally (i.e. without the "OO" from
uucico), your line may stay connected forever.  Not good for one's pocketbook
on a long-distance call.  One should ALWAYS respect the condition of DCD & DTR
for unattended (i.e. automatic) modem usage.

2) I would never care, under normal circumstances, to write to the modem direct
from the shell, but when I do, I would simply do:

	ls -l /dev/tty*

	and for each ttyXXX's [major,minor] pair, simply do:

	mknod modemXXX c major (minor+128)

and then you can do what you wanted to do, WITHOUT the (improper) need to
continuously assert CD from the modem.  In case this isn't clear:

	$ ls -l /dev/tty0* /dev/modem*
	crw-r--r--  1 root    root      0,128 Feb 20 19:49 /dev/modem000
	crw-r--r--  1 root    root      0,130 Aug 25 15:26 /dev/modem001
	crw-r--r--  1 root    root      0,131 Aug 25 15:26 /dev/modem002
	crw-r--r--  1 root    root      0,132 Aug 25 15:26 /dev/modem003
	crw-r--r--  1 root    root      0,133 Feb 16 06:59 /dev/modem004
	crw-r--r--  1 root    root      0,134 Aug 25 15:27 /dev/modem005
	crw-r--r--  1 root    root      0,135 Aug 25 15:27 /dev/modem006
	crw-rw-rw-  1 uucp    users     0,  0 Feb 20 19:48 /dev/tty000
	crw-rw-rw-  1 uucp    users     0,  2 May 13  1990 /dev/tty001
	crw-rw-rw-  1 uucp    public    0,  3 Jan  7  1990 /dev/tty002
	crw-rw-rw-  1 uucp    users     0,  4 Feb 20 14:22 /dev/tty003
	crw-rw-rw-  1 uucp    users     0,  5 Feb 16 06:59 /dev/tty004
	crw-rw-rw-  1 root    users     0,  6 Mar  2  1988 /dev/tty005
	crw-rw-rw-  1 root    users     0,  7 Mar  2  1988 /dev/tty006

I exploit that capability in my highly-modified version of Boyd Ostroff's
"modemon" package for the 3B1.  Hmmmm, perhaps I should email that stuff to
Dave for posting to comp.sources.3b1 since it easily solves EVERYONE's modem
and uucp problems.

Having created such "modemXXX" devices permits handling them from the shell
or other programs as do the "\M" and ",M" for HDB UUCP.

All this can be summed up as:

  * The correct assertion of a CD signal from the modem to a DTE (i.e. *
  * a 3B1) is as important as is a DTR signal from a DTE to a modem.   *

Bruce continues:

	Sidebar: many modems have a hardware (and possibly software) option to
	continuously assert CD so that writing to the modem is possible when
	carrier is not present (e.g. refer to page 2-4 of the Digicom Systems,
	Inc. 9624LE User's Manual).

I have 2 of those modems (and their manuals); the page is "1-4" in the Digicom
9624LE manual, and the description is either:

	"DCD Forced on"
	"DCD normal RS-232"

The "normal" state of DCD is for the signal to be asserted true ONLY when there
is a data carrier detected (DCD) (i.e. one's modem is talking to another).

I hope everyone can convince Bruce to pay your phone bills for "terminated" but
still live phone calls if you take his advice in this regards!  :-)

And please note I'm NOT trying to impugn Bruce.  Modem problems are a common
question thread I handle at user and technical meetings.  Most modem manuals
would have been better never written due to how much they confuse the issues,
and I have yet, after 25+ years, to find a "good" modem manual.

Thad "Mr. Modem" Floryan [thad at (OR) {decwrl, mips, fernwood}!btr!thad]

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