Seeking modem pinouts (3b1)

Bruce Lilly bruce at balilly.UUCP
Wed Feb 20 13:39:29 AEST 1991

In article <1840 at public.BTR.COM> thad at public.BTR.COM (Thaddeus P. Floryan) writes:
>bruce at balilly.UUCP (Bruce Lilly) in <1991Feb17.174820.18716 at blilly.UUCP> writes:
>>	CD           8 ___
>>	DTR         20 ___|_______ 20
>I disaggree with that wiring of DTR to CD at the 3B1 end.  It is MOST
>important for the 3B1 to be able to detect when the modem:
>1] connects, via its CD signal going true, and
>2] disconnects, via its CD signal going false.

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

> [ Thad thumps his breast for a bit ]
>The ONLY real "problem" I've had with modems has concerned the HDB UUCP
>software suite re: the frustrating "Cannot connect to device" problems, which
>now, after resolving all the documentation errors, are easy to fix in the
>software config files.  If you have a problem in that regards, post the
>question and I'll reply; I just fixed another person's system several days ago
>which requires use of not-well-documented tricks in the Devices and Dialers
>files and requires about 30 seconds with an editor once one knows HOW to do it
>(for those who remember my "even put Mother Theresa on a killing rampage"
>criticism of HDB two years ago :-)

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

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?

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).
	Bruce Lilly		blilly!balilly!bruce at sonyd1.Broadcast.Sony.COM

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