Seeking modem pinouts

[Thaddeus P. Floryan]

andy at progress.COM (Andrew Klein) in <1991Feb13.172049.21792 at progress.com>
writes:

	I have a 3b1 but no documentation.  Can anyone provide 
	me with the recommended cable pinnings for an external 
	modem?  Your help is much appreciated.

	Please e-mail me.

Email has been sent, per:

For the 3B1, you simply need a cable that passes all 25-wires straight through;
its RS-232 port pinnings are as "standard" as anything I've seen on any other
computer.

If you cannot readily find such a cable or don't relish the thought of 5 pounds
of wire hanging off the DB-25 connector, the minimum pinnings with which one
can connect to a modem comprise (and is what I use to connect to ARK 24K,
Digicom 9624LE, Telebit T2500, VenTel, etc. modems from my 3B1s):


	 (1)-----(1)	<-- optional, but recommended
	 (2)-----(2)
	 (3)-----(3)
	 (4)-----(4)	<-- only if hardware flow control is used
	 (5)-----(5)	<-- only if hardware flow control is used
	 (6)-----(6)
	 (7)-----(7)
	 (8)-----(8)
	(20)-----(20)

If you want to connect a terminal to one of the RS-232 serial ports on the 3B1,
you must make a "null modem" cable which, for the 3B1, is:

	 (1)-----(1)	<-- optional, but recommended
	 (2)-----(3)
	 (3)-----(2)
	 (4)-----(5)	<-- only if hardware flow control is used
	 (5)-----(4)	<-- only if hardware flow control is used
	 (7)-----(7)

	 (6)--+
	      |
	 (8)--+--(20)

	      +--(6)
	      |
	(20)--+--(8)


The above "null modem" cable "fakes" a modem's DSR (6) and DCD (8) signals to
a DTE (terminal or 3B1) device based on the DTR (20) signal at the other end.

If you're going to be using the HDB UUCP software suite on your 3B1, you will
quickly encounter some frustrating "Cannot connect to device" problems which
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 ... 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 :-)

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