Xref: utzoo comp.periphs:646 comp.terminals:507
Path: utzoo!mnetor!uunet!husc6!bbn!gatech!mcnc!ecsvax!ehr
From: ehr@ecsvax.UUCP (Ernest H. Robl)
Newsgroups: comp.periphs,comp.terminals
Subject: Re: Help -- Making a modem with DB9 connector --> DB25
Message-ID: <4299@ecsvax.UUCP>
Date: 11 Dec 87 20:01:35 GMT
References: <860@seradg.Dayton.NCR.COM> <3150@batcomputer.tn.cornell.edu>
Organization: UNC Educational Computing Service
Lines: 52
Keywords: US Robotics modem DB9 DB25
Summary: DB9 serial connections



On AT-type machines the pins on a DB9 serial connector are:
   1  CD
   2  RD
   3  TD
   4  DTR
   5  Sig.Grnd.
   6  DSR
   7  RTS
   8  CTS
   9  RI

   For straight-through cables DB9 on computer to DB25 on
   modem, we have used the following:

   DB25 side     DB9 side
   pin 2     to  pin 3
   pin 3     to  pin 2
   pin 4     to  pin 7   
   pin 5     to  pin 8
   pin 7     to  pin 5
   pin 8     to  pin 1
   pin 20    to  pin 4
   pin 22    to  pin 9

   For a null-modem (DB9 computer to DB25 computer) we have
   used the following:

   DB25 side     DB9 side
   pin 2     to  pin 2
   pin 3     to  pin 3
   pins 4&5  to  pin 1
   pin 6     to  pin 4
   pin 7     to  pin 5
   pin 8     to  pins 7&8
   pin 20    to  pin 6
   pin 22    to  pin 9

Since you are going from a DB9 modem to a DB25 machine, the
above may or may not work.

Some electronics stores, including Radio Shack computer centers
now sell DB9 to DB25 adapters.  I presume they are wired as in
the first example above.

Hope this helps. -- Ernest
-- 
My opinions are my own and not necessarily IBM-compatible.--ehr
Ernest H. Robl          (ehr@ecsvax)         (919) 684-6269 (w)
Systems Specialist, Library Systems,         (919) 286-3845 (h)
Perkins Library, Duke University, Durham, NC  27706   U.S.A.