Null modem wiring configuration?

Null modem wiring configuration?

Post by Matt Falens » Wed, 25 Jan 1995 14:40:23



: I am setting up a second terminal into my Linux box and would like to
: know if anyone knows the exact configuration to use when you have DB9
: ports at both ends.  I need to know specifically which pins to hook to
: which.  It is not a 'straight through' hook-up.  I would have just
: bought a cable but they do not sell 50' null-modem cable so I went and
: bought the components and the spool-type cable.  I read the
: Serial-Howto and it is precise about the DB25 but tells you only the
: minimum about the DB9s.  Also, what do I do with the shielding itself
: (i.e. which pin is 'frame ground')? Any help appreciated. BTW, the
: 'terminal' is an old 286 and the 'server' is a 486-66.

The pins on a DB9 connector are:
1 DCD
2 RD
3 TD
4 DTR
5 SG
6 DSR
7 RTS
8 CTS
9 RI

Dumb terminals only need like rd,td,sg

Matt
--
----------------------------------------------------------------------
 Matt Falenski  Westmoreland County Community College  Data Center WS

      Do you need a silencer if you are going to shoot a mime?
----------------------------------------------------------------------

 
 
 

Null modem wiring configuration?

Post by Mathias Niem » Thu, 26 Jan 1995 18:59:17


I simpy use a cable with big v24 plugs and an adapter. The cable is from my
good old cp/m mashine and is simply wired 1,2,3 and 20.
--
Mathias Niemz
Snailmail: Lisztstrasse 11 - 31141 Hildesheim - Germany

Phone: (priv)+49-5121-876 932 (business): 15921  Fax: 15405

 
 
 

Null modem wiring configuration?

Post by Stephen Lo » Tue, 31 Jan 1995 10:37:52



: : I am setting up a second terminal into my Linux box and would like to
: : know if anyone knows the exact configuration to use when you have DB9
: : ports at both ends.  I need to know specifically which pins to hook to

: I assembled the cable OK and hooked the two computers. I am now having
: problems getting a login on the 286.  I use a DOS shareware program as
: my terminal emulator.  It's called Telemate, if that rings any bells.
: I have the following in my gettydefs:

: #9600 bps remote dumb terminal

: This is straight from the Serial-Howto.

: I also have in inittab:

: # Serial lines
: s1:456:respawn:/sbin/getty ttyS1 DT9600 vt100

: I have a modem attached to cua0 but I'm not sure how the cua numbers
: relate to the ttyS numbers.  In other words, is ttyS1 right for the
: serial port?

: I also see the following message when Telemate comes up on the 286:

: Caution: CTS is off

: and then:

: RTS/CTS flow control is off because CTS is off

: I DO have the RTS and CTS lines wired correctly.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

try setting up your DOS proggy to hardware flow control, this worked for me!


: Is there any way to simply verify that I am even sending anything to
: the terminal?  Also, does anyone know of a DOS program that *simply*
: does terminal emulation?  Telemate is a full blown comm program that
: is a little top-heavy for the job I want it to do.  I tried Kermit but
: couldn't get anywhere with it.  This problem is very tricky since
: right now, I don't know which component is malfuntioning, Linux getty,
: Linux inittab, the physical cable itself, the 286s hardware,
: Telemate... Just being able to knoe what is wrong would be a great
: help!  Any suggestions welcome.

: ===========================================================================
: | Greg Propf, Towson State Univ   |  "First things first, not necessarily |
: | Towson, MD (physics '96)        |    in that order" - Dr. Who           |
: ===========================================================================

 
 
 

Null modem wiring configuration?

Post by Perry Gri » Sat, 28 Jan 1995 23:23:16


You can use a standard straight through cable if you also get
a small (2" long or so) null modem adaptor.  I think I got a
null modem adaptor from (don't tell anyone) Radio Shack/Tandy.
Works for me.  I use an old XT I picked up for peanuts for the
dumb terminal.  Cables I make tend to be somewhat unreliable.
They just don't seem to have a good life expectancy...
--


"I wouldn't have made it up if it wasn't true."

 
 
 

Null modem wiring configuration?

Post by Marc Dufo » Wed, 01 Feb 1995 13:45:58



Quote:>If you happen to also have DOS on your machine, or can get to a DOS
>6.0 or higher (I think---but definitely with 6.2), use ``help
>interlnk'' from the DOS prompt.  It gives all possible wiring
>combinations for DB9 and DB25 ports.  Mind you, I only know this
>because a friend of mine juryrigged a 25--9 connection last night to
>link his PC and my laptop. :-)  Amazing, the things one can learn. :)

   Here's the straight dope, directly from the deep bowels of Messy Dos:

Pin Connections for a Serial Cable

This section describes the wiring specifications for serial Interlnk
cables.

Make a serial cable with either a 9-pin or a 25-pin female connector on both
ends. Three wires are required for data transmission: Ground-Ground,
Transmit-Receive, and Receive- Transmit. Seven wires are required if you
want to use the remote copy feature. Wire the cable as follows:

9 pin           25 pin              25 pin          9 pin
=====           ======              ======          =====
pin 5           pin 7   <------>    pin 7           pin 5
                        (Ground-Ground)
pin 3           pin 2   <------>    pin 3           pin 2
                      (Transmit-Receive)
pin 7           pin 4   <------>    pin 5           pin 8
                           (RTS - CTS)
pin 6           pin 6   <------>    pin 20          pin 4
                            (DSR - DTR)
pin 2           pin 3   <------>    pin 2           pin 3
                    (Receive-Transmit)
pin 8           pin 5   <------>    pin 4           pin 7
                           (CTS - RTS)
pin 4           pin 20  <------>    pin 6           pin 6
                          (DTR - DSR)

Jean de Lafontaine was kinda right, when he said:
"On a toujours besoin d'un plus petit que soi"...

 
 
 

1. Telephone wire TWO WIRE null modem cable?

I want to make a serial connection between two computers in
the house using regular telephone lines.  I already have a TWO
WIRE telephone line between the two computers, but the
following diagrams asks for a ground (GND) connection, does
anyone know if this is really required, or if there's a way to
get around that third ground wire.  

Thanks.

Marc

Diagram in my communications terminal program:

      Simplest Possible 3-wire Null Modem Cable

      MALE                                    FEMALE
      =============                           ========
      25D RS232 pin     signal       signal   25D   9D (as in AT)
      =============     ======       ======   ===   ==
                  7     GND <------> GND        7    5
                  3     RD  <------- TD         2    3
                  2     TD  -------> RD         3    2

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