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:
2 RD
3 TD
5 SG
9 RI

Dumb terminals only need like rd,td,sg

 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

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
pin 3           pin 2   <------>    pin 3           pin 2
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
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.  



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

2. [Fwd: Masqueraded win98 can't send email over a few hundred characters]

3. RH: 3 wire null modem install from computer with cdrom?

4. solaris 2.4 x86 & windows 95???

5. slattach over a null-modem wire

6. Help w/ dialback PPP (not in FAQ)

7. how to measure wire speed at wire level

8. need help with jerky DVD playback and pci bus interrupt assignments.

9. Need help with mixed wired/wireless network (the Bob Hauck configuration)

10. SSA wiring configuration - fastest config?

11. Null Modem Cable fr RJ45-to-DB25 Modem Adapter.

12. modem/NULL-modem

13. ADSL Modem : router or switch,Wireless or wired