×
INTELLIGENT WORK FORUMS
FOR COMPUTER PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you a
Computer / IT professional?
Join Tek-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Tek-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Null Modem adapter pinout from pc to pc

Null Modem adapter pinout from pc to pc

Null Modem adapter pinout from pc to pc

(OP)
Hello,
I cannot seem to figure out how to wire up a null modem cable.  I used a rolled cable with what I think is a null female db9 connector on each end.  This did not work for me.  Do I need one null connector and one straight through connector?  If some one knows the pinout I need please let me know.
thanks
abm086

RE: Null Modem adapter pinout from pc to pc

you need to swap pins so the signals from one computer arrive on the correct pins at the other computer. Pins 2 and 3 are the send and receive pins and pin 2 on one end needs to go to pin 3 at the other. pin 7 is ground at both ends. (this is for a 25 pin plug cause I can't remember the nine pin type.)

RE: Null Modem adapter pinout from pc to pc

The data pins on a DB9 are 2 and 3 also, a basic null modem cable will need to swap these to pins at one end.  Now...it isnt always that simple.  In theory, you may get away with just having pins 2 and 3 connected (but swapped at one end) and the ground pin 5.  However, depending on the requirements of the hardware and software, you may need to loop back or connect the hardware flow control.

So, if the regular 3 wire one doesnt work, give this a try:

DB-9 signal                         DB-9 signal
1 - DCD ---------------------|----- 7 - RTS
                                      |----- 8 - CTS
2 - RXD --------------------------- 3 - TXD
3 - TXD --------------------------- 2 - RXD
4 - DTR --------------------------- 6 - DSR
5 - GND --------------------------- 5 - GND
6 - DSR --------------------------- 4 - DTR
7 - RTS -----|
8 - CTS -----|--------------------- 1 - DCD

The reason you may have problems is that the hardware and/or software may be implementing the two controls it can.  The above cable connects Data Set Ready to Data Terminal Ready so that the devices can signal each other.  Also, we are fooling the Clear to Send, Request to Send, and Carrier Detect.

There are more ways to configure thing if this still doesnt work.  Depending on the equipment, I sometimes have to throw in my serial analyzer and see what is happening, then jumper accordingly.

Good Luck!

It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Tek-Tips Forums free from inappropriate posts.
The Tek-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Tek-Tips forums is a member-only feature.

Click Here to join Tek-Tips and talk with other members! Already a Member? Login

Close Box

Join Tek-Tips® Today!

Join your peers on the Internet's largest technical computer professional community.
It's easy to join and it's free.

Here's Why Members Love Tek-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close