Cable Spec 2 - RJ-45 to DB 9 Female - "CO" or Cross Over adapter for all applications except for the CB-EL1 board
Written by Michael Cone
Updated at January 25th, 2026
Table of Contents
Spec for RJ-45 Female to DB-9 Female Adapter - "CO" or Crossover
This is the original RJ-45 to DB-9 conversion spec for the crossover. It is good for all applications except Benderlink Ethernet Modules with the CB-EL1 current loop board.
Crossover Pinout
| RJ-45 Side - Female DB9 Side - Female |
| Function | Wire Color |
RJ-45 Pin |
to | DB9 Pin |
Function |
| RTS | Blue | 1 | ---- | 8 | CTS |
| DTR | Orange | 2 | ---- | 6 | DSR |
| GND | Black | 3 | ---- | 5 | GND |
| TXD | Red | 4 | ---- | 2 | RXD |
| RXD | Green | 5 | ---- | 3 | TXD |
| DCD | Yellow | 6 | ---- | none | none |
| DSR | Brown | 7 | ---- | 4 | DTR |
| CTS | Grey | 8 | ---- | 7 | RTS |
Yellow Wire
Pull the yellow wire out of this adapter.
Gender
Assume that the DB-9 gender is female for connection to standard male COM ports.
Label
It is important to label these adapters with "CO", which means "Crossover" - so that they are not mixed up with the ST adapter (cable spec 1).
For Use with Cable Spec 1
Use this connector with a standard RJ45 cable connected to the Cable Spec 1 adapter to create a crossover cable good for connecting two RS-232 ports for communications.
Important Testing Note
| The receiving pins in this adapter can jump out of their inserted holes if they are not properly pressed in. With the plug NOT snapped into the cover, plug the port into a DB9 male port to be sure none of the receiving pins are pressed back out of the inserted holes. |