I'm new to wiring and I have this RJ11 to DB9 RS232 adapter, and I'm not sure how to correctly insert the RJ11 wires into the DB9 female end. http://www.blackbox.com/Store/Detail.aspx/DB9-RJ-11-Adapter-Kit-Female/FA067?CAWELAID=414464303

I've searched google but haven't found any clear explanations. It's hard to see which cable is which, but there are six: black, white, green, red, blue, and yellow.

  • \$\begingroup\$ what is connect to the other end of the rj11 cable? \$\endgroup\$
    – jsolarski
    Commented Aug 10, 2011 at 4:06
  • \$\begingroup\$ Personally I think RJ11 for RS-232 is a bad idea. Why not stick to DB-9 connectors? \$\endgroup\$ Commented Aug 10, 2011 at 11:45
  • \$\begingroup\$ @Olin Lathrop - Talk to networking equipment manufacturers. They decided to use RJ11 for serial. I think it's because you can use the same connectors/patch-panels as the actual network. \$\endgroup\$ Commented Aug 10, 2011 at 20:47
  • \$\begingroup\$ @Fake: Networks tend to use RJ45, not RJ11. \$\endgroup\$ Commented Aug 10, 2011 at 21:50
  • \$\begingroup\$ @Olin Lathrop - Yep, and RJ11 cables plug into RJ45 jacks without problems, but not the other way around. That way, you could run serial over existing wiring, but plugging a ethernet connection into the serial port would take some effort. \$\endgroup\$ Commented Aug 15, 2011 at 22:55

2 Answers 2

  1. Note what Olin says - why do this? You may have a good reason but (as noted below) RJ11 is non standard for this purpose and you are inviting compatability problems.

  2. There is NO RJ11 serial data standard. See examples below.

  3. Advising whatyou want to connect to and why may make this task FAR easier.

  4. Example at end of RJ11 serial data pinouts.

  5. Brief comment below on finding unknown pinouts.

The answer to your question is given on the blackbox page that you referenced

  • Pin your own modular adapter to connect your serial equipment.

The reason that they did not connect the RJ11 connector to the DB9 is that there IS no standard way available.

The reason that they left the wires uncommitted was so that you could connect them in the way that suits you.

If you do not know what the pinout you need is, who does? (Really). What are you connecting the RJ11 circuit to? What equipment? / model? / brand? Do they provide a datas sheet or connection diagram?

Worst case you may have some equipment that has a serial circuit on an RJ11 connector that you want to connect to. In this case, the very best method is to get the manufacturer's information. If this is not available then there are ways to proceed.

Finding the pinout of a 6 pin serial connector.

This is just an overview -m knowing the equipment brand and model or, failing that, type of equipment and intended use will help geatly.

  • 6 wire connector.

  • Power off. Do any wires make low resistance connections with device chassis? Label as possible grounds.

  • Power on. Is any line at -5 to -12V wrt chassis ground. If only one this is probably TXD. Compare to diagrams below. Any clues?

  • If more than one low line one may be CTS or RTS or similar. With scope on check lines on turn. Depending on equipment TXD may have data burst. RTS may toggle or play around during startup.

  • etc.

More on this if needed.

Examples - these are useful mainly to show how thoroughly non standard the various arrangements are.

Dell RJ11 - one implementation

enter image description here

H2Ns page describing their RJ11 serial pinout and connections for interfacing to other equipment

H2NS's contribution to the fun.

enter image description here

Here's an interesting page from Unitronics they have a number of somewhat different "arrangements"

Here's a plug pinout from one of their several arrangements - it's notable for being different from but similar to the Dell arrangement above. TXD and RXD are the same and there's some other partial similarities.

enter image description here

  • CISCO RJ45 (NB not RJ11) (from)

    1 n.c. <- 7 RTS bn

    2 DTR <- 4 DTR bn/wh

    3 TxD <- 3 TxD gn

    4 GND 5 GND bl/wh

    5 GND 5 GND bl

    6 RxD -> 2 RxD gn/wh

    7 DSR -> 6 DSR or

    8 n.c. -> 8 CTS or/wh


The db9 connector will have the pin position numbers stamped on the front of the connector. They can be seen with a magnifier. The pins are inserted from the rear of the connector into the appropriate pin hole. Care should be taken to insert the correct pins as they can not be removed without a removal tool. These adapters work well, I have used them for RS232 many times before. As far as the pin out of the RJ11 you need to see what device it connects to and which pins correspond to the db9. The standard db9 pin out can be either a male or female connector and also DTE or DCE. You need to know what you are connecting to before you can determine the correct wiring.


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