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I need to connect some Dell servers to a WTI TSM-40 serial port console. The serial console uses RJ45 connectors, and the Dells have DB9. I have DB9-RJ45 adapters (the ones you can customize with whatever pin layout you need).

So the question is this: Is there a recommended way to hook these up? Should I get straight-through serial cables and handle the null-ing inside of the adapter, or setup the adapters as straight-through, and get crossover serial cables?

This delves into the arcane world of serial and telecom equipment and things like DTE/DCE, which I'm not that familiar with. Are there any standards for this sort of thing? I've noticed that Monoprice seems to distinguish straight-through cables as used for data and crossover cables for voice.

P.S. Dells are running Linux and this is for a serial console on them.

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3 Answers

I highly recommend the Yost Serial Device Wiring Standard.

From that page:

Here is a scheme which solves four of the six RS-232 hassles:

  1. All cable connectors are the same sex (male).
  2. All cable connectors are of the same type (RJ-45).
  3. There is no distinction between DTE and DCE plugs and sockets.
  4. You can mass-terminate the connector cables with a crimping tool.

The other two hassles that remain are:

  1. Baud rate matching.
  2. Flow control problems.

All of your cables are wired the same and have the same connectors.

  • No more null-modems or "null-terminal" adapters.
  • No more changing pins on cable connectors.
  • No more building special cables for each kind of hookup.
  • No more soldering or messing with pins on cables.

Be sure to see the section on conflicting RJ-45 pinouts.

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Is the Yost Serial Device Wiring Standard the same thing as a "Rollover" cable? Wikipedia says that they are the same thing, but I can't always trust Wikipedia. Yost Serial Device Wiring Standard –  Stefan Lasiewski Sep 20 '10 at 3:21
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@Stefan: The Yost cable is the one on the left in my answer to your question (labeled "crossed"). Yes it's a "rollover" cable. Pin 1 on one end is connected to pin 8 on the other. –  Dennis Williamson Sep 20 '10 at 6:22
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The pinouts should be handled inside the adapter, or at least that's what we're doing. That way standard pre-crimped Cat5 can be used to provide the cable. Yes, it may involve figuring out how to tweak the adapter (I went several rounds coming up with a similar RS232 adapter for an older Liebert UPS, so I know). But it'll ease things in the long run.

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Google "RS-232" and that should really tell you everything you need to know as far as standards are concerned.

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What makes you think he didn't Google this already? SF exists to help provide answers, not just direct people to Google. I have 8 RS-232 adapters on my desk-- each is different and not interchangeable-- RS-232 can be arcane and non-trivial. –  Stefan Lasiewski Sep 14 '10 at 22:53
    
You're right. I guess I should have read the question more carefully. –  ultrasawblade Sep 16 '10 at 3:53
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