How to create an APC compatible serial cable

I’m presently working on some Cisco certifications and I’m rebuilding my home lab mostly from scratch.  My old APC Rack PDU (essentially a network controls power bar) was showing it’s age (it was beige) and not functioning reliably.  I bought a used APC AP7901 Metered Rack PDU to take over the job of remotely turning off and on my various Cisco switches, ASAs and routers.  I found my new (circa 2010) AP7901 on eBay for $99.99 including shipping, but it didn’t come with the super special serial cable (part number 940-0144) that was originally provided by APC (they never come with them used).  I tried the various DE-9 (yes, DE-9, not DB-9) adapters that I had, but none worked in this application.

Why didn’t I use DHCP to issue the unit an address?  Well I did, but that didn’t work.  My home DHCP server (Sonicwall NSA250M) was giving it an IP address, but no amount of NMAP probing could get anything from the device).  A serial cable was the way to get things rolling.

These cables are no longer available from APC, so you’ll need to make your own.

Here’s how to make the 940-0144 serial cable

  1. Start with a standard Cisco serial cable.  This has a Female 9-pin serial port at one end and a RJ-45 connect at the other.
  2. Cut off the RJ-45 cable connector.
  3. Identify the two grounds, RX and TX pins.
  4. Crimp on your own RJ-11 connector with the wires in the correct order.
  5. Connect your new cable to your APC and get a working serial connection.

Sounds easy right?  Well it is, but I’ll give a few additional detailed instructions below in case this is your first time making this type of cable.

In more detail…

1. The Cisco standard serial cable is the cable that everyone gets when they buy a new Cisco switch or router.  You can find them on eBay or from Monoprice as well.
2. The pin positions on the end of my Cisco cable are #5 = GND (yellow), #3 = RX (red), #2 = TX (green).   Orange (or peach?) was also a ground, but it must be connected internally in the cable. Yours might be different.  You can tone these out for yourself using a multi-meter that can measure resistance and some little lengths of wire.
3. Place the wires into the RJ-11 plug.  RJ-11 connectors have size pin slots, but often only four gold plated contacts.  Ignore the first and last positions (1 and 6), they are not used.  Positions #2 (yellow) and #4 (orange) should be the two grounds.  Position #3 (red) is the RX and position #4 (green) is the TX.  If you get things wrong, just flip the #3 and #4, but I think these pictures are sufficient to figure things out.  Don’t use pins #1 or #6, they aren’t needed.  Make sure you’re counting the pin positions even if the there is no gold contact in place.
4. Trim off all the unused wires.
5. Fire up your favorite terminal program (I like Putty) and hit enter a few times until you see a username prompt.  (make sure the APC is on of course).  Settings should be 9600 bps, 8 data bits, no parity, 1 stop bit.
6. Default username and password are both “apc”.

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