APC SmartUPS Serial Cable Pinout

I replaced my old APC SmartUPS 620 with an updated model. I had lost the serial cable that allows you to communicate with the UPS via a computer for the old unit. The new unit came with the serial cable and for a while I was looking for the correct pin out so I could build a cable myself. So I wanted to get the pin out documented. The cable is a male to female DB9 cable. Well I got my voltmeter and using the continuity setting I mapped the pinout. It would not be difficult to create this cable. Many of the cables DB9 serial cables I had laying around were female to female and it was hard finding a male end. Hopefully this will help others out there that need this cable and don’t want to pay $30 for it.
UPDATE: I have updated the diagram based on the comments I got on this post. Apparently I counted the male pins incorrectly so I made the correction. Thanks for your feedback.apc-smart-ups-serial-pinout


  1. Hi, you have the SmartUPS cable slightly wrong. The picture is correct, but you have counted the pins on the male connector incorrectly. The correct table should be:
    Fem Male
    2 2
    3 1
    5 9


  2. Mr Ball (posted on 7/3/2009) is correct you should correct the db9 male side pin numbers. Other wise nice diagram!

  3. I’ve got with my APC 620 a cable imprinted 940-0024c with your pin assignments, just to confirm. Checked for R of 10K, but no resistors found.

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